Propane heat for garage... (long)

I have an attached 2 floor 2 car garage that was built about 100 years ago, here in New Hampshire... It's balloon framed, and the second floor joists sit on a 1 x 4 set into the Studs, which run from the ground to the gabled roof. (It's pretty cool.)

I need to heat the first floor. I have a full size propane grill in there, which I can simply turn on to supply some heat...

2) Is there something I can do to help old the heat in? Perhaps plastic on the floor above to hold the air in? The entire barn is uninsulated.

Thanks for your thoughts

A new and novel way is called INSULATION, I and DOW and Owens Corning and EPA, and every gov site recommend R 36 minimum to R 78+ in your area, Zone 5, I have R 100 +.

Wake up insulate

Very dubious. CO2 does not support life.

A 1 x 4"? Does not sound sturdy.

First, do NOT use the grill. It is not designed to be used in a closed space and it can give off carbon monoxide. There are unvented heaters that can be run indoors. Reddy Heater is available from 30,000 to 80,000 Btu.

Do you want to heat the garage all the time or only when you are working in there? The answer to that will determine how much insulation you need. I have a detached garage and I've insulated a portion of it. The 30,000 Btu heater will not get it to 40 degrees when it is 0 outside. I get a 25 to 30 degree temperature rise. If you insulate, vapor barrier and sheetrock the walls, do the same on the ceiling with even more insulation, you have a chance of getting the smaller heater to do the job.

If you are going to spend short periods of time there, an infrared heater aimed at your work area may be best. It will keep you warm instantly.