If you use a heater without a vent, the burning of any fuel (propane,
alcohol etc.) will produce a warm but humid boat.

Just running a gas stove with the clay flowerpot will work to warm you up
but keep a hatch open for fresh air.

A bulkhead mounted heater using diesel, kerosene, or propane is the next
step up in cost and complexity. In North America, about $400-500 USD for a
decent one with an exhaust pipe. I had a Force 10 propane "cozy cabin"
heater 5000 BTU heater on our 30' boat. 10 minutes on high would heat it
hotter than you would like and you would quickly have to reduce the heat or
you would start to sweat.


--
Evan Gatehouse

you'll have to rewrite my email address to get to me
ceilydh AT 3web dot net
(fools the spammers)