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bath fan/heater on old wiring?

Hi all -

I'm in a 1930's single family, and looking to install an overhead bath fan/heater/light, many of which call for a dedicated 20amp circuit. First, how do I know if I have 14 or 12 gauge wiring? I assume I have 15 amp only, but can my wiring withstand a 20 amp breaker, or do I have to rewire from the 2nd floor to the basement all just for this unit?

Thanks for the advice.

Re: bath fan/heater on old wiring?

My assumption would be that your bathroom circuit shares with other outlets and lights in other rooms. This by default means it is not a dedicated circuit. Dedicated circuits serve only 1 item, which in your case is the heater/fan/light. Its time to run a new 12 gauge wire from the panel to the bathroom.

Re: bath fan/heater on old wiring?

Don't do it. It needs to be dedicated because electric heater draw a ton of current. Overloaded circuits seem to be the primary cause of fires in old homes. Usually from plug-in space heaters. This isn't much different.

Either find a way to run a new circuit, or install a hook for a nice thick bathrobe.

As a general rule, any-time you have a appliance or device that consumes more than 1/2 the total circuit current, it should have it's own circuit. This includes dishwashers, garbage disposals, refrigerators, entertainment centers, furnaces, window AC units, microwave ovens, washing machine.. and so on.

Re: bath fan/heater on old wiring?

I agree with the previous posts.
Houstonremodler summed it up nicely.:cool:

58 chevy
Re: bath fan/heater on old wiring?

There are several things you need to know before you attempt this project since you live in a 30's house: Type of wiring you have, if you have room to add dedicated breaker on your panel, age of your panel, size of your main service panel in amperage(adding a dedicated circuit might be your last nightmare if you don't do your home work)Your main service panel has a main breaker the total of your individual breakers can not exceed your main breaker size in amperage, what type of wires are in the area where you would be installing your fan-heater-light combo and what is mfg. recommendations and follow them (modern wires are insulated with vinyl type of insulation,(some houses have added extensions to the original wiring don't be fooled to think that yours is modern up to code wiring know for sure its your house don't gamble) older houses, such as yours, wiring insulation was cloth material, some running parallel bare copper wire on the attic then cloth insulated running down to plugs and switches etc.(night mare). This is no small work. Wire size from 12 to 14 is one larger than the other 14 is small than 12 wire gauge:), smaller the number thicker the wire fyi. Wire size can be determined by a wire gauge tool(most major dyi stores would have it) to use it you have to have wire in your hand or sticking out of the wall. don't try it if you don't know the principals and safety precautions of working with electricity. You also need to check that you have a dedicated ground coming to this unit since you have 3some unit one being heater, safety is the best home owner insurance you have that you don't pay for. You might be better off getting a licensed electrician who knows the NEC and your local electrical code.
Good luck,:)

Re: bath fan/heater on old wiring?

If the circuit has a 15 amp breaker leave it 15 amp. Just because some of the cable in the circuit is 12 ga does not guarantee that all the wiring in the circuit is 12 ga.


Re: bath fan/heater on old wiring?

Thanks to all for your posts. Sounds like I should consult with a pro to sleep better at night.

Re: bath fan/heater on old wiring?

We had a similar need in our 1940 house and decided to kill two birds with one stone. We ran a dedicated 12/3 line from the breaker box (which has been upgraded to 200 amp) to the attic above the bathroom and installed a dual 20 amp breaker in the box. In the attic the 12/3 is broken out into two circuits, one circuit for the heater/fan and one circuit for a new GFCI outlet. This covers two requirements for the bathroom, but we only had to run one line to the attic. This is a multi-wire branch circuit and it was suggested by the electrician.

We were also installing A/C equipment in the attic, so the running of one more 12/3 electrical line was not much extra work. However, it did take a while to find a chase that allowed access all the way from the basement to the 2nd floor. I had hoped there would be enough space around the soil stack cutout to fit some electrical lines, but we had to open up plaster instead and drill holes to use the adjacent wall cavity to run the wires. My plaster is installed over rock-lathe, so its a like cutting really thick drywall. However, if you cut carefully its also relatively easy to patch the hole with the piece you cut out.


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