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Old 09-05-2019, 01:16 PM   #1
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Default Whole house fan

I’ve wired a few on new construction but never bought one and was thinking about one for my home. What do I need to know? It’s 2k sqft and 2 stories

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Old 09-05-2019, 01:23 PM   #2
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I have one, I don't use it anymore.

When it is cool and dry outside but stagnant (no wind) a whole house fan can draw that cool air inside very well.

But it only helps if the air outside is cooler than the temperature you want the inside to be, and less humid.

The biggest issue with me was dust, it brought in an awful amount of dust that covered everything in the house. Depending on the time of year, pollen too. I would find neon green dust on everything in the house. It also brought in fruit flies (gnats) by sucking them right thru the screens. I had to leave the light on in the hallway to attract the flies, then they would get sucked up thru the WHF.

In most of the situations that I would use a WHF now, I just leave the AC on. Clean, dry, cool air.
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Old 09-05-2019, 01:30 PM   #3
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WHF work best if they just extract air from the garage after the Sun goes down.

A fan that just extracts air from the attic also has merit.

Both locations are heat traps that eventually bleed through heat into your living space.

Also of merit: insulate your garage door. That puppy is a solar collector, no doubt.
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Old 09-05-2019, 01:34 PM   #4
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Quote:
Originally Posted by telsa View Post
WHF work best if they just extract air from the garage after the Sun goes down.

A fan that just extracts air from the attic also has merit.

Both locations are heat traps that eventually bleed through heat into your living space.

Also of merit: insulate your garage door. That puppy is a solar collector, no doubt.
In my opinion, you would be better off spending the time/monty both air sealing the attic and installing more insulation. The heat in the attic generally goes up anyway, less intrusion into the house than cold air. So if you spray foam around any protrusions, foam a cocoon over ceiling boxes, and install gaskets on device cover plates, it should seal it up pretty well. Then allow passive ventilation to remove the heat from the attic. In my research, using a powered attic fan doesn't make up for the electricity that it uses.
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Old 09-05-2019, 02:20 PM   #5
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We LOVE our whole house fan and have used them for about 40 years in two different houses. We keep the house sealed up during the day keep AC off while at work. Turn the AC for maybe 2 hours or so in the evening, then use the whole house fan after the sun goes down. Only open the windows for where you are sitting, like in kitchen or living room and this gives us a nice breeze.

Opening and closing windows as needed takes a little thought but is worth it. Our monthly energy report from electric company always shows us using less than an “energy efficient house” of similar size.

It can draw in dust but that may be somewhat controlled by not having mulch or dusty areas near the open window(s) that is used as air intake.

Constantly breathing recycled air from AC’s can’t be good for us either.

Fortunately, no one in our family has allergies. That may be a deal breaker for you.
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Old 09-05-2019, 02:27 PM   #6
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If you are going to do like bill39 does and only open a few windows at a time, then you might want to try a powerful window fan before investing the time and money into a full WHF installation.

Put the window fan into a back window somewhere that it's not in the way. And I don't mean one of those little plastic dinky 2-fan things. Something powerful. That's what I do now to bring in more of the cool air on nice nights.
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Old 09-05-2019, 02:27 PM   #7
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To answer your question about how to size your fan, just go to a big box store an look at the various fan sizes. The recommended house square footage is usually listed.

https://www.lowes.com/pd/Air-Vent-30...se-Fan/3563350
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Old 09-05-2019, 09:30 PM   #8
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The newer whole house fans need air flow to keep from kicking thermal overload, be sure attic has enough ventilation (learned this the hard way)

We use ours a lot, even had one summer when we never turned on AC, been about 50/50 this year
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Old 09-06-2019, 12:42 AM   #9
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Hack... They make dust control window screens.

We have a WHF and it is simply awesome. I am adjacent to Cali farm land, which means a lot of dry and dusty tilling goin on. We have dust screens installed, and it isn't perfect, but better than without and running the AC.

Our electric bill in the summer used to be in the $500-$600 range. After the WHF and a smart T-Stat with room sensors, we are down in the $300 range. Halved without doing any other modifications.

This winter we will be installing radiant sheeting in the attic and extra insulation. That should further reduce the bill. After that I will finally look over solar, but only because I can personally install it.
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Old 09-06-2019, 06:24 AM   #10
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Quote:
Originally Posted by Switched View Post
This winter we will be installing radiant sheeting in the attic and extra insulation. That should further reduce the bill. After that I will finally look over solar, but only because I can personally install it.
Before the insulation, make sure to take a few cans of spray foam and seal any protrusion. Fiberglass does not stop airflow thru it so any hole underneath it around vent pipes or wires will have air flowing thru.

When insulating, fill up the joist space, then go across the top of the joists to stop thermal bridging.
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Old 09-06-2019, 06:56 AM   #11
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I have an attic fan, it works pretty well keeping the AC use to a minimum. Summer here, even in the hottest weather it usually cools down quite a bit at night.

I just open the front and back door and the attic door and let the fan run a couple hours at night and an hour or so before I leave for work in the morning. Barely any air conditioning needed this year, occasional ceiling fan use. Nice to get some fresh air, too.

During the day it's on a thermostat to keep the attic from getting too hot. Not comfortable to be in there on a hot day, but not so hot that the stuff I store up there gets baked daily.
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Old 09-06-2019, 08:09 AM   #12
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Quote:
Originally Posted by Switched View Post
Hack... They make dust control window screens.

We have a WHF and it is simply awesome. I am adjacent to Cali farm land, which means a lot of dry and dusty tilling goin on. We have dust screens installed, and it isn't perfect, but better than without and running the AC.

Our electric bill in the summer used to be in the $500-$600 range. After the WHF and a smart T-Stat with room sensors, we are down in the $300 range. Halved without doing any other modifications.

This winter we will be installing radiant sheeting in the attic and extra insulation. That should further reduce the bill. After that I will finally look over solar, but only because I can personally install it.
After reading that I'm never going to think about my electric bill again....

Run a 2 ton an 3 ton heatpumps, 100 gal water heater, pool pump, stove, ovens, and never more than $200 bill.
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Old 09-06-2019, 08:14 AM   #13
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We've had energy codes for decades now and often it's much cooler outside yet our A/C systems are chugging along. Makes no sense.

If you want more efficient air conditioning, get a big dehumidifier. I don't mean one that sits on the floor. One with duct work. We run a dehumidifier at 30% and have the t-stat for the A/C at 84 and it feels cold inside. Electric bill went way down when I did that.

The specific heat (how much energy it takes to change the temperature) of water vapor is more than 4x that of N2 or O2. Get rid of the water vapor and it's much easier to cool the air.
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Old 09-06-2019, 09:46 AM   #14
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Quote:
Originally Posted by MikeFL View Post
We've had energy codes for decades now and often it's much cooler outside yet our A/C systems are chugging along. Makes no sense.

If you want more efficient air conditioning, get a big dehumidifier. I don't mean one that sits on the floor. One with duct work. We run a dehumidifier at 30% and have the t-stat for the A/C at 84 and it feels cold inside. Electric bill went way down when I did that.

The specific heat (how much energy it takes to change the temperature) of water vapor is more than 4x that of N2 or O2. Get rid of the water vapor and it's much easier to cool the air.
Interesting idea.

I have a fish tank and I think it makes my house humid.
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Old 09-06-2019, 09:54 AM   #15
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Quote:
Originally Posted by MikeFL View Post
We've had energy codes for decades now and often it's much cooler outside yet our A/C systems are chugging along. Makes no sense.

If you want more efficient air conditioning, get a big dehumidifier. I don't mean one that sits on the floor. One with duct work. We run a dehumidifier at 30% and have the t-stat for the A/C at 84 and it feels cold inside. Electric bill went way down when I did that.
That's good info, I know that when it's reasonably dry people don't really start turning on AC until it's over 75-77F. It gets humid, it's on at 72.

Quote:
The specific heat (how much energy it takes to change the temperature) of water vapor is more than 4x that of N2 or O2. Get rid of the water vapor and it's much easier to cool the air.
This part I have heard people go back and forth about. I thought that regular AC worked much better with humid air, basically the water vapor carries the heat to / from the coils better. In desert areas they use swamp coolers so it's a different dynamic.
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Old 09-06-2019, 10:31 AM   #16
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A couple videos on adding dehumidification to central AC:


Dehumidifier discussion starts at 4:40 and more at 11:50:

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Old 09-07-2019, 12:02 AM   #17
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Those videos cracked me up.

Who has such clean, empty attics?

I, like so many, have absolutely ZERO chance of adding additional insulation.

I'd have to rip off my roof to get to half my attic.

Yeah, other than the HVAC junk, I don't have an attic.

I'm screwed for solar, too.

There are a LOT of homes like mine.

For us, forced ventilation is the only viable solution.

Such is reality.
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Old 09-07-2019, 03:40 PM   #18
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I put in a 36” whole house fan when I knocked the house down and rebuilt it. It was just one of those things I put in many houses that I always wanted myself. Like an intercom system with music. Well at least I use the intercom system. For me there’s only a few days a year that are good to turn on the fan. Must days are just to humid. In the evening, as the air gets cooler, the humidity goes up, so it’s just as uncomfortable.

I run a dehumidifier in the basement all summer. I think it does a pretty good job of doing more than just the basement. My house is pretty well insulated, except the big hole in the ceiling for the hole house fan. I can keep the windows closed and the air turned up to 80 all day when I’m not home. When I come home the house is still less than 80. If it’s real dry out I may open the windows, if not then I just turn on the AC. Maybe two or three times a year I’ll turn on the fan for a quick cool down. It also came in handy when I set off the smoke detectors while cooking.

I have a switch next to it in the attic. In the winter I shut off the switch and pack it with insulation. I also put it on a hinge with two thumb screws on the other side with small “L” brackets. So I just lift it up, pack it good, and close it.

I also built a angled box to help push out the attic air. I’m not sure if it helped put it on the same angle as the gable louver. I was hoping not to add any other vents in the attic for the whole house fan. I have gable vents, soffit vents, and a ridge vent. It probably is starved a little for exhaust air. I can hear a difference in the fan when I open the attic pull down stairs.

Heated some pics. Yeah I know, it’s not legal to put the Gable fan on a cord. At the time the box was experimental. My solar DC circuits are run inside the house so you don’t see it outside. It pokes through the roof under a panel with a roof flange. There’s an LB under the panel with a chase nipple in it, pointing down the roof.
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Whole house fan-db9f1140-2052-4c1c-b7bd-2a66b82deaf2.jpg  

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Old 09-07-2019, 03:56 PM   #19
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Nice! Clean work.

I have an antenna mounted in my attic too, aimed directly at the Empire State Building for HD network channels. I don't use it much, but it's good to have incase I ever lose the internet.
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Old 09-07-2019, 04:20 PM   #20
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https://www.ecomfort.com/fan/quietco...0aAmSQEALw_wcB



No centrally located noisy fan in your ceiling and no noisy louvers.
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