I use the single below to heat my 2 car garage in the winter. I find myself turning it down/off after an hour or two as sometimes it gets too warm. I run a small business installing automotive remote starters thru the winter months and generally just wear a sweatshirt/jeans and this is my only heat. I usually refill the propane 2-3 times a winter. On Saturdays/Sundays, I usually am in the garage all day. Last year was a relatively mild winter and I think I only filled the propane tank once.
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That all said, I'd like to do a more permanent radiant setup, but really don't have the height in my home garage. My buddy's body shop has 15-18ft ceilings with Nat Gas Radiant Tubes in the ceiling - awesome heat! I plan to build a detached garage and want to go with heated concrete floors.