Without something to stir the air up you will get a large temperature gradient. I got it when I heated my house with wood and I got it in my camper with a catalytic heater. High temp at ceiling and cold at floor. A fan distributes the heat more evenly.
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a)
We use convection to move heated air... and no electricity nor contraption required!
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At all times, our rig has two windows open on opposite walls.
"Windows?!?, open in winter!?!" [faints]
Yep.
With our obsessively excessive insulation, with our Wave 3 catalytic heater set on 'LOW', the place gets too hot.
We open our tiny windows in different amounts -- for example: a half-inch to windward, an inch on the lee -- to regulate the interior temperature.
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A 'plus':
* the escaping heated air carries humidity and odors.
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b)
As I understand most built-in heaters such as a RecreateVehicle uses, they are designed for some outside air to be sucked in.
That amount varies, although fifteen percent sounds right.
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So, for each hundred cubic feet of air the heater squirrel-cage circulates, about fifteen cubic feet is added.
This replaces leakage through holes in the walls and ceiling... the usual suspects:
* windows and window-frames
* doors and door frames
* electric outlets and light fixtures.
Some folks try to plug those leaks, but the heater still adds the engineered amount of filler, causing a corruption in the energetic flow.
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As I understand it.
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Retro-fitting the type of heater you describe may be more than plug-n-play for Brian.