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The owner's manual for our fridge specifies that it should be on a dedicated 15A circuit. I understand that this is considered best practice, although not strictly required by the NEC.

However, our fridge is on a 20A circuit that is shared with several kitchen outlets, which are used only for a few lights, a clock, and occasionally a toaster. Now my wife proposes to plug a 12.5A space heater into the same circuit, and I'm wondering if I should be concerned. The heater would be replacing the toaster, so at least they wouldn't be in use at the same time.

The fridge is supposed to draw 6A, although it's not clear to me whether this is the peak or the steady state load. So 12.5A (heater) + 6A (fridge) < 20A (circuit breaker), and perhaps this is OK, although cutting it a little close. (The lights and clock on the circuit are under 1A.)

If there is a safety concern here, can anyone help me to explain it to my wife? Or if you can clearly explain why this won't be a problem, it would help me sleep easier.

Thanks in advance!

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  • A 20 amp circuit is limited to 16 amps running all the time(heater and fridge). Add the lights and you are planning to run 19+ amps. Put the heater on a different unused circuit. The toaster is okay since it is only used for a few minutes, the space heater will be on for hours.
    – crip659
    Oct 30, 2023 at 15:58
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    If the owners manual specifies, that means code does too, because code specifies that you will follow the manufacturer's instructions...as part of code.
    – Ecnerwal
    Oct 30, 2023 at 16:08
  • Have you considered running the space heater on "low"? Typically that would be half-power, around 6A, which makes the math work out a lot better. It still produces quite a lot of heat. Oct 30, 2023 at 16:36

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A space heater is a toaster, whether you can see the coils or not. So with respect to "how much power" and "direct impact on the rest of the circuit when in use" it should be basically the same.

However, there is a HUGE difference: time.

A toaster is in use for perhaps 1 - 15 minutes per day, with each usage probably under 5 minutes.

A space heater is in use for hours at a time. That is called continuous usage and is treated differently in the electrical code (NEC) from short-term usage like a toaster. Almost all residential portable space heaters sold in the US are rated at 1500W. Why? Because a 15A circuit at 125V (nominal US voltage, though in most areas it is closer to 120V) can provide 1,875W. Multiple that by 0.8 (80%) for continuous use and you get 12.5A and 1,500W. So nearly every portable space heater, whether:

  • With or without a fan
  • Visible coils or hidden coils
  • Oil filled or not
  • Ceramic, quartz, infrared or any other fancy things
  • $29 to $597 (and that's just the price range at Home Depot)
  • Rated as 5,120 BTU or rated as 1,500W

is putting the exact same amount of heat into the room.

And that amount is the maximum to run with nothing else in use on a 15A circuit.

A 20A circuit does provide some leeway for other stuff. So yes, 12.5A for the heater plus 6A for the refrigerator and 1.5A for other stuff (lights, clock, etc.) will most likely work OK. But it is far from ideal and does run a serious risk of damage to wires (== fire) over time. A 20A breaker does not trip at 20A. It may not even trip at 22A. It will trip at 25A but only after a while (a few to many minutes, depending on various factors).

So definitely do not use a space heater, except for a few minutes at a time (like a toaster...) on a circuit used for significant, critical, things like a refrigerator.

In fact, I am very much against use of portable electric space heaters at all except in limited circumstances:

  • Failure of primary heating system (whether heat pump, gas furnace, electric coil whole-house heater (those are designed to run on separate, large, circuits and are very different from space heaters except in the cost-per-BTU), hot water radiators, electric baseboard heaters, etc.), in which case space heaters are a useful temporary solution.
  • Limited use in garage, shed, etc. where heat is only needed on an occasional basis.

If you feel a real need to install additional heat in your kitchen for regular use, you really need to look into (a) dedicated circuits as needed and (b) heaters designed for permanent installation such as Cadet heaters. A heater designed for permanent installation will be much safer and more reliable than a portable heater. It will also cost more, but safety is worth something.

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    Thanks to manassehkatz for taking the time to provide a clear and thorough answer. You've helped confirm my concerns. Thanks also to Glen Willen, who suggested running the heater at half power. That does seems like it might be an acceptable compromise, although I'd be interested to hear what manassehkatz thinks. I appreciate the help responses from everyone! Oct 30, 2023 at 16:52
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    Running at half-power does pretty much solve the wire/circuit overload problem. And in fact many permanently installed space heaters (e.g., Cadet) are actually less than 1,500W because they are designed to run continuously on cold days and can do so safely because they are installed on appropriately-sized dedicated circuits. Running a standard portable heater on low is safer than on high for long periods, but still not ideal. Oct 30, 2023 at 17:07

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