Wonder what your experience is with propane wall mounted heaters used to supply water to existing hot water radiators? Specifically, does there exist any particular risk of fire caused by sawdust or fumes? It's my belief that these units use intake air from outside and thus there should be no such risk. But I'm wondering what the "real world experience" is. Let's look specifically at units installed in the last 5 or 6 years please.

Thanks in advance!