Caveat: I have no experience with propane heaters, but I do like to burn stuff.

That's a big heater for your average shop. Can you turn it down alot so you're not burning through so much gas? A 40,000 btu electric heater warms up my shop (16x21' or 2688 cubic feet) pretty quickly, even here in the canadian winter.

I doubt if the ice outside the tank had much to do with thing the heater slowing down, other than it's a sign of how quickly you were burning through the gas. As the gas comes out of the bottle, more propane within the bottle expands turning from liquid to gas. As it does so, it sucks up alot of energy and quickly makes the tank cold. A BBQ tank can have ice form even on a mild day.

The reason the manual suggests such a large bottle is probably so that you don't have to fill the thing every other day.

Hopefully some others here can provide more insight.

: 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