I use a 75,000 btu Modine Hot Dawg, I love it.

For my dad and my shop i think we are going to use hotwater coils in the floor.

I just snagged a used overhead infared heater. It's complete with 30' of tube, reflector, and the hangers, for $400.
So now I have another project slated for this summer, after the ins and drywall.

Boomer ,
Be very careful when installing the in-fared heater . Minimum distance from floor to ceiling is 10 -12 feet . If the style you have has an aluminum shield that looks like half an octagon this will project a six foot cube of heat to the floor, (the length of the heater) & also anything in its path. (car ?) In which can cause havoc to your vehicle .

I mainly install these in large garages or firehouses where there is substantial heat loss & quick recovery required . Along with the required clearances .

If you have the make & model I should be able to send you specs on that unit .

But I will attest to one thing they heat the slab very well .

Although nothing is better than radiant floor heat . Water temperature in a concrete slab only requires to be set @ 100 degrees by use of a mixing valve if connected to an existing hot water boiler .

Too many options , I could go on & on . Hope this was helpful . 55 mole

Mole,
My new shop has 12' cielings, otherwise I wouldn't have snagged it.
In my original garage I used an air tight wood stove. It would drive you out of there. But it isn't big enough for the new one
Boomer

I'm in Ohio also, I have a propane forced air that stays plenty warm and runs for about 10 to 15 seconds about 3 to 4 times an hour. My shop is about 6400 square feet and is insulated. It's a Modine 250,000 btu. I found it at an auction almost new for $500.

I have the equivalent of a 2.5 car garage that is uninsulated but does have insulated doors. I installed a Reznor 45,000 btuh natural gas space heater that brings the coldest temperatures up to 55 in about 15 minutes. The unit is hung overhead so it is out of the way and has a fan that moves plenty of air without a lot of noise. I control it by a thermostat and when I don't want it to run, I have a switch that shuts off the heater entirely. I also installed two shut-off valves so I can shut off the gas from inside the house or inside the garage. I'm not sure yet what the thing costs to run since this is my first year using it.