Help with heater choice!

In regard to the "ventless" claim - yeah they are - but like anything burning oxygen, they need oxygen - just as we humans do to breathe. The heaters have a low-ox automatic shutdown. I assume you don't run a snorkel out your wall to breathe, so air must find it's way into your house already. Subsequently, the heaters are sized BTU output to room size. I've got a pretty tight house and never had one crap out yet from oxygen. That includes a small one we have in a small bathroom. It's 6000 BTU. We heat all here with wood - but - in below zero days my wife uses the heater in the bathroom to warm it up a bit when our little kid gets a bath. That heater also has never shut down in that small bathroom with the door closed. I think they are bargains - I've got them here, in my shops, and at several remote properties. Some states don't allow them though - but no problem here in NY. In regard to wood-burners that run on convection/radiation alone - there are hundreds if not thousands. If you want a good one that holds heat and wood for a long time, burns very clean, etc. - I can tell you that our Hearthstone has been absolutely fantasic. It replaced a 1920 pot-belly stove we had that ran hot and burner out in three hours. We heat our house with a large wood-furnace during very cold weather - but in warmer days we use the Hearthstone. We've got the biggest one they make called the "Mansfield." It is lined with stone with retains heat for a long time after the fire burns down and sends it out evenly. Since woodstoves are regulated and tested by the EPA, all have to be pretty efficient now - but I'd stay away from the ones that can only do it with a catylitic converter.
The non-converter models are more reliable and usually bette built.

The AGA never should have let the term ventless be used on fuel burning appliances as that's not a true statement and confuses people.

All though the non-external vented appliance works well, they still have to have fresh air "cross ventilation" to keep CO build up to a minimum therefor they are vented to the outside, just not direct connect vented.

Yes they make several kinds of non-fan natural/LP gas heaters but there not as efficient as a heater with a fan.

You didn't say how large of shop so were guessing as what to recomend, but as mentioned, the RV industry has a 12v 32kbtu furance for LP that can be converted to natural gas use. The efficiency is approx 85%. Add a PV solar charger and a 12v deep cycle battery and your in bizz for 24/7 operation.

In your area tho, nothing beats wood heat as it's so easy to get and will out produce any type of fuel burning appliance for warmth.

Maybe Wardner will stop in a recomend his Russian wood stove design. Takes very little wood to produce alot of heat and easy to build.

Another is a forced air solar hot water system. Another easy DIY project. In your area, you would need about a 2000gal HW cistern. Parts including concrete about $1000. Avantage is the sun heats the water for free. Trouble free for about 10 to 15yrs before minimum componet replacement is required, ie; pump, sensors, fan motor, controller maybe a inside sand/cement coat to patch leaks.

T_Bone

I have a couple extra if you are interested.

NG wall unit with standing pilot light and thermocouple safety, heat on thermocouple ran thermostat

not all that efficient but very simple and reliable, not sure if they still make them

It's my understanding that practically any gas stove can be run without a fan. The heat just won't be spread as well. Same as a wood stove. Exhaust gas venting is an entirely different issue, and not what you asked about.

All the best, Stan