SOLAR ATTIC FANS. I am thinking of installing some solar powered attic fans on my new roof. I’m looking at “Fan Attic”, Natural Light”, “SRS” and “Solatube” brands. Does anyone have any pros/cons as to these brands or any other brands that I failed to mention? Thanks and have a nice day.
Lance
Replies
Sure, I installed a couple of these... then I did the math and figured out what a dork I was for installing them.
A cheap solar attic fan costs $250. This is cost effective in only one scenario: You have to hire an electrician to run a new wire up to your attic. If this is not the case, and you are capable of extending an existing household circuit to a new position in your attic, then you are better off buying a thermostaticly controlled unit for $77 or less. Now, do the math to make sense for yourself... How long will this powered fan need to run to use $173 worth of electricity?
Rebuilding my home in Cypress, CA
Also a CRX fanatic!
If your hair looks funny, it's because God likes to scratch his nuts. You nut, you.
Without entering hte discussion over energy used vs. saved, they do have one very good use: wired with an on/off override switch they can keep the attic cold enough to prevent ice dams
CEB,
Solar-powered attic fans will not operate after a snowfall, since the PV panel will be covered with snow. They are therefore undependable as a possible remedy for ice dams.
By the way, PV-powered attic fans do not include a battery. When the sun is out, they operate. When the sun goes away, they stop operating.
AC-powered attic fans often pull conditioned indoor air through ceiling air leaks into the attic, raising energy prices for the homeowner. One study documented problems from backdrafting appliances (water heaters) that was traced to powered attic ventilators. The ceilings in the affected houses were so leaky that the powered attic ventilators depressurized the entire house.
Lance Jenson,
You and Paul CP are both wrong. Neither a PV-powered attic fan, nor a hard-wired AC-powered attic fan, makes any sense. What attic problem are you trying to solve?
Depressurizing an attic with an attic fan is more likely to cause problems than solve them. If you have a list of problems, solve the problems directly. What's your problem? Attic ductwork? (Move the ducts into the conditioned space, or else seal the duct seams and insulate the ductwork heavily.) Inadequate ceiling insulation? (Beef up your ceiling insulation.) Ceiling air leaks? (Seal the ceiling air leaks.)
AC-powered attic fans use more electricity than they save in lowered air conditioning bills -- this has been shown by several studies.
Edited 3/12/2008 8:24 am ET by MartinHolladay
You make the assumption that I have air conditioning!Rebuilding my home in Cypress, CA
Also a CRX fanatic!
If your hair looks funny, it's because God likes to scratch his nuts. You nut, you.
Paul CP,
On the contrary, I made no such assumption. I asked Lance (and, perhaps by implication, you as well), "What attic problem are you trying to solve?" Moreover, I provided a list of faulty reasons often offered to explain the decision to install a powered attic ventilator, and suggested better solutions to all of the problems.
So, as long as you are interested in continuing the dialogue, please tell me: "What attic problem are YOU trying to solve?"
Edited 3/12/2008 12:07 pm ET by MartinHolladay
I have a leaky attic full of hot air that needs to be completly redone, as it needs a real passive ventalation system AND insulation. But until then, I need a stopgap to move the 110 degree cloud out. For me, it's a band aid, not a solution.Rebuilding my home in Cypress, CA
Also a CRX fanatic!
If your hair looks funny, it's because God likes to scratch his nuts. You nut, you.
To make a long story short, Mike Smith and Shelternerd convinced me to simply blow cells on top of whatever junk is up there now. So I had it done up to R 60. I'm in Denver with 10 to 15% humidity and 140 to 150 temps upstairs. Adding a few passive roof mushrooms would help, but the cells keeps the heat outta the house.
It was only $ 1 per sq. ft. all done for me.
"You and Paul CP are both wrong. Neither a PV-powered attic fan, nor a hard-wired AC-powered attic fan, makes any sense. What attic problem are you trying to solve?" If their problem is anything like mine then it would be a Summer Hot weather condition in which the outside air and attic air temps are off by 20-30ºF.
Last Summer I measured the outside air at XºF and the temp range based on elevation went from X+5, to X+15, to X+30 at attic floor, 4' and 14' at the vents. I cannot imagine how a flat roof would have made it worse than the pitched roof I do have.
Isn't it the idea to maintain same temps inside the attic as the outside air?
Nuke,
Assuming your attic is properly built -- with no ductwork or HVAC equipment located in the attic, with good air sealing of the ceiling plane, and with deep insulation on the attic floor -- attic temperatures are basically irrelevant. If there are design problems in the attic -- poor air sealing, insufficient insulation, or attic ductwork -- it is best to address these issues directly rather than to paste on a band-aid like powered attic ventilation.
The most difficult of these issues to address is attic ductwork. Relocating attic ductwork is difficult. If the ductwork is there, the best remedy may be careful sealing of the duct seams with mastic, followed by burying the ductwork in deep insulation (assuming, of course, that the issue of condensation on cold ductwork during the summer has been addressed; closed-cell spray foam addresses the question best).
Powered attic ventilation often increases energy costs by pulling conditioned interior air into the attic through ceiling cracks, increasing the need for air conditioning during the summer or heating during the winter. Cases have been documented where powered attic ventilators depressurized a house so much that dangerous backdrafting of atmospherically vented water heaters occured.
Whether or not there is attic-installed HVAC ductwork seems to be moot in terms of attic temps. This is a cookie cutter home with the entire 2nd floor zone in the attic, ductwork included. This should be much in the way of contributing factors for excessive summertime heat in the attic unless you are suggesting that heat on the 2nd floor is leaking into the attic and adding to that load.
Nuke,
I've read your most recent post a few times, but I'm not quite sure what you are driving at.
"This is a cookie cutter home with the entire 2nd floor zone in the attic, ductwork included." If I understand correctly -- if your house includes an air handler as well as ductwork in the attic -- the best solution to your problem would be to bring the entire attic within the conditioned envelope of your house by installing insulation between the rafters and sealing all ventilation openings.
"This should be much in the way of contributing factors for excessive summertime heat in the attic unless you are suggesting that heat on the 2nd floor is leaking into the attic and adding to that load." I'm confused by this sentence. I did not suggest any mechanism to explain why your attic is hot. Most attics are hot in the summer -- that's normal. Instead, I merely suggested that if your attic is hot, the fact is irrelevant, IF your attic is properly designed. However, it sounds like your attic has HVAC equipment and ductwork in it. You have my sympathy.
Martin & Nuke...
I've been looking into insulating my attic. If you have a furnace or other gas-burning appliance in your attic (like a water heater), you defintely can't seal all the ventilation openings.
Martin--why do you term an attic "improperly designed" if it has ductwork and/or HVAC equipment in it? If that's the case, just about everyone I know has an improperly designed attic.
JD Lee,
I agree that if you have a water heater in your attic, and if you are contemplating a conversion to a sealed conditioned attic, then you would need to be sure you were providing combustion air to your water heater -- for example, by switching to sealed-combustion water heater. Unfortunately, that's expensive.
"Just about everyone I know has an improperly designed attic." The problem you describe is regional. In some parts of the country, builders have traditionally used slab foundations; they tend to put ductwork in the attic. In other areas of the country, where basements are traditional, builders almost never put ductwork in the attic.
But the times are changing. Progressive builders, even in regions of the country like Florida where attic ductwork is common, are beginning to understand the principles of building science, and are learning how to bring ductwork inside the conditioned envelope of the house.
Martin...
I guess the climate here in San Diego is different enough that things just aren't going that way. I can't think of a single home built in the past 30 or so years that I've seen that doesn't have the ductwork in the attic. Even in new homes over $1 million, that's where you'll find it.
From what Nuke said, I took it that his furnace might also be in the attic, which is another reason he might not be able to seal it.
JD Lee,
San Diego has the mildest climate of any location in the continental US. If you feel like it, you can easily live without any heating or air conditioning at all. That provides less of an incentive for builders or homeowners to care about energy efficiency.
You do not mention your location (could fill in your Profile <hint,hint>)
Down here around 29ºN, I've heard my neighbor's solar attic fans whining on and off a bit (the bearings have been shot for more than a year, you can hear them over the crickets).
Mind you, I can think of no reason in my climate to haul humid (60+%) air into an attic as is; even less when only through 3-4 12x18 gable vents. Temperature reduction in this latitude is about the same as cracking open the windows on your car, about 4-5º maximum. May to October, that means only hitting 130 instead of 135 in the attic.
Solar is better than wired to the house's AC, in my thinking. And, if flashed and installed correctly a low leak risk, working or not (remember, around here, 15-18 months is about when the motors die from overuse). The thing to use to select which solar brand is to find out what NiCad battery is being charged by the solar collector. If it's an odd asian brand (or worse yet, shape) battery, that can be a real pain (I've a half dozen solar lights that don't use a "stock"--US format--AA battery <grrr>).
But, I'm biased.
Great information. Thanks a lot. I failed to mention that I live in sunny Southern California and my house pretty much gets hit by the sun all day long when it is exposed. I thought of a thermastaticly controlled fan but felt that even at night it would run constantly. Have a great day.
Lance
thought of a thermastaticly controlled fan but felt that even at night it would run constantly
Well, I've not opened all the boxes, but I'll wager the solar fans run on a thermostat, they are just powered from rechargable batteries charged by a solar collector. As opposed to only running when the sun is out. That being the way most powered attic fans work.
Only argument for AC-powered fans in my book is that you could have an over-ride (master) switch to cut them off (or on) on demand.
But, I'm biased, too. I find powered attic ventilation in about the same place as a powered vent for your car. We have a special term in cooking for a heated box with a fan in it after all . . . Occupational hazard of my occupation not being around (sorry Bubba)