Attic Fan Worth It?

[jacob_coulter]

I have a rental house that has an attic crawl space and a gable vent, but no attic fan to pull out the hot air in summer.

I've heard mixed things about them, some say they make a difference, some say they don't. The attic has good insulation already, but I feel like the AC unit is strained. Most of the neighbors have the "whirly bird" type of fans, I was considering something like this with the included thermostat.

 

[Exceller8]

We had one when we lived in Huntington Beach, CA. I liked it but it was noisy. That was almost 20 years ago so maybe they have quiet ones now?

 

[sands35]

A) where do you live?
B) how well insulated is the attic?
C) how well vented is the attic?

You can get solar powered vent fans.

 

[ddawg16]

Good questions by sands

I had one...besides being noisy, the wind blows into it 90% of the time when your trying to get air out.

I could not tell any difference in comfort. I have since removed it and installed a turbine vent. I think it does a much better job.

For an attic fan or any vent to work, you need plenty of eave vents. Without them, all the fans in the world are useless. .

 

[JakeKohl]

I put two smaller ones in mine and sequenced the thermostats. My attic isn't that well insulated and they made a big positive difference on my energy bill for the summer. They are a bit noisy, though.

I'm a bit torn over whether or not the powered fan is more effective than a properly configured ridge vent with sofit vents (a WELL vented soffit) and no gable vents. I see my neighbors get new roofs with a ridge vent but they don't do anything to address a complete lack of soffit vents....anyway, I have noticed that ridge vents in Florida are few and far in between and most houses have powered attic ventilation. That should probably tell us something.

 

[ffjosh]

My house is only 5 years old but I see no reason to have one

 

[Hpozzuoli]

I have one in each section of my roof in the attic. They move a decent amount of air. My main concern was keeping all the AC equip up there cool. I am not sure if the equip itself gets warm, but a 100+ degree attic in the summer doesn't help the cause. When I go up there I can feel the fan moving air so I think it helps.

 

[arnwoodwheels]

I live in the hot inland area of so cal hot during the day cool at night.
My attic is well insulated. But the house would get hot at night despite being cool outside.
I checked the temp in the attic after a hot day and at 1am the attic was 130deg despite being only 65 deg outside.

I installed a fan with the thermostat like you are thinking about.

it made a huge driffrence, what i really noticed was the house no longer heated up at night.

It did hover make a lot of noise. kind of rattles the walls. It also made some fan moving air noise outside.
I went back up and spring mounted it and the rattle went away.

Hope this helps.
Ron

 

[hoffman912]

here is a question - what about for a garage? I have no AC, and no vents in my 100 year old garage (not even a ridge vent). I am looking to add ventilation to **** the hot air out during the summer when working on cars. I dont have an attic, or even a ceiling right now, its is all open to the a-fram roof.

by adding an attic fan will it help **** heat out of the garage?

here is a pic to get an idea of size

https://scontent-a-ord.**.fbcdn.net/hphotos-prn1/t1.0-9/10167976_10153944333530510_790608197_n.jpg

 

[3/4 drive]

ddawg got it right you need other vents in the attic to displace the hot air if your attic fan is in a gable end wall you need at least another vent of equal size in the opposing wall more is better. Same goes for you Harry even a simple gable end vent in both gables would help ,but both gable end vents and vent-a-ridge would be better.

 

[JakeKohl]

You don't actually want to mix a ridge vent with a gable vent. The incoming cool air from the gable vent goes right out the vent and doesn't help to cool the roof sheathing.

 

[stage20]

ive got a metal building and was looking into a shutter fan. saw a few at tractor supply and then looked some up on nation fans website. im not sure which is the best method, but it can get near scorching in the summer.

 

[skyking]

I thought an attic fan was this big *** fan I have in the hall. I love it , it will cool the whole house when the weather is right.

You guys are talking about Exhaust fans I think.

 

[hoffman912]

Skyking, you're talking about a whole house fan.

Yes, what i want to add is an attic exhaust fan. I want to **** all the hot air out in the summer and keep air moving.

I dont have a ridge vent or soffits, so would i need two gable vents (one with fan and one with out to move air from outside in?), or just one gable with fan to get all the hot air out of the garage?

what i would also like to do is put in some make shift duct work and have paint fumes exhaust from there when i restore my car year from now (would have filters etc too)

 

[Steves32]

Attic fans were popular 20 years ago. Not so much now.
Here's why.
Attic fan will cause attic to go negative pressure. That means every void, can light, holes drilled for electrical, plumbing or whatever will pull conditioned air from your home & into the attic. A better choice is a passive system- like a turbine or gable vents. These won't cause attic to go negative.
In the old days- common thinking was to install attic fan to reduce attic temps & lower load on a/c system. Everyone was doing it including us! What we found was it rarely lowered operating expenses of a/c but now you have a fan in attic running all summer!
Insulate attic to separate living space from attic. Treat house like an envelope- sealing & insulation walls & ceiling.
Not a good idea IMO.

 

[Rob_b]

Using a fan to exhaust the air from the attic is somewhat senseless. If you have "decent" insulation, your half way there. Using soffit vents and standard attic vent should be enough. Do not mix the whirly bird style and standard vents on the roof. The draw from the spiining vents will draw air in from the regular vents and not the soffits and only ventilate the upper part of the attic. We have to remember that hot air naturally rises if it has a path to go too. If there are no soffit vents, the gabled end vents will help.
Powered attic vents along with things like "booster fans" that installed in a furnace vent are bandaides to the real problem...lack of proper ventilation and air movement.

 

[Deltarat]

It made a difference in my cooling. Thinking of adding another.

 

[Steve in Louisiana]

I do & always will stay away from powered attic vents.
They are a potential fire hazard.
You are putting a cheap chinese 1/5hp motor in a 130F+ environment to run unattended out of view.
Insulation and proper venting will move more air than that fan ever will.
I worked as a State Farm contract adjuster for years, I learned they are a definite fire hazard.
Ask a veteran firefighter his opinion.

 

[tdkkart]

I thought an attic fan was this big *** fan I have in the hall. I love it , it will cool the whole house when the weather is right.

 

[tdkkart]

I have a rental house that has an attic crawl space and a gable vent, but no attic fan to pull out the hot air in summer.

I've heard mixed things about them, some say they make a difference, some say they don't. The attic has good insulation already, but I feel like the AC unit is strained. Most of the neighbors have the "whirly bird" type of fans, I was considering something like this with the included thermostat.

Why does it look like it's installed over a hole the squirrels chewed in the house??

 

[J Persons]

I use one to vent my compressor room. Works really well and you can feel a breeze coming through the door when it's on. I also installed a on/off switch inline.

 

[Jim Sperry]

It'll lower house temp by 8˚~10˚ on the hottest days, is what we've told customers . . .

 

[pattenp]

That's an example of how not to install a fan.

Why does it look like it's installed over a hole the squirrels chewed in the house??

 

[gayler]

I wondered about venting options too. I have soffit vents, but nothing in the roof or endwall of the attic area. Should I have vents in the roof or end wall as well?

 

[Modern Jess]

I have two anecdotes of my own here.

1) I installed a solar attic fan in my garage (which has open rafters) and it made a big difference in how hot the garage gets. There's no insulation on the roof at all, just open rafters and the underside of the roof decking. Here in my part of the Bay Area, it gets pretty hot at the height of summer, and prior to this installation the garage was just a hotbox during those months. It's still warm, but not unbearable.

2) Based on the success of the garage, I installed a solar gable fan in one of my gable end vents of the house attic. But prior to that, I started gathering a large data set of temperature readings from my attic using a little device from ControlByWeb that plugs into ethernet and has hookups for a bunch of hardwired temperature sensors. Once I installed the solar gable fan in the attic, I could see that it reduced peak temperature in the attic by about 10 degrees. Prior to the fan, temps were hitting in the 130+ range. Now they're generally in the 120+ range. Still damn hot up there, but an improvement nonetheless.

Was it worth it? Well, once installed, it doesn't require any power to run, and it's quiet -- I can't hear it at all from inside the house. I have no idea if it made an impact on our power bills or not.

 

[crucible]

I have one in my main attic and with it, the temp stays signifcantly cooler in the attic itself and the upper living spaces.

I had a new roof installed in the last year and had ridge vents installed at the same time which no doubt helps air movement significantly, possibly even to the point where the fan itself my be superfluous.

However, mine as also has a humidity sensor on it as well and if (for whatever reason) the humidity level gets past a certain set point, it will run. (This is more of a winter setting, where high humidity in the attic air might cause, or significantly contribute to, the creation of ice dams.) Of course, if I have high humidity in my attic during winter it's either not winter, or I have some kind of air leak from the living spaces

Still, I'm leaving it.

 

[Kevin54]

I thought an attic fan was this big *** fan I have in the hall. I love it , it will cool the whole house when the weather is right.

You guys are talking about Exhaust fans I think.

My parents house had the same sort of fan. When you kicked that sucker on, and you had windows open, the curtains would start to stand out. It made a hell of a difference in their house.

An attic fan of that type WILL help to cool a house. Cool air doesn't come in through a gable vent when it's 95 degrees in the dead *** of summer. And even though a house is well insulated, and the attic is well insulated, if you have a good attic fan, just like the fan in my parents house, and like in Skyking's house, it will FORCE the hot air out of the attic. Instead of pulling air in through a ridge vent, or pulling hot air in through soffit vents, it will force the hot air out through those vents. If you can get air circulating through, even though it may be 95 degrees or more outside, once you start pulling that air through and start dropping the attic temps down from 150+ degrees, it will make a difference in the inside house temperatures. Plus once you drop the attic temps down, even though you are insulated with R30...once the attic temps drop, it will be less taxing on running the AC in the summer.

And there is a huge difference between a whole house fan that may be in a hallway, and the mushroom attic fan that is sitting on top of the roof, or the little whirligig types of attic vents.

And if a person doesn't want to hear a fan running in the hallway, you could even mount one in the attached garage and pull outside air in and through to cool the attic. The whole idea behind that sort of fan is to circulate air and cool the attic down.

 

[Riverside]

Attic fan will cause attic to go negative pressure.

As people have said in various ways, if you are going to exhaust air, you need to have a source of supply air (typically eave vents). If the supply and exhaust are well matched, there should not be significant negative pressure. If you can't install eave vents, then consider an intake fan at the farthest point from the exhaust fan. Preferably, the intake air will come from the coolest side of the building.

In comparing fans and passive systems, keep in mind that a fan can move a lot of air through a small hole.

Some type of attic ventilation system will definitely keep your building cooler, or easier to keep cool. A few years ago, we finished a room in our attic. The first summer, it was too hot in the room to be there during the day. I didn't want to pay for air conditioning, so I installed a 8" fan through the top of the wall at the far end from the stairs. (Edit: This fan functions like a whole house fan, except it is really just for one room.) It draws air from downstairs (not air conditioned) and exhausts to the outside. Last summer it ran 24 hours a day, drawing 7 watts (so ~17 cents per day), and it kept the room comfortable on all but a few very hot days. We also have attic fans and eave vents in the unfinished spaces around the upstairs room.

 

[RPH]

There are two types of fans being discussed here. The whole house fan and the attic fan. One can install both. The whole house fan will pull air from the living space and exhaust it into the attic. The attic fan will only pull air through the attic. That being said, it has been mention by many that the air coming into the fan has to come from somewhere and has to have sufficient area for intake and exhaust. The sucking in the drapes is a whole house fan usually ran at night to pull in cool air through the house. Attic fan is used to reduce attic temperatures. They all work if you have the correct area for flow. I have used both and at times had both in the house. For the attic one look at the roof mounted solar vent fans. They appear to work very well with no energy cost.

 

[Steves32]

This is why I never talk about my HVAC trade here.
I do this for a living. You can do whatever you like.
Google "Infiltration" and see for yourself.

Here's the facts on power ventilators, inc solar.

http://www.energyvanguard.com/blog-...c-****-Power-Attic-Ventilators-Are-a-Bad-Idea

http://airconceptsllc.com/blog/attic-ventilators/

https://www.dom.com/about/conservation/pdf/attic_ventilation.pdf

http://www.greenbuildingadvisor.com/blogs/dept/musings/fans-attic-do-they-help-or-do-they-hurt

 

[Riverside]

I'm not a HVAC professional, so my comments can be taken with a grain of salt. I would not argue that attic fans will not cause problems if there is not adequate supply air. Those articles make many good points. Additional insulation may be a better investment than an attic fan.

When I installed my attic fans (the ones in the unfinished attic space, not the 8" fan I mentioned in my previous post), I found this recommendation for supply air: CFM of fan X 1/2 = needed supply air in square inches. So, if a fan moves 1,200 CFM, it needs 600 sq. in. of free-flowing supply air. (A screen over a vent reduces the free flow of air.) In my case, this meant drilling ~80 3" holes in the eaves and adding vent covers.

 

[AP514]

I thought if you have RIDGE vents(vents at top/peak of roof) then Powered fans are a no-no...the fan just draws air in from top/peak so no hot air get pulled out.

 

[MTW]

Have a look at this thread for a workshop.

Need help with exhaust fan
http://garagejournal.com/forum/showthread.php?t=211121

 

[theoldwizard1]

• Bigger is better. Large diameter fans spin slower and are quieter.
• If you are blowing hot air out of the attic how is the cool replacement air getting into the attic ? If you don't want a big vent into a hallway inside the house, make sure you have adequate air flow from the soffit vent. If you don't have soffit vents or an inside vent, then you are wasting your money.

 

[rwf]

I can get a lot of supply air for my attic by opening the door for my attic ladder. Open a garage window or the big door a couple of inches and you can feel the draft.

 

[rwf]

My attic door is spring loaded so I just block it open about 10 inches or so.

 

[PT Doc]

If you are inquiring about a whole house fan or house house ventilator, then yes they work very well. They need to be located in the appropriate location. Broan was very helpful with locating the best place for the best airflow. This 36" fan can drop ny attic temp from 130 to 105 degrees.

 

[Eddy N]

Exhaust fans work well- best when installed in the highest area. If they have a thermostat, set it to 85

 

[FTG-05]

A) where do you live?
B) how well insulated is the attic?
C) how well vented is the attic?

You can get solar powered vent fans.

Bigger question: How well sealed is the home ceiling/attic roof floor?

All the powered attic fan pictures and diagrams show the typical hot (red) air going out the fan and cool (blue) air coming in from the soffit vents. What they don't show: Cool, air conditioned air (read $$$$) being sucked in from a poorly sealed home ceiling/attic floor. Essentially, you are now trying to use the home AC to cool the attic. Unless it was specifically done, the vast majority of homes will leak at the home ceiling/attic floor into the attic. See some Dr. Energy Saver videos on this subject.

Sealing an attic floor = $$$$ (remove the old insulation, seal, add insulation). Cheap version: Blow 8-10" of cellulose on top of whatever insulation you currently have. Unlike fiber-****, cellulose will seal (somewhat) the attic floor.

I've added powered fans to my attics since my first home in 1982. In all cases, the first thing I did was: a) add cellulose insulation and b) cut additional soffit vents; this reduces the vacuum effect on the home ceiling/attic floor.