: I just got an 80-110,000btu propane heater for my shop to get it warm enough
: for glassing the Arctic Tern I am building. I tested the heater last night
: as I was filling the hull seams, with the heater hooked to a 20lb bottle.
: It put out great heat for a little while, but the propane bottle began
: icing up on the outside and the heat output was greatly reduced. The
: manual for the heater recommends a 100lb bottle. Is that size to combat
: the icing? What sizes are you all using? Could I get away with a 40lb? The
: 100lbs are only $20 more than the 40lb bottles, but dont look to be very
: easy to handle when full.

: Thanks!
: Miklos

The 100lb. bottle recommendation is to combat icing. The larger the bottle the less icing. However, it is not the ice on the outside causing the problem, it is the reason the ice forms in the first place - the propane inside the take has gotten very cold. What happens is that as the propane vaporizes from the liquid state (the normal state in the bottle), the evaporation cools the rest of the liquid until it gets so cool that it can't evaporate fast enough to meet the heater's needs. This is basically the same as your sweat cooling off your body temp. The larger the bottle of propane, the more evaporating it can sustain before cooling off to the point of not meeting the heater's needs. This is one of the reasons that small bottle appliances are not recommended for very cold weather use, the propane just gets too cold to evaporate.

A 100lb. bottle may be a pain to handle, but it would improve this situation. If your heater can efficiently burn smaller quantities of propane, you can get by with the smaller bottles because you probably don't need that much heat to begin with. However, many propane heaters dont' burn very cleanly when they are starved for fuel because it is difficult to build a burner system that can handle a wide range of btu output and do it efficiently. That is why you dont' see heaters that will run a wide range say from 1,000 to 100,000 btus.

If you have a good long hose, put the bottle in a warmer part of the room, not back in a cold corner that gets little heat. Just be careful not to put the bottle in the heated air stream where it may overheat and pop the relief valve. You won't have a garage if that happens. Personally, I would either find a smaller heater or go with the 100lb. bottle.