# Convert downflow to upflow



## yuri (Nov 29, 2008)

The first scenario sounds the best too me.

Make the elbows as large as possible so they add the least amount of resistance to the airlflow.

You cannot change the fan mounting or flip it in any unit. Illegal in furnaces as the high temp limit controls won't work and it won;t meet the UL and other codes or for insurance company reasons.

Same if you have electric elements in a airhandler. If the unit is a certified multi-position airhandler or furnace then you can flip it and use it any way you want.


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## John Smith_inFL (Jun 15, 2018)

eeewwwwwww been there - done that !!
in FL, the building inspector said I could build my own plenum box
and run my own flex duct as long as it all meets "code".
plenum boxes are fun to build yourself. just know the code
for your area. mine says no zip-ties on any connections.
LOTS and LOTS of foil tape, spray adhesive and gray mastic.
I made the attic plenum box, ran all the flex duct, and connected
all the new vents myself and was very satisfied with the results of my
very first project of that type.
running new 6" flex duct from the attic plenum box to the room vents
is not that difficult of a task - even for the inexperienced.
then when the A/C company came to install the new unit, all they had to do
was connect the air handler to the part from the attic (chase??).
now is the time to fully address any concerns with the closet that you
intend to put the air handler in. air leaks, sound insulation, painting, etc.
find a HVAC supply company that will sell you the duct board and all the
supplies that you need for the project.


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## 57TinkerMan (Jun 17, 2018)

What is the make/model # of your furnace and a/c coil ? Many furnaces and coils are multi-poise meaning that they can be configured as upflow, downflow and/or horizontal.


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## netxtown (Mar 18, 2014)

"Illegal" and "insurance" - enough scare for me! 



Option one it is! That said, my thoughts went to the 45's...and maybe eliminating them all together by utilizing a plenum box with the 'in' and 'out' on the same side. Shouldn't be too difficult to strap it to the floor joists...and the cost for sheet metal wouldn't be staggering to prevent any critter encroachment. It could definitely be mounted diagonally across floor joists to line up with a new floor opening (about 3 feet min in length). Would be kind of a big plenum box...but it would take the 45's out of the equation. Or am I missing something...?


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## netxtown (Mar 18, 2014)

57TinkerMan said:


> What is the make/model # of your furnace and a/c coil ? Many furnaces and coils are multi-poise meaning that they can be configured as upflow, downflow and/or horizontal.



it is a Goodman ADPF304216. The literature I can find says it is a "dedicated downflow" or "one piece air handler"


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## yuri (Nov 29, 2008)

Ideally you want a elbow so it "turns" the air. Not just dump it straight down as then you get back pressure/resistance.

In large ducts for commercial units and some resi units they put "turning vanes" inside the return duct to actually direct the air towards the fan. Not in the supply but you get the idea. You want a round or curved duct if you are going to make a 90 deg turn. It can work with a square box plenum but those are big and you only have a 90 deg turn vs the 180 deg turn I imagine you are planning?


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## netxtown (Mar 18, 2014)

the plenum would serve to make a 180° turn. Howevber...I see the point in 'turning' the air. There is plenty of room to use 45's to make the 180° - and also to make the subsequent 90° turn to run horizontally across the ceiling. 



FWIW - my part in all of this will be framing/drywall/finish-out of the new duct runs through the house. with the new duct and vents running at the ceiling I'll have to do some patching where the existing floor vents are - which is no problem.


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## netxtown (Mar 18, 2014)

I'm continuing to dig around...and i see there is an insulated ductint with a semi-rigid aluminum core. 



http://www.novaflex.com/productcart/pc/T-L-T-Insulated-Aluminum-Flex-Duct-60p565.htm


I would think it would be easier to route - and any bends cold be stretched out to afford smoother transitions. I would suspect that the ripples in the core would be somewhat restrictive - but in the long run it may be overall less restrictive due to the smoothing of the bends???


I can always wrap it in a 1/4" hardware fabric to prevent critters from making a meal of it.


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## supers05 (May 23, 2015)

I'm not sure if the installers around there would do metal duct, but that's how I'd do it. I'd get the elbows made, then run a square supply up the wall. It's easier to frame in, and will last forever. You come then elbow at the top and run down your attic and get much better distribution. I'd probably get all insulated duct. 

The aluminum flex is way better then the plastic stuff and when stretched out, isn't so restrictive. (The metal duct would be even less restrictive.) 

Cheers!


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## viper (Jul 30, 2009)

I might just mention about ducting "outside the conditioned space". Any ductwork that is outside conditioned space needs to be insulated. Attic, crawl space, etc. You can use metal ducting but make sure to install the best insulation you can get. 

Personally I used 100% flex with Aluminum liner and in the attic, I buried everything with new blown insulation. I was able to quantify results with vent temps just by burying the attic flex. You will lose a LOT of BTUs without insulation and risk condensate in some areas. 

I did make sure as part of this installation to mouse guard every possible opening in my structure. I have not had a rodent in years.


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## netxtown (Mar 18, 2014)

I am trying to figure out how to scream in text! lol!

Just had another contractor come out and size up the project. At first, all he wanted to do was replace the mess that is already down under. I finally had to get a bit ..uh...firm and tell him 'you are not listening to what I want'.

From there, it was like he was imagining every thing and anything to make this some contraption fit for a palatial estate. Obviously, he has a boat payment coming up! Once i convinced him we would not be doing anything other than a straight line system - he settled down.

But - his plan is using 16" square duct. The guy before was 14". And of course, one guy pegged it at 15". If i apply the Goldilocks formula (porridge too hot, porridge too cold, porridge just right) then 15" would win out. But - this ain't porridge. 

My understanding of the ducting is that it is mostly science - which then parlays into standard HVAC sizing. I certainly don't want air vents that hiss at me - nor do I want to set 20" box fans around to aid in cooling/heating. 

The outflow port on the exchange unit is 12" diameter. The unit is rated at 1600CFM (high) and 1425 (medium). From the Engineer's Toolbox, I see that a 10" square duct will carry the same as a 12" round @ 1425 (which really makes no sense to me). So how the heck did he get to 16"?

I can't tell what is 'best' for performance vs what is 'best' for profit. And i am nearing that point where they all get the finger and i wade through this myself. I built my own workshop (14x32), ran all the electrical, set a new panel, installed the lights fans, did all the insulation and drywall, etc. Surely running duct can't be that much more of a challenge!


lastly - I'd like to express my thanks to all who have provided their expertise and experience. I appreciate your leading me out of my HVAC ignorance. Thank you!


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## netxtown (Mar 18, 2014)

viper said:


> I might just mention about ducting "outside the conditioned space". Any ductwork that is outside conditioned space needs to be insulated. Attic, crawl space, etc. You can use metal ducting but make sure to install the best insulation you can get.
> 
> Personally I used 100% flex with Aluminum liner and in the attic, I buried everything with new blown insulation. I was able to quantify results with vent temps just by burying the attic flex. You will lose a LOT of BTUs without insulation and risk condensate in some areas.
> 
> I did make sure as part of this installation to mouse guard every possible opening in my structure. I have not had a rodent in years.



My thoughts were to definitely insulate - and then wrap that with 1/4" hardware fabric to keep any critters at bay. The perimeter 'skirt' is also being replaced so that should block any adventurous critters.


In regards to the aluminum flex - I was thinking it would be lighter and much easier to install than 10'ft run of rigid square duct. Can it be cut to allow smaller ducting to the vents?


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## viper (Jul 30, 2009)

I can move a LOT of air through a small pipe when I push it hard! AKA PSI! 

You need to keep pressure and velocity in check for both noise and blower efficiency. 

I have a single 18" return on my 1000cfm system. My system does NOT howl like most new cracker box homes.


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## supers05 (May 23, 2015)

For 1600 cfm, you'd need at least 15x16, inside dimensions. (insulation takes some space.) An equivalent size would be 8x30 or 10x24. 

What size is your AC? 

Engineering toolbox is nice if you know the engineering behind it. Otherwise it can be a bit vague, and easy to misinterpret the charts. For ductwork, we design around 0.1"wc/100ft loss. 

Cheers!


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## netxtown (Mar 18, 2014)

supers05 said:


> What size is your AC?
> 
> Cheers!



Size is 3.5ton


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## viper (Jul 30, 2009)

netxtown said:


> In regards to the aluminum flex - I was thinking it would be lighter and much easier to install than 10'ft run of rigid square duct. Can it be cut to allow smaller ducting to the vents?


The stuff I am referring to probably won't be as rodent proof as you want. It is the basic insulated duct, just with an Al foil liner inside. Yes, you can cut and do anything with it. People just do dumb stuff with it like really tight radii. Not cool. Most of my runs were designed to be straight. Virtually no radii and easily replaceable. 

I ran a stack into the attic with dedicated takoffs for each supply line. Once it was all plumbed, the blankets came in to insulate it all. 

I like header systems. Just the engineer in me to want things simple and replaceable.


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## supers05 (May 23, 2015)

So you only need 1400 cfm. (we'll use 1425) You still need 16" round duct, or 10x22, or 15x15.

Cheers!


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## netxtown (Mar 18, 2014)

It might then be best to go with full metal elbows down under, come up through the floor, alum-flex to the ceiling, a 90° right turn - and then it is a straight line of 30 ft aluminum-flex duct. I can frame/drywall it all in pretty easily as the entire thing will be inside the conditioned space (no attic). A simple drop soffit of 2x2's should suffice (I hope) to hide it all. A little texture, a little paint...


The largest size I saw of the aluminum flex was 16". I figure full outside diameter (with insulation) would be ~18" --- which will definitely fit in the soffit areas. Is 16" diameter sufficient for proper/adequate air distribution?


(total of 9 vents: 1 @ 4" duct, 3 @ 6", and 5 @ 6/8")


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## netxtown (Mar 18, 2014)

I just hit a mental roadblock. I'm not clear how i would fit 16" duct through 14.5" between joists.


The supply port is 12" diameter. My floor joists are 16" OC - 14.5" between joists. So - from the 12" port do i use 12" elbows down under to make the 180 turn to go up through the floor...then transition to 16" diam duct for the rest. Can I screw two start collars back to back (one 12, one 16), then drop the 12 side through the floor cutout (to attach to elbows)...and 16 from there for rest of the run?


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## supers05 (May 23, 2015)

netxtown said:


> I just hit a mental roadblock. I'm not clear how i would fit 16" duct through 14.5" between joists.
> 
> 
> The supply port is 12" diameter. My floor joists are 16" OC - 14.5" between joists. So - from the 12" port do i use 12" elbows down under to make the 180 turn to go up through the floor...then transition to 16" diam duct for the rest. Can I screw two start collars back to back (one 12, one 16), then drop the 12 side through the floor cutout (to attach to elbows)...and 16 from there for rest of the run?


The sooner you transition the better. If you can split the run into two, 12" will handle 750ish cfm.

Cheers!


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## yuri (Nov 29, 2008)

" The sooner you transition the better ".:biggrin2:

That is how they measure steam flow thru a small thin plate orifice in a large pipe and get away with a orifice. Has to do with Bernoulli's principle.

Point is you can go larger than the outlet opening of the air handler but you want to make that transition as close to it as possible. Then you can go with a larger duct(s) and gain the advantage of less resistance and better flow.

If you go with 2-3 feet of small duct and then transition you get back pressure on the fan and resisitance.


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## supers05 (May 23, 2015)

yuri said:


> " The sooner you transition the better ".:biggrin2:
> 
> That is how they measure steam flow thru a small thin plate orifice in a large pipe and get away with a orifice. Has to do with Bernoulli's principle...


You mean like metering devices in refrigeration, flow stations in creeks and rivers, eg.  Indeed this is all science/physics. All things really are related. 

Thanks for making my point more clear. 

Cheers!


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## netxtown (Mar 18, 2014)

Yuri - 


I need to tip my hat to you guys who do this for a living. I'm trying to do one piddly project - and i'm already ready to tear my hair out! lol! And to add insult to injury...

All of this is being paid for by a Veterans Assistance group. An email this morning from one of the contractors pretty much explained why I haven't received any quotes: they think it is a scam. Work here - get paid two weeks later over there. That tells me, the guys doing this have been ripped off before. Maybe i'm just old (I am) - but the world seems to have gone crazy.


If i use 12" elbows (45° each) to make the 180° turn to "upflow", it would span probably 3-4 feet. Following your advice that 3ft is too much, I will crawl down under and see if sistering a couple of joists on the outsides of two adjacent joists is feasible. If it is, then i can cut out part of the original joists to allow for a 17.5" hole. With that, I can transition from 12" to 16" directly at the supply. I may have to use round pipe - and then transition (again) to square once i get up through the floor. Is there such a thing as a 16" square start collar?


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## yuri (Nov 29, 2008)

Not sure about that but you can get custom sheet metal fittings made at some sheet metal fab shops if you want to pay the $$.

You need exact dimensions and very clear drawings of what you want but it is possible to get them made.

If you do go thru with the project please post some pics of it during construction as it is now a "class project".:smile:

Go Advanced > Manage attachments.


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## supers05 (May 23, 2015)

We get all of our stuff from sheet metal shops. The only difference between a standard and odd shape is price. Transitions and elbows are the most expensive. 

Now you could go 14" down through the floor. If you can sister the joists and then cut an opening with the appropriate bracing, you can come back up as 16". It might be too much work for you, so 14" will do, but will be a bit more noisy and quite a bit more restrictive. Personally I'd probably transition to rectangular and go 14" wide. (14x18 internally insulated in your case.) Then I'd order the elbows to match, and return back however you want. If you're using solid 16" elbows you could make it a bit tighter with 90* elbows. I wouldn't use 12", but 14" should do if you don't want to reframe the house, but keep the elbows long. (14" is almost double the restriction, with 12" being almost 4x the 16" at that airflow.) 

Each tight 90* elbow equates to about 8 ft or so. A sweeping 90* (or 2 x 45* will be closer to 5ft.) With 3 short elbows at 14" your ductwork would have to be less then 31ft to fit within common design. With 2 sweeping 12" elbows, you'd have to be less then 11 ft. (i don't recommend the 12, just adding it so that you get the idea.) 

If you go with tight 14" elbows, with about 3 ft of connecting 14" duct, then transition to 16 after coming back through the floor, and continue with 16", you would be OK with another 64 ft. (including 1 more elbow.)

Cheers!


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## netxtown (Mar 18, 2014)

yuri said:


> If you do go thru with the project please post some pics of it during construction as it is now a "class project".:smile:



Finally something I CAN do!! I have a 35mm camera and will capture pics from start to finish!


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## supers05 (May 23, 2015)

netxtown said:


> Finally something I CAN do!! I have a 35mm camera and will capture pics from start to finish!


I didn't know people still used those. 

Cheers!


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## yuri (Nov 29, 2008)

35mm?? A digital one is required.:smile:

I still have my old school Olympus OM-4 gear and yes they still produce slide film and there is a market for it with photographers who want to be artistic and use film.

I may get back into it. 

No challenge with digital and photoshopping.


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## supers05 (May 23, 2015)

yuri said:


> 35mm?? A digital one is required.
> 
> I still have my old school Olympus OM-4 gear and yes they still produce slide film and there is a market for it with photographers who want to be artistic and use film.
> 
> ...


Well the average Joe doesn't use one anymore. They are too expensive to develop. A friend was sending his film to California because it was the last place in North America to still accept his film type. (i forget what it was called but it was something special.) 

Cheers!


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## yuri (Nov 29, 2008)

Kodachrome was/is very expensive and obsolete but the other types can be developed at specialty camera shops like Henry's or Photo Central in Winnipeg.

It is expensive but so is fishing. By the time you pay for all the gas/travelling to a lake and a boat and gear etc the fish costs $100/lb if you are lucky enough to catch them. You do photography for fun and the cost is not a issue to me.

I can get fresh pickerel from Lake Winnipeg from a relative for under $5 a lb delivered to me.


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## supers05 (May 23, 2015)

yuri said:


> Kodachrome was/is very expensive and obsolete but the other types can be developed at specialty camera shops like Henry's or Photo Central in Winnipeg.
> 
> It is expensive but so is fishing. By the time you pay for all the gas/travelling to a lake and a boat and gear etc the fish costs $100/lb if you are lucky enough to catch them. You do photography for fun and the cost is not a issue to me.
> 
> I can get fresh pickerel from Lake Winnipeg from a relative for under $5 a lb delivered to me.


That's what it was called! Lol. He was so mad when the last place in Toronto closed down. 

Now i remember why I don't do either very much. I have a house to pay for.  I do like photography, but can only use my cell phone, so I don't bother sharing any of the pictures. Well, that's enough of hijacking this thread. 

Cheers!


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## netxtown (Mar 18, 2014)

supers05 said:


> Well the average Joe doesn't use one anymore. They are too expensive to develop. A friend was sending his film to California because it was the last place in North America to still accept his film type. (i forget what it was called but it was something special.)
> 
> Cheers!





Ok - I'm busted. Its a Canon EOS. Completely digital. I call it 35mm just cause the lenses are the same. er...well... I think they're the same! It did come with this wire thing that plugs into my computer....


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## netxtown (Mar 18, 2014)

Wrench in the cog!

Got a call from one of the contractors that had come out - and he wants to use fiberboard on the inside of the dropped soffits - and no pipe. he says he can seal it up with no leaks - but IMO it leaves the space unusable for anything else (I had thought about some can lights - especially in the LR). He also claims there is absolutely no problem with re-stacking the exchange unit to make it upflow. 

The "drop soffit" is roughly 32"w with 26" high right at the ceiling crest - sloping down to 20" high at the wall. A 16" square pipe towards the high side would leave plenty of room near the low side for a couple can lights - or something! 

After the previous conversations here, I was pretty confidant in the design and functionality of the project. His design seems to be rather 'large' - and I'm just not sure about any of it.

How is condensation handled in either design? If the fiberboard isn't lined on the inside, what's to keep the fibers from blowing around and into the living spaces? It just seems like it would be a lot of fiberboard...


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## yuri (Nov 29, 2008)

I dunno. From the Goodman spec it is only a downflow unit.

If the model # was ARPF instead of ADPF you could reverse it. R is reverse flow/multi-position and D is downflow.

If you have electric heat strips in it then I would not reverse it as it may be unsafe.

If it is AC only and there is extra drain ports on the cooling coil then it may work. Once you flip it then the drain has to come out a different spot and the drain pan has to be designed for that too.

I kinda wonder if this contractor knows what he is doing?

https://www.hvac.com/media/manuals/technical/GOODMANAWUF.pdf


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## netxtown (Mar 18, 2014)

the unit is heat and cool...and right there on page 5 it does say 'dedicated'. No mention of reconfiguration with this model.


The biggest issue i have had with this unit has more to do with the plenum box than anything else. The plenum is one of those triangular things positioned so that the top is parallel to the floor - leaving the other two sides pointing kitty-wompus downward. The issue is the positioning of the heat coils aligns directly over one of the exit ports of the plenum. The box is just too small for any 'mixing' to happen. Hence, one side of the house is toasty warm - the other not so much.


My first impression of the guy was that he is capable and skilled. But i find I am doubting his design. I appreciate his following up (and apologizing for not having a quote sooner) - but he seems to be going in a direction that just doesn't make much sense to me. From re-stacking the exchange unit to massive airways....i'm not sold...


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## 57TinkerMan (Jun 17, 2018)

For the money and ease of installation I would just buy a new air handler:


https://www.acwholesalers.com/Goodman-ARUF43C14/p58563.html


Not saying this is the exact unit to use but I think you would save an equal amount of $$$ doing this instead of spending money/labor on sheet metal fittings, joist cutting etc. converting your down-flow to up-flow.



Solves your down-flow to up-flow conversion, streamlines your (unit) ducting requirements, eliminates all duct in the crawlspace, better airflow design and definitely more professional...


If your lucky your electric heat strips will just bolt in directly. Expect additional costs with the line-set connection, evacuation, charging and some miscellaneous things.


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## supers05 (May 23, 2015)

57TinkerMan said:


> For the money and ease of installation I would just buy a new air handler:
> 
> 
> https://www.acwholesalers.com/Goodman-ARUF43C14/p58563.html
> ...


Don't forget that he still needs a return, and that'll take work. With round duct, the OP could do this all himself. Repiping the coil is often beyond what most DIY's can do. 

Cheers!


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## supers05 (May 23, 2015)

netxtown said:


> Wrench in the cog!
> 
> Got a call from one of the contractors that had come out - and he wants to use fiberboard on the inside of the dropped soffits - and no pipe. he says he can seal it up with no leaks - but IMO it leaves the space unusable for anything else (I had thought about some can lights - especially in the LR). He also claims there is absolutely no problem with re-stacking the exchange unit to make it upflow.
> 
> ...


That must be what he's used to. I can't imagine fiber board being faster then round duct. A single truck like that would be very fast for us. (that's even if we used saddles and not tees for the branches.) 

That air handler has one piece side panels from the pictures I've seen. It's not going to be plug and play changing the blower around. You already get better heat transfer when you pull air through a coil rather then push through the coil. (Even though it's very common in some places to have the coil down steam.) After all that, you'd be voiding the manufactures certifications. It means if anything goes wrong, insurance companies will use it against you. (Or at least sue the contractor) 

Cheers!


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## 57TinkerMan (Jun 17, 2018)

supers05 said:


> Don't forget that he still needs a return.....Repiping the coil is often beyond what most DIY's can do.
> 
> Cheers!



You bring up a good point, a lot of supply air talk here and nothing about the equally important existing R/A.


I was under the impression that an HVAC contractor would be used.


In general, just giving the asked for advice/ideas.


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## netxtown (Mar 18, 2014)

I will be using a HVAC contractor. It is a requirement of the Vet's group paying for all of this. That said, I have to sort through the contractors. And i am fine with doing that - if I could find any level of consensus from them of how to do it all. 

Last week I had 3 guys from one company show up all together. No one took measurements, no one took pics. I told them basically what i would like to have done of bringing the ducting inside rather than it being in the crawl space. They never heard a word I said. Finally, I got a bit gruff - and immediately they clicked into the next great episode of xtreme home makeover.

I've also spoke with two other contractors. Neither has come by to see what is here. I have supplied them with basic drawings to bring it inside, and then nothing more. I even stated in large bold lettering inside the drawings that these are ideas only - and not a blueprint. Still, no quotes.

So, with the excellent input of the folks here, I have been able to assemble what needs to happen, what components, and why. After two weeks of calls, if i can't get some level of consensus from the contractors - then I will provide the consensus to them. The goal here is to get three quotes that are apples to apples. In any case - I have to move forward with this quickly as the funding has a window. Once the window closes - it's over.

This isn't the only work being done here. For all the other areas but one - I've gotten the three quotes, submitted them, and the work was awarded. In fact, one contractor picked up two of the projects and begins work Aug 20.

Could i do the work? Absolutely. But I can't get it done in the time frame needed. Quite frankly, I'm still moving more than a bit slow after 45 radiation treatments for cancer. It will take the wind out of your sail! I may be able to get the "big" aspects injected into the job - but i will be relying on a skilled contractor to know and do the detailed stuff to make it not only right - but good.

But! if all that falls apart..then yes, I _will_ do the work - probably hire someone to help me. It _will_ get done - one way or the other.


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## netxtown (Mar 18, 2014)

supers05 said:


> That air handler has one piece side panels from the pictures I've seen. It's not going to be plug and play changing the blower around. You already get better heat transfer when you pull air through a coil rather then push through the coil. (Even though it's very common in some places to have the coil down steam.) After all that, you'd be voiding the manufactures certifications. It means if anything goes wrong, insurance companies will use it against you. (Or at least sue the contractor)
> 
> Cheers!



A few years back, I replaced the two runs of 12" flexduct that come off the plenum box. I also removed the plenum to see if i could re-position it so that it didn't scrunch one of the flexduct runs so badly. Once the plenum was down, I looked up into the supply port. What i saw from the bottom was heater coils first, then the blower. And of course, the AC coils are on the topside of the unit with the filter above that. 



So, from top to bottom....



Filter
AC Coils
Blower
Heater Coils
then plenum box
then 2 x 12" flex duct runs.


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## supers05 (May 23, 2015)

netxtown said:


> I ...The goal here is to get three quotes that are apples to apples. In any case - I have to move forward with this quickly as the funding has a window. Once the window closes - it's over....


It's been a warm and busy season for most people in North America. I can't wait for winter, lol. Good contractors will be still be pretty busy. Keep trying, and tell them what you want, and be firm. However, you may have no choice, but go with what the locals are used to. 


Cheers!


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## netxtown (Mar 18, 2014)

Another week is coming to a close - and still, not one quote/bid to do the duct work. I have emailed/texted all - and only two responded that they were still interested in doing the work.

I'm running out of time.

A local sheet metal company will make the square ducting. All the round is available from local suppliers. right now, my biggest concern is the elbows. I could use 3 - 90° adjustables to get the 180° below floor turn. Biggest issue here is the short distance between down and up. Would a custom made "plenum box" - rounded, half moon looking - be better? I could make the transition for 12" to 16" within the box.

I've tried to attached a drawing - but the upload says it exceeds the limit. Still trying to figure out how to reduce the size of a pdf! 

And thanks to all who have greatly helped to move this along!


Edit: got the image resized. it's a bit sketchy....


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## yuri (Nov 29, 2008)

Rounded is better so you don't get turbulence. I have seen rounded plenums on old school oil furnaces and it is common in commercial and larger units.


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## netxtown (Mar 18, 2014)

Ok..I'm kind of stuck. I will always try to lay out a 'blue print' of what I'm about to do- complete with measurements and notes, etc. One thing I haven't come across anywhere is how to calculate the space required to make the 180° U-turn. I even pulled down a dwg from mcmaster and I could get pretty close to what was needed using full 90° elbows. And just using 90's, I can fit in a piece to make up the distance from outflow of the exchange to the opening in the floor to come up through. Same goes for dedicated 45's.



But! Following the advice of smoothing the turn as much as possible - I can't find anything on the span distance by using 90° adjustable elbows at 45° or 60°. Is there a table or chart that maybe has the data?


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## netxtown (Mar 18, 2014)

And........this has now become a bonafide DIY. two contractors came out yesterday. Cheapest of the two - just to install new ducting - was $8k. 



I'm not trying to take food off anybody's table. But it makes no sense to me to empty my table to put it all another. That is insane - or maybe i'm just not that generous.


Time to take the drawings and turn them into the real stuff.


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## supers05 (May 23, 2015)

netxtown said:


> And........this has now become a bonafide DIY. two contractors came out yesterday. Cheapest of the two - just to install new ducting - was $8k.
> 
> 
> 
> ...


Was that just ductwork, or also dealing with the bulkhead too? (Framing, drywall, etc?) Just ductwork, that price does sound a bit high. I don't think that they wanna do the work. It's probably not something they do often. 

I was thinking about this thread the other day. How much room do you have between the discharge of the air handler and the floor? Is there any play to increase that distance? 

Cheers!


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## netxtown (Mar 18, 2014)

supers05 said:


> Was that just ductwork, or also dealing with the bulkhead too? (Framing, drywall, etc?) Just ductwork, that price does sound a bit high. I don't think that they wanna do the work. It's probably not something they do often.
> 
> I was thinking about this thread the other day. How much room do you have between the discharge of the air handler and the floor? Is there any play to increase that distance?
> 
> Cheers!



the distance from the downward discharge port and the "hole" in the floor to come back up through is right at 5.5 ft. I will probably go the route of having a custom box built to give a smooth flow (from down to up). 



I've also been reading about main trunk lines - and how they should diminish in size - from large to smaller to maintain good air flow (velocity). The main trunk will consist of 3 - 10ft sections. these sections are being made my a local sheet metal shop. My thought is to use each piece as as stepping stone - 16" to 14", then 14" to 12" - and 12" to the end. I would have to also order some transitions for square to square for the two points of change. Any thoughts/advice on this?


My other concern is condensation. Will the components inside the house need some means to drain condensation? Of course they will be wrapped (2") - but last thing i need (with asthma) is a stew pot in the ceiling for mold!


ugh - I forgot. With 1400 cfm and 1100 sqft - I'm not sure about vent/duct sizing. O've found a dozen or so charts with sizing info - and in most cases I chose a vent/duct that is closest to the rated CFM for a particular room. But, when i then add up all of them - I come out 125 CFM more than what my system is rated. Is that good? bad? indifferent?



here's the latest and greatest...


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## supers05 (May 23, 2015)

netxtown said:


> the distance from the downward discharge port and the "hole" in the floor to come back up through is right at 5.5 ft. I will probably go the route of having a custom box built to give a smooth flow (from down to up).
> 
> 
> 
> ...


You won't need to reduce. As the ductwork will be inside conditioned space, and it's fairly short, it's not needed. It'll be cheaper without the transitions. 

Condensation shouldn't be an issue again because it's inside conditioned space. We use 1/2" insulation to protect against it, when we expect very humid conditions. So, in the end, you should be fine. 

I was asking about the distance between the unit and the hole going through the floor, down. 

Cheers!


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## netxtown (Mar 18, 2014)

I need to re-measure tomorrow to make certain i have correct measurements.


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## netxtown (Mar 18, 2014)

netxtown said:


> I need to re-measure tomorrow to make certain i have correct measurements.



Due to the bunched up mess at the plenum box - I can't get a good measurement. In that, I have decided to go with 16" elbows to make the transition (180°). And, being that i don't know the minimum or maximum distance that the elbows will reach - I'll add an extra piece of 5 ft duct to my materials list.


As I noted above, I am unsure of vent/duct sizing for the 10 vents in the system. I have sized the vent/duct based on cfm for room size - and moving up to the next closest whole number size. BUT!! When i add up the cfm's for those sizes - the sum is greater than the rated output of the system. To me - this means reduced air flow (velocity?).


I have three rooms that have two vents each. My thought is to reduce the size of one vent in each room by an inch to hopefully get a cfm sum that is a little less than the rated CFM of the system.


Truth is > i don't know which way it needs to be. Does x=y, x<y, or x>y ?? Is there an established relationship between system rated cfm and vent/duct total cfm?


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## netxtown (Mar 18, 2014)

Ok. I have rounded up all that I need - except boots and grills. The problem is two fold. (1) Sizing the boot. (2) Sizing the duct for the boot. I have downloaded 4 or 5 charts that show 'duct size = cfm'....but i can find nothing that says 6" duct should connect to X sized boot. As such - I am completely stuck from moving forward.


With the single run of 18hx12w metal duct comes 10 vents. Three rooms get two, the rest get one. I've tried sizing it all up by comparing the total CFM of each duct to the total CFM of the system (1400). I read the duct's total should be greater than or equal to the system CFM. OK. Fine. how much greater is too great?


Then - when I try to 'standardize' the sizing of the ducts - it just goes stupid. I can get 5, 6, 7 or 8" aluminum flex duct without any problem. BUT! I can't find (locally) boots for 5 or 7". And when i go back and change the duct data to reflect 6" or 8", the total cfm rating jumps way up. (1425 to 1610)



Add to this that I have not been able to figure out the other two dimensions of a "boot". 6x4x6? 10x4x6? 12x4x8? I'm not finding the rhyme or reason to size these.


Can someone guide me to a resource, or a method, or anything and anyone who can show me the way?


FWIW - 

Rated CFM: 1400
All ducts come off a straight run of 18hx12w metal duct, 32 ft long
Total of 10 ducting runs (to the vents)
Half of those 10 are no more than 2ft long. The other half is less than 1ft.


If needed I can post the cfm per room calcs.


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## 57TinkerMan (Jun 17, 2018)

Grill and register selection depends on how far you want the air to throw, velocity, noise criteria (NC) and deflection pattern. Open the link below and click on the PDF's for deflection patterns and engineering bulletin. Try to keep you NC around 30. You know what you need per room cfm wise. Browse the selections available and pick what fits your rooms and select your boot size based on your selection.

https://www.supplyhouse.com/Hart-Cooley-80042-A618OB-10-x-6-White-Sidewall-Ceiling-Register


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## supers05 (May 23, 2015)

I could have sworn that I replied to your previous post, but I guess I'm losing my mind. 

Anyhow, the ducts have to be big enough to allow enough airflow at the friction rate that's standard. They can be bigger, without issue. This is especially true if it's only 1 or 2 sizes larger. You'll want each vent to have a damper so that you can restrict it as needed, so you don't over cool/heat the room. As you restrict, duct pressure will build and you'll feel the velocity out of the vents pick up. All, exactly the way you want. 

4x10 registers are very common. Unless you need otherwise, it's what I'd recommend. Use 4, 5, or 6" boots wherever required. (the size of the duct connection.) They should all be available, but if you have to use a reducer, and use only 6" boots with smaller pipes, then that'll work too. You'll want dampers on the grills though. 

https://www.homedepot.ca/en/home/ca...ct-transitions-and-connectors/duct-boots.html

I like the speedi-boots they have. Very convenient for retrofits, especially for DIY'rs. 

I'll get to the actual sizing after work. Hopefully i don't forget. 

Cheers!


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## user_12345a (Nov 23, 2014)

Sizing for sq footage is wrong. You need a room by room load calculation to see how the load is distributed and use 400 cfm per 12 000 btu/hr.


If your unit size exceeds calculated btu/hr, you adjust for that.

Say you have a 3 ton unit on a 2 ton cooling load, you up the cfm by 50%.

---------
There is such a thing as too large ducts relative to airflow -> can have most of the air come out of vents near the furnace/air handler while rooms further from the unit don't get enough.

Unless you have like a 1.5 ton a/c and use 6" or 7" pipes for everything, you probably won't have this problem with 10 vents.

A 6" metal is good for around 100 cfm. Flex, maybe 60.


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## netxtown (Mar 18, 2014)

user_12345a said:


> Sizing for sq footage is wrong. You need a room by room load calculation to see how the load is distributed and use 400 cfm per 12 000 btu/hr.





See a couple posts up. i posted a grid of the sqft/room, cfm per room, etc.


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## supers05 (May 23, 2015)

netxtown said:


> See a couple posts up. i posted a grid of the sqft/room, cfm per room, etc.


He was saying that you should also do a load calculation, whole house and room by room. 

Cheers!


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## netxtown (Mar 18, 2014)

supers05 said:


> He was saying that you should also do a load calculation, whole house and room by room.
> 
> Cheers!



Ok. I may be not understanding. I started with the system at 3.5 tons x 400 = 1400 CFM. Then I measured every room. Total of all rooms is 1099. So, 1400/1099 = 1.273885. Then i went back to the sq ft for each room to get the cfm for that room.


From there - I looked at the CFM for duct sizing across several charts. Unfortunately, there was a wide variance in ratings.


Then i found a basic formula for the grille: H x W x 3 = CFM So, is a 4x10 grille roughly/safely 'good' for 120cfm?




Did i miss a step....or am I off on something completely different?


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## user_12345a (Nov 23, 2014)

Load is not proportional to square footage in each room. You will get in trouble using square footage.

Heat gain/loss is proportional to exposed wall surface area, window area (direction having an impact), exposed ceiling area with adjustment factors applied. There's also infiltration which is at best an estimate.

Think about basic math for a second -> When you calculate area of a square or rectangle, relationship between perimeter and area is not linear. 

Use sq ft to size and smaller rooms won't have enough airflow, bigger rooms will have too much. Corner rooms may have too little, rooms with only one wall too much.

3.5 ton BTW is a heck of a lot for 1400 sq ft space. Hope you're in a brutally hot climate.

------------
You can play with register/grill size quite a bit.

It's a question of what velocity you want. With ceiling vents, at least for cooling, I wouldn't want high velocity - air being forced towards the floor. I would want the air to come out slowly and mix properly.

For heat and ceiling vents, would want the opposite -> air being forced down to the floor, plus some low returns to prevent stratification.


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## supers05 (May 23, 2015)

user_12345a said:


> .....
> You can play with register/grill size quite a bit.
> 
> It's a question of what velocity you want. With ceiling vents, at least for cooling, I wouldn't want high velocity - air being forced towards the floor. I would want the air to come out slowly and mix properly.
> ...


For residential applications, 4x10 universal boots/grills work quite well. Once you include free area, you can very decent velocity. Great mixing at about 3-5 ft from the vent, depending on system pressure and damper position. It is why they are so common. 

The low and high return is a good idea. He will have his mid level anyways, so it'll have similar effects. (better then high or low only, but not as good as if he had both.) 

Cheers!


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## user_12345a (Nov 23, 2014)

Depends on the cfm.

3x10 seems to be common for 5"/50 to 60 cfm.

For 4" metal, the throw may be really lousy using 4x10. But those are only for small bathrooms, walk in closets. don't think op will have any 4" pipes though.


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## supers05 (May 23, 2015)

user_12345a said:


> Depends on the cfm.
> 
> 3x10 seems to be common for 5"/50 to 60 cfm.
> 
> For 4" metal, the throw may be really lousy using 4x10. But those are only for small bathrooms, walk in closets. don't think op will have any 4" pipes though.


It's actually 3.5x10 which is also called 4x10. It's like a 2x4 is actually 1.75 x 3.75

Cheers!


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## netxtown (Mar 18, 2014)

Well - I am way past confused. Unfortunately, when i get to this place of confused- I tend to take the bull by the horns and just plow right on through.


right now - this place has 10 vents - all are 4x10. I can't tell what size pipe is on the back side. 



So - it looks like I am going with 4x12x8 with the associated grill. I'll have to use the dampers on each register to balance out the rooms. There are 4x10x7's but have concern that 2 of them in the largest rooms (LR, Mbdrm, Kitchen) won't be enough. I figure with 8" flex duct to each - I can always turn it down at the register if needed.


I guess this is my way of moving forward. I've lined up all the other parts and pieces - and while I do have concerns about going from the 16" dia hard pipe to the 12x18 duct run - I guess it is just kinda bite the bullet and go.


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## user_12345a (Nov 23, 2014)

Do things right. You're jumping ahead of yourself.

Start with the basics, see how much cooling/heating each room actually needs so the conditioned air can be distributed accordingly.

Don't guess. This is a science.


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## supers05 (May 23, 2015)

netxtown said:


> ...
> right now - this place has 10 vents - all are 4x10. I can't tell what size pipe is on the back side.


Does each room feel the same as the others? Are they noisy? 

Cheers!


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## netxtown (Mar 18, 2014)

It's kinda amazing - and frustrating - when you makeout that final materials list. the overall design goes from 16" diameter pipe to 12x18 main trunk. And, good luck for finding any type of transition!


So, i went back to the original 16x16 square custom bend duct. I'll have some strips cut/bent to seal up the corners. I did find a 16" round to 16" square adaptor, but have yet to find a 16" square end cap.


Being the main trunk runs smack down the middle of the house (at the ceiling), my longest duct run will be less than 12". Typically, I will have about 12" to fit in the take-off and the boot - so the flex duct will only be a few inches long.


I decided to 'oversize' the ducts (8" and a couple 6's) and use the dampers on the registers as a means to hopefully somewhat balance this mess. Most rooms are getting 12x6 - but the larger rooms are 14x6. One is getting a 4x10, and the smallest is getting a 4x8 (tiny bathroom). But again - I'll be depending on the dampers at the registers for balance.


I know this is full of assumptions and guesses. But the bottom line is that the science surrounding HVAC calcs is talked about - but mostly supplanted by 'experience'. And if it really is all about science - then why the hell is most of it hidden behind costly software programs? I guess i just have run into too many 'secrets' in my planning and research. Besides, if in the end the design yields really crappy performance - I can take myself out side and kick my own butt. :biggrin2:


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## supers05 (May 23, 2015)

netxtown said:


> ...
> ..... Besides, if in the end the design yields really crappy performance - I can take myself out side and kick my own butt. :biggrin2:


LOL! [emoji23] 

In the end, all of the math is not that complicated, and can be done by hand on paper. Spreadsheets make it less repetitive. The programs don't make you learn some hvac theory first. 

It's been a lot of posts. Refresh our memory. It's a 3.5 ton / 1400CFM? How long is the main branch and riser going to be? (I couldn't read enough to find it.) 




netxtown said:


> It's kinda amazing - and frustrating - when you makeout that final materials list. the overall design goes from 16" diameter pipe to 12x18 main trunk. And, good luck for finding any type of transition!
> 
> 
> So, i went back to the original 16x16 square custom bend duct. I'll have some strips cut/bent to seal up the corners. I did find a 16" round to 16" square adaptor, but have yet to find a 16" square end cap.


I get everything from sheet metal shops here. It's all hand made. So I'm not sure what's easily available. Some websites will make custom for you, but won't list it. You have to specifically ask. 

Instead of upsizing the vents, the other option is to add more vents. You can push about 1.7xarea in inches worth of air through most grills without hearing at all. When you get to 3x area it's getting a bit noisy. You won't like anything above that. Add up all your grills and it has to be above your total cfm from your unit. (1400) Your grills can add up higher without much issue. Lower and you'll have noise issues. I try to aim for about 2-2.5x area range for cost and noise. 

As long as you have dampers on every grill, oversizing by 1 standard size or so won't hurt at all. We do it all the time too reduce noise. 

Cheers!


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## netxtown (Mar 18, 2014)

Starting from the blower port:
about 5.5 feet of 16" hard pipe to form the 180° turn.
then up about 9 ft to about 3 ft for a 90° turn.
from there it is 30 ft of straight main trunk (16x16)

Due to the positioning of headers above doors - there is only 11" of space between the trunk and the outside edge of the drywall for 4 of the boot/registers. Five will have about 17" to the drywall, and the remaining 1 will have to be a right angle boot due to the angle of the framing that will occur.

I will use semi-rigid aluminum flex (insulated) to connect collars to boots - and i am real glad the drywall won't be in place yet!

FWIW - the LR is the only room that 3 vents might work in. When i added up the CFM for the boots/registers, I got 1330 - so a third vent may well be in order to calm any noise. the LR is also the only room with large windows facing east that gets direct sunlight. (All other windows are heavily shaded by the surrounding trees. I have light - but no direct sunlight)


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## supers05 (May 23, 2015)

netxtown said:


> Starting from the blower port:
> about 5.5 feet of 16" hard pipe to form the 180° turn.
> then up about 9 ft to about 3 ft for a 90° turn.
> from there it is 30 ft of straight main trunk (16x16)
> ...


That sounds like it should work. Try to add the extra registers. 

That'll keep your total friction rate at or just below 0.05"wc. Add the resisters and you should be at or below around 0.1"wc. Should provide plenty of air without much noise. 

Cheers!


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## netxtown (Mar 18, 2014)

And....I'm back.
Insulation. Is it needed when the ducting is INSIDE the house? My plan is to hang the ducting from the ceiling (leaving the sheet rock in place). Being I am using square duct, it becomes imperative that the entire run (32ft) be as straight and level as possible to prevent stress points at the joints.

If i pre-wrap the 5ft pieces (leaving a few inches on each end open for the S&D's), I don't see anyway to make sure all is level and straight. But - hanging the duct first (un-insulated) creates its own problem by making the insulation process virtually impossible due to close proximity to the ceiling.

Which brings me back to my question: Is insulation necessary within the conditioned spaces?


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## supers05 (May 23, 2015)

It's usually not necessary. If you live in an extremely humid place, then I'd tell you try your best to get the insulation on. You can tape it to the top, then stick the duct work up, followed by the insulation for the bottom and sides when you're done. 

Use foil tape to seal the joints. Mastic if you really wanna make sure you have no leaks. However, being inside conditioned space, it's not nearly as important.

PS. The joints will be quite tolerant of stress. Don't stress yourself out over it. Lol. 

Cheers!


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## netxtown (Mar 18, 2014)

Doh!! I really have to let go of this 'all or nothing' thought process! Thank you!!


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## netxtown (Mar 18, 2014)

Your suggestion brought inspiration....so I went back to my drawing board. I can insulate three sides (top, left, and right) but leave the bottom undone. It will allow the ducting to slide across the supports for connecting the sections - and leveling it all. Once done, the bottom can be insulated without much problem at all. I'm using suspended strut channel so no biggie to fidget the insulation into place and then tape it up.


FWIW - my second pair of hands arrives next friday - and I'll post pics as we progress through this. Hopefully all will go smooth and without incident!


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## supers05 (May 23, 2015)

netxtown said:


> Your suggestion brought inspiration....so I went back to my drawing board. I can insulate three sides (top, left, and right) but leave the bottom undone. It will allow the ducting to slide across the supports for connecting the sections - and leveling it all. Once done, the bottom can be insulated without much problem at all. I'm using suspended strut channel so no biggie to fidget the insulation into place and then tape it up.
> 
> 
> FWIW - my second pair of hands arrives next friday - and I'll post pics as we progress through this. Hopefully all will go smooth and without incident!


Strut is good, but a bit overkill. Lol. You could do the whole Hollywood crawl though the ducts thing. Lol. We use 1" wide strips of sheet metal. Sometimes we just use "drive cleat". If you've already bought everything don't worry about it. Your just doing it above the average install. 

Tips: 
- seal the top and sides before you put it up. (seems are under the insulation so that makes sense anyways.) 

- cut the holes for the take-offs (branches) before putting up the ductwork. If you have the room, I even put the spin-on (collar) on age seal it before putting it up. Your supports and other objects may be in the way, so use your best judgment. 

- cut the tabs on one side of the drive on a 45* angle. It'll look like a "V". It'll help you slide them on easy. Open them up a bit with a screwdriver. (Twist, don't push, it'll save your skin from cuts.) http://www.durodyne.com/images/dd_dom_flatdrive.jpg

- use a screw driver to bend open the S lock on one end. It'll make your life easier. 
http://www.durodyne.com/images/dd_dom_flats.jpg

- sheet metal screws are you friend. Use them to keep the ductwork from sliding on the supports. 

- leave a 1/8" inch above the ductwork, below the ceiling. It'll leave room for expansion during heating and will reduce the associated noises. 

- don't forget to put the block end on. Lol, it happens. 

- I'd suggest to wear gloves, as things get sharp. 


Cheers!


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