We use the OIL-FILLED 1500WATT Electric heaters. I picked this model because they do not have an open flame or visible red hot core. They are quiet running and 1500WATTS of heat is 1500WATTS no mater how you produce it... I personally like the low profile version of this heater verses the tall ones.
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If we need some more heat to be pushed around the room this type heater is perfect for sitting one of those O2COOL 10-inch 120V-12VDC-Dcell type portable fans behind them...
I feel this is the most safest type portable electric heater for us - Have no problem running it all night long or unattended in our trailers.
We usually run an extension cord in from the camp ground pedestal connected to their 20AMP SERVICE connections just for the Electric heaters when running from Electric sites.... This does not take away any power from our 30AMP Connections...
We use the Electric Heaters as primary and the propane furnace set to a low heat number for back-up...
As others have mentioned we can't stand the noise of the propane heater fan as well as the bite from the propane fumes generated from the propane furnace.
Also like said above if the temps are going to get very cold it over-night is a good idea to use the Propane Furnaces so the underbelly area around the tanks are heated to keep them from freezing up...
Roy Ken