Attic Fans | Install an Attic Ventilation Fan for Energy Savings
An attic fan is a fan that circulates air from the outside of the house through the attic of the house. The goal is to reduce the temperature of the attic, and therefore reduce the convective and radiant heat transferred to the top living floor of the house. This, in turn, reduces the amount of energy that must be expended on cooling the home in the Summer. (Note that there is no real benefit to attic fans in the Winter).
Attic Fans vs. Whole House Fans
As Todd notes in his article, an attic fan is different from a whole house fan. A whole house fan is normally installed in the ceiling of the topmost floor of the house, between the topmost floor and the attic. While an attic fan only circulates air in and out of the attic, a whole house fan pulls air through the house and out of the attic. This essentially creates a draft throughout the house. Air enters the house through open windows, wall cracks, outlets, and other places, and leaves the house through the attic fan which blows the air up and out. A whole house fan creates an artificial chimney effect in the house that cools it down.
Whole house fans are great in climates where you don’t need to use air conditioning. If you use air conditioning, a whole house fan will waste the energy by pumping the A/C out of the roof of the home. Whole house fans and air conditioning should not be run together.
Why Attic Fans Work
In the Summertime, the attic can heat up to 40-60 degrees hotter than the ambient outside temperature. In extremely hot climates, this means that an attic could reach 160 degrees F. This heat is transferred to the house via radiation (heat energy transferred as electrmagnetic waves), and convection (heat energy transferred as the hot air contacts the insulation and other ceiling materials).
An attic fan can reduce the temperature of the attic by as much as 40 degrees F or more. If an air conditioner is trying to keep the house at 75 degrees F, a reduction of 40 degrees in the attic may save as much as 30% off the energy required to cool a second floor, while requiring only a fraction of that energy to run itself. Plus, it will keep the second floor feeling much cooler than may otherwise be possible.
Solar Attic Fans vs Electric Attic Fans
There are several varieties of attic fans including solar and electric varities. As a general rule, solar fans operate at a lower wattage and thus can’t cool as much area. Check the CFM and appropriate square footage rating on the fan. If you already have electric in the attic, we recommend installing an electric fan. It will run much faster, and its cheaper. If you decide to go with a solar fan, make sure you will get sufficient air flow. It may be a waste of your investment if you don’t. Consider running electric if you don’t have it to avoid the solar option.
Attic Fans Extend Roof Shingle Life
Attic fans can also increase the life of the shingles on your roof by preventing cracking damage due to extreme heat and cold cycles. By reducing the extreme temperatures, shingles can last up to 20% longer on roofs with attic fans. Since a 20% longer life equates to a 20% cost savings on roof replacement, an attic fan pays for itself when considering only this facet alone.
Avoid Roof Leaks During Installation
You may want to have an attic fan professionally installed, especially if you aren’t comfortable working on the roof. During a typical shingle replacement is the best time to have a unit installed, but they can be installed anytime. Make sure that the shingles overlap the base of the fan and that appropriate flashing is installed to avoid roof leaks around the fan. Roofing mastic can be applied around any edge gap. The fan will come with detailed installation instructions. If you aren’t comfortable working on a roof, you’ll definitely want to pay for installation.
Attic Fans vs. More Insulation
One alternative to an attic fan is to add additional insultation. The advantage of insulation is that it works in both the Summer and Winter, whereas an attic fan only benefits the homeowner in the Summer. Each installation is unique, and so determining whether a fan or insulation is the better route is not always easy. That said, an attic fan probably won’t be nearly as expensive to gain a lot of performance in the Summer. If you’re attempting to “go green”, we suggest over-insulating and adding the ventilation fan.
Attic Ventilation Fan Cost & Pricing
Attic fans can run anywhere from $100-$500 dollars depending on the model. Decent models command between $150-300, and may run quieter and last longer than their less expensive counterparts. Solar attic fans will be on the high end of the spectrum (another reason to avoid the solar option if possible).
Attic Fans Running All the Time / Won’t Come On
Most attic fans are controlled by a temperature regulator and turn on and off automatically. It is possible for an attic fan temperature probe to go bad and need replacement. You should watch your attic fan on very hot days and make sure it is turning on when the sun is hitting the roof, and turns off during the evening.
What do you think? Have you installed an attic fan? Will you?
(Photo: MaryTClark)
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8 Responses to Attic Fans | Install an Attic Ventilation Fan for Energy Savings
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June 17th, 2009 8:29 am
Solar attic fans are not only the least expensive (in terms of total cost of ownership, which is purchase price + operating costs), they are also the most environmentally friendly way to ventilate an attic. Unlike conventional electric attic fans, solar attic fans don’t use any electricity from the power grid at all! I have really been trying to get the word out about this method of attic ventilation at Solar Attic Fan Info because I think not enough people are aware of the benefits – please check it out!
June 17th, 2009 12:35 pm
We had an electric attic fan years ago when our house was built. 8 years in we had an attic fire that did extensive damage, which the firemen claimed was started by the attic fan when the motor burned up. They said this happens frequently!
We were not willing to risk another fire, so we replaced the electric fan with two turbine (wind driven) fans, which do not work as well to cool the attic.
We looked into a solar fan for the attic, but the cost was too high to justify in this house, as we’ll be selling in a year or so. Our neighborhood does not support this type of improvement in terms of ROI.
We will consider solar for our next house.
June 17th, 2009 5:18 pm
I believe the benefit of an attic fan during the winter months is to ventilate the moisture caused by the hot air leaking up into the cold attic from the warm level below.
June 17th, 2009 7:28 pm
Peter – good thoughts on the solar attic fan. I’ll take a look at your site. I’d like to see total cost of ownership numbers and payback period. Is it a short payback period after considering electric costs?
Steve – running an attic fan in the Winter will create a draft through the attic (and across the insulation) that will tend to cool the attic even faster than if it were directly exposed, and thus cost more in electric bills.
June 18th, 2009 5:42 pm
Fred,
I agree that running the fan all the time during the winter is not the right thing to do. But in your opening paragraph you noted that there was no benefit to having an attic fan in the winter. I just thought having an attic fan is a good idea and that there is a benefit during the winter. http://www.naturalhandyman.com/iip/infattfan/infattfan3b.html
Steve
June 25th, 2009 3:57 pm
Hi Fred,
Here’s a rough payback calculation:
A top of the line 1300 cfm solar attic fan will run you around $600, installation (no electrician required) another $300, so total installed cost is $900 minus your $270 Federal tax credit = $630 out of pocket cost.
An electric attic fan of similar capacity will cost around $125, installation $400, so the total installed cost = $525 out of pocket.
First cost differential: Electric fan is $105 less expensive.
Solar fan is free to run.
Electric fan uses 0.5 kw per hour of operation. If electricity is $0.12/kw-h, cost to run the fan is $.06 per hour.
So the electric fan will run for 1,750 hours on $105 worth of electricity. Say the fan runs only when the solar attic fan would run, 6 hours a day. The breakeven point or payback period is 292 days!
June 29th, 2009 5:18 pm
Hi Fred and Peter,
The problem with the payout calculation is that you would be hard pressed to find an attic fan with a 500 watt motor. I think that the consumption would be much closer to .15 kw per hour for a typical roof fan or gable fan.
Given that you had the option of installing a new electric or a new solar, the payout would realistically be closer to 972 days.
If you are simply upgrading to a solar fan from an existing electric, even with the tax credit the economics make very little sense. It would take about 16 years to pay out the expense of taking your attic fan off-grid.
Just my $0.02…
June 29th, 2009 5:20 pm
Oh, and battery technology isn’t quite where it needs to be for that solar unit to last 16 years…