There is NO QUESTION that the exhaust fan we choose will be solar. I would like some of your opiniions on the solar attic fans that exhaust out the gable vent, rather than install through the roof. Obviously it is a much easier installation (handy hubby can do either way). But will having one fan, sized to suit the 1400 sq. ft. of attic, installed on one end do as well as one that can be installed centrally through the roof?

We do have adequate passive venting for the air to come in to replace what the fan draws out--50% of the 3 ft. soffits are full vents (not just little round "pucks") and the ridge vent runs the entire length of the roof and the gable ends have 18" X 24" vents.

Any experience greatly appreciated!

One of the recent issues of Home Power Magazine had an article on installing solar vents -- I'm sure you can find it on the www.HomePower.com -- probably worth the cost of the download.

There has been some controversy over whether attic fans are a good idea or not. Some work says that the fans tend to pull a very slight negative pressure in the attic, which then tends to draw air for the living space through any openings (like electrical or plumbing pentrations). If you go to www.southface.org, I belive they have a fact sheet or paper on the subject. The fact that your attic is well vented, and the ceiling of your living space is well sealed(?) would probably minimize this effect.

If you lower the temperature of the attic 10F(?), and your existing insulation is R60(?), then the improvement might be:
(1400sqft)(1 BTU/60 hr-ft^2-F)(10F) = 230 BTU/hr less heat flow from attic to living space

For 12 hours per day, and 120 days (summer), this would be:

(230 BTU/hr)(12hrs/day)(120 days) = 331000 BTU/season

This is about 3.5 therms of gas in an efficient furnace, -- worth about $5 per year?
You can ratio that up or down if you think you will get more or less temperature drop in the attic -- e.g. for a 20F drop you might save $10 per year.

The savings might be about twice this if you are using propane for heat.

I think that for a lot of people who don't already have a lot of insulation in the attic, it makes more sense to add more insulation, and maybe improve the attic venting, but since you already have lots of insulation, the fan might be a good next step.

Gary
www.BuildItSolar.com

I never thought about it before, but a solar attic fan would also run on sunny days in the winter. It would (I think) on average make the attic colder by bringing in more outside air. I would guess this might slightly increase your winter heating bills? Anyone have any thoughts on this?

Gary

Gary

I don't think it would matter much where you put the fan.

That is just my opinion though.

I hope it helped.

from http://www.mananasun.com

Contact us:
Justin Kwok
Email: justin@mananasun.com
Skype: goself
MSN: goself@hotmail.com