Downstairs bathroom has a dedicated 20 amp crcuit. First in line is a GFCI outlet which trips the downstream light switch (for over mirror light) and a three-switch (for ceiling vent/light/heater combo unit).

I want to replace the vent/light/heater unit with a 1300 watt unit with the same functions and a better vent fan.

I discovered that the prior owner unplugged the heater cord in the housing. Why would they have unplugged the heater?

Will my upgrade have any foreseeable problems or can I sleep well at night?

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    Is there a reason you want the heater in your bath fan? Are you actually having an issue with the bathroom in question being colder than the rest of the house? Oct 13, 2020 at 23:28
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    @ThreePhaseEel I have combination light/heat/fan - they are great. It isn't the bathroom being colder than the rest of the house - it is how it feels (~ only 72 degrees air temperature vs. much warmer with the heat) when you get out of the shower. Oct 14, 2020 at 0:26
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    I made a couple of edits to make this more readable. Please ensure that I've got everything correct (especially the part about the wattage of the new unit you're proposing).
    – FreeMan
    Oct 14, 2020 at 15:34
  • FreeMan, thank you for your edits, someday I'll learn to write better questions. ThreePhaseEel, yeah want it because it's in bottom basement and no forced air to heat in cold Idaho winter. Oct 14, 2020 at 22:27

3 Answers 3


I am sure someone else can cite code, but generally speaking if the hardwired loads on a circuit are > 50% of the capacity of the circuit then you can't have ordinary receptacles on the same circuit. With a 20A circuit, that means if you have 10A of fixed load (1300 W on a 20A 120V circuit qualifies, plus you have some other lights as well).

The reason for this rule is that if you used a hair dryer (bathroom example) or toaster (kitchen example) or similar item that draws 1500 W and the heater was on at the same time, you would trip the circuit breaker very quickly. Nobody likes nuisance trips - this rule helps avoid them.

Bottom line: A heating fixture pulling 1300 W should be on a circuit by itself (which includes the light and fan that go with it) and possibly with other lighting, but should not be on the same circuit as any general use receptacles.

As far as why the heater was disconnected previously, that could be:

  • Nuisance trips!
  • Malfunction - easier to disconnect than to replace.
  • I'm sure you're right. My naive logic wonders in a hair dryer and heater situation, wouldn't the GFCI outlet trip, not the circuit breaker? But I've had two brain tumors so I get confused a lot. Oct 15, 2020 at 20:11
  • The GFCI detects an imbalance. It doesn't know or care about an overload. The regular circuit breaker detects an overload. It doesn't know or care about an imbalance. Two different problems, two different solutions. (Except of course if you install a circuit breaker that includes GFCI protection.) Oct 15, 2020 at 20:34

Having the hardwired loads on GFCI protection is silly unless they are inside a tub or shower. If they are grounded that is good enough. Why be plunged into the dark on a GFCI trip?

You cannot have receptacles on a circuit where more than 50% of the load is hardwired. So on a 20A circuit only 1200W can be hardwired. The lights + fan + heater must total < 1200W.

It sounds like that's a problem right now.

Also, don't put a heater on a triple switch. Put the other lamp on the triple switch and give the heater its own full gang space. That way you can put a timer there. That protects you from accidentally leaving the heater on.


They could have unplugged the heater because those old vent/heaters were terribly inefficient and they could end up drawing even more current if parts of the coil shorted when they failed. A 1300W heater left on continuously is a giant load for the house. Also...
Shouldn't a bath fan pull air OUT of the bathroom to remove humidity or 'fumes'. Im not sure it will serve the same propose as a heater if there is not a dedicated vent fan...

  • 1
    it's a radiant heater that sends out hot infrared rays theses are not dimished by the extraction fan.
    – Jasen
    Oct 15, 2020 at 7:52

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