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52Caddy 03-16-2011 09:49 PM

Any thoughts on using attic heat?
I keep thinking how warm my attic is during the winter months, or how warm it could be with some work. Now, I understand why we need to ventilate the attic to prevent ice dams, but what about when there is no snow built up on the roof?
I'm thinking if I was to put some sort of fan in the attic space and draw the air into the basement it would provide a substantial source of heat during the winter months. I would think allowing the make up air into the attic at a lower point in the space would negate any humidity issues.
I'm imagining it would take a few dampers and some automation sequencing to stop the fan and ventilate the attic back to a cooler ambient temperature when it was required to prevent ice damming. But luckily I work in the HVAC industry and have a few actuators, relays and control modules at my disposal. I also have a nice dark roof with a southern exposure.
So, what do you guys think? Any issues you could think of that could potentially cause problems?
Thanks guys

DexterII 03-17-2011 10:30 AM

Interesting concept, except for the fact that, ideally, in my opinion, the attic should not be warm. Without some manner of heat, and perhaps discounting the winds of an Alberta Clipper, in which case a wind break is a nice thing to have, the inside of your home would essentially be the same temperature as the outdoors. Correct? So, if we could magically heat just the living space, our attics would still be cold. Correct? But, since there is no such magic, meaning that we cannot simply tell heat to stay in one area of the home, we compensate by attempting to contain the heat, i.e. insulatation. Attics get warm in the winter because of heat loss from the living space. The objective is to insulate a home, in order to lose as little heat as possible; not to lose heat so that you can reclaim it.

Jackofall1 03-17-2011 10:44 AM

52Caddy, a good concept and one that I think has merit, if you were to work at it hard enough, it just may work at least on those sunny days.

I would be concerned with recirculation part of your idea, as the air leaving the conditioned space as far to much humidity (or should have) and undoubtedly would cause issues in an unconditioned space.

Unless of course you insulation the attic, except for an area say 6" wide the width of the southern expose roof.

But isn't this what solar energy is already?

I once saw a show where the owner of a house took his southern exposed wall, added a second glass wall creating a space inbetween, painted the inner wall black and then circulated air through the space into the basement. In the basement he had placed many 50 gal drums of rocks, this held the heat generated, then at night the heat captured by the rocks was then released and circulated throughout the house.

I guess you could do something similar with your roof concept, not sure if the efficiency would warrant the effort though.


52Caddy 03-17-2011 10:56 AM

Dexter and Mark, thanks for the replies.
I understand what you're saying, but I think there is the prospect of having a large heat load in my attic if I was to control the amount of ventilation coming into the space. I'm assuming this is only possible on a sunny day with fairly moderate outdoor air temperatures. Remember my roof has a direct southern exposure with fairly dark shingles.
After having my place re-roofed and a horrible installation job of the ridge vent, my attic temperatures during the summer months were running over 130F. So I know there is heat in the attic generated by the sun.

Mark, I haven't thought too much about what to do with the exhaust air, other than running it out of the house from the first or second floor to create some sort of flow through the living spaces, but not back into the attic. I agree humidity could become an issue if it was just recycled back to the attic.
Maybe some sort of air to air heat exchanger that could pull the make up air from the attic when it would be adding heat to the house, and damper it over to outside air to provide cool air on during the summer months when the OAT drops at night?

JohnHPerkin 03-29-2011 05:09 PM

Using attic heat to heat home
Like you I have wondered if attic heat could be used to heat my home.
I am in the process of finishing a large bonus room in my ohio home. before beginning the project I considered how the roof heat could be used and designed and integrated an automatic system to bring the heat from the space just between the roof and the insulation layer into the room. I am now testing the system using multiple data logging temperature and humidity detectors and am very pleased with the results.
Now the system is running I checked to see if anyone else had come up with the same idea and found your posting.
Please contact me if you wish to know more.

user1007 04-11-2011 08:58 PM

Use to drive around hoods with houses next to some I restored with insulated attics. Not an inch of snow on their rooftops. Mine had a reasonable amount.

Obviously we didn't get so much or ice that it threatened the roof but it sure was a graphic illustration of how much heat escapes through the roof of most houses in the winter. Why not contain it.

dberladyn 04-24-2011 11:35 AM


Interesting idea... I had similar thoughts in the past. We too have a warm attic in the winter, but if your attic is anything like ours you wouldn't want to ventilate that air downstairs. Moisture aside, don't you have years of dust, fiberglass (from insulation) among other things floating around in the air up there? I would think you'd need some form of heatexhchanger.. so that you are transferring the heat, but not the actual air.

I'll try to remember to follow this thread to see if you come up with something.


HomeInsulation 05-27-2011 08:53 AM

Solar Air Furnace
Hey 52Caddy,

Save the HVAC fans, relays and controls for a solar air furnace. Which is exactly what your describing. The main difference is the air inside the solar furnace is clean and not contaminated with mold spores and mice poop.

Jackofall1's description of solar air furnace with glass plates trapping hot air and directing the air into a mass to collect the heat is spot on. In my opinion the hardest part of building one is controlling the air with the fans, relays and controls that you already have laying around.

The rest of the solar air furnace is nothing more than an insulated, air-tight box with a black background and piece of glass on the front. You can buy them for a few thousand dollars with the controls and fans etc. But I would go that direction. It's safer and the air is much less dangerous.

Perry525 06-24-2011 01:09 PM

The solution is a simple expanding 4 inch aluminium pipe that passes through the roof collects the heat, heat always moves to cold, and pipes it to where ever.
Provided the air leaves a clean room and returns warm to the same room there is no chance of pollution.
A low wattage fan should do the trick.
By the way, the moisture in the roof comes from inside the home, though any openings, or through the ceiling.

jklingel 01-28-2012 10:49 PM

Man, if I had a properly insulated lid and STILL had a hot attic in the winter, I'd sure consider installing solar panels and run the heated "water" into the house. That is proven, simple, and it's all worked out for you. No need to reinvent the wheel here. Plus, you'll be using the sun 365 days for domestic hot water, heating the swimming pool you are going to install so my kids have a place to swim, etc.

joecaption 01-28-2012 11:20 PM

A few flaws in your plan coming from a laymen.
Where is the make up air going to come from?
Once there's been one air exchange where is the make up warm air going to come from?
Once it's gone it's going to also start sucking in cold air through the soffits and ridge vent.
Would that not create a negative pressure in the attic and suck warmed air out of the rooms below?
As pointed out an attic needs to be the same or close to the same temp. as the outside air, if not there will be condinsation and shorter life for the shingles.
If the attic is hot in the winter it's from heat lost through the insulation or air leaks (or really the lack of the proper amount of insulation).
Ride through any area after a snow storm. the ones with the proper insulation still have snow on them. The poorly insulated ones will have steam coming off of the roof from heat lost through the ceilings.

jklingel 01-28-2012 11:33 PM


Originally Posted by joecaption (Post 837635)
Would that not create a negative pressure in the attic and suck warmed air out of the rooms below?

That was just brought up on another forum. Answer: Not if the conditioned space is well air sealed. Agreed; if the place is insulated and air sealed properly, the attic won't be hot, unless this cat has a whole lot of sun, which he/she may.

Exeric 08-10-2012 10:27 PM

I think this idea needs some work. Generally it doesn't seem like a good idea to me to try to reclaim heat lost from the living space in this way. It would be much better just to make sure the ceiling is thoroughly sealed and heavily insulated so no lost heat gets in the attic in the first place.

Here's an idea that "would" make sense though. Many people put up aluminized radiant heat reflectors against the bottom of the rafters to reflect heat up and away from the attic space. This is used to keep the attic cool in summer and should be in addition to a well insulated attic. The best installation is when this heated air between the bottom of the of the rafters and the roof is allowed to flow upward continuously to roof vents at the peak of the roof. Allowing this air to flow up keeps the roof from trapping the air and heating the roof itself. But this installation would have another benefit: it should be possible to terminate this flow of air near the roof vents with a diverter. One could then run this bidirectional diverter to both the vents or to a fan that directs it down and into the living space.

The beauty of this system is that you could have a very dark colored roof and still be very energy efficient. The attic would stay cool in summer and would also contribute a fair amount of heat in winter. One trick you have to plan for ahead of time is to make sure air is not trapped where rafters meet at the valleys and hips and so forth. It would be best to extend the valley and hip rafters down an inch or so at those places. Then attach the radiant insulation to the extension so hot air has a way to leak below the hip and valley rafters where the other rafters attach to them. That way air doesn't get trapped.

Perry525 08-11-2012 08:24 AM

Yesterday my roof reached 124F/50.8C and was hot for 13 hours.
Where I am sitting now, reached 87F/30.5C for a couple of hours, before gradually dropping down to 74F/22.4C this morning.
A 36F/20C degree difference due to filling the spaces between the joists with 4 inch thick sheets of polystyrene and having a layer of 3 inch thick polyurethane foam sheets fixed below the joists.
This to reduce the heat passed into our home by radiation, conduction and convection.
I have a dark uninsulated south facing slate roof, that gets very hot, whenever the sun shines. This suites me as I am happy to
keep my heating bills as low as possible, and free heat from the sun helps. The roof is not ventilated, except with natural gaps between the slates.
I have a simple system, a 4 inch diameter aluminium pipe runs for some 30 feet through the roof, it picks up heat by radiation, convection and conduction from the roof and using a small fan moves the hot air down into my lounge. As an enclosed system it picks up no dust or smells.
It is controlled by two temperature sensors one in the roof switches on when the inside roof temperature moves above 74F/23C, the other in the lounge switches on when the temperature in the lounge drops below 74F/23C. With both on, the fan runs.

We have no problem with ice dams as all the heat stays inside the comfort zone.

SPS-1 08-11-2012 08:44 AM

Perry, your signature says you are in Florida.
I wouldn't think a house needs much heating, in Florida, in August.
I am in Canada, and I have had my furnace switched off since May.

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