Shop Heating

downsizingnow48 · May 2, 2014

I recently installed a ceiling and insulation in a previously unheated 36x24 shop. It was originally constructed with eave vents but no gable vents. After installing the ceiling/insulation I was getting ready to put in gable vents for air circulation in the now enclosed attic. This is on California's north coast which is fairly cool much of the year. So I was thinking, the attic is full of really hot air, heated by the sun on the roof, which I am now going to vent outside. At the same time I am thinking about either propane or electric heating for inside the shop, neither is cheap. It occurred to me that I might be able to solve both problems at the same time by pulling the hot attic air into the shop. Nothing ventured nothing gained. I put a $55 dollar window fan into the ceiling, with ducts extending up to the roof peak. I got some remote thermometers, put one up at the roof peak, another outside, another in the shop at chest height. The window fan has a thermometer too which shows temperature at ceiling level. I have been running this setup for a couple months now. Typical temperatures at noontime during this early spring period would be 55 degrees outside, 95 degrees in the attic, 75 degrees at ceiling level, 65 degrees at chest height in the shop. When it is really sunny it gets too hot in the shop. When it is overcast for a couple of days the differential between outside and inside drops to 5 degrees. I leave the fan on all the time. In the mornings when outside air temperature might be 48 degrees or so, the shop is still 60 degrees or a bit more. There is a lot of heated mass (roof sheathing, trusses etc) in addition to hot attic air itself. So it stays warm longer than I thought it would. I have a 220v 5kw resistance heater installed but havent used it yet, so far the attic fan arrangement is keeping the shop comfortable all day long. The fan draws about 1/2 amp which isnt very much, not sure what that would cost in electricity over the long term. I wonder what folks might think of this. I am not too sure what to make of it myself. I think I have a pretty cheap solution to shop heating and attic ventilation, which seems to work OK in this particular climate. It would never pass muster with a building inspector, but I can't think of any definite safety or building maintenance downside. Anyway I don't have much invested (55 bucks plus a hole in the ceiling) and can easily shift to a more conventional setup if need be.

CalG · May 2, 2014

Win! Win!

Passive solar with no plumbing! I would say you have it all good.

Here in the East, I would need to watch the humidity....

dave1949 · May 2, 2014

Sounds good to me. As long as it works, I'd stay with it and be happy.

I don't know if it is really a concern, but you may want to be prepared to deal with a warm/hot spell by installing a gable fan with shutters. Get the type with a thermostat and set it to come on around 120-130 degrees. You would never need to worry about overheating your attic that way.

downsizingnow48 · May 3, 2014

Thx for feedback! Appreciate it. Will set up a proper thermo controlled gable exhaust fan as backup good idea.

George2615 · May 4, 2014

I use a mobile home furnace for heating my shop in winter. Used ones are available that use home heating oil or propane. For summer I have two window A/C units mounted in the walls. I only have to use them on the hottest of days. My garage has insulated walls and ceiling. Your fan idea sounds good for recapturing heat or exhausting the heat outside of the attic.

Citydude · May 4, 2014

downsizingnow48 said:
I recently installed a ceiling and insulation in a previously unheated 36x24 shop. It was originally constructed with eave vents but no gable vents. After installing the ceiling/insulation I was getting ready to put in gable vents for air circulation in the now enclosed attic. This is on California's north coast which is fairly cool much of the year. So I was thinking, the attic is full of really hot air, heated by the sun on the roof, which I am now going to vent outside. At the same time I am thinking about either propane or electric heating for inside the shop, neither is cheap. It occurred to me that I might be able to solve both problems at the same time by pulling the hot attic air into the shop. Nothing ventured nothing gained. I put a $55 dollar window fan into the ceiling, with ducts extending up to the roof peak. I got some remote thermometers, put one up at the roof peak, another outside, another in the shop at chest height. The window fan has a thermometer too which shows temperature at ceiling level. I have been running this setup for a couple months now. Typical temperatures at noontime during this early spring period would be 55 degrees outside, 95 degrees in the attic, 75 degrees at ceiling level, 65 degrees at chest height in the shop. When it is really sunny it gets too hot in the shop. When it is overcast for a couple of days the differential between outside and inside drops to 5 degrees. I leave the fan on all the time. In the mornings when outside air temperature might be 48 degrees or so, the shop is still 60 degrees or a bit more. There is a lot of heated mass (roof sheathing, trusses etc) in addition to hot attic air itself. So it stays warm longer than I thought it would. I have a 220v 5kw resistance heater installed but havent used it yet, so far the attic fan arrangement is keeping the shop comfortable all day long. The fan draws about 1/2 amp which isnt very much, not sure what that would cost in electricity over the long term. I wonder what folks might think of this. I am not too sure what to make of it myself. I think I have a pretty cheap solution to shop heating and attic ventilation, which seems to work OK in this particular climate. It would never pass muster with a building inspector, but I can't think of any definite safety or building maintenance downside. Anyway I don't have much invested (55 bucks plus a hole in the ceiling) and can easily shift to a more conventional setup if need be.

Nice! That's a great idea.

teejk · May 4, 2014

Great idea! My dad beat you to the concept decades ago though! He being a good german in a bitter cold climate built a new supermarket and thought the heat generated by the refrigeration equipment (compressors and condensers concentrated in a small area) was a waste so he piped it into the store during the winter (big louvered panel to push it outside when not needed). That was back in the 1960's and his design failed because he lacked proper filtration and we spent a lot of time "dusting" cans of peas. My point is that you might want to check your filtration. A big temp/humidity difference might introduce whatever you insulated with into the shop.

downsizingnow48 · May 4, 2014

Thats a good point. Fiberglass dust is not good. I was figuring that having the intake right up at the peak would avoid sucking dust but maybe not. Will have to put a filter on the intake and then put sticky tape on the grill to see if there is fiberglass dust pumping in. Thanks for raising that.

tman1020 · May 4, 2014

Yes the filtration will definitely be a must plus I was wondering if you could set that fan up to reverse and suck hotair out of the shop and into your attic for when the temperature gets hot instead of cold if need arises.

downsizingnow48 · May 5, 2014

Yes the fan can blow either way. Actually it has 2 8" fans (quiet) and can also be set so one blows in and the other out. That might be useful for a tight structure.