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c4qeizlr 04-07-2012 07:28 PM

Installing attic fan (options)
 
Hi there,

I'm looking into installing an attic fan on the roof to vent hot air in the summer times, so to hopefully help reduce somewhat of the AC bill.


The residence is a single-story SFH that faces NW(15 deg)/SW. On a typical day (like now), the wind is from NNW @ 10-15mph.

There is a huge tall tree about 40 feet away facing the SE-side of the house by the curb. The tree is about 80 ft tall.

I am wondering about the following:

1. What kind of attic fan is best
- the motor needs to last, and is also quiet (I should not hear anything from inside the house)


Are gable fans ok--like this one?
http://www.amazon.com/Broan-353-Gable-Powered-Ventilator/dp/B001E6JC1C/ref=sr_1_1?ie=UTF8&qid=1333847688&sr=8-1


Or roof-mounted attic fan is better:
http://www.amazon.com/Broan-355BK-Mount-Powered-Ventilator/dp/B003LBCE5E/ref=sr_1_5?s=hi&ie=UTF8&qid=1333848899&sr=1-5


I'm also looking into solar fan like this:
http://www.amazon.com/Solar-Attic-20-watt-25-year-warranty/dp/B001OULVQM/ref=sr_1_3?s=hi&ie=UTF8&qid=1333848899&sr=1-3


Some info say that solar attic fan is DC motor so it's a lot quieter and lasts longer then the AC-motors in powered attic fans. True?


2. Best location to install the attic fan

For the solar attic fan option, the tall tree doesn't seem to be blocking the sun so perhaps middle of the roof facing SE side is ok to capture the sun fine during day time?

Should the attic fan be as close to the top of the roof as possible? Anything to pay attention to when I install (I'm a fresh DIYer)?

Sunrise is @ 80 deg (East), and sunset is @ 280 deg (West).


Thx.

woodchuck 04-08-2012 06:44 AM

The gable mount is the least invasive, least expensive and much much easier to install. Mine came from Lowes. Mine is mounted in a gable directly above my den and when it comes on we sometimes notice the sound unless the TV is on. It's the motor vibrating on the wood frame and not the air sound on the blades which you can hear from outside. I stapled cardboard to seal the remaining part of the gable so the air would have to come from the other end. I would mount it in the other gable at the other end of the house if I had it to do over again. It would be best to pull the air across the part of the attic you wanted cooled most first.

AndyGump 04-08-2012 08:42 AM

Personally I would not waste my money on any of those things.

As long as you have the proper amount of insulation between the attic and the living areas you should be O.K.

In my opinion it would take maybe 20 years to recoup your costs for the units in any energy savings.

Andy.

GBR 04-08-2012 07:40 PM

I agree with Andy, above. The cost of running the fan doesn't give the savings on the air conditioner usage cost; http://www.fsec.ucf.edu/en/publications/pdf/FSEC-CR-1496-05.pdf

Depends on where you are located, and if HVAC units/ducts are in the attic, air sealed attic, and if you even need the outside air in quantities with the moisture that comes with. If the intake isn't more than the CFM exhaust of the fan, you will be drawing conditioned air through from below, or possibly drawing the exhaust fumes from below if gas units and the crawl/basement isn't air sealed.http://www.nachi.org/attic-ventilation-systems-part1-25.htm

Payback on solar fans; http://www.fsec.ucf.edu/en/publications/html/FSEC-GP-171-00/

http://epics.ecn.purdue.edu/hfh/_team_documents_web/02_SolarProject_Results/solarresults.htm

Gary

joecaption 04-10-2012 08:50 AM

Air seal the attic, add a ridge vent if there is not one now, make sure you have the right amount of insulation for you area.
http://www.energystar.gov/index.cfm?c=home_sealing.hm_improvement_insulation _table

Make sure the soffit vents are not blocked.

I'd never install a roof fan in a house I own.

A ridge vent will vent the whole roof not just a circle like a fan will.

strategery 05-10-2012 01:04 AM

I think that study that GBR posted supports the notion that powered attic fans aren't a very good investment if you're looking to cut AC costs or try to cool the house. What about moisture issues though? Shouldn't that be the primary reason for adding a powered fan? A solar powered fan is easier because you don't have to worry about operating costs or electrical wires.

A powered fan would be a terrible idea if you haven't first air sealed all of the leaks into the attic, that I agree with. But for some a solar attic fan might be a good option if you don't have ridge & soffit vents and you're several years away from putting a new roof on but NEED better ventilation.


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