Whole house fan cooling attic

[PassnThru]

I have a whole house fan in my garage. One of the things it does well is to cool the attic which I use as storage. So I'm going to show you how it does that. First off, the garage is 24X32 and the height of the attic is about 6 feet from the floor to the ridge board. There is a full length ridge vent along with a gable vent on each end.
So here is the fan:
View media item 10555Here is the 'outdoor' portion of a wireless thermometer. I put the 'outside' transmitter in the attic to see the temps. It is mounted about 5 feet up so it's close to the top:
View media item 10556And here is the starting point:
View media item 10557It's currently only 95 today and partly cloudy so the attic isn't as hot as it can get but the roof is still getting full sun on one side. Also, the garage temp itself started out about 6 degrees cooler than the outside temp since it has been closed up all day. So at 5:12 (when I started the fan - on the lowest speed) it was 88.7 in the garage and 120.9 in the attic.
Will be updating.

 

[Riverrojo]

Interesting to see what you'll get. I was thinking of installing one in my 18x20 attached garage to clear fumes and as well open the door from the house to the garage to clear the house of heat as well. In the meantime, it will also cool the attic. Win win in my book. How many cfm did you get and what did it set you back (if you don't mind me asking)?

 

[PassnThru]

I'll have to do a little digging for that info. Give me a bit - no problem.

 

[Mavawreck]

The ventilation is nice I can't deny that. But I would never put one in a conditioned space. If you're looking for garage fume ventilation there are units available on a timer or that can be wired in to your automatic door.

 

[PassnThru]

34 minute update:
View media item 10558The indoor temp is going up because my Explorer is cooling off after coming home and the doors weren't opened until after 5.

 

[luvit]

your fan may be pulling-in some hotter outside air, yes?
your window and door seals can only take so much. lol.

 

[PassnThru]

Interesting to see what you'll get. I was thinking of installing one in my 18x20 attached garage to clear fumes and as well open the door from the house to the garage to clear the house of heat as well. In the meantime, it will also cool the attic. Win win in my book. How many cfm did you get and what did it set you back (if you don't mind me asking)?

Looks like I paid about $150 back in 2003 at Home Depot. Nothing special about the fan - in fact, I got the smallest one I could find since the garage is 768 square feet and they start out about 1000 square feet. I don't remember the brand or the model but I would say it is pretty much this one:
http://www.homedepot.com/h_d1/N-5yc1v/R-100018252/h_d2/ProductDisplay?langId=-1&storeId=10051&catalogId=10053

 

[PassnThru]

your fan may be pulling-in some hotter outside air, yes?
your window and door seals can only take so much. lol.

Not sure what your point is. The doors are open - I'm trying to pull outside air through the attic to cool it off. Sure - the outside air is 90+ degrees but the attic is much hotter. The fan pulls from the garage ceiling side and exhausts into the attic forcing the hot air that is already there out.

 

[luvit]

naw, you just summed-it up clearly..
my whole house fan habits were for a house, not a garage. sorry.

 

[PassnThru]

1 hour update:
View media item 10559Looking at 17.5 degrees in one hour. The initial 30 minute drop is more dramatic - it starts slowing down after that. But continues to go down. According to another thermometer it is 94 outside right now.

 

[PassnThru]

1.5 hour update:
View media item 1056121.1 degrees in 1.5 hours. I should mention that at this point about one half of the roof is now in the shade from a nearby tree. I think it drops quickly as the hot air is exhausted out of the attic and then slows because the roof and the objects in the attic hold latent heat and it takes longer to cool them off. But it's getting there.

 

[lwlobo]

Primarily, it drops quickly because the temperature difference is high at first. It's a classic Newtonian cooling problem.

Whole house and attic fans are fantastic. That hot attic is a huge inefficiency (in many cases, AC is cooling the space just below it to 78 degrees or less). It's hard to believe how inefficient some things are.

 

[PassnThru]

Final update - 2 hours:
View media item 1056224 degree drop in 2 hours. The roof is mostly shaded now and I would normally turn it off at this point. If I left it on for another hour or so the attic temp would be the same as the garage temp. Even on the hottest days, if it is turned on early afternoon it will keep the attic temp close to the outside temp.
Again - I have a full ridge vent (32') but even then I only run it on the lowest of two speeds. I don't think the air can get out fast enough to run it on high - the motor seems to strain some at the highest setting. If you have very little ventilation to begin with then it probably will not work as quickly.
So - FWIW - a less than scientific (but hopefully still useful) study of the effect of a whole house fan on attic temps. Sometimes it's nice to be able to get stuff out of the attic or work up there when it isn't 120 degrees.

 

[Matt M PA]

I must be missing something. Does this fan pull into the attic or out of the attic?

I need to also vent a storage area....I have a ridge vent but nothing else. I was thinking of putting a vent on the halfdoor to the storage area and a powered fan on the roof or gable.

We had a full house fan in our house when I was a kid...worked wonders.

 

[luvit]

I must be missing something. Does this fan pull into the attic or out of the attic?

I need to also vent a storage area....I have a ridge vent but nothing else. I was thinking of putting a vent on the halfdoor to the storage area and a powered fan on the roof or gable.

We had a full house fan in our house when I was a kid...worked wonders.

--***** air from the story below the attic floor, pushes the cooler air into the attic, and all the air escapes the attic via generously sized attic vents/roof vents.
--at night, if your windows are open, lights are on, your window screens will collect many bugs from the vacuum this can produce. not messy, though.

 

[PassnThru]

I must be missing something. Does this fan pull into the attic or out of the attic?

I need to also vent a storage area....I have a ridge vent but nothing else. I was thinking of putting a vent on the halfdoor to the storage area and a powered fan on the roof or gable.

We had a full house fan in our house when I was a kid...worked wonders.

It is mounted in the ceiling of the garage. Technically, it pushes air into the attic. The air then is forced out of any passive vents for the attic. It would be the same as putting a fan in the roof and having it exhaust out of the roof. However, the attic fan moves a lot more air than a typical powered roof vent.
The attic cooling part is not the main reason for the whole house fan in the garage. It's just a nice side benefit that I can actually measure. The other main advantage is the ability to pull cool air into the garage at night with the doors down and the windows (with screens) open to work on things at night without dealing with mosquitoes and other bugs. Also, fumes will be pulled out but I would be a little careful with that one since they are being pulled past the motor. Plus, with the fan running the garage is not going to get any hotter than the outside temp because hot air cannot collect at the ceiling. It's the same concept as the fan you had as a kid. Only in a garage instead of a house.

Edit: luvit types faster than me

 

[Matt M PA]

Thanks for the explanation. Since I only have a ridge vent, I'm guessing this idea won't work for me.

 

[luvit]

Thanks for the explanation. Since I only have a ridge vent, I'm guessing this idea won't work for me.

adding a gable vent to your attic wall may be much less labor intensive than cutting into your ceiling... typically, these fans will be wider than your rafters, so there is structural changes you would need to be familiar with.

but you could have great results with a smaller one that fits between your rafters.

 

[CCShopgirl]

I also have a whole hose fan mounted in my attic .. a slightly different variation of yours , the fan itself is mounted at the gable vent .. and where your fan is I have an electrically operated louvered panel in the ceiling that opens and closes when I turn the fan on or off , but like you I absolutely Love it .. One of the best investments I ever made ~ CC

 

[Jackfre]

We had one in the house for 18 yrs. It was there when we bought the house. Our 4br colonial had hot water baseboard heat. We had, for many years only one window unit in the family room. When I began representing a Mini split manuf I upgraded but still only cooled the family room kitchen area. I had plans to do the upstairs, but we sold it before doing so.

In the summer, in MA, when the temp would stack up we would wait until the sun dropped below tree level and fire up the whole house fan. The velocity of air and the air movement itself would generally make it pretty darned comfortable. You control things pretty well by closing the doors of rooms that you didn't care so much about.

Oh, and one more thing. When the Boss would make a mistake cooking, nothing got the smoke out faster

 

[luvit]

i need to clarify my statement.
cutting a hole for the gable vent so you can add the whole house fan is less work than cutting the hole for the whole house fan.
lol.
i like what passnthru did here

 

[PassnThru]

adding a gable vent to your attic wall may be much less labor intensive than cutting into your ceiling... typically, these fans will be wider than your rafters, so there is structural changes you would need to be familiar with.

but you could have great results with a smaller one that fits between your rafters.

Actually, if you look at the fan in my first post you'll notice that the fan sits on top of the ceiling joists. There is a joist passing through the center underneath the fan. No cutting required. Some plastic baffles were supplied with the fan to block off the open spaces between the joists but I cut and nailed in 2X6 pieces for that.
They may not all be that way but this one was so they are available.

 

[6768rogues]

Our code requires that a whole house fan be shut down by activation of a smoke detector. The fan will pull a fire through a house and into the attic very quickly if not shut down.

 

[PassnThru]

Thanks for the explanation. Since I only have a ridge vent, I'm guessing this idea won't work for me.

I guess that depends on how much ridge vent you have. Mine is the full length of the roof - 32'. I also have a gable vent on each gable. Actually, I'll have to verify this but I wouldn't be surprised if there was air blowing out the soffit vents when the fan is on. The attic is being pressurized so I don't think it cares at that point where it comes out.

 

[PassnThru]

Our code requires that a whole house fan be shut down by activation of a smoke detector. The fan will pull a fire through a house and into the attic very quickly if not shut down.

Probably a good idea. In this case, the fan is in a detached garage. It doesn't run during the night when no one is around.

 

[Matt M PA]

I do have a full ridge vent.

I have to go look more carefully at how I could mount a fan and where.

 

[JohnMcD348]

I can remember as a boy, my house had a whole house fan in it and it worked great in the Florida summer time. When I was helping my father build the addition to the house, we used the fan to cool off the attic space by running the window unit A/C's and pulling the cool air into the attic. It made it down right comfortable up in that tin roofed Wood framed house. I had to spend the most time up there since I was only 6 and he needed someone tiny to help run all the electrical wires and cabling through.

You know, come to think of it, all that electrical work I did. I never did get my Journey Man's card..........

 

[Falcon67]

The fans require a certain amount of exit area for sure. However, if you have ridge and soffet vents, you best not cut in any gable vents or you will kill your venting circulation.