Dr. Johnson, I wonder if you could advise me on my heater project. I have the
original DuoTherm furnace in my '66 Globe Trotter. It is a convection or gravity
style heater only. Last year I finished rebuilding it. It is now powder coated and
has a new/old stock burner and regulator. The temperature is controlled by a
thermobulb that runs to the regulator. It heats well, although sometimes I still have
trouble keeping the pilot lit. I found that its efficiency improves dramatically by
facing a small fan at the base of the grill. That helps force cold air into the
bottom which in turn forces the heated air out of the top. It really is remarkable
how much better the furnace works. Of course this is why new trailers have forced air
furnaces. What I've now done is attach two 4.72 inch diameter 12 volt DC fans
directly to the bottom of the grill at the intake so that I can stop using the 110
volt AC free standing fan. The fans are mostly used in computers and each use only
about 0.32 Amps and move about 85 CFM each. I can simply attach a switch to turn them
off and on as needed, but what I really want to do is run the power through a
thermostat so that as the furnace heats up to about 130 degrees the fans turn on.
There isn't much room between the grill and the furnace, so whatever type of
thermostat I use has to be fairly small. It also has to be the cooling type so that
the contacts close when the temperature goes up. I think I could canabalize this type
of contact from a household mechanical heating and cooling thermostat, but the
cheapest ones are $20 and the temperature setting is designed to close at
temperatures below 80 degrees. I've not been able to find anyone selling thermobulbs,
and although I think that might be the way to go, I'm not entirely sure how they
work. Any suggestions would be greatly appreciated.
Forrest McClure