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I have purchased a bathroom exhaust fan that also has a built-in heater. The heater is 1300W and in the instructions manual they say to use a 20 amp circuit

However... the electrician just installed the circuit, and he used a 14/2 cable because he understood it was just a fan. It took him 3 hours to install everything.

It says on internet that a 15amp circuit can run 1800W. But the installation manual of the fan/heater says 20amp circuit. Should I ask the electrician to redo everything (and pay again)? Or is 15amp ok?

Machavity
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Thomas
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3 Answers3

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If the instructions require a 20A circuit then that is what you must do. If they recommend a 20A circuit but it doesn't actually require it based on total power, then a 15A is OK. Two keys:

  • Dedicated circuit - a hard-wired device using more than 50% of the circuit capacity (which at 1300W is the case whether on a 15A or 20A circuit) should be dedicated to that device.

  • Total power requirement.

Have you ever noticed that nearly all plug-in space heaters are rated at 1500W? Doesn't matter if they have a fan or not, ceramic, oil-filled, whatever. They are always 1500W! Why? Because 125V x 12A = 1500W. And a 15A circuit can only have 15A x 0.8 = 12A continuous usage. Heaters are assumed to be continuous usage because you might plug them in and walk away. Same thing with a bathroom heat fan. 1300W is actually on the low side, but that may be to allow for the exhaust fan and for a 100W incandescent light bulb, getting the total very close to 1500W.

Based on all of that, I am fairly certain that this device is going to be OK on a 15A circuit.

For those who might think "15A circuit breaker + 14 AWG wire, what's the possible problem - wouldn't the breaker trip if the device drew too much current?", it is not, unfortunately, quite that simple. If you have a 16A continuous load (max. for a 20A circuit) and you put that on a 15A circuit, the breaker might never trip because of the way breakers are designed. 30A and it will trip very quickly, 20A (33% over) and moderately quickly, but 16A is in the sweet spot where it might not trip for hours or never at all, but which would potentially be a major problem for the wire (which is why you are only supposed to have 12A continuous on 14 AWG wire). As with many other things, just because it seems to work doesn't mean it is safe!

In the end, manufacturer instructions and nameplate ratings are what really matter.

And finally, an update based on the specific model:

If it is this Broan NuTone 80CFM with 1300W heater, model # 765H80L, available at Home Depot:

Broan NuTone 80CFM 1300W 765H80L

then there is no problem, as the instructions say:

Provide a separate 15 AMP circuit. Use 14 GA. power cable of type which meets code. If providing a separate 20 AMP circuit, use 12 GA. power cable.

However, if it is this Broan NuTone 80CFM with 1300W heater, model # BHF80, also available at Home Depot:

Broan NuTone 80CFM 1300W BHF80

then you must use a 20A circuit as the instructions say:

Provide a separate 20 AMP circuit. Use 12 GA. power cable of type which meets code.

This is a perfect example of why at DIY SE we ask for model numbers. Just the manufacturer (Broan-Nutone) and the basic specs (1300W heater, 80 CFM fan) are not enough!

Assuming that OP's problem is they have a BHF80, it is likely that they can swap it for a 765H80L and solve the electrical issue. Leaving a BHF80 in place with a 15A/14 AWG circuit is a code violation. A fire 10 years from now, for example due to accumulated dust or other problems, could be denied coverage based on an investigation showing invalid wiring.

All that being said, it is the responsibility of the electrician to match the circuit to the device, assuming that the electrician was either (a) doing the actual device installation or (b) was given full details and not just "Broan-Nutone 1300W 80CFM".

manassehkatz-Moving 2 Codidact
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    Good answer with the known power requirements, but as you say, it does depend what the instructions say to be in code. Think down voters should need more points. – crip659 Jan 31 '23 at 01:17
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    How did you arrive to 20A being 25% over? It seems to me that 20/15 = 1.33, so 20A on a 15A circuit is 33% over, not 25%. – jaskij Jan 31 '23 at 08:56
  • We run 3KW kettles on a 13amp circuit (limited by a fuse, UK) - is this different? – Paul Jan 31 '23 at 15:14
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    @Paul 13amps x 240 volts = 3120 watts. It's half that on a 120v circuit – Machavity Jan 31 '23 at 16:02
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    @Paul the difference: I believe you're on a 30A ring with a 13A fuse protecting a 17A plug-in appliance cord. OP here is talking about a permanently installed, concealed cable feeding an appliance that consumes about 1400W but because of rules for permanent concealed cables and heaters requires cable capable of more than 15A. – jay613 Jan 31 '23 at 21:16
  • Does that 16A case imply there's a bit of a "gap" in the code? If I plug in a space heater and a big TV or something, and they draw 16A, the wire might burn up in my wall, despite a totally correctly functioning breaker and everything installed to code? – mbrig Jan 31 '23 at 22:58
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    It is a small gap in the code. But it goes along with allowing multiple receptacles on a circuit. The problem can even happen with just 2 (a standard duplex). However, the reality is that most people, most of the time, have few high current devices going for long periods on non-dedicated circuits. So there are really two somewhat separate issues: High current on continuous usage on a dedicated circuit that is too small - which is OP's question. The second is the "two space heaters on one circuit" problem. And in reality, two space heaters on one circuit will trip the breaker (whether – manassehkatz-Moving 2 Codidact Jan 31 '23 at 23:11
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    15A or 20A) and most people, most of the time, don't have a space heater together with several amps of other stuff continuous on one circuit. Vacuum cleaner? Sure, but that's only a few minuets, no problem. Computer, etc.? Unless you're bitcoin mining or running a server farm, the current needed is minimal and it simply doesn't cause a problem. Laser printer? Yes, draws a lot, but only when printing, so again hardly ever a problem. And all the normal things - everything except lots of grow lights, bitcoin mining, space heaters - put together rarely get to 15A on a circuit, – manassehkatz-Moving 2 Codidact Jan 31 '23 at 23:13
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    with the exception of kitchen appliances (toaster, coffee maker, etc.) and people learn to manage their kitchen circuits (which is why there are supposed to be at least 2 circuits) to take care of that problem. But dedicated and wrong-sized, that's a problem! – manassehkatz-Moving 2 Codidact Jan 31 '23 at 23:14
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    thanks a ton for looking that up and going so deep! – Thomas Jan 31 '23 at 23:50
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    @manassehkatz-Moving2Codidact (and others) - Thanks for clearing that up. It's interesting to see how other countries do things like this. (As you can tell, I'm no sparky!) – Paul Feb 01 '23 at 16:07
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    I wonder why they use 15A breakers with 14awg wire if they take so long to trip at 16A? Wouldn't it have been safer to require 14A breakers or 12awg wiring everywhere? It seems like a weird decision in the code doesn't it? – Jason C Feb 01 '23 at 22:43
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Following the manufacturer's instructions is part of code NEC Article 110.3(b) so new cable or new fan would be indicated. Based on your description of broan nutone 80cfm (fan+light+heater) I find these instructions, which state quite clearly, and without any wiggle room for "recommending rather than requring" (I also checked a few other results, since you did not give a specific model number - they all said the same thing):

  1. Provide a separate 20 AMP circuit. Use 12 GA. power cable of type which meets code.

Unclear from here where the fault in the electrician's understanding of what was to be installed came from.

I would leave the 15A circuit and add the 20A circuit since removal is a waste of time and there might be use for it for other purposes.

Ecnerwal
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Maybe. Heaters require a 125% de-rate, so 1300W becomes 1625W. That leaves you 175W for fan and light. Maybe. You'd have to look at the instructions to be sure.

Mind you, lights also require a 125% derate, and if the fixture is physically capable of taking incandescent bulbs, it must be provisioned for the largest bulb allowed in it e.g. 75W x 125% = 93.75W). You can't just go "la la la, I'm using an LED screw-in, so I get to provision less power" no you don't, because Johnny cold-dead-hands who buys your house will slap an incandescent in there.

I would check the instructions as maybe it's designed for a 15A circuit. Otherwise probably be cheaper to send back the heater/fan and get one with a lower rating made for a 15A circuit. It should be perfectly possible with a gentle fan and integrated LED lighting.

Harper - Reinstate Monica
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  • Good advice to get a smaller heater but very hard to find a suitable one in this style with a concealed heating element designed for a 15A circuit. May need to replace with one designed for a heat lamp. Those all easily sit on a 15A circuit. The fan is about 50W and the heat bulbs are 100 to 300W. (Conversely with a 20A circuit the ones with built-in heater and built-in 11W LED lights have 1500W heaters!) – jay613 Jan 31 '23 at 18:20