On Fri, 30 Oct 2009 06:25:51 +0000, John Rumm
wrote:

Combustion of any hydro-carbon will produce water - so some ventilation
is required. With an appropriate flue much of the water will be expelled
with the flue gases.

Sorry, I was thinking about portable heaters such as:
http://www.amazon.co.uk/Delonghi-Fla.../dp/B001LS0QCC

which don't have a flue.

I'm still puzzled why these use butane and everything else used
propane though. Particularly if butane doesn't work at temperatures
around freezing, which is when you are most likely to need to use the
heater?