Thank you in advance,
Scott Schildknecht
What do you think? what type (model) of water heater was installed? typical water heater uses 30amp @ 240v of power.
Well I’m not sure what to think that’s why I’m here asking a question, It was a Navien high efficiency tank less water heater and the power supply is 120 Volts, being powered by a double pole 20 amp breaker. My question again is is it okay to only use one side of a double pole breaker?
I googled this and came up with all the info you need:
“is it okay to use one side of a double pole breaker”
Very easy to do
Wow thank you I never thought of that of course I GOOGLED it. But is this not the purpose of the forum ? Is everyone on here jerks ?
Wow, you joined 1 hour ago and you’re already calling people names?
Yes, you fit right in. Welcome to the forum!
Yes it is.
Welcome to the Forum.
Yes it’s perfectly acceptable to use one pole of a multi-pole circuit breaker for a 120 volt load.
Pretty well most of them are,
Welcome to our forum, Scott!..enjoy participating. 
Although most electric on demand water heaters use 240V, sometimes two sets of 240V.
Was it electric, or gas?
Sounds like a gas unit.
Yes, obviously.
But I seriously doubt this one is electric, with just a single, 20 amp conductor.
Hence my question, it is likely a gas unit, and I wanted the OP to answer, in case he needs to call it out.
It was gas
Well that makes more sense than what I thought you were asking….never mind. 
Here’s one on the opposite end of the spectrum. 240V electric baseboard heaters on single pole tandem breakers. Obviously, this service has other issues, but what are the implications here? This setup was probably not in the manufactures installation instructions.
Hello Scott -
I’m late, but…
Yes. You can use one side of the breaker…if you are a homeowner. It will likely not kill anyone, but should be re-labeled on the panel legend. A professional would’ve changed the breaker.
Now - about that water heater - and here’s where it gets tricky. I’m assuming it is gas-fired. Some of which require 15A breakers, not 20, 30, 40A. So that would make your configuration (in your photo) double-wrong.
If you are not able to determine this on the jobsite (cuz not everyone can look it up on-the-spot), you may need to research it later (ASAP) or call it out on your report.
ME? I would call this out on my report as unusual configuration that should be evaluated and corrected as necessary by a qualified contractor.
Just sayin
They do appear to be on different phases, but has missing handle ties, and the improper double taps.
