Can I put an electric heater and window A/C on the same circuit?

[Gary Radice]

For my garage I have an electric space heater (5 kw, 220 volt) direct wired to a dedicated 240v/30 amp circuit. I'm upgrading the wiring with for new lights and receptacles and would like to provide for a window air conditioner. With the size of the garage (20 x 24 x 12 ft) I'm right at the upper border of window A/C units that use 120/20a circuits, so I'd like to provide for using a 220 volt unit if necessary. Since the heater and the A/C won't be used at the same time, can I just add a 240v outlet near the window onto the heater circuit, or is that a no-no?

[Tom Veatch]

Well, it's been about 4 hours since you posted and no one has yet replied, so, in all my ignorance, I'll take a shot at it.

With the exception of the heater being hardwired, I see no difference between your proposal and having a couple of 3HP tools plugged into a 240/20a branch circuit. The circuit is capable of supporting either load sequentially, but not simultaneously.

A potential problem is there's nothing that prevents the added receptacle from being used for something other than the A/C at some point down the road, either by you or by your successor. If the heater were plugged in through a receptacle, an argument could be made that it's a branch circuit and adding a second receptacle wouldn't be a problem. With the heater hardwired, that takes the circuit out of the branch circuit category, as I understand it, and adding a receptacle would likely be red flagged by the local code enforcement authority.

That's simply my uninformed view. My advice is ask the question of your local authority. They are the ones who have to sign off on the work.

It's been said that it's easier to beg forgiveness than to ask permission, but I'm not sure that's applicable to electrical work. When an inspector says, "Yeah, but ....", it can get expensive.

[Ed Hazel]

It should not be a problem, if you try and pull to much juice the breaker will trip. However if you are reworking some wiring why not just run a separate circuit for the A/C unit in the future you may want to use it for another machine I started with one 220 recp and now I am up to four.

[Gary Radice]

I could just make receptacles for both the heater and AC, but the heater manufacturer specifically calls for hard wiring it. Running a separate circuit for the AC is an option but panel space is a little tight. I don't have the amp headroom in the garage subpanel to add another 30 amp breaker, but I might be able to add the 30 amps to my main panel if I move a smaller circuit from main to sub. Main and subpanel are side by side and nothing has been insulated or drywalled yet so the wires are all readily accessible.

I'll give the county building dept a call and see what they have to say.

Thanks, guys.