I must admit I have wondered if one ran an engine and used the heat from the engine to heat the house something like the system used in canal boats how efficient would it be?
I believe it's quite efficient if you have good heat recovery - including the exhaust.
So put "cool" return from heating through HE with exhaust, then HE with engine water jacket - and top up with lecky from the alternator as required. You'll still need a thermostat in the engine coolant as you need to keep the engine running reasonably hot or it doesn't burn the fuel well.
Rig things up properly and you can use the genny to keep the lights on in the house as well when we start getting power cuts in a few years time.
If the issue is your wifes buiness taking unmetered power from the house, fit a meter.
if the issue is that the bills are huge, you want to look at how the place is insulated/ventilated.
Unless you actually just want to play engines, in which case, start looking at 'micro chp' systems, which as said, start dong things like recovering exhuast heat.
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