Larry is right on the water vapor. They do a good job of taking the chill off in the AM, but I would keep the run times short and air the boat as soon as there is some warmth outside. A couple years ago I used one every evening and morning for about a month and the condensation was horrible. On the colder evenings it almost felt like it was raining and everything in the cabin was damp. When I am using it, I turn it off before bed time and sit it in the cockpit. I still have the heater on board, but it doesn't get much use.

Friends tell me the Origo also produces condensation, but perhaps not as bad. Then there is the alcohol stove smell.