two parts here...
first part.
I know the flowerpot trick to work fairly well, because it causes the heat to radiate.
i also know if you had a flower pot without a bottom in it but a with a cover for the top opening, and put it on the burner right side up, the shape of the sides will help to radiate the heat downward a substantial amount more.
but on a regular sized stove top it gets reflected back upwards by the stove top itself.
on a small single burner coleman stove setting on the floor, using the shape of the container inverted, you can immediately tell the difference on your feet.
but its true what
MaineSail said, the BTU output doesnt change...and you need enough of them, but its not always the amount of the BTU's being created by the device that count as much as how they are distributed.. it depends on the temperture differential between outside and inside, and how much air transfer between the two.
if you have all the heat rising to the top of the cabin and its 85 degrees up there, but at your toes its only 60, then there is going to be some discomfort, and a bit more actual loss of the usable heat, than if it was mixed up in the cabin...
if you have a concentrated amount of heat at the ceiling and that is where the vent is, the hotter the air, the faster it will want to escape thru the hatch..(its concentrated, so a small volume can mean a lot of BTU's escaping).
as it leaves the boat thru the hatch an equal volume amount of cold displacement air will creep in around the companionway, and settle to the floor. air that has to be heated again, to maintain comfort
if you could mix the two, you will slow down the interior/exterior exchange a small amount, but the greatest difference is that you will be warming your feet, while putting some of the heat to use to warm the other stuff in the boat.
because, as the heat is distributed more evenly thruout the interior, the heat will slowly be absorbed into the surrounding structure that makes up the space, so even though you are losing less heat out the escape hatch, and can be somewhat more comfortable, you still need a good BTU output to bring the interior up to a given temperture. once everything equalizes, the btu output can be cut back a little...
the flower pots only purpose is to better radiate what is being produced....
the second part...
and im only sayin', not preaching, cuz i believe we should all get to make our own decisions based on the information that has been offered to us
...
I am a proponent of having an oxygen depletion sensor, a CO sensor, and a Gas sniffer on board... I personally dont have a gas sniffer (yet), but the other two offer some comfort in the evenings when we are boarded up and have the furnace going, even though its a vented furnace, there is always something that can go wrong.....
it can be a very dangerous practice to use an open flame for interior heating of an enclosed space, and a 2 inch opening in the overhead hatch is not adequate. you also need a dedicated inlet....
there are two things that can go wrong... oxygen depletion and carbon monoxide (CO) poisoning...
the ONLY reason they are so dangerous is because you only get one chance with them..... once past a certain threshold, its lights out.
CO gas settles, so as long as you are up and moving around you may be fine, but once you set down, or go to bed, it can get you.
oxygen depletion just makes you tired, so you nod off... there isnt any waking up from either condition.
the catalytic heaters somehow catalyze the CO gases and the only concern then is O2 depletion, which if the directions are followed, its not much of an issue
so if i were to offer any advice, it wouldnt be to tell you not to do whatever it is you want to do, but only to "be aware... and, be responsible"
