Probably not in reality. Couple hundred for the boiler gun and a few more depending on how many circulators you have in the system. The newer ones use even less power. My newer Taco's use about 44w while the older and most common 007's use about 80w. Either way it's a tiny fraction compared to an electric water heater. But it's a plus to have oil hot water when trying to size a generator for sure. Other things to avoid and really you should not have a need to power them off a genny are things like toasters, microwaves, electric dryers and the worst of all electric stoves/ovens.