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rav 03-15-10 06:36 PM

Solar attic fan
I am planning to have a solar attic fan installed this year. I was curious if any of you here have them and what's your feedback about them. My attic has the usual soffit and ridge vents, last fall i installed an attic tent and was very pleased with the heat savings compared to 2008.



Daox 03-16-10 06:28 AM

I think solar attic fans are a great way to go if you can't get enough natural convection through normal ventilation. However, if you can do it naturally, all the better/easier/less costly.

rav 03-16-10 06:14 PM

We had a new roof put this year and even though we have the soffit and the ridge vents a couple of the plywoods for the roof had some discoloration. I think that happens because of the moisture build up. I guess i will try the attic fan, plus i can get some tax rebate on it too for next year.

Daox 03-16-10 06:18 PM

Yeah, if you are getting moisture you probably need more ventilation. You really don't want that new roof rotting out on you.

Xringer 03-16-10 06:30 PM

I saw some solar attic fans online at..
Solar Attic Fans

And I think similar products can be had at Lowes or HomeDepot these days.

We have an old AC powered gable fan installed, but the thermostat seems to have
died after 10 or 15 years of use.

So, I'm also thinking of adding some extra ventilation to my attic this summer.
But first, I'm going to stick a wireless temperature probe up there for a few hot days.
If the new ridge vents are working well, I may not need any extra air flow..

Patrick 07-27-10 08:07 AM

I had a 200W 120V gable fan that I replaced with a solar fan from Home Depot. I figure I'm saving about $0.25 a day when it's in operation, or about $30 a year. It cost about $250 for the fan and the panels, so payback is about 8 years.

bennelson 07-14-12 10:55 AM

I'm also thinking about installing a solar-powered attic vent fan.

I saw one at an energy fair a couple of years ago, and it really seemed to move the air. Makes sense too that the heat from the sun ends up cooling your attic.

We just went through a big heat wave, so the main thing I am looking at is cycling more air through the attic, to keep it cooler, to run the air-conditioning less.

Anyone else have more direct experience with this?

I was also thinking that maybe I could put my wireless indoor/outdoor transmitting thermostat in my attic to get some temperature info for before and after.

Xringer 07-14-12 12:18 PM

I have one of those cheapo remote temperature sensors hanging up near the peak of my attic.
I've seen it hit 120F recently up there, when the outdoor temp was in the high 80s, low 90s.

I've checked out my old attic fan and it still works. Not sure how much power it uses,
but I'm sure that it's not real efficient. It's on the east wall.

When we aren't using the house AC, we keep the attic stair (pull-down)
open a few inches to allow the house air to be pulled up into the attic.
Acts a little like one of those 'Whole House' fans.
But, when we are using AC cooling (like today), most of the air input into
the attic comes from the peak vent on the west wall.

It starts up just a little above 100F and tends to stay on until late in the afternoon.
I don't like the hysteresis of it's sensor, since it stays on for so long.
I think the attic temp drops down to around 90F before the fan shuts off..

I'm trying a Timer experiment now. AC power goes off for 30 minutes and
comes back on for 30 minutes, all day long.
So, during the heat of the day, it's going to running on a 50% duty cycle.
Should save us 50% on fan power use.. :rolleyes:

MarkM66 07-19-12 07:24 AM

If hot air rises, will a cooler attic really have an effect on the lower living area?

I'm also looking for ways to run my a/c less.

bennelson 07-19-12 07:50 AM

The way I see it, it's all about "Delta-T", that is, the DIFFERENCE in temperature.

The bigger the difference on one side of the wall than the other, the more heat tries to push through to the other side to even out the temperature.

Insulation slows down this process, which is why we insulate our houses, to keep warmer longer in the winter, and cooler in the summer.

I recently put the remote reading sensor from my wireless indoor/outdoor thermometer in the attic of my house. It's been hot lately, and we've been running the air conditioning, set to 80 degrees F.

In the attic in the middle of the afternoon, it's been 120-125 degrees. So, that's a 40-45 degree difference than in the house. If it were winter, we might have the furnace set to 70 and the outside temperature might be 25 or 30. That's that SAME 40-45 degree difference!

Basically, the AC is working as hard in the summer, as the furnace is in the winter when it's below freezing! Imagine if you had a way to warm up the outside in the winter - your furnace would have to run that much less because of it.

That's kind of what you are doing if you can cool your attic. If you can drop the temperature there, it's that much less heat trying to beat its way into your house!

Anything you can do to reduce the Delta-T (including raising the thermostat in the summer) reduces how much energy is used to heat and cool the house. It just seems like a good attic fan is a simple, cheap, way of doing that.

(The summer/winter comparason isn't perfect. In the winter, heat loss is sort of everywhere - walls, attic, foundation, etc. In the summer, the attic is the hottest thing, but you also have to consider solar gain, and that the walls of the house are unevenly heated as well)

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