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-   -   Solar Attic Fan: Does it Work? (http://www.diychatroom.com/f97/solar-attic-fan-does-work-51727/)

Casey12081 08-26-2009 12:03 PM

Solar Attic Fan: Does it Work?
 
I have been reseraching solar attic fans for my 3 level town house in Virginia. I am aware of the pro's and cons (tax rebate, no electricty, extended roof life, lower A/C -- expensive, blocked by clouds). What I have NOT found is anyone saying they have installed one and are happy with it. As in, does it actually do what manufacturers say it does? Anyone that has installed one I would love to know what you think!:thumbsup:

Mo-Town 08-26-2009 12:54 PM

Casey:

I've been doing a lot of research on attic fans and decided against installing a solar fan. In fact, I decided against installing any motorized attic fan. I live in the California central valley, where summer temperatures consistently hover around 100 degrees. In reading user reviews for attic fans, I noticed that people in hot summer locations like Texas were all experiencing the same problem with these fans: the extreme heat on the roof would kill the fan's motor. These were user reviews for standard attic fans, but the same problem would presumably apply to solar models.

Another thing to be wary of is the material the fan is made from. Almost all of the standard attic fans I've seen are aluminum or galvanized steel. In contrast, the $300 solar attic fan they were selling at my local Costco had a black plastic housing. I'm not sure that would last too long in my area.

Anyways, if you're interested in a green and cost effective way to cool your attic, you may want to consider turbine vents (the "chef's hat" vents you see on warehouse roofs). Turbine vents will move about the same volume of air as an attic fan, and they don't need any power - solar or otherwise. All they need is a light breeze.

If you decide you'd like to go with a solar attic fan, you might want to consider mounting it under your eaves and using as a soffit fan. It will perform the same function as it would mounted on your roof, but the eaves will protect the fan from some of the heat and probably help prevent than fan's motor from crapping out.

Casey12081 08-27-2009 08:46 AM

Thanks, that is definitely something that I did not think about, although I don't have the temp extremes that you have. I just came from California, so I understand what you mean. You have a link to where you found the testimonials? All I have been able to find is people that have installed them, nothing about effectiveness.

Mo-Town 08-27-2009 09:48 AM

I don't have a specific link, but the user reviews I read were all on the Lowes and Home Depot websites and were made in connection with the wired attic fans.

Casey12081 08-28-2009 07:12 AM

Mo. thanks for the reply, I appreciate it. I think that based on what I have read, and a lack of reviews from people that have actually installed solar attic fans, I will not go that route.

Scuba_Dave 08-28-2009 07:20 AM

Others have also reported that they do not move enough air
Solar is a good idea, but they still need to make it better

Casey12081 08-28-2009 08:44 AM

Mo, I found some pretty good info on www.amazon.com, here is the link: http://www.amazon.com/Solar-Attic-Fa...owViewpoints=1

This guy actually posted some tangible results, although not what is advertised, an improvement nonetheless! So now I am undecided once again...lol...

Mo-Town 08-28-2009 10:16 AM

I took a look at the amazon link, and while it does appear that fan is well built, I'm not sure I would spend that amount of money to simply lower my attic temperature 6 degrees. That's why I ultimately went with a combination of thermal radiant barrier and turbine vents. The turbines move a larger volume of air and are cheaper, but they also have the advantage of removing moist air from the attic during winter months. The radiant barrier is probably, dollar for dollar, the most effective way to cool your attic space, but to get the most out of it, you have to install it along the rafters, and that's a much more time and labor intensive job than installing an attic fan.

I don't think there's any harm in giving the solar fan a try. If it does the job for you, great. If it turns out to be a little underpowered, or dies after a few years, you can always use the hole in your roof to install a new fan or a turbine vent. :)

Casey12081 08-31-2009 07:53 AM

Yeah Mo, you are right on that. I didn't really look at the cost until you mentioned it. It's just like the tankless water heater, just not worth the money based on the return. I am just going to wait and see how this winter goes (just moved in a few months ago) and make a decision from there.

telldon 09-22-2009 10:42 PM

Hey , just a short note,
I was investigating them for awhile also , but found that they didn't move enough air to be useful. the object is to remove the air before it has enough time to heat the mass around it, which in turn heats other things, IE, the Ceiling and the rooms below it.......
you may consider foil radiant barriers to further insulate the insulation and block the heat transfer. and or look into an electric fan with thermal control , they move much more air...
Good Luck

dave4881 04-21-2010 06:14 PM

I just installed a solar attic fan. It is a Natural Light SAF-20, which is rated at 1200 cfm, which is adequate to vent an 1800 sq foot home with a 4:12 pitch roof.

The installation was easy. When the sun is bright, it runs well and sucks a lot of hot air from the attic. I also used a thermal switch that keeps the fan from turning on until the attic reaches 85. The unit has a 25 year warranty on the solar panel and motor. It cost me about $475.

I have just ordered another one just like it so I'll have double the capacity on my roof.

You can install whirlybirds, solar attic fans, or ridge vents and get the job done, but you must have adequate eave vents for these items to work well.

I'm very happy with mine and the 30% tax credit also makes them a good deal.

To the poster that recommended installing solar attic fans under the eaves, that sounds ridiculous. Hot air rises and should be drawn from low to high using devices made for it. But, there are people that walk around on their hands too. It's possible, but not efficient.

Yoyizit 04-21-2010 07:57 PM

Quote:

Originally Posted by dave4881 (Post 431702)
It is a Natural Light SAF-20, which is rated at 1200 cfm, which is adequate to vent an 1800 sq foot home with a 4:12 pitch roof.

I find 1200 CFM @ 20w hard to believe
http://www.mainerural.org/energy/fie...efficiency.pdf, last page
How much temp drop do you get?

"Attics can reach temperatures of 150 to 160 degrees F during a summer day, although outside air temperatures are only 95 to 97 degrees F. . . .reduction of attic temperatures from 155 degrees to 105 degrees F will result in a significant reduction in cooling load. . . Attic temperature depends on the amount of solar radiation, construction details and the rate of ventilation. Calculations indicate that on a July day in Texas, a ventilation rate of one air change per minute for a typical attic using 95-degree F air will lower the peak attic temperature to about 101 degrees F.

Your attic is about 3200 ft in volume?


"Two PV attic ventilators were installed near the peak of the asphalt shingle roof in August 1997, one on the east face and the other on the west. The fans are designed to provide 600-800 CFM of attic ventilation at peak solar irradiance (1,000 W/m2) depending on the free soffit ventilation area. A five-bladed radial fan coupled directly to a DC motor provides attic air exhaust. The fans were purchased for about $300 each; installation would add about another $150 per unit.

The study's authors looked at several weeks of similar weather before and after the retrofit. Once the fans were in, the daily peak attic air temperature dropped by an average of 22F. Air conditioner energy use was also measured. This consumption was reduced by an average of 6% (2.8 kWh per day) by the addition of the ventilators; the difference was greatest around midday. Space-cooling electricity use, which had been submetered at the home for the entire year before the retrofit, totaled some 7,730 kWh. Annual space-cooling savings are on the order of 460 kWh, based on extrapolation from similar periods. These savings have a value of about $40 at current Florida energy prices. Given that the installed cost for the two units was about $850, the payback period would be more than 20 years. "

dave4881 04-21-2010 08:37 PM

1200 cfm for the 20 watt model is stated by the manufacturer, Natural Light.

I'm waiting for warmer weather to determine the actual temperature drop. I will also wait until I get the 2nd fan installed. The manufacturer only recommends 1 - 20 watt or 2 - 10 watt fans for my home. I figure going with 2 - 20 watt fans will be more efficient since my house is a ranch-style home that is 85' long. Attic volume is about 4050 cu ft.

spark plug 04-21-2010 08:47 PM

Quote:

Originally Posted by Mo-Town (Post 320502)
I took a look at the amazon link, and while it does appear that fan is well built, I'm not sure I would spend that amount of money to simply lower my attic temperature 6 degrees. That's why I ultimately went with a combination of thermal radiant barrier and turbine vents. The turbines move a larger volume of air and are cheaper, but they also have the advantage of removing moist air from the attic during winter months. The radiant barrier is probably, dollar for dollar, the most effective way to cool your attic space, but to get the most out of it, you have to install it along the rafters, and that's a much more time and labor intensive job than installing an attic fan.

I don't think there's any harm in giving the solar fan a try. If it does the job for you, great. If it turns out to be a little underpowered, or dies after a few years, you can always use the hole in your roof to install a new fan or a turbine vent. :)

Yes. But experimenting (with solar fans) is very expensive. A/O to standard fans. The same goes for A/C compressors that are mounted on the roof. Their life would be prolonged (and probably would perform better) if they were shielded from the extreme summer temperatures, which are well over 100o on a rooftop, even in the Northeast.:yes:!

Halen12 07-14-2010 01:19 PM

Pro Attic Fan
 
I installed a 25W solar attic fan before last summer that states it moves upto 1550 CFM in my 1700+ sq ft. attic. I like it. Whenever I stick my head into the attic, I can feel the slight breeze from the fan sucking the cooler air through the opening. I also put one of those remote thermometers in my attic to monitor the temps. I find that in the heat of the summer, my attic will get up to 20 - 25 degrees warmer than outside, however, once the sun sets enough to put the eastern facing side of my roof in the shade, then the attic fan cools even more until by 9:30 pm, the attic is about as cool as the outside air. I bet my attic would take over half the night to cool down without one, and it sounds like it could get 50 degrees warmer during the day. I've been meaning to disable my fan to see what the temp would be without it running. It is hard for me to figure out exactly how much $$$ I save during the Summer months, but I can say that before I installed the attic fan, I would have bills around $200 or more per Summer month, now they seem to hover around $150. Plus I got about 1/3 of the attic fan cost back via fedreal tax credit. A lot of websites say my roof/shingles should last longer because of a cooler attic. BTW, I installed an Attic Breeze attic fan and it has a lifetime warranty so I not worried about the motor failing, and I haven't read about others having that problem.

I don't know about thoses turbine vents since I don't have them, but from what I've read it's debateable if they work much. First, they require wind to spin the turbine. Second if that bulb (turbine) spinning around was such a good design for moving air from one side to another then all of our powered fans we use to blow air would utilize that method instead of the blades.


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