My new construction is bitter cold as i'm trying to work in it to get it finished. Got a forced air kerosene last night from a buddy, 80k btu, barely takes the chill off... can't wait til the soffit is up and the spray foam insulation is done...Salamander......all I got for you.
My shop was the same construction. Built in 1958 and bare bones. We ran all the power, gas lines, insulated and drywalled it. We had to.
Used to have the old fuel oil furnace we pulled out of the house when we went gas. Man that thing would heat up fast.
Now we have a unit heater and keep the shop 50* except when we are in there....60* work temp. Maybe warmer.
FWIW, the old single car was terrible even though it was partially insulated, the roof was not. I put up that foil covered bubble wrap on the ceiling with a staple gun and it made a world of difference. Did some of the walls too. It was almost a complete faraday cage... lol.
Heated it for working with a single propane topper like this: MH15T Single Tank Top Heater | Mr. Heater
This is the kind insulation stuff. : https://www.westsidewholesale.com/r...MIptLB24Wr2AIVj4uzCh02Ewb9EAYYBiABEgIp0_D_BwE
Full disclosure, i got it for free because it was left over from a job he did. I could get that single car garage to 80 if i wanted with that little heater.