Whole house fan - push the air into the attic? Or duct it outdoors?

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Old 05-01-18, 08:43 AM
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Whole house fan - push the air into the attic? Or duct it outdoors?

We have a powered 'whole house' fan mounted in the ceiling of our 2nd floor. It pulls the air up into the attic, where it then should find its way out the gables and soffits.

Causes a nice breeze in the house when we open windows throughout the house.

This came with the house when we bought it 23 years ago (and still running : )

Over the last few years (not sure if I just became aware of it or something changed), but sometimes if I put my hand over a wall switch on the 2nd floor, I can feel air coming OUT of the wall switch when the fan is running.

Yes, best practice is to caulk around the wires coming up into the attic. But skipping that, this kinda points to the attic getting pressurized from the air being forced up there and can't get all of it out the soffits / gables.

We are getting a new roof soon and mentioned this issue / wondered if the ridge vent the roof installed said he'd install would solve the issue.

He made an offhand comment about the whole house fan not being ducted out of the house.

I had never thought of that... the powered fan is 2' in diameter at least. That would need 2' ducting and a hole on the side of the house 2' in diameter, right? (and not through the roof, right?

Of course, the fan is kinda in the middle of the house so you'd have 15 - 20' of 2' duct in the attic?

What are the experts thoughts on ducting the whole house fan out of the attic? Or just putting it up in the attic is OK? It has worked for these 23+ years.
 
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Old 05-01-18, 09:03 AM
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In my last house, I had an 24"X24" gable vent installed on both ends of the attic space which was more than adequate for exhausting the air from a 30" whole house exhaust fan. The fan had a 2 speed motor which we would run at night or on days when the high speed was not necessary. Ducting of the fan is not necessary if you have gable vents that can handle the air volume.
 
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Old 05-01-18, 09:08 AM
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Steamboy - thanks!

What do you think of the gable vents interrupting the flow of air from the soffits through the ridge vent? It'll pull air from the gable vents rather than the soffits and the attic won't be as cool?

Then you use louvered gable vents? do they chatter / more moving parts to deal with. Just like keeping things simple.
 
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Old 05-01-18, 09:13 AM
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If you have a ridge vent then you will need the soffit vents. Gable vents will not work properly with ridge.
 
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Old 05-01-18, 09:34 AM
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thanks... yeah, the roof guy talked of closing up the (small) (12x12"?) gable vents at each end of the hours we have now because of the ridge vent.

so if I want to keep the whole house fan, what are the choices?

1) the ridge vent will be enough (ridge vent area likely larger than the 2 small gables)
2) run a duct from the whole house fan in ceiling of 2nd floor out side of house? (that seems like an eyesore).
3) something else?
 
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Old 05-01-18, 10:09 AM
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Hi Baba,
Actually, you want them all, gable, ridge, and soffit vents. A whole house fan moves a lot of air and will pressurize the attic which forces hot air down through the many leaks into the house. Having more vent area will help reduce that pressure. The concerns about having gable vents along with ridge and soffit vents are overstated (actually wrong). Leaving the gable vents will increase the soffit air flow, which is good. But when that WH fan is running you want as much of that attic air as possible to be going outside.

In addition, you should seal as much of that attic to house air leakage as possible. Hot topic (pun intended) and a lot of guidance available.

Bud
 
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Old 05-01-18, 10:24 AM
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I've been thinking of getting a WH fan, but don't know if it would help or hurt. I live in Northern VA and it gets very humid here in the summer. Wouldn't running a WH fan pull even more warm humid air inside and make the air conditioner work harder? Or would I turn the AC off at night and only use the WH fan? It would be nice to purge all the warm air that makes its way to the upstairs bedrooms before bedtime, as well as push all that hot air out of the attic. Maybe I run the WH fan for a few minutes until it cools down upstairs then let the AC takeover the remainder of the night. Maybe a whole house dehumidifier would make more sense.
 
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Old 05-01-18, 10:37 AM
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Hi Moss, whole house fans have their best times and off times and each house and climate will dictate what those are. A good friend in NJ installed one with a large powered louver in one gable. WOW could it exchange air. In 30 minutes the inside was the same as the outside.

The drawback as you stated is the flood of humidity but an ac system will make quick work of that. Exhausting that oven in the attic eliminates the overshoot where that heat keeps soaking into the house for hours after sunset.

Of course the other solution to attic heat is air sealing and more insulation. But that nice breeze when conditions are right is extra special.

Bud
 
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Old 05-01-18, 10:40 AM
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Often times it is so muggy outside here on summer nights that you start sweating within minutes. Not sure I want to be pulling all that air inside.
 
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Old 05-01-18, 10:57 AM
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That's where you have to judge, do you have enough of those perfect nights to justify the install. Humidity is a major part of comfort.

Bud
 
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Old 05-01-18, 11:06 AM
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Mossman, I'm in Maryland so we're dealing with the same climate. I have an old house with lots of windows, and a whole house fan, and I love it. We have central air, but it's only used when things get super toasty. Most of the time, we have windows open and ceiling fans going during the day. In the evening, as the sun goes down and temperatures drop, we'll run the whole house fan for a couple hours to pull in cooler air. We can see inside temps drop by about 5 degrees in a couple hours. Then we just leave the windows cracked and ceiling fans on over night to stay comfortable.

Since we use the A/C so little, we're not going from, say, 68 inside with the AC, to pulling in 75 degree outside air with the house fan. Our house will push 80 in the summer (but with shade and a breeze from fans), and the house fan helps bring the inside temp down at the same time the outside temps drop. I don't know that I would cycle from A/C to whole house fan and back to A/C, just because you'd reintroduce the humidity. Really, that's the true value in the A/C in this area -- being a whole house dehumidifier.

The big caveat here is, as I get older, my joints tolerate the cold less. I sweat like a pig in the heat, but at least I'm not in pain and I can move freely. So, I put up with it being warmer.

Babaganoosh, our fan is a monster, and it overpressurizes our attic when run on "high." We can only really tell from the attic door clunking when the fan starts up. I haven't noticed any other air leakage (knock on wood). We have large gable vents, and a ridge vent that was installed a few years ago with a new roof. Virtually no soffit venting. On a windy day, without the fan running, I can actually feel a breeze through the attic if I'm up there. I considered trying to duct the fan before, but it seems to have worked OK with just the gables before, and vents even better with the ridge now. That said, our total gable vent square footage is something like 14 square feet. I'm sure not everyone has that much gable venting.
 
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Old 05-01-18, 11:24 AM
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Mossman, I'm in Maryland so we're dealing with the same climate. I have an old house with lots of windows, and a whole house fan, and I love it. We have central air, but it's only used when things get super toasty. Most of the time, we have windows open and ceiling fans going during the day. In the evening, as the sun goes down and temperatures drop, we'll run the whole house fan for a couple hours to pull in cooler air. We can see inside temps drop by about 5 degrees in a couple hours. Then we just leave the windows cracked and ceiling fans on over night to stay comfortable.

Since we use the A/C so little, we're not going from, say, 68 inside with the AC, to pulling in 75 degree outside air with the house fan. Our house will push 80 in the summer (but with shade and a breeze from fans), and the house fan helps bring the inside temp down at the same time the outside temps drop. I don't know that I would cycle from A/C to whole house fan and back to A/C, just because you'd reintroduce the humidity. Really, that's the true value in the A/C in this area -- being a whole house dehumidifier.
It prefer it to be no more than 72 upstairs at night, so it doesn't sound like a whole house fan will do what I need. Except if I could get the humidity down, I could probable tolerate up to 78 degrees. There don't seem to be many whole house dehumidifiers on the market, and those that are available don't have the greatest reviews (e.g. Aprilaire).
 
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Old 05-01-18, 12:58 PM
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As stated Humidity is the issue. That is why whole house fans are not recommended in Green grass areas( High Humidity). It will take the AC so long to over come the humidity that its not a big energy savings. Plus what about all the pollen this time of year.
 
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Old 05-01-18, 02:02 PM
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I have a whole house fan. It's an old 42" belt driven Chelsea slow spin. An awesome performer. It's mounted in the gable end of the house. It changes the air inside the house quickly. In this type of weather we are having now it's a real asset. It will do absolutely nothing for high humidity.

On a high humidity day the central A/C is is run. I also have a roof mounted vent fan which does the routine heat removal. I have a split level home which requires me to open the attic access doorway for airflow. I don't have the room for a grill in the hallway as that's where the attic pull down stairway is.

I have an electronic timer on the fan so that I can have it shut off before the night humidity builds up. I usually have it shut off by 3AM and then when I get up I close the windows if it's a hot/humid day. The house stays cool most of the day. The A/C will come on late in the afternoon.

There are periods when the heat is too high for the fan but that usually only amounts to 3-4 weeks of the year. The fan is a real money saver.

I wouldn't trade that fan for anything but it does have it's drawbacks. It does draw in a high amount of dust and in some cases pollen. That needs to be kept in mind.
 
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Old 05-01-18, 03:27 PM
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Interesting the interest to talk about whole house fans.

For me, with the whole house unit already installed (in the 2nd floor ceiling pushing air into the attic, NOT on the side of the house in the attic (just non powered / not too big screened vents up there) and we do like the benefits to run it on cooler days, I'm curious what I should do. And we have 2 big contributors with opposing views!

Bud9051 said The concerns about having gable vents along with ridge and soffit vents are overstated (actually wrong).

At this point we just have the gables and some soffit vents. WeI DON'T have the ridge vent in yet, that'll be in June when we get the new roof. But yes, I am seeing the attic pressurization with the air coming back IN to the house - putting my hand near a wall switch in 2nd floor, I can feel the air coming out around the switch.

Airman.1994 said If you have a ridge vent then you will need the soffit vents. Gable vents will not work properly with ridge.

Airman - to be clear, I DO have soffits. would you say gable vent in addition to ridge and soffit woudl be OK?

The roofing guy we have doing the job said he was going to close up the gables. 'cause on a hot summer day, the air will come in the gables and go up / out the ridge vent. We won't get as much flow from soffits to ridge and that you won't get the full circulation you want from soffit to ridge.

again, there's 2 issues - what's the 'right' way to vent the whole house fan in the ceiling and with that in mind, do I need / should I keep the gables?

the attic is 43 x 26".
 
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Old 05-01-18, 03:48 PM
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@baga "The roofing guy we have doing the job said he was going to close up the gables. 'cause on a hot summer day, the air will come in the gables and go up / out the ridge vent. We won't get as much flow from soffits to ridge and that you won't get the full circulation you want from soffit to ridge."
That's the old school claim that never understood attic ventilation. The explanation is long but I'll try to shorten it. Air exits the upper vents because there is a positive pressure up there. Air enters the lower vents (soffits) because there is a negative pressure. If the gable vents remain in place it that upper area doesn't suddenly become negative so air will continue to exit high vents including the gables. In fact leaving them in place increases the air flow from the soffits.

As for gable vents working with a ridge vent (no soffit vents) they don't do well unless the wind is blowing. So, not zero but no where near as good as a high to low combination.

Bud

Venting through the ceiling does two things, moves air through the house and pushes the heat out of the attic. Keep the gable vents.
 
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Old 05-03-18, 10:18 AM
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When the whole house attic fan is turned on, the soffit vents will change role to be exhaust vents. Still, there is usually not enough exhaust capacity unless there are also some gable vents.

When the fan is turned off, the soffit vents will resume their normal role as intake vents.

If the whole house fan is turned on in winter, the warmer, more humid air from the house may cause some condensation in the attic. There will need to be enough times in between with the fan off for the normal soffit to ridge vent flow (which is of a much lower volume) to resume and carry away the moisture.

When everyone comes home and the outdoor temperature is not much lower than the indoor temperature then it is better to use air conditioning rather than the whole house attic fan. Then, in the evening when the outside temperature has gone down, it is better to keep using the air conditioning and leaving the fan off if the outdoor temperature is still not much lower than the indoor temperature after a few hours of A/C.
 

Last edited by AllanJ; 05-03-18 at 12:08 PM.
 

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