# New 22' Trunk Line



## unixb0y (Sep 30, 2008)

What are your opinions on this DVD
http://www.ductworks.net/xcart/home.php?js=y


----------



## unixb0y (Sep 30, 2008)

or this
http://www.alpinehomeair.com/installVideos.cfm

I'm also going to be replacing the the furnace. I would like to keep the AC however it seems to me that I might have to buy a new coil for the furnace. I'm wondering where the coil part number is located. Right now, I can't get to the coil.


----------



## AndrewF (Dec 29, 2008)

I dont know about either of those links.

I did upgrade my main trunk for both supply and return, not something I really want to do again. Was a lot of work and took two guys many hours to do the project. My supply trunk was about 50' long and my return was about 30'.

My thread can be found: http://www.diychatroom.com/f17/hvac-airflow-issue-34616/

If you have a lot of takeoffs, getting them cut in the exact spot again and sealed will be very time consuming. 
If you plan on using hand cutters to cut them in, find some thick gloves, otherwise, plan on having cut up hands.

Is your furnace in the middle now? What is the size of your current trunk, what about your return trunk?
What is the size of your furnace? How many takeoffs? Any photos?

Is this an oil or gas furnace?


----------



## unixb0y (Sep 30, 2008)

AndrewF said:


> I dont know about either of those links.
> 
> I did upgrade my main trunk for both supply and return, not something I really want to do again. Was a lot of work and took two guys many hours to do the project. My supply trunk was about 50' long and my return was about 30'.
> 
> ...


People have quoted several thousand the do the work.



> If you plan on using hand cutters to cut them in, find some thick gloves, otherwise, plan on having cut up hands.


I was planning on getting an electric shear ($90) and ebaying it after the project is complete. Thanks for the info on the gloves.



> Is your furnace in the middle now?


That the other end of the basement

crappy diagram would be:
---a------------------b---

Moving from a to b




> What is the size of your current trunk, what about your return trunk?


It's staggered from "wide" at the furnace end to small at the other end. I have to get the replacement duct/furnace sized.




> What is the size of your furnace?


100,000BTU is the current furnace.



> How many takeoffs?


There will be 9 or 10 Takeoffs



> Any photos?


Not yet. Maybe someday :jester:


> Is this an oil or gas furnace?


Natural Gas. Where I'm moving the furnace to is the location of where the gas line comes into the house.


----------



## beenthere (Oct 11, 2008)

What size is your A/C, and is it the right size. Just because it cools the house, doesn't mean its not oversized.
What size furnace do you really need.


----------



## plummen (Jan 10, 2010)

Sizing ductwork is more complicated than most people realize,ive been in the trades many years and even I tend to leave that part of the job to my tinner.


----------



## unixb0y (Sep 30, 2008)

I have another related question. I'm thinking of getting a Rudd modulating furnace.

Reading the spec sheet I noticed "Optional indoor or outdoor combustion air".

What are the advantages/disadvantages of using combustion air from outdoors or indoors? Is it just a mater of temp rise requirements?


----------



## beenthere (Oct 11, 2008)

Outside comustion air i cleaner then inside.

When you use inside combustion air. You end up drawing in cold dry air into the house. And lower the humidity of the house. Causing you to either have to have a dehumidifier, or tolerate the dryness.


----------



## jogr (Jul 24, 2007)

I suppose it would be too much to hope for that you could reverse the existing trunks and that at least some of takeoffs would line up.


----------



## BobCaygeon (Apr 19, 2010)

Sizing duct is bit more involved, depending on the need for offsets, risers, 45*,90* ect.. But far as installing the duct work goes, it's not all that difficult really, 

"S" cleats are for the top and bottom of duct, Drive cleats are for the sides, Bend the Short side of duct 1\2 " for drive cleats, take your measurements from the 1\2 " fold for overall length of duct section, and take offs. Don't put any take offs in fittings such as reducers or 90*, 45*. Cut your duct before you snap it together with a pair of bulldogs, you'll have to knotch out the button lock and the 4 corners 1" notch on field cuts for your "S" cleat to fit.

Make up a template from the take off's or just place them on the "snapped together" duct where they need to be and mark in the 4 corners of the take off, get a good blade screw driver and hammer a slice diagonally across the cut out for the take off, grab Red= Left cut, Green= Right cut Yellow = straight cut snipes and cut it out.


----------



## hvaclover (Oct 2, 2008)

unixb0y said:


> I have another related question. I'm thinking of getting a Rudd modulating furnace.
> 
> Reading the spec sheet I noticed "Optional indoor or outdoor combustion air".
> 
> What are the advantages/disadvantages of using combustion air from outdoors or indoors? Is it just a mater of temp rise requirements?


You are one brave man sizing duct work for the most temperamental style of furnace when it comes to air flow.

I don't wish you ill but you WILL have uneven temps if you don't use a pro who has had some trail and error experience with a mod furnace.


----------



## unixb0y (Sep 30, 2008)

hvaclover said:


> You are one brave man sizing duct work for the most temperamental style of furnace when it comes to air flow.
> 
> I don't wish you ill but you WILL have uneven temps if you don't use a pro who has had some trail and error experience with a mod furnace.


Well I have not purchased anything yet. So for the time being, I'm not tied to anything.

The HVAC person connecting the gas/vent recomended a mod. I guess I did not think it as temperamental but that does make sense.


----------



## Marty S. (Oct 31, 2009)

Google Malco HC1. That's what you want to use to make the take off holes. With an electric drill and that tool each hole will take you less then 30 seconds. Measure and cut the holes before you hang each piece of duct.


----------



## hvaclover (Oct 2, 2008)

Marty S. said:


> Google Malco HC1. That's what you want to use to make the take off holes. With an electric drill and that tool each hole will take you less then 30 seconds. Measure and cut the holes before you hang each piece of duct.


~snicker~ only guys who can't cut round holes use those. And there is a learning curve to overcome so for a one time installation I would not recommend it.


----------



## unixb0y (Sep 30, 2008)

I finally got the information entered into HVAC calc. It's showing gain of 22376BTU and a loss of 54843

THe RGFD-06EMCK that I'm thinking of getting is 55800BTU. That 1.7%

I think I'll need to triple check hvac calc and make sure my load is correct.


----------



## unixb0y (Sep 30, 2008)

Looks like I was missing the basement walls.


----------



## beenthere (Oct 11, 2008)

So what size is your current A/C?

I don't see anything added for your kitchen appliances.
What infiltration rate did you use?


----------



## unixb0y (Sep 30, 2008)

beenthere said:


> So what size is your current A/C?


 It's a Carrier 38RE030 installed in 1982.



> I don't see anything added for your kitchen appliances.


I guess I'll have to read more about this in the hvac calc manual.



> What infiltration rate did you use?


I used poor. The house was built in 1945. But I have triple pane windows from 1988.

For the walls I used R11. It has the original siding on. I know that there were the following retrofits

1) Cellulose was blown in at one time
2) Aluminum siding was added and there is some foam attached to the sheathing.

Changing the infiltration to average seem to drop the cooling to 1.5ton and the heating to 44000 BTU.

I did have an infiltration test done before BUT that was with a 6" make up air, 6" fresh air and 7" chimney. 

Those results were:
5.03 ACH(Air Changes per hour) @ 50Pa
Equivalent air leakage: 860cm2 (334.6 inches squared).


----------



## unixb0y (Sep 30, 2008)

unixb0y said:


> Those results were:
> 5.03 ACH(Air Changes per hour) @ 50Pa
> Equivalent air leakage: 860cm2 (334.6 inches squared).


From the googling I did, It looks like the ACH can be divided by 20 to get the infiltration rate. That gives me an infiltration rate of 0.2515.

That seems low considering the value that can be set in HVAC-Calc. I guess I'll use the setting of average in HVAC-Calc.


----------



## hvaclover (Oct 2, 2008)

unixb0y said:


> From the googling I did, It looks like the ACH can be divided by 20 to get the infiltration rate. That gives me an infiltration rate of 0.2515.
> 
> That seems low considering the value that can be set in HVAC-Calc. I guess I'll use the setting of average in HVAC-Calc.


I'd ask Beenthere about that first. I have heard there are some discrepancies in the soft ware.


----------



## beenthere (Oct 11, 2008)

How dry was/is your home in the winter? 
Do you have to use a humidifier to keep the house from getting to dry?

If no to any of the above questions. Using .25, or tight in HVAC calc is fine.


----------



## unixb0y (Sep 30, 2008)

beenthere said:


> How dry was/is your home in the winter?
> Do you have to use a humidifier to keep the house from getting to dry?
> 
> If no to any of the above questions. Using .25, or tight in HVAC calc is fine.


We have been living in the 1945 house for 4 years now. The house had a humidifier BUT it's not connected. It got disconnected during a past galvanized pipe to copper conversion.

I'm not sure under what circumstances we would use a humidifier.

He haven't had a problem with static on carpet or clothing. I'm not sure if that helps.


----------



## beenthere (Oct 11, 2008)

A humidifier would be used in the winter.

If you don't have a low humidity problem in the winter.

You can use .25 for summer and .5 for winter infiltration.


----------



## unixb0y (Sep 30, 2008)

If I'm going to have a furnace, AC, Humidifier and possibly a HRV(in the future), What is the spec on the wiring to the thermostat?


----------



## beenthere (Oct 11, 2008)

Depends what thermostat you use.


----------



## unixb0y (Sep 30, 2008)

beenthere said:


> Depends what thermostat you use.


White Rogers 1F95-1291


----------



## beenthere (Oct 11, 2008)

That stat can't control a humidifier or ERV.

So for a single furnace, and a single stage A/C, 5 wires.


----------



## unixb0y (Sep 30, 2008)

I have noticed that some furnace installs have raised the furnace off the ground.

In one case, I presume this is an effort to reuse the plenum. THey used cinder blocks and dense foam insulation.

In another case, i suspect the installer wanted the keep the furnace off the concrete in case of the flood/damp basement. The installer used PVC pipe as legs to get off the floor.

Are there any other reasons to not put the furnace directly on the concrete basement slab?


----------



## unixb0y (Sep 30, 2008)

beenthere said:


> That stat can't control a humidifier or ERV.
> 
> So for a single furnace, and a single stage A/C, 5 wires.


Do the cables come in 5 wire bundles?


----------



## beenthere (Oct 11, 2008)

Keeping the furnace jacket off the floor, helps to prevent rusting out. They make plastic feet for this.

Yes, thermostat wire comes in 5 wire. Should always run extra. You would be surprised how often having extra wires has saved another thermostat line from having to be ran.


----------



## unixb0y (Sep 30, 2008)

beenthere said:


> Keeping the furnace jacket off the floor, helps to prevent rusting out. They make plastic feet for this.
> 
> Yes, thermostat wire comes in 5 wire. Should always run extra. You would be surprised how often having extra wires has saved another thermostat line from having to be ran.


I was planning on running 2 cables(each with 5 wires) to future proof things.

In reading the specs, it looks like the furnace will use 8.7A. Should 14.2 be ok or should I use 12.2?


----------



## beenthere (Oct 11, 2008)

14/2 is fine for a furnace.


----------



## unixb0y (Sep 30, 2008)

I need to tie into square stack boots that are 3x12 inch. There doesn't seem to be anything on the market that is affordable that will tie in to round duct.

So what I was going to do is reuse the stack boots, add a 3x12 to 3x10 reducer and then add a universal boot to convert the 3x10 to either 4,5 or 6 inch round pipe.

I spent some time tonight trying to build a paper template for a 3x12 to 3 1/4x10 reduction. I was attempting to make a one piece reducer that I could bend with a 24" brake.

So far, I haven't been successful designing a reducer with the least amount of pieces.

At this point, I think I'm going to make a top, bottom, and 2 sides with 90 deg bends and screw/mastic the reducer.

I'm looking for suggestions on how to build the reducer with the least amount of pieces and screws


----------



## beenthere (Oct 11, 2008)

Can you get a 3¼X12 boot to fit on the 3X12 stack?

A reducer like that, is generally made from 1 piece of metal. Just have to decide if you want it to reduce to one side, or reduce tot he middle/center.


----------



## unixb0y (Sep 30, 2008)

beenthere said:


> Can you get a 3¼X12 boot to fit on the 3X12 stack?
> 
> A reducer like that, is generally made from 1 piece of metal. Just have to decide if you want it to reduce to one side, or reduce tot he middle/center.


I'd like to reduce it in the middle as the duct is located between floor joists. So far I have not been able to find a template or stocked piece online.


----------



## unixb0y (Sep 30, 2008)

Well I managed to get the reducers made for $10 each. So that was nice.

Now I'm wondering if It a good idea to have a take off on the top of the supply plenum?


----------



## beenthere (Oct 11, 2008)

50/50.

A single take off or 2, is no real problem.


----------



## unixb0y (Sep 30, 2008)

beenthere said:


> 50/50.
> 
> A single take off or 2, is no real problem.


This particular take off will only need to be 3 feet long.

It will be going to an inside wall in the living room. I have an older house and in this case, I'll be working with what I have.

My concern is the noise with this particular register. Am I wrong to assume that this takeoff/register will get the brunt of the pressure and therefor be noisy?


----------



## beenthere (Oct 11, 2008)

It could be noisy only being 3 foot long. Being flex duct will help to minimize some of the noise.


----------



## unixb0y (Sep 30, 2008)

beenthere said:


> 50/50.
> 
> A single take off or 2, is no real problem.


Does it matter if the take off is on the side or the top of the plenum?


----------



## beenthere (Oct 11, 2008)

Side has less turbulence from velocity.


----------



## unixb0y (Sep 30, 2008)

Is the using the duct calculator in HVAC calc good enough?


----------



## beenthere (Oct 11, 2008)

Unfortunately. It leaves a lot to be desired.

Your furnace blower. Won't be able to work against the amount of static pressure that a 4" pipe moving 85 CFM would need.
It would take a supply static of .5" to move that much air through a 4" pipe. Add on what the return would be. And its too much for the blower.

On some 6" runs. Its hard to get a full 85 CFM through them. Depending how long they are, and if they have any ells in them.


----------



## unixb0y (Sep 30, 2008)

beenthere said:


> Unfortunately. It leaves a lot to be desired.
> 
> Your furnace blower. Won't be able to work against the amount of static pressure that a 4" pipe moving 85 CFM would need.
> It would take a supply static of .5" to move that much air through a 4" pipe. Add on what the return would be. And its too much for the blower.
> ...


I was going to disregard hvac calc and use 6" for the upstairs runs. 1 room run is 10' while the other 2 rooms are 14'.

All the other runs are shorter. I was then going to use 5 inch on the main floor and 3 inch in the basement.

Can the CFM in hvac calc be trusted? Should I go off of that to figure things out?

Is there anything I can use that's inexpensive to figure it out myself?


----------



## beenthere (Oct 11, 2008)

You'll find a fair number of your rooms upstairs will be better off with 7". Better off not using 5" on the first floor. First floor needs more heat in winter. Second floor more cooling in summer.

Its easier to install dampers in the supply runs and throttle them down for balancing. Then it is to get more air out of a smaller pipe.

The CFM's are generally ok in HVAC Calc.

A copy of Manual D and a duculator will help you figure out what size ducts to runs.

Manual D will help you determine what friction rate to use. And eh Duculator will tel you what size duct will have that friction rate for that CFM.


----------



## unixb0y (Sep 30, 2008)

beenthere said:


> A copy of Manual D and a duculator will help you figure out what size ducts to runs.
> 
> Manual D will help you determine what friction rate to use. And eh Duculator will tel you what size duct will have that friction rate for that CFM.


Is there maybe a typo in the above?

That or I'm confused

I managed to pull out each room cfm (HVAC-calc) and picked an existing duct size (7 inch) and was able to figure out the friction rate based on the length of the run.

Now what do I do with all the friction rates?


----------



## hvaclover (Oct 2, 2008)

Now u try to stay as close as to those friction numbers.

Never seen a resi duct redesign that didn't have to scarfice somewhere to make any kind of an improvement to gain optimal airflow and till be quiet enough


----------



## beenthere (Oct 11, 2008)

unixb0y said:


> Is there maybe a typo in the above?
> 
> That or I'm confused
> 
> ...


How did you determine what the length was. What did you use to determine what the equivalent length is of the register boots, and the take offs, and transitions in the duct.

How did you determine what the friction rate was? Did you measure the actual CFM through each of those pipes, and then measure the pressure drop for each of those pipes?


----------

