Heater sizing for 40x76 pole building?

[ManCave]

Hi Guys,

I have a 40 x 76 pole building with 12 foot ceilings. I just had pole building metal installed on the ceiling and insulated with R44 cellulose and vapor barrier. The walls have +R19 foam. The building is very well insulated. There are three 16 foot wide garage doors which I'll be insulating with foam panels. One utility door. No windows.

My goal is to be able to keep the building at perhaps 40 degrees when not used. And then be able to turn on the heat and warm it to 70 degrees in about a half hour to an hour.

I have an outdoor wood boiler that I'll be using to heat it. It will pump 185F water to the heat exchanger(s). Originally I was thinking of putting in two water-to-air hanging heaters (the kind with a fan behind the HX radiator). I was thinking one on each end of the building.

The place where I buy from has 140K heaters in stock. They can get 220K heaters if they order them.

What I don't know is if I'll need two heaters or if one will be enough. The foam insulating company said it won't take anything to heat the building and one heater will be plenty. But I'd like to hear some other opinions.

I can go with two 140K heaters, two 220k heaters, one 220k heater or one 140k heater. Obviously I don't want to waste money and buy more than I need.

I'm in Minnesota so -10F to -20F temps are not uncommon.

What do you guys think?

 

[dave67fd]

Well i am just taking a stab at this one but because of the size and 12' ceilings and you want to heat it from 40f to 70f in an hour or less and cost isin't an issue i think the two 220k's would be more than plenty. If it were me though i would probably go with the two 140's which i think would still be adequate. Your looking at a 3000+ sq/ft area. A 75K pretty easily heats a well insulated 1000 sq/ft building so i would think the two 140's would be fine. I think your biggest factor would be the warm up time your looking at. Usually at 50 or slightly above is enough to start working. You usually aclimate quickly so if you could live with a longer warm up time i think the 140's would be the ticket. Some of the experts might chime in and give you a better guess.

You may also want to consider additional convection on the ceiling (ceiling fan/s) to help more evenly distribute the heat.

Also mount the heaters so they blow the warm air towards your largest area of heat loss. Probably/usually the garage doors.

 

[ManCave]

Hey Dave,

Thanks for sharing your thoughts! I'm going to put the louvers on the heaters so that the warm air is directed towards the floor. Your idea of ceiling fans is a good one. I had planned on installing those for summer use but hadn't really thought about that I could also use them in the winter to even out the temps in the building. Good idea!

One other thought I came up with is to look and see if there isn't some kind of remote controlled wireless thermostat available. So if I got up one morning and on a whim decided to work in the shop, I could get on my PC and turn up the heat in the pole building and let it warm up while I'm having breakfast. The pole building is about 300 feet from the house.

 

[Grape Ape]

Unless you have a 7260, I don't think your furnace will run two 220K btu heaters. I would go with one 220K btu unit.

 

[NUTTSGT]

I'd consider trying to keep the shop about 50 degrees rather 40. Once you get the concrete warm, it's easier to keep it warm and allow it to be the heat sink and retain heat for the entire bldg. If you're using wood, it's basically a matter of burning a little more wood, maybe an extra day cutting in the woods.

If you buy two heat exchangers, I'd aim them along the length of the building at each end. I'd also offset them and not center them. I think it would allow the warm to completely circulate and create a warm cycle not a bunch of turbulence.