heating workshop

[MattF]

Was it propane? My understanding is that burning gas produces water as part of the combustion chemistry.

As far as I recall, whichever type of fuel it uses is irrelevant if it uses a liquid fuel. Volume of liquid fuel in roughly equates to the volume of moisture it outputs, so burning a litre of fuel will chuck around a litre of water into the air. Solid fuel or electric heating is the only real source of dry heat.