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  1. #1
    Join Date
    Feb 2008
    Location
    Tennessee
    Posts
    91

    Do power attic fans help?

    Do power attic fans do a better job of venting the heat out? I have heard some people say they are a waist of money because the motors won't last long running in the heated condition they run in. I have 3 in my attic and all 3 motors are done. I want to replace them with either a higher quality moter or take them out completly and use something else. I live in Tennessee so our arttics here get pretty hot.

  2. #2
    Join Date
    Oct 2006
    Location
    The Beach
    Posts
    718

    Hmm Roof Fans

    They seam to help a little. I have to change them out about every three years. A ridge vent works much better. You do have to have opening in the boxing or in the eaves for the air to circulate.
    Blue Fox

  3. #3
    Join Date
    May 2007
    Location
    Naples, Fl
    Posts
    889
    http://www.fsec.ucf.edu/en/publicati...sec-gp-171-00/

    Go to conclusions for summary and this is with a solar/battery fan.
    HTH

  4. #4
    Join Date
    Jan 2007
    Location
    bowie md
    Posts
    116
    If home has ridge vent system we will not install or repair fans.The fan will not allow the ridge vent to work as designed

  5. #5
    Join Date
    Jul 2005
    Posts
    717
    IF an attic space has the proper amount of soffit and ridge (or other high ,near the peak ) vents, then no other type of venting is ever needed.
    Gravity air flow, entering the soffits and exiting high near or right at the peak will do the trick.
    No electrical powered or high priced turbine fans are required.

  6. #6
    Join Date
    Mar 2008
    Location
    Baltimore MD and Ridgebury PA
    Posts
    542
    If you have a ridge vent then don't bother replacing the fans. If you don't have a ridge vent then you may consider adding a ridge vent rather than replacing several fans.

  7. #7
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,915
    Powered attic vents, aka PAVs, pull conditioned air up out of the house through light fixtures, wiring penetrations through the top plates in walls, the attic access, and any other path it may find.
    The more passive ventilation from outside, the less air it will pull up out of the house, but it will always be pulling air out of the house.

    I have been in a number of homes where the difference between not cooling to the set point on a 85-95º day, and maintaining the set point up through our 100º outdoor design condition, was simply to disconnect the power to the PAV.

    See the 2nd part of my signature.
    If more government is the answer, then it's a really stupid question.

  8. #8
    Join Date
    Feb 2008
    Location
    Tennessee
    Posts
    91
    Quote Originally Posted by mark beiser View Post
    Powered attic vents, aka PAVs, pull conditioned air up out of the house through light fixtures, wiring penetrations through the top plates in walls, the attic access, and any other path it may find.
    The more passive ventilation from outside, the less air it will pull up out of the house, but it will always be pulling air out of the house.

    I have been in a number of homes where the difference between not cooling to the set point on a 85-95º day, and maintaining the set point up through our 100º outdoor design condition, was simply to disconnect the power to the PAV.

    See the 2nd part of my signature.

    This has been one of my major conserns about using power attic fans, sucking the conditioned air out of the house. That said, this house does have plenty of soffit vents.

    Switching to a ridge vent system would seem to be very labor intensive unless a new roof was being installed.

  9. #9
    Join Date
    Mar 2008
    Location
    Long Beach, CA
    Posts
    3,437
    Quote Originally Posted by printmanjackson View Post
    This has been one of my major conserns about using power attic fans, sucking the conditioned air out of the house. That said, this house does have plenty of soffit vents.

    Switching to a ridge vent system would seem to be very labor intensive unless a new roof was being installed.
    PAV’s may very well be too powerful to be used in an attic, especially multiple units. I’ve used inexpensive turbine fans for years with good results. With a slower and more consistent exhaust, they will draw only through the existing eave vents, not affecting interior air.

  10. #10
    Join Date
    Jul 2006
    Location
    NW burbs of Detroit
    Posts
    6,058
    Quote Originally Posted by mark beiser View Post
    Powered attic vents, aka PAVs, pull conditioned air up out of the house through light fixtures, wiring penetrations through the top plates in walls, the attic access, and any other path it may find.
    The more passive ventilation from outside, the less air it will pull up out of the house, but it will always be pulling air out of the house.

    I have been in a number of homes where the difference between not cooling to the set point on a 85-95º day, and maintaining the set point up through our 100º outdoor design condition, was simply to disconnect the power to the PAV.

    See the 2nd part of my signature.
    Amen to that. If your using any attic fans at all you might as well have a whole house attic fan going while running your a/c. It would be just as bad as opening all your windows and trying to cool the house with a/c. Ain't gonna happen cause you are pulling in hot air at a higher rate then the ac can handle.

  11. #11
    Join Date
    Dec 2005
    Location
    California/Nevada
    Posts
    3,648
    i guess every house needs to have the attic inspected to make a good decision.

    i was at a customer's house last month, the outdoor temperature was just warm enough to turn on the AC, but when i went into the attic, the attic was well over a hundred and something degrees.

    the attic was completly sealed and i think they could have really profited from an attic fan,
    but i wouldn't place one there without installing a vent on the other side.



    my mom's house could use one too, her attic has openings under the roof overhang, and its still too hot.

  12. #12
    Join Date
    Feb 2008
    Location
    Tennessee
    Posts
    91
    I found this on another site about venting:

    >The rule with attic ventilation is 1 : 300 with a vapor barrier and 1 : 150 without a vapor barrier. So if you had insulation in the attic with a vapor barrier and the attic was 900 sq. ft., you would need 3 sq. ft. of free venting. If it was blown in insulation without a vapor barrier, you would need 6 sq. ft. of free venting. This is when you have an equal amount of square footage of high and low vents ( gable and soffit).

    Your concern about attic fans is correct. The problem is not the fan but the over sizing of attic fans. Most attics can only handle about 1500 cfm of ventilation because of the vents. Your fan that you have probably moves about 2000 to 5000 cfm. In which case it could cause a problem with drawing air from the home and causing the problems you mentioned.

    Properly sizing the fans is important because of this. You could increase the size of the vents but you're looking at more than doubling the amount. You're much better off putting in the proper size fan. The volume of air in the attic remains constant. So if the vents only allow 1500 cfm and the fan moves 2500 cfm, it will seek to get the air from somewhere, like the home. If the fan couldn't get the air from anywhere else, you would just burn out the fan.<

  13. #13
    Join Date
    Mar 2008
    Location
    Baltimore MD and Ridgebury PA
    Posts
    542
    Quote Originally Posted by printmanjackson View Post
    This has been one of my major conserns about using power attic fans, sucking the conditioned air out of the house. That said, this house does have plenty of soffit vents.

    Switching to a ridge vent system would seem to be very labor intensive unless a new roof was being installed.
    Not really assuming you have a typical shingled roof. Consider this, you install a shingles starting at the bottom and working your way up. Since the ridge vent goes at the top you don't actually have to disturb any of the lower shingles. Generally, one would simply use a circular saw to cut a parallel line about 6-12 inches from the peak of the roof. Remove the shingles and OSB or underlayment that was cut away. Install the ridge vent material. Re-install shingles at the peak of the roof over the ridge vent. A new roof by comparison takes considerably longer.

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