Hi,
I getting ready to install an gable attic fan and I was just wondering if anyone has any pros/cons in terms of going with a solor powered unit or a electric powered one.
Thanks in advance.
I'm considering a solar attic fan as well. Not needing to pull the wires is of value to me. I'm curious what the experts have to say about the daytime-only running of the fan, as most attics stay hot well after sunset during the summer.
The primary purpose of an attic fan is to prolong the life of the roof. Heating deteriorates roofing shingles and the greater degree of heat, the greater degree of deterioration. In other words, if an attic fan reduces the average temperature of a roof by 20%, the roof shingles should lasts 20% longer than an average roof without an attic fan. This usually pertains well to certain types of constructed houses, like Cape Cods or finished attics.
The secondary aspect of attic fans is that it will lower your cooling costs and/or make the house more comfortable in the summer. Both aspects are accomplished by what is known as convective heat transfer. This states that air that has a lower temperature than objects it comes in contact with, the lower temperature air will extract heat from the objects it comes in contact with, thereby lowering the temperature of the objects. With heating your home the exact opposite occurs. The objects inside the home extract heat from the heated air produced from the heating system.
mrchris made a very good observation by stating that most attic stay hot well after sunset. The reason for this is the insulation in the attic. Insulation prohibits conductive heat transfer. As part of this process, the insulation retains a good deal of heat. Which results in most attic staying hot well after sunset during the summer.
Both types of attic fans will induce the convective heat transfer which will extract the heat inside the insulation during the summer. The disadvantage to the solar attic fan is that it will run during the winter, unless you cover the solar panel or disconnect it. In the summer you do not want the insulation to retain that much heat because the hotter an object gets, the more heat that object will radiate. Which is the dominant heat transfer mechanism in the summer. The dominant heat transfer mechanism in the winter is conduction, which means you want the insulation to retain as much heat as possible.
The implication here is, if the heating contractor sized your heating system properly which is influenced by how much insulation you have in your attic. And the solar attic fan induces a convective heat transfer in the attic, which will extract heat from the insulation. Thereby reducing the effectiveness of the insulation. On very cold days, your heating system may not be able to heat your home.
By the way, the same applies to wind turbine attic fans.
Thanks for the advice Resercon.
Thanks Resercon. I'll make sure any solar fans I consider can be turned off in the wintertime.
My opinion:
I think solar anything for the consumer is not worth a hoot!
run the wiring, add a thermostat and an elec fan.
fred
Forget the solar fans not worth a D**
Solar pool heater's very very good.
Been there did both.
ED
Well, it was my wallet that settled the issue for me. $40 for an electric fan or $400 for a solar is a no-brainer for me.
I know you bought your electric fan but I just wanted to chime in with my understanding of this for future readers.
If you buy a quality solar with a decent cfm, then they work fine. They are much more expensive initially but it is a one time cost. You do not have the annual electrical expense, I have been told to expect to pay 70-100 a year in electrical depending on your climate for an average attic fan. In four years your solar fan would be paid off in savings, assuming the figures are accurate, which is my experience with most high efficiency products. They are an investment that often take ~5 years to see a return.
If you go electric, you should have a quality electrical fan installed with a high temperature shutoff so that it doesn't run when your house is on fire.
Regarding the attic fan running in winter. If your attic is properly ventilated, then the fan is not pulling heat from the insulation but is pulling it from the attic air itself, not considered part of the interior house climate. A fan alone in any attic without a ventilation system (soffit vents or low roof vents) will pull climate from the house interior, sucking air conditioned air in the summer and heat in the winter through ceiling gaps.
In Oregon, for example, if you have an attic fan based ventilation system, it needs to run in the winter because we need to pull the humidity out of a house. Humidity traps heat and traps cold, thereby causing most of the temperature problems attics have to begin with. Having soffit vents below that provide a fresh intake of air (not in contact with the insulation because of baffles and vent placement) provides the best scenario that doesn't pull air from the interior of the house yet provides a continuous stream of ventilation.
If I am misunderstanding something here, please feel free to clarify.
6 years down in the caribbean .Know many that got solar power fans, Me to, all brands In boats and home. Talk about sun we had sun. None of them would put out are work as a fan should.
my .02 cents
ED
I think that winter is one of the more crucial times to have proper attic ventilation. Think about all the moisture vapor that travels up through the cracks and holes in the vapor barrier and condenses in the cold attic without a good system to exhaust it to the outside. You need ventilation year 'round for different reasons, but what it comes down to is having a properly balanced system. If you have a small attic with little net-free area and you put in a monster CFM fan, of course it will pull air out the insulation and even your house. But if you have sufficient intake (preferably soffit) ventilation to match the fan's output, then you have a system that will function well any time or season.
The only drawbacks to a solar fan is that it won't handle much more 1000 sqft of attic area and will only work when the sun is out. But the advantages are quiet DC motor operation, no operating cost and ease of installation.
Bottom line is, it's the owner's decision that largely depends on a particular situation and need. I have a solar fan on my small attached garage roof, where I used to get water in the ceiling from moisture condensing on the cold air duct. Obviously, when AC was on on a hot sunny day. Ever since the fan installation - problem gone.
Your better electric fans will come with not just a thermostat, but a humidistat. Think about it, it's really meant to control both heat and moisture build-up.
Just had to jump in to this thread.
I am the maker of the leading solar-powered attic fan. I'm not trying to promote it here, but I can offer a website upon request.
A few thoughts:
As for winter operation in a warm climate, Ishmael hit the nail on the head with this comment:
Having soffit vents below that provide a fresh intake of air (not in contact with the insulation because of baffles and vent placement) provides the best scenario that doesn't pull air from the interior of the house yet provides a continuous stream of ventilation.
In other words, let the fan run year round. Solar attic fans will regulate themselves in the winter because the sun is not as intense. Simply put, the same intensity that causes sunburns is the same energy that makes a solar panel operate at full power. The gentle winter operation is just enough to keep air moving through the attic to keep it fresh.
The benefits of keeping fresh air circulating year-round are many. An attic with good ventilation will save on cooling costs, extend the life of shingles, keep the insulation from losing it's effectiveness, protect roof sheathing, make the hvac equipment last longer, and keep the attic from having a stale smell.
Another benefit is cost. A $40 electric fan will require an electrician to properly install it. Most electricians we have interviewed across the country want from $150 - $250 just to hook them up properly. Now the $40 electric fan is more like a $300 fan, and it can cost up to $20 a month to run it. Because the solar fan is it's own mini electric generation station, the power is free. Once the initial investment of say $400 has been paid, the unit operates at no cost to the homeowner. Plus, they are very easy to install by any roofer or handyman.
Thanks for letting me put my two-cents in.
I had read that having an attic fan operate during the winter months, it could help prevent ice jams forming on the roof. Any truth to that? I live in Chicago and have a problem with ice jams.
That theory comes about because in a properly vented attic the snow won't melt and later refreeze causing the ice dam. Properly insulating the living space from the attic along with proper attic ventilation will be a better idea.
You need the incoming attic ventilating air coming in at the base of the roof (soffit) and exiting at the ridge or as close to the ridge as practicable. The idea is to keep the underside of the roof at the same temperature as the great outdoors.
Thanks. I will look into putting vents in the soffit.
Tags: solar, electric, gable, attic, heat transfer, attic fans, contact with, extract heat, heat from, after sunset, convective heat, convective heat transfer, during summer, extract heat from
