Boiler circulator- pumps typically take 150 to 400 watts for large
residences ,boilers 100 to maybe 500 watt. Check your load first .
You can do what you suggest but in generators you get what you pay for.
Cheap unregulated voltage units can swing 45 volts or more from no
load to full load. And HZ swings to. Many motors wont start unless
60Hz is there. Electronics can be ruined also. Cheap units are really
for outdoors work, saws etc. Honda is expensive but the electronics are
superior to ALL other small units. And the motors are tops. A 300 $
6 circut transfer kit from Generac at Lowes is the way to go, its a
complete system. Transfer panels make generator use safe . Dont let
the generator run out of gas that can damage the Capacitators on your
boiler motor , if it has any , and other motors, Fridge etc.