I have a steam boiler (natural gas fired) and I'm wondering if I can safely use a small UPS to backfeed power to the boiler, in case of a power outage.
I'm not sure how much total run time I'd get - we're talking a 1500VA UPS with conditioned (sine wave) power output. However, the boiler only has an automated damper, the control circuitry, and the pilot ignition system - no fans, no pumps, no power vents - so the draw should be very low and not even constant.
I'd like to find out/test, in any case, how much run time I'd get with this setup (for emergency purposes).
The boiler is fed from a non-dedicated 15A breaker in the main panel. The feed goes into a J-box containing a dual socket receptacle and a switch. I have confirmed the switch cuts power to the boiler, when thrown. Therefore, the switch acts as a kill switch to the boiler.
Therefore, I concluded that if I were to throw the kill switch, throw the breaker for good measure, and then back-feed the UPS into the receptacle, the risk of back-feeding into the grid would be nearly zero. And it's temporary, no modification of existing wiring is required.
I know that folks can't really say this is safe, I know it's against code.
Are there any considerations that I haven't listed here?