# Anyone want to help me build my own ducted whole house fan?



## mikegp (Jul 17, 2011)




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## Bud9051 (Nov 11, 2015)

Hi Mike, as always, the devil is in the details.
Some of those details involve where you are and how you heat and ac your house. I'll just number a couple of thoughts.
1. If you have any naturally drafted appliances, like a furnace, water heater, or wood stove, then you need to be concerned about backdrafting.
2. When the fan is not needed, you need to be able to seal off any air flow.
3. When the fan is running, where will the replacement air come from. If you forget to open a window or even with one open, air will be pulled into the house through all of the leaks, filtering out any dust particals and leaving them inside your walls.

Bud


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## ChuckF. (Aug 25, 2013)

Mounting the fan like in the first picture will give excellent isolation from the noise of the fan, which is considerable. Mounting it solidly to the ceiling joists and sheetrock tends to amplify that sound.

Further to Bud's #3, you need a lot of intake openings to balance the outflow from the fan. You also need to distribute those openings; if for example you have one large window in one room feeding the fan, then all you have is a single column of air in that window and up into the attic, and nothing in the other rooms. You need to do more to circulate the air, like leaving 'Fan' on the thermostat on, or running every ceiling fan you have. All this adds to power consumption.

You will definitely want a speed controller and a timer on the fan.

I believe a better solution to whole-house fans is a open/closeable fresh air intake on the HVAC system. Advantages: inherent filtering, inherent distribution, results in positive pressurization of home rather than negative, quiet. You might still need to open a window or two, but you would be blowing out rather than sucking bugs in.


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## mikegp (Jul 17, 2011)

ChuckF. said:


> I believe a better solution to whole-house fans is a open/closeable fresh air intake on the HVAC system. Advantages: inherent filtering, inherent distribution, results in positive pressurization of home rather than negative, quiet. You might still need to open a window or two, but you would be blowing out rather than sucking bugs in.


Any idea where I can find more info on that or what I can search? I'm guessing I would want to connect the return side of my air handler to a gable vent or something similar? Only concerns there would be pulling in outside air and filtering issues leading to a dirty coil and/or the air handler using more power than the WHF. Thanks for the idea.


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## mikegp (Jul 17, 2011)

Also, I have a 3 ton system. Wouldn't that only move about 1500cfm?

Condensation in the ducts also would worry me.


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## SeniorSitizen (Sep 10, 2012)

For noise to cfm ratio I'd go with a squirrel cage blower.


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## Bud9051 (Nov 11, 2015)

I didn't see a reply to #1 the issue of naturally drafted appliances. A WHF, if you go that route, can pull all of that exhaust back into the house. 

I do like WHFs but one needs to be careful.

Bud


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## mikegp (Jul 17, 2011)

Thanks Bud. Yea, I'm aware of the pros and cons of the WHF. I've been researching it on and off for a couple of years now. I have a gas water heater and a furnace for a hydro-air setup in my basement. Both are power vented and in a room with a weather seal door. I don't think it should be an issue. The furnace won't ever be on at the same time which just leaves the water heater. Also, it doesn't have a pilot.


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## mikegp (Jul 17, 2011)

SS, can I get that in a decent CFM rating? I looked at them a few weeks ago, but couldn't find anything with 3000-4000cfm.


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## mikegp (Jul 17, 2011)

Also, looking for a decent source for the flex vent. Do I need something reinforced so it doesn't get sucked closed?


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## SeniorSitizen (Sep 10, 2012)

mikegp said:


> SS, can I get that in a decent CFM rating? I looked at them a few weeks ago, but couldn't find anything with 3000-4000cfm.


Dayton has a few cfm choices but don't see anything with near your requirements. May need to go industrial.


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## craig11152 (Jun 20, 2015)

I've often thought a whole house fan that vented straight outside and skipped the attic space would make some sense. I used to have this vision of somehow combining one with a roof exhaust fan in a giant duct would be swell. Turn both those on and make sure your toddlers don't get sucked up to the ceiling. :biggrin2:


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## mikegp (Jul 17, 2011)

craig11152 said:


> I've often thought a whole house fan that vented straight outside and skipped the attic space would make some sense. I used to have this vision of somehow combining one with a roof exhaust fan in a giant duct would be swell. Turn both those on and make sure your toddlers don't get sucked up to the ceiling. :biggrin2:


I've seen those. The issue with that is I want to cool my attic as well. The WHF should blow enough air out of all of the attic vents to help. It's going to be filling the attic with 3000+ cfm of 60-75 degree air. Should help reduce the extra heat that radiates down causing a temperature rise even after the sun goes down and outside temps drop.


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## carpdad (Oct 11, 2010)

Only time I'd think about the whf was in the evening when the outdoor was cool but inside was still hot. These would be the only times when I wanted the whf. But my parents had one, and they'd rarely use it, foremost being it was very drafty in the winters (NJ). As they got older and got used to spending some money on AC bills, they stopped pestering me for the yearly tape on/tape off of the plastic sheet on the grill.:smile:
But if you love the idea of whf, I'd build min R30 foam door that can be closed when the house is cooled. Beveled foam block insulated door panel that closes tight to the matching block of foam. You'd still manually have to open and close this vent/door, but the auto kinds are expensive. The fan on the roof and no need for a duct. You want to cool the living space as well as the attic, so using a duct to bypass the attic would be a waste.


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## mikegp (Jul 17, 2011)

I made an insulated box cover for my attic stairs. I would do the same if got the regular WHF that goes in the ceiling. I haven't decided what I would do with this one. It would end up leaving a 16 inch or so hole in the ceiling so I'd probably just disconnect the duct and either make a round R5 foam board cover to fit in the hole and caulk it in every year, or a small square piece with weatherstripping and some weight to push it down. Then just throw the bats over it. Should have better R value than just the drywall would, so as long as the air seal is tight it should be fine.

Also, I open my windows almost every night in the summer. Unless it's humid out. I don't really use AC at night. This would actually use more energy, because I normally have nothing on at night, but it would make comfort levels better quicker. Plus I like the idea of being able to clear the house of smells, smoke, etc in minutes.


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## ktkelly (Apr 7, 2007)

I posted about this same thing in another thread.

Used an old squirrel cage from when I replaced the air handler in the old HVAC system.


I mounted a prefab 24x24 air return plenum and a nice fold down air return grill in the laundry room at the far end of the house, connected some 18" duct to the plenum, and to the squirrel cage fan mounted in the attic.

Wired in a timer switch and it was off to the races.


It moves plenty enough air, and I can simply install a piece of stiff foam board, where the filter usually goes, for those cold months when the fan isn't used.



I've had one of the big whole house fans, and honestly, it pulled too much air. Who needs gale force winds going thru the house....:surprise:


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