I have 12/3 running from two 20 amp breakers in the panel to my garage. Currently each of the two 20 Amp circuits (wired with this 12/3) feed two receptacles in the garage. There is nothing else on either of these 20 amp circuits. Neither of the 20 Amp circuits is required... I just had them put in for running power tools... Probably total overkill.

Anyway, in a bathroom adjacent to the garage I want to add a wall heater. The heater can be configured to use 120 or 240. With my existing 12/3 wiring can I either tap into one of the 20 amp circuits for the 120 configuration or both of them for the 240 configuration?

My two concerns: Is it allowable for garage and bathroom to share a circuit? Can I use these two circuits and 12/3 wiring to feed 120 and 240 things?

I would recommend that one of the receptacle circuits be dedicated to the 120 volt heater, assuming it does not exceed 1920 watts, and connect the receptacles on that circuit to the remaining circuit.

This would prevent the possibility of having an overload condition in the event the heater is on the same time as tools are used.

No, you cannot piggyback a 240 volt heater onto the two 120 volt circuit breakers that currently are for the receptacles.

Thank you so much for the response - I really appreciate it. For some reason my local building department couldn't / wouldn't (not sure) answer this question for me.

The wall heater isn't that big... it can be wired to 500W at 120VAC and the instructions say it does not require a dedicated circuit. It does have an option to wire with 240... so I was just curious.

Given the remote (at least for me) likelihood of running a big power-tool at a time when that heater would be running, is it OK (per code, though I appreciate it is not your recommendation) to have the receptacles and the heater share one of the circuits?

Also, if I leave it shared, so I have both circuits available in the garage, could one day I change one of the receptacles to make it a 240 volt receptacle?

Thank you,

Considering I now know it is only 500 watts, my mind always goes to 1000-2000 watt units, it will probably work just fine connect to a receptacle circuit. 500 watts at 120 volts is 4.2 amps, but must be considered as a continuous load, as it cannot be predicted when to run.

The issue with wiring, while you would be aware of it on the circuit when you used the outlets, and not use large tools on that circuit when the heater is running, we need to wire buildings "idiot proof", so to speak.

You connect the heater to the outlet circuit, and sell the house anytime later. The next occupant comes in and is not aware, and uses the outlet circuit for a large table saw, etc. and the circuit begins to trip.

We, as electricians, need to think ahead, eliminate as many possible issues as possible. I am unable to find a specific code preventing you from sharing this outlet circuit with a 500 watt heater unit. No different than if you were t o plug in a portable unit in the garage while working with power tools. Proper labeling would help anyone using it in the future.

A better job would be, which is any electrician's instinct, is to give the heater a dedicated circuit.

I do not understand your last question about 240 volts.

Thank you again.

Regarding the last question. I was just suggesting one potential advantage for me to continue with both 20 amp circuits going into the garage is that one day, I think I could wire a 240 volt receptacle if the desire arose.

I will try and do what you suggest and maybe try and add a new dedicated circuit for the heater. Aside from the work it will be to pull the wire, one reason I did not want to go that route is that I only have one breaker slot open in my panel and I thought I better save it. Also, I know nothing about how many circuits I am allowed to put in my 100 amp panel.

No, a 120 volt and 240 volt circuit cannot be shared.

If you look at the label on your panel, it will tell you the types of breakers allowed, some are halfsize breakers, and allows more circuits, two for one space, so to speak.