Attic Fan

Good write up. One more thing that would make this article even better would be to talk about how much electricity it would take to cool the attic and if that would still save money because the AC won't have to run so much.

Do they make replacement motors for the electric powered attic fans? Mine went out and I can't say that I'm overjoyed with the prospect of changing out the entire unit.

Tim. I had a new roof put on last year and had the wind turbine type attic fans removed - I had ridge vents placed in lieu of the turbines. Do the ridge vents do any good. Oh yes, I live in Texas. Thanks.

Tim

Good article on attic fans. Your caution regarding the extended use of AC because of attic fans is very important to remember.
And like Ralph who writes above, i to find the
moving boxes very annoying. please stop that.
thank you
nitto

Roof mounted fans seems to be the subject of this topic, but I wonder about the effectiveness of gable mounted fans. Are they more or less efficient than roof mounts?

My attic fan just stopped working after thirteen years of thermostatically controlled ventilation, and after calling numerous electricians for a replacement, I was informed by one that replacing the attic fan when my roof has soffit under the edges of the front and back edges of the roof, side, trianglular gable ventilation, and a ridge vent that runs the length of the roof is of no cooling/energy value. I read your entire article and comments, but I am still confused as to whether I should just check the insulation depth and not replace the attic fan as natural air flow is the best or replace the attic fan for some help in energy savings. I do have a centrally air conditioned two story with basement home in the Washington, DC area(Fairfax VA).

i live near the ocean in Miami. i was considering the powered roof ventilators for a 1500 SF house to lessen the heat load on my central AC system. there is a product that moves 1050 CFM but i'm concerned about the 200 watt 1/10th HP motor(2.8 amps) constantly running. do you feel it would be cost efficient and help cooling inside? has sucking to much outside air through the attic ever been a problem? (moisture)? thanks,
Keith

Thanks Tim for this article. It has caused me to rethink the use of my household elestic powered attic fan.I live on the Canadian praries where we have very hot days but tend to have cool nightime temperatures. After reading your comment regarding the amount of air required to handle the daytime heat load I have decided to turn the fan off in the daytime and put it on auto in the evening.
I have just had the motor replaced after 15 years of use. It was running fine but I have heard stories of roof fires being caused by overheated roof fan motors.
Terry

We purchased a 2 story house containing approx. 4,200 sq feet with a 3 car garage. The house had two (2) attic exhaust ventilator fans on the top rear roof but neither worked. I asked a contractor to replace the thermostats and he did. He said that he first bypassed the thermostats to see if the motors ran and they reportedly did. After installing the new thermostats and setting them to kick on at 100 degrees F, they haven't come on.
another contractor later put on new and stronger AMP thermostats and the fan motors still won't come on.

any suggestions as to what I should do?

Thermostatic controlled attic fans can make a big difference in your monthly A/C bill. I have two (2) in my attic. Here in Texas with 100 plus degree days, they are worth the price. Important however is you must have vents under the eves of the house all the way around for the fans to pull in outside air. Minimum three vents per side. Attic ventilation is very important no matter where you live. Those vents need to be flushed out several times a year with a water hose to wash out the dirt that will clog the screens. The motors are easy to replace. You can find them on-line and at Lowes and some hardware stores. They run about $50.00. In answer to Richards problem with the fans not coming on after having the thermostats replaced; the guy who did it wired them wrong. It's not that difficult. The incoming hot wire is connected to one side of the thermostat. The hot wire from the motor is connected to the other side of the thermostat. The neutral wires are connected together. Thats it. Also, set at 100 degrees is to high. Set them at 80. You want a good jump on the heat of the day. Hope this helps everyone.

What about the formula for air intake vents square inches versus exhaust volume?
If there is inadequate soffit and gable air intake can exhaust fans and vents work effectively?

An excellent and well-written column. My only question is that, throughout the whole column, you never specify whether you are examining these various attic fans as replacements for natural attic ventilation or as augmentations to natural ventilation. I gather, reading between the lines, that you are describing attics without ridge vents - is this accurate? I am building a 2000K sqft 1-story house in upstate SC. I have read that continuous soffit-to-ridge vents running the whole perimeter of your eaves and the whole length of your ridge can supercede the need for mechanical ventilation, whether solar or electric or windpowered. Would you agree, or do you feel that, even with such vents in place, the cost of additional fan installation is worth it?

I have a 1980's home, one-story w. crawlspace, and an attic fan with gable vents. The fan died a few years ago, but I can't say that it made any noticeable difference in the power bills, thus probably not much difference in temp reduction. So, given the cost of replacement I have decided to just wait until an upcoming roof replacement and just remove the fan and seal/roof over the hole. With just two gable vents, I am debating the merits of going with a ridge vent (need to install soffit vents) or trying a reflective insulation system to keep the heat out of the attic rather than try to remove it once it's in. Any thoughts about pitfalls?

I live in the deep south and just had wind turbines installed on my roof and have seen a big difference in the inside temps. The slightest breeze will have them twirling like crazy. And my AC no longer runs constantly during the day.

Phil
I had two (2) different contractors install two different new thermostats on my attic exhaust ventilator fans and neither was able to get them running. The last or second contractor concluded that a surge must have burned out both motors.

Since we recently had a new roof put on after a complete tear off of the old, I don't want that new roof disturbed by ripping out the entire attic exhaust fans and replacing them with new units. Instead I would rather see new motors installed (assuming that can be done from the inside of the attic).

What a pity the roofing contractor told me that he didn't think the old fans needed replacement at the time he put on a new roof because he said they looked fairly new or recent ones.

Thanks for your advice. Much appreciated.

Seems like just too big a task for my area where the past 12 days it has been around 104 to 107 outside. Must be 108 in the attic. I have soffit vents every 6 feet and I open the attic door in the garage and the garage door with the wind out of the south blasting in and that seems to help some. I don't know I may be biting off my nose to spite my face!

Above is suppose to be 180 not 108!!!

I live in San Diego, California. It sounds like electric attic fans are the way to go. Can you recommend the best brand of fan to use in this part of the country?

My husband has "jury rigged" a large box fan on it's side wedged into the square entry (closet ceiling)to the small attic space in our townhouse condominium. He draws in the "hot" air up into the attic. Hmmm. Is it a bad thing to do? And can there be a fire from this? And will it trap dirt and catch fire, etc.
Thanks so much.

Hi, the article is very good. Now I understand why we have these things. Last night one of our electric attic vents started this whining noise. It sounds like the fan may need to be greased. Is this a common problem and how do I do this?
Thanks!

I have a new question. Shingles do get
very hot especially in Texas in the summer. Why use a product to roof a house that will transmit so much heat?

Is there a roofing product that is cool and reflecting neat instead of producing more heat?

I enjoy your comments very much.

Thank you, Marlys Kosel

We live in northern Michigan, and it is nothing to get 2'-3' of snow on our roof. Here's our problem: we live in a manufactured home with cathedral ceilings and a 3-12 pitch so there is virtually no attic space. But we do have 12" of pink insulation. In the winter months we get severe ice damming, which causes water to leak into the house. The roof is only 5 years old, and we had one row of rubber ice guard installed at that time. We have a ridge vent with soffits all around the house. What can we do to get some proper venting into our attic? And, prevent ice damming. I just hate getting up on the roof and shoveling it each time it snows, not to mention the fact that I'm 66 years old!

I found this site to be very helpful when choosing my solar attic fan. The correct amount of free inlet area is just as important as fan size, remember to pay attention to that!

http://www.solar-attic-fan-info.com/

I have a relatively new house, with an attached and insulated 2 car garage, and an attic exhaust fan in a gable end over the main part of the house. There is an area where the interior plywood sheathing on the roof was cut to provide access from the storage area over the garage to the area over the main part of the house. Closing that off with some 1/4" plywood, just tacked down, would effectively cut off the cubic area over the garage from the rest of the attic, and IMHO, reduce the area the attic fan is attempting to cool, thereby increasing its effectiveness..there are plenty of soffit vents and other gable vents all around as well. Do you think my plan has any merit?

My husband has "jury rigged" a large box fan in our unfinished attic Hmmm. Is it a bad thing to do? And can there be a fire from this? And will it trap dirt and catch fire, etc.
Thanks so much.

I'm all for energy efficiency as much as anybody but if I put a solar powered fan in my attic, why not have it continue to work at night or when it's cloudy if the air is hot in the attic? So, besides the thermostat, I would add an AC operated power supply that would automatically kick in when the solar panel output dropped below a useful value.

Tim,

I need to vent my attic. I want to install a power vent but my house has no eaves. The roof line ends at the exterior walls, with a gutter attached to the soffit. I was figuring on sizing an opeing and installing a grill in my ceiling to provide the intake air in the attic. I have no a/c. Any thoughts or suggestions.
Thanks

My two cents...Was here searching for help on how to test to see thermostat was working or my motor was bad. I saw the post on bypassing the thermostat which is what I will try...had not occur to me. Anyway, as a homeowner that has experienced roof without and with I must say the power ventilator does help especially because at evening time the roof is not as hot as if it was only ventilated with turbine fans....allowing the a/c to cool my second story faster than without it.

Interesting article! Question for you Sir: In a 2-story townhouse here in Las Vegas, NV, would it be advisable to try and create an "attic draft" by installing an attic fan behind one of the roof gables, and then allowing the rising hot air to exit the upstairs of the house through the fan/gable? If I remember my high-school physics, the hot air should rise and then be able to exit via the gable fan. I appreciate any advice you could give!

Just like any other ventilation fan, sizing is one very important key to satisfactory results. The average home attic is about 1,600 sq. ft. and it sometimes takes two solar powered fans to do the job OR one that moves about 1,600 cfm. Also, a good solar powered fan with a large solar collector will pick up the suns rays very early in the morning BEFORE the attic gets hot and will therefore be able to keep the temperature down by moving air all day long as long as the sun is shining. SO, keep in mind to chose a solar fan that has as large a collector as possible, and is rated as close to the proper size.

While this doesn't directly relate to attic fans, I wonder why people don't line the underside of their roof rafters with aluminum-coated plastic sheeting to reflect the radiant heat back outdoors BEFORE in get into the atttic and is retained by the insulation in the attic. One thing has prevented me from doing this - potential condensation from the water vapor that emanates from the interior of the house.

Any comments on this approach?

Phil makes some great points. Let me comment from Eastern New Mexico.

1. Our 40 year old house had 165+ degrees by summer's noon -- and many leaks in a 6 yeaer old shingle roof in good repair. We now have 10-12 degrees above the outside temp -- at the hotter 3 pm hour. Here is how.

2. We discarded the idea of end gable fans and ridge vents, because they do not move enough air or do not move it in the right areas. (Ridge vents with power turbines can pull air-with-rain in the wrong direction.)

3. For soffits, the best choice is continuous venting along the soffit. The second best is an enlongated vent added every other truss -- to equalize air flow throughout the roof.

4. In areas with a lot of wind, a combination of wind turbine and power turbine is often best. For an 85 by 40 house we have three 14 inch wind and two large power turbines. Even on windy days this is barely adequate.

5. Find the formula (on the web) for the correct vent sq footage to match your total turbine needs -- and follow or exceed it religiously. If after a year, the insulation near your soffit vents is pulled away from the walls, it may indicate you need to add more soffit venting. That will prolong the life of your power vents. (Try using insulaation bats near soffits.)

6. You want to do more than cut the air temperature. You want to cut the temperature on the underside of your shingles, trusses, etc. This generally takes more air movement than the formulas mentioned in # 5. Doing this significantly can lengthen the life of your shingles by 5-10 years -- and cut down on water leaks, saving the associated expenses! This factor alone goes a long way to pay for your vents and the power to run them.

Want to vent? It's a great idea!

Randy,

You can get the motor rewound. I have done this in the past with an appliance that I wanted to keep.

What about open cell foam insulation sprayed on the underside of the roof between the rafters. It seems to be common practice now in the gulf coast area of the USA to completely seal the attic space (no vents, none at all). I've been in an attic with this foam insulation on a hot summer day in Louisiana and it was about 90 deg F. (about 5 degrees cooler than the outside temp, the A/C was on inside the house)

Tim,

Excellent article, thank you. I have a question on attic fans and moisture build-up in the winter months.

I live in Canada, and I get ice build up inside the attic. If I install a fan with a humidistat and increase my insulation depth, will that help eliminate the conditions that create the ice?

Tim - This refers to a question in this list. I had a new roof installed last year due to hail damage. The attic fan was removed and ridge vents were installed. Can an attic fan be reinstalled and work with ridge vents?

All well and good. If interested, one can refer to a roofing material manufacturers installation handbook. It has formulas for calculating the amount of inlet and exhaust air square inches you need for a specific square footage of attic space. It includes the net effective square inches of a soffit vent, rather than just multiplying width times length.
It will also tell you how many cubic feet per minute is ideal to move the attic air via a fan. And no, more is not necessarily better. If you don't balance the inlet air and the outlet air, you are doing yourself a disservice. Thanks for reading this.

how many vents

What about the opposite approach - Spray foam insulation between the roof rafters. In the south this is becoming popular. With spray foam your attic is sealed tight and becomes like a big ice chest.

I have a 1926 farmstead home and just had turtle vents installed to reduce the temperature in the attic. I have a 3.5 tonne heatpump. My question is, with a small 1 foot by 1 foot static vent at the end of the attic, no soffit vents, no eave vents and no other airflow vents, will this be effective in reducing my internal cooling costs? I live in West Texas.

I wonder at Tim's experiment with the solar fans. If the fan pictured is the one he is talking about then it may be too far down from the peak and if the thermostat is up high (a good place for one) then the fans might be leaving a hot bubble at the peak of the roof and sucking out the hot below. Otherwise it is hard to explain how swapping out 130 degree air and pulling in say 90 degree air is not helping even a tiny bit.

The roof warranties I have read (yup - read some) have as a condition sufficient ventilation. And sufficient is a lot by their lights and I'll bet money very few inspectors on warranty claims think _any_ amount is sufficient to pay on.

I live in a climate with lots of sun but mild weather so I vent for the hot days and for the life of the roof materials. The roof that lasts an extra 5 years past the 40 of the planned shingle life is like getting discounted by 12%... and the comfort boost makes it worth the bother.