Heating BTU Requirements?

[Gunnert]

Trying to figure out how big a propane unit I need. Detached garage interior is 33 x 28. Walls are 10' (8' insulated with fiberglass under tongue/groove 3/4 plywood and 2' is concrete block). I have a two-post lift with the ceiling height peaking at 19'. The ceiling was insulated this week with 6-8" spray foam.

My calculations tell me I need 45k BTU to heat the garage. But, I'm wondering with the benefits of the foam insulation if I only need 30k-35k. I'm doing my heater shopping on Craigslist and would hate to pass up a 35k heater if it would do the job.

What do I really need to heat the garage? Thanks!

 

[regguy1]

I have a 45K BTU in my 26' x 30' / R13 in walls and ceiling.
It heats the place just fine.

see it here: http://www.garagejournal.com/forum/showthread.php?t=140674

 

[Kev442]

Depends on whether you are going to maintain steady temperatures or want a 20-30 degree temp rise in one hour when you hit the go button from stone cold. You also have no location listed. There is a big difference in heating BTU needs between SD and AR.

 

[rodm1]

This calculator worked well for me.

http://www.ultimategarageheater.com/garage-heater-calculator.php

 

[StingRay]

It really depends on how cold it gets and your average r values in the walls and ceiling. The recovery rate desired and the number of air changes per hour can also be considerations. I have a 28 x 44 with R 52 in the attic and 3 in of foam in the walls. I have two 9x8 r6 doors, one 8x16 r14 door and 6 double glazed windows. It's a stick frame building with a 10 ft ceiling. A 60k unit heater is just enough to heat the whole shop even in harsh Saskatchewan winters. When it gets really cold below -30 I try to close off half the shop to save on heat and the cold side still stays quite warm anyway.