MrWizard wrote:
it takes a xxx amount of energy to move yyy amount of air
you can get a furnace with lower btu and smaller fan motor
or you can eliminate all fan power use by getting the Wave cat heater
thats what we did, use to have a wave 6, now have a wave 8
we are 34ft DP, the bed sets over the engine compartment and gets COLD
It's not really true that a fixed amount of air movement requires a specific amount of energy; there can be significant differences in fan efficiency. A large fan will move a given quantity of air with less energy than a small fan, as the air velocity is lower and hence the pressure differential created is lower. This incidentally is why a helicopter is able to fly without needing impossibly large engines. Also, some fan designs waste less energy in making noise or eddy currents or turbulence than other fan designs.
For a furnace, there's also the option of heating a little air to a higher temperature vs. heating a lot of air to a lower temperature. The heat output can be the same, but the volume of air moved is different (and the evenness of the heat presumably suffers with the lower volume fan).
Looking online, an Atwood Excalibur 30,000 BTU ducted furnace is rated at 7.5A, while a Suburban NT30 (also 30,000 BTU and ducted) is rated at 5.5A.
