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.
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.
Go to conclusions for summary and this is with a solar/battery fan.
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
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.
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.
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.
~ 9 year pay back is not attractive to nearly all Americans.
Originally Posted by adrianf
PV powered fans need to be cheaper and electricity rates need to increase.
And with updated code requirements for AHUs and ducts in a conditioned space and high ceiling R value,
the future impact of attic fans will be nil.
" Photovoltaic Attic Ventilators
Two PV attic ventilators were installed on the house's asphalt shingle roof on August 6th, 1997.(3) Both were installed near the peak of the A-frame roof with one on the east face and another on the west face as shown in Figure 2. The fans are designed to provided between 600 and 800 cfm of attic ventilation at peak solar irradiance (1000 W/m2) depending on the free soffit ventilation area. The ventilators consist of a 19.5" x 16" mounting with a 10 Watt thin-film PV module. A five bladed radial fan and a direct coupled DC motor provides attic air exhaust. The units were purchased for $300 each; installation would typically add another $100 - $150 per unit. "
" ... Comparing periods with similar weather conditions, the test revealed that the PV vent fans have the potential to reduce measured peak summer attic air temperatures by over 20oF. However, the impact over the cooling season is fairly modest with well insulated attics. Measured space cooling reduction was approximately 6% - worth about 460 kWh annually at the test home. "
Last edited by dan sw fl; 03-30-2008 at 08:46 AM.
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"9 year pay back is not attractive to nearly all Americans."
Agreed. I haven't been a FAN of pav(s) for many years now.
Just wanted to throw this out here...I was a firm believer in PAV's until reading along on this forum. I have done a lot of work over the winter in the attic. Adding insulation...making sure all soffet vents were not blocked. Also, my roof has many ridges, all have ridge vents. Taking the advice from people on this forum, I have added an attic tent, caulked all the penetrations through the top plates and disconnected my PAV. Today it was 96* and sunny...my attic temp reached only 110* Now it is currently 88* outside, my attic temp is also 88*. My upstairs Temp was 76* throughout the day, although my upstairs AC runs contantly from 1pm till 10pm, the humidity is very low. Every pro I have spoken with saids this is normal for a properly sized unit. I have 2 high efficency units(Ruud, 3 ton upstairs 2 ton downstairs) and cannot complain about my electric bill which runs about $50-$60 more than my electric bill in the winter. With my PAV, I could not achieve a temp below 78*. Thanks to all on this forum who know what they are talking about.
Ask yourself this. Can a sealed attic with a PAV achieve only a 14* temp difference? Or is a well ventilated attic better (and no $$$ wasted on running the fan) Ditch the PAV
Joe, I am curious what your attic temperature was running before you did the work. I have been told by some A/C guys that my attic is the hottest they have ever been in.... Not sure about that, but it was 120 deg this morning at 10AM when the outside temp was about 80 deg. I have been up there before when it was 130-140 and that was on a day when the outside temperature was in the low 90's..... It has been over 100 here past several days, but i have not had chance to check attic temperature.
Originally Posted by Joe Mascitti
I have soffit vents (not sure if they are all open but would presume they are since there has not been any new insulation blown up there since house was built in '90's). I also have the little rectangular vents on top - I think they call them air hawks (???) - but they are not powered vents or turbines, just vents. I have about 5 of those - I think my attic is around 2000 sqft.....
NO ridge vents and NO PAV's... About 9" of the pink rolled insulation R-30 and I also saw some R-19
I really don't think my house stays that comfortable and the A/C runs freaking constantly..... Just got a new Trane 4 ton 14 seer last year and think it is a tad undersized (about 2500 sq ft).......
Curious your thoughts AND ANYONE ELSE'S !!!!! on what are best things to do to help the situation.
97* yesterday..my attic peaked at 113.7*...I cannot remember exactly before, but even with the PAV I think I was in the 120's...When I had my roof re-done a few years ago after a big hail storm. I asked the roofer to be sure to put a Full ridge vent on every ridge. Prior only the "Main" roof had one, and it was about 1/2 the length of the ridge line....
6:30 here...outside 94.1* inside 77.3* Attic 103.6*
Heat Index 101*
I am taking my attic measurement 8ft about the floor...