The online calculators are all over the place. I am planning to buy a propane heater for my garage. I want to heat it to 60-65F once or twice a week when I am working on a project. Climate: On a hill in Vermont. Winter days can be in the single digits and nights can reach the -20's. The side with the doors face south and will get the most direct sun. Structure: 28x40 stickbuilt (2006) with 2 10 foot insulated doors, one insulated man door, and 4 single hung metal frame average size windows. Fiberglass Batt insulation (R19 walls & R30 ceiling). It has 10ft ceilings. I'd like to pick up a Big Maxx Mr. Heater unit and they come in 50,000 btu or 80,000 btu. The online calculators range from 35k btu to 100k btu. Obviously this will end up determining which one I get. I want to avoid over or undersizing this.
Sounds almost like my pole barn I built in '07. 9' ceilings with r-30, and r-19 walls. I messed up and didn't put any kind of thermal barrier under the slab, and could kick myself for it. One 12' x 8' insulated garage door, and a service door....insulated. 6 so-so vinyl windows. I put in an 80,000 92 % furnace, and it runs too much. I don't have the ducting finished, so I think that has something to do with it. It struggles to get the place over 65 when it's real cold out. I really think it's the slab.
A simple rule of thumb for a decent insulated garage (sounds like you have) is L x W X 60. 67200 btu's will be close for your size. Something else to keep in mind that furnaces/heaters are usually rated input btu's so a listed 80,ooo will have around 60 some thousand output. Gaps, seams and air leaks (under big pull up doors and the sides of them) are usually your worst heat loss. I have installed my share of garage hanging heaters and for a little more money the Modine Hot Dawg unit heaters are the best IMO. USA made also. I would say if it is sealed up pretty good 80,000 sounds about right. Go for the t-stat with the fan option so you can blow the heat down continuously or put up a ceiling fan this really helps with a slab floor.
You are correct Sir. If you can continuously push air from the ceiling to the slab it will balance out alot better. thats why the ceiling hanging unit heaters do better in garages and shops with slabs.
Todd that is really helpful. I didn't know that the recommended btu's were based on the output rating. That alone puts me well over the 50k btu unit. I like the modine also but after a lot of research I decided that if it goes down I can afford a little downtime and customer support for the Big Maxx is pretty good- also they seem to have worked the bugs out by now so it is worth saving a couple hundred to me. If I was using it everyday and relying on it for income I would be getting the modine.
Thats great, its been 4-5 years since I have installed any so makes sense that they have the bugs worked out of the Maxx. $200 will really help cover the additional materials needed.
What do you do in the shop? In a big fan of radiant heaters any time you have a shop where you might be opening the big overheads regularly in the winter. I worked in a shop where we opened the bay doors to roll equipment in and out for years. With a convection type system that warms the air, every time that door opens the whole shop felt it for quite some time. We switched to the propane fired radiant tube heaters and the comfort level in the shop was a night and day difference. Less noise than the unit heaters too. Not that anything can be heard over the shop stereo but......
This is my garage for parking and general work on cars / tractors / ATV's in my non existent free time. I'm not sure I have the height for one of those overhead radiant heaters. They need clearance above, right?
Good question. There was some clearance over ours but they also had a big polished reflector hood over top of them. The ceilings in that shop were not high.
I worked in a shop that had radiant floor heat. The building is 80'x150', with two 14'x16' doors at each end. We could open all four and pull trucks out and in, close the doors and be comfortable in about a minute. In subzero temperatures, with a couple of subzero 50000 lb hunks steel and aluminum sitting in the middle of it. Do the tube heaters make sense if you don't heat it 24/7? Never had any experience with them for occasional use. I know they are nice to stand under when you come in from the cold
They warm the place much faster than radiant floor heat would and like you said, even if you are in only for a short time, they are nice to stand under.
Boss used to have a party every winter, complete with 'dancers'. Took 3-4 days to get the building over 70, and another 3-4 days to get back down to a comfortable working temp, around 58 or so. The man pizzed away a lot of cash, but that shop had the best of everything. He's lost it all now. Don't feel sorry for him at all.
There was an overhead radient at the old supermarket in my previous town. Checkers were next to the automatic doors that let in a lot of cold and wind. That thing rocked!!
Garage here has one of these old Modines on the back wall. Hot water oil fired. Does a good job. When it's cold outside I can go out and turn up the temp to 65, to work out there... takes about an hour to bring it up from 45... 3 hours from stone cold.
