I disagree with a lot of the posts here.
To burn gasoline to make electricity to turn around and make heat is generally inefficient- particularly with a small engine.
Gas engines are not all that efficient...lots of heat blows out the exhaust, lots of heat blows off from cylinder heads and crank case and etc. Then your generator even has a cooling fan, and the wires to the water heater can heat up...lots of waste.
Lots of good heat that could OTHERWISE been used to heat water.
The water heater isn't 100% efficient either, but the burning gas goes 'directly' to heat up the water, instead of being blown off from a cylinder head, muffler etc. (At least it goes a lot MORE directly).
Now, I also get it that there's additional layers of complication. "The generator is already running"...that might move the scales some. LP from the camp store can sometimes be pricy versus gasoline- and $ wise? Who knows.
Also, there's a lazy factor...filling the gasoline tank can be easier than unhooking the LP tank, hauling it to the refill place, hauling it back, reinstalling it.
Still- small gasoline generators operate well below 50% efficiency while water heaters are generally above 50% in their energy conversion / transfer.
This is a geeky and pure engineering thought, but I've always wondered if there'd be significant energy harvested (and efficiency increases) if an 'exhaust pipe' could be routed into a boiler (or water heater)...Then we'd really be on to something ๐
