Heating a detached garage in Maine

[Spudland_Dave]

Thanks Mike. The garage is across the street so running off one take likely won't happen. Any reason why I would want to do this?

I was under the impression 60k would be too much and oversizing a propane heating unit makes it less efficient. Any thoughts?

I had a unit "professionally spec-ed" for my shop 30x50x10, came out to 60k BTU unit.
After chatting with my HVAC guy, he agreed with my thoughts of going with a 75k.

From what I've read, its not so much a larger unit is less efficient, from what I gather, going with a unit which is too large causes the unit to not run long enough which in turn allows for condensation to accumulate in the combustion chamber and cause it to rust out. When a unit is sized correctly, it will run enough to get to "operating temp" and minimize any condensation effects in the chamber. In my case...the application is I will keep it off or just barely heated to prevent freezing, then if I need/want to work jack up the heat from 40 to 70. So for me, he said 2 fold...75k is still within the realm of correctly sized and given my intended use of kicking the heat from 40 to 70 every time I need it in the winter, I should be all set.

 

[Ralbert]

So True!

 

[Ralbert]

Hi All - wanted to bring this thread back to life... Had to laugh when I was building this garage back in 2014/2015 and just installed a heat source this last year! I ended up putting in a Fujitsu mini-split heat pump that can heat in temps down to -15 or so... The garage is insulated so well and so tight that I was warned by many of condensation with propane; especially because I wash vehicles in the garage. I’ve had it installed for several months now and it really was a great decision; electric bills have been higher by about 70/mo, but that’s because I keep messing with the thermostat and crank it up higher than 50 often. I’m washing the car today; it’s -20 with wind chill and a balmy 60 degrees in the garage. The other part is air conditioning...

Prior to installing this thing, I was getting moisture where the floor and wall framing meet up (the floor is coated with the polyaspartic coating, so very well sealed)... With the July/August humidity the moisture didn’t have anywhere to go, but with the A/C on or “dry” mode - no moisture. Overall, no complaints - - now researching hot water options for the 1st level and 2nd level; I’m thinking another heat pump for the top level (to also get A/C) and an on-demand hot water heater since the use is so infrequent. I love this forum and loving my garage even more!

 

[airmaxximus]

Hi Ralbert, glad to see you’re happy with the mini-split. What model did you go with? I’m in a similar situation trying to decide on the “best” method of heating for my garage space and worry about sizing the unit correctly.