I have several heaters that were in my old shop, they work perfectly one is natural gas one is electric and three of them are diesel parking heater style portable diesel heaters. You can find them on Amazon under the brand wippro diesel heater. If you have natural gas the wall mounted heater or floor it actually sits on the floor too is pretty good with natural gas.
The electric I call a bathroom heater even though I didn't have it in the bathroom, small space heater is a 5000 watt 240 volt heater. And I bought it at Northern tool the brand is profusion 5000 watt heater.
The natural gas heater is a comfort Glow 18,000 BTU wall mount heater even though I don't think you have to mount it on the wall the model number is cgr18n comfort Glow.
They all work, All brands and model numbers are represented in this listing so please do your homework. But if you have questions please ask.
The wippro diesel heaters. these have been used for two winter seasons so very low usage they are $65 each.
The h calory diesel heater is $55 brand new is.
The profusion 5000 W Northern tool small room heater electric is $50.
The comfort Glow natural gas wall mount heater is $50