A typical home boiler uses 3000 Watts.
3000 watts is not the correct answer. Watts = volts x amps, or if converting to btu 3000 watts = 10236 btu. At typical household votage of 120, 3000 watts would equal 25 amps and no boiler uses that much current and if your desire is to convert btu to watts I would suspect the average boiler output is far greater than 10K btu.
Determine the output in btu/hr of the boiler in question from the MFR`s nameplate and divide by 3.412
3.412btu=1watt/hr.
My home boiler uses 3000 watts, it's in my kitchen cupboard and it runs on a 240 v supply.
Too much
That would depend on the boiler - look on the boiler plate it will tell you the answer for that boiler there.
If this question is about electrical home heating then use ten watts per square foot.
45 watts
It is a type of boiler that you can use in your business. There are many different types that you can choose from.
In a fire in the home, or in a boiler to run an electricity generator.
Hoovers use 1000 - 2000 watts
Abut 20 watts.
650 watts
189 watts
About 10 watts
25 watts.