6000XP with electric, on demand water heater

> The specs for the water heater I was considering say 240v, 27amps. My question is, can I damage the inverter if I attempt to use this? I wouldn't be cranking it at the max setting which is 140 degrees--we'd probably set it at 105-110. So, I'm thinking we'd probably be under the 25amps

The inverter can only produce 25 amps. When asked to do more, it flips an internal relay and goes into Grid bypass mode (or if there's no grid power, then it shuts off all power).

An on demand water heater likely has a large heating element that is only either on or off, The temp you set it at will only likely affect how often it turns on or off, not its max power.

I would opt for a heat pump water heater (This is what I've done with my 6000XP). Same connections (240v + water), but way less peak electricity usage (300-400 watts) and about 2-4x as efficient. They are more expensive though.

It won't cause any damage. While the 6000XP is rated for a continuous output of 6000W, it does support a surge capacity of 12,000W for up to 3.5 seconds and 11,000W for up to 5 seconds. If the load exceeds 6000W for a sustained period, the inverter will trigger an error code and automatically shut off the output to protect itself.