I have small 11.5″ x 14″ gable vents in a loft above my garage. I would like to install a gable fan but the smallest fan I have found is 16″. If I install a 16″ fan over a 11.5 x 14″ opening will the blocked space on the edges force air back into the rafters and just defeat the purpose of the fan?
The other idea I’ve consdered is to install a fan which is not designed as a gable fan but will fit the opening. One option is a 12″ inline duct fan (DAYTON 2C223) the other is fan is 10″ axel fan designed for spot cooling (COMAIR ROTRON CLE2L2X 032237)
Your experence /suggestions would be great.
-John
Replies
The one and only gable fan I installed, not designated as such, I had to go back and install vibration dampers. It's amazing how much can get transmitted through the structure. This was a situation where I was not allowed to make any exterior changes.
If you don't want larger vents, I'd go with the smaller fan. You're thinking thermostat control? It's reasonable to size the fan to your attic volume, although just about any fan will increase the air flow.
PAHS Designer/Builder- Bury it!
I'd say give it a try as is. Hang it as close the vent as practical. A little blow back isn't going to hurt anything. That's the way all the window fans at my house work, and they manage to cool the house off at night.
If you're not happy with that, you could build a plywood box with sloped sides from the outlet side of the fan to the edges of the gable vent.
Using a standard 16" attac fan is less expensive so maybe installing a reducer would work. Its probably less work to make the reducer than try to adapt a fan that doesn't come with a thermostat control and mounting brackets.
Thanks for the input.
-John
I ran into this problem a couple of years ago. I had a pair of knee wall attics and a wall mounted fan on either end would have looked ugly. Also, the capacity of the smallest fan was way above what I needed. Does one really need a 1500 cfm fan in a 750 cf space? I ended up mounting a small 70cfm bathroom fan up high in the center of the attic and running a duct down to the soffit in the center of the house. On each end I put in a 4x12 soffit vent. I control it with a 24 hr timer. I haven't been able to find inexpensive thermal timers. In the summer it runs from noon to 10PM to keep it cool and in the winter for an hour in the morning and an hour in the evening to pull out any moisture that may have migrated up there after showers. After installing the fan, I no longer needed to run the room AC as much and the ceiling was now cool to the touch. The nice thing is that it is so quiet you hardly notice that it is running. I've been in houses where an oversized attic fan is really noticable.
Sorry to say, but both gable vents and attic fans are old science. Research has shown that the return on energy consumed for attic fans is marginal, and gable vents generally, only do a good job at ventilating the ends of the structure. In addition gable vents have the additional "feature" of possibly admitting wind driven precipitation (rain & snow) into the attic unless your gable overhangs are very wide, which further reduces their performance.
Install ridge vents and block your gable vents. The cost will probably be similar to an attic fan, but there will be no operational costs.
But all the books (including the one from Taunton on ventilating and insulating) STILL show the need for circulation from soffit to ridge. If there is only a ridge vent, where is the make-up air coming from???
I am going to join in on this one as I am contemplating a gable fan as well.
In my case, I have a bungalow with no soffit, extended eaves and flying rafter tails. There is no ridge vent either. Hence, there is no attic ventilation. With only one cold air return in the second story, the upstairs gets extemely hot in the summer, even with the central AC running.
My thought was to place a gable fan at one end and a gable vent in the other. By reducing the attic air temp at night I am hoping it will have some effect on my cooling. Not to mention it will reduce moisture build up in the attic.
Any problems with vening an attic this way?
It's critical that you have enough make up vents in the attic to supply the air your fan will remove. I doubt that having a similarly sized gable vent on the other end of the attic will fully supply a halfway powerful fan. If you don't provide sufficient outside air, the air that's ventilating your attic will come from your air conditioned interior. I don't think that's the result you're hoping for.
AndyArguing with a Breaktimer is like mud-wrestling a pig -- Sooner or later you find out the pig loves it.
Thanks. I was planning on adding gable vents in the able across from the fan and in the gable ends of the front and rear dormer. Guess I better take a close look at the fan size and vents before starting
Sorry for the misunderstanding. I was not supporting the use of ridge vents only. You are correct that they must be used in concert with soffit vents. I was only saying that gable vents do a marginal job of doing an even job of ventilating the attic. Matt
I plan to have roof replaced before air-sealing (as best I can) and insulating attic with cellulose. I have to decide if I want the soffits as well as the ridge vents. Here are reasons I was *not* planning to put in soffits, until this thread made me think about reconsidering. I'd appreciate any reactions to my reasoning. BTW I'm in northern NJ.
First reason: All roof installers say they only install ridge vents, one guy (highly rated roof installer) said he stopped installing soffit vents after getting calls to come back because of cold attics. I guess the response is: not a problem if the attic is insulated, but that seems naive, I'd like more than one line of defence against heat loss. I have a soffit vent in the hall ceiling for an attic fan, a walk-up attic, will have a return for AC. In my copious free time (not!) I hope to build insulated hatches from wood, foam board and weatherstripping for the former two, but abandoning the attic to the elements is putting a lot of reliance on these measures.
Second reason: I do have an attic fan that I use as long as temperatures don't go into the 90s. Although I will have CAC installed, my impression from neighbors and others is that our summer utility bills have been quite low compared to people running their AC, so I plan to only rely on CAC when it gets really hot and humid (I am expecting that there will be more days like that in the future). If I have soffit vents, surely the attic fan will lose effectiveness in cooling down the house since it will be sucking a lot of air through those. Someone tell me if there is something wrong here in my thinking....should I plan on getting rid of the attic fan if I get CAC?
Third reason: I think I'm about to contradict Reason 1, but isn't there a debate about the real issue being sealing the envelope rather than venting moisture out of the attic? I've read about "hot attics" and such. I suppose venting is useful as a backup as has been said.
Taylor, for ridge vents to be effective, you have to let air into the attic, and the best place is a continuous soffit vent all around the house.
The attic whole house exhaust fan does not suffer from having soffit vents, as the fan is pulling air from the house interior and blowing it into the attic.(Open enough windows and watch for gas appliance back drafting). The more venting for the attic, the less back pressure. I definitely suggest the insulated/hooded cage over the exhaust fan housing; they can be real air leakers.
Another solution I have done with attics without ridge vents but with two gable vents, is to install an exhaust fan in each gable. With one running, air is pulled through the attic from the opposite gable. With both running, and a ceiling vent opened or door to attic open, the two fans serve as a whole house exhaust system. (once again, house make up air has to be provided.)
Re air conditioning in N.J., I have a clientin N.J. who found after some improvements were made, that keeping the house tight in the summer was more cost effective and less dusty than opening the house at night. The humidity is expensive to eliminate each day.
Hope this is helpful. PaulEnergy Consultant and author of Practical Energy Cost Reduction for the Home
DIRISHINME is correct - Gable vents are a waste.
If you add ridge vents or other vents near the ridge, the hot air in your attic will rise and exit on it's own. Then you don't have the expense of running the attic fans.
Borrow money from pessimists--they don't expect it back.
John, believe Loewes, Hd have 13" gable fans. Don't over power the cubic footage. If you frame out a bit and use some rubber cushions at the attachment points, you can greatly reduce vibration.Be sure to have adequate supply air vents. If you really want to remove the hot summer air, see my post 39157.16. Paul
I like the idea of ridge vents so I'll plan for them when it comes time for a new roof. Until then, I did find a 13" gable fan, which I've not had the time to install yet. I'll post my observation on its usefulness as soon as the temp in the loft starts to climb.
Thanks for all of the great information.
(I had to order the Fan online from HD)
Just a dumb question for my own purposes, but on an unfinished, unattached garage in the cold northeast, is there any need for ridge/gable venting?
Some sort of venting will make it a lot cooler in the summer. I have a roof vent fan in my garage, wired to two switches so it can be "ON", "AUTO", or "OFF". When I flip it on in the summer the temp in there drops 20 degrees.
I'd put ventilation in if it were me. If for no other reason, it keeps your options open.
One of these days you might want to insulate it. Then you'll be glad the ventilation is there. It's a lot easier to put in now than later.
I wouldn't put in gable vents though. Soffit and ridge vents are the best combination.
With a ridge vent, it would help clear out fumes if someone ran their car while it was in the garage. It certainly shouldn't be relied on for that, but would help."Brevity is the soul of lingerie." [Dorothy Parker]
i have an attic fan i got from grainger brand name certainteed with built in thermostat, moves 1900 sq. ft. per minute of air cost 50 bucks its been up there for three years and it works great! in our two story house it easily cut the temp. by 15 degrees on warm days, in fact the second story is often cooler than the 1st. story where i live (central coast calif.) it rarely gets over 90 degrees so i didn't need an air conditioner so this works perfect!
fm2"the large print givith, and the small print taketh away" Tom Waits
"those with accurate observation are often called a cynic by those who have not got it" george bernard shaw
I had a humidity sensor on an attic fan but I took it out because it does not work well. When it rained outside the humidity level would of course go up, triggering the humidity sensor to turn on the fan. Who needs the attic fan on when it is raining outside????
If you want to vent based on humidity you need a differential humidity sensor -- that is, you need one humidity sensor in the attic and a second humidity sensor outside with a controller to turn on the fan only when the attic humidity is a certain percent higher than the outside humidity. It ain't cheap and it takes a lot of tweaking.
One product is the Humitrak-D model by Tamarack:
http://www.tamtech.com/humitrak.htm
It's yet another factor to consider in choosing powered attic ventilation.
Billy