Heater sizing check

[gj67stang]

I've read countless articles/posts about heater sizing and ran the numbers several times through the online calculators, but I'd like one more confirmation on proper sizing before I make my final decision.

I am wrapping up the construction of a 40x60x13 pole building in north-central Ohio that will serve as my workshop. The exterior walls have housewrap, R19 fiberglass batts, vapor barrier and OSB while the ceiling is steel with R45 cellulose.

There will be a 600 sq ft (20x30) "tool room" in one corner which will house the majority of my tools, machines and equipment. The plan is to keep this at ~50 deg during the heating season and only bump it up during prolonged work sessions. For this task, a 50k BTU hanging propane heater should be sufficient (maybe the Mr. Heater Big Maxx?).

The remaining 1800 sq ft (L-shaped) will be used for truck, tractor, mower, material, etc. storage. I was thinking to heat this to ~40-45 deg with a 75-80k BTU hanging heater and bump up the thermostat during large projects out there and in the springtime to combat humidty/sweating.

Thoughts? Suggestions? Opinions? Ideas? Thanks!

 

[Charles (in GA)]

It sounds as if you have a tight building with lots of insulation. Given that, my gut feeling is that you will be OK with a total of 130-140K BTU, but I'm no HVAC man.

Charles

 

[jvitez]

10 watts per sq ft is a rule of thumb we use for heating here in the Great White North, and Ohio is milder than here, (-31°C right now). That's 34.13 btu/sq ft net, divided by an average 80% efficiency for fuel burning unit heaters= 42.7 btu/sq ft, so this calculates to 25,600 btu gross input for your tool room and 76,800 btu for the rest of the shop.

Don't forget you'll need less heat in your tool room because 2 of the 4 sides are abutting heated space, so heat loss isn't really lost because it's heating space you want to heat anyway, and the L-shaped space will heat the 2 inner walls of your tool room. The only time this would not hold is if you wanted vastly different design temps for each space.

Another point: L-shaped spaces are hard to heat with one forced air heater, as air circulation will not be equal to each arm of the L. One thought is to use two heaters installed like a warehouse, each facing 90° from each other installed on the lower corner of your tool room wall, so one will blow towards the 40x30 ft lower part, and the second heater will blow "upwards" toward the 20x30 ft part. You'll also need different sized heaters for this, eg. 50K for the lower part and 30K for the upper.

Another option is to use a ducted unit heater/furnace for the L-shaped part. Put the furnace wherever you want and run ducts for even heat. You can still use a small unit heater for your tool room.

Sorry if I only gave you more options and confusion instead of helping…..

(disclaimer: I'm not an HVAC pro either, and before any pros chime in I'll give the boilerplate statement of "Get a professional heat loss calculation for each space.")