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My spouse and I like to sleep with rice bags in the winter, which we microwave to heat up. To avoid having to go back down to the kitchen, we’re considering adding an outlet in our closet and plugging in a microwave on top of some wiring shelving.

Is there any reason this is not a good idea / dangerous?

Craig
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    don't use it at the same time as a space heater and you'll be fine. – dandavis Sep 16 '19 at 21:00
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    Where in the world are you? Outlets in closets are governed by special rules in some jurisdictions. – J... Sep 16 '19 at 21:55
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    In the United States – Craig Sep 16 '19 at 22:11
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    @J... +1. *"adding an outlet in our closet"* is the part that needs a question mark. – Mazura Sep 17 '19 at 01:56
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    Have you considered getting an electric blanket? – Melebius Sep 17 '19 at 09:37
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    @Craig Thanks. No restriction for NEC. In Canada, by contrast, inspectors usually want to see an outlet in a closet being for a *definite purpose*, meaning they will generally not pass a general purpose outlet in a closet. This is usually up to the discretion of the inspector, but they typically want to see what the outlet will be used for and they also want to see that that thing is present and connected in the way it is intended to be used. Not sure about the US, but for a microwave I think it would probably need to be a dedicated circuit. – J... Sep 17 '19 at 12:50
  • @Melebius is right, just get yourself an electric blanket (get two, actually, one for the bed and one for the couch) but be prepared to not want to move for the rest of the winter. – Mike G Sep 17 '19 at 12:56
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    One reason why this is not a good idea would be that heating rice with a microwave oven is terrible in general. Electricity to microwave conversion works at about 60-65% efficiency, and microwave-to-heat conversion depends on the water contents. Rice contains around 12% water only. Thus about 93% of your electricity doesn't go into your rice pillow. But I'm guessing "USA" rules out energy efficiency considerations, so... – Damon Sep 17 '19 at 15:15
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    @Melebius Or alternatively, an [electric mattress pad](https://www.amazon.com/Sunbeam-Premium-Mattress-Heating-Controllers/dp/B004DQU9C6/). It seems warmer when it's underneath. – bta Sep 17 '19 at 22:05
  • I heard one shouldn't heat this kind of bag without giving enough recovery breaks. Reason: the heated water in the bag vaporizes, then at another immediate heating there is no more water left to absorb the heat, the bag becomes too hot and starts to burn. Just to have mentioned... – puck Sep 18 '19 at 16:21

2 Answers2

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There should be no problem assuming that you leave adequate clearance around the unit. Any appliance becomes a fire risk if there's flammable junk piled against it.

Also be diligent about vacuuming up lint and dust. The microwave's cooling fan will draw in more debris in a clothes closet than it probably would in a kitchen. You might blow it out periodically with compressed air.

isherwood
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    Unusual but I don’t see anything that it would violate in code. + – Ed Beal Sep 16 '19 at 13:59
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    I would certainly see a microwave oven as far safer in a closet than any other cooking device because it is always on a timed shutoff. Even a toaster that normally shuts off when toast is done can jam (even if you put butter on your toast instead of jam...) and most other cooking devices - hot plate, etc. have no guaranteed time limit at all. – manassehkatz-Moving 2 Codidact Sep 16 '19 at 14:05
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    +1 for clearance. The unit will probably have some ventilation holes. Wherever those are, air must be free to flow. – Monty Harder Sep 16 '19 at 22:01
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    More fluff in a clothes cabinet: OTOH, there will be less grease to glue that fluff to the inside of the microwave. – cbeleites unhappy with SX Sep 17 '19 at 06:58
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    @manassehkatz I've heard of numerous cases of a microwave oven spontaneously igniting (and taking the whole house with it) when not in use - simply being plugged in was enough. – Pavel Sep 17 '19 at 07:52
  • @manassehkatz Toasters can indeed jam, and the second sentence of isherwood's answer is spot on. I accidentally started a kitchen fire which rendered the flat uninhabitable exactly like that. – Martin Bonner supports Monica Sep 18 '19 at 07:23
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It should be safe as long as you unplug the microwave oven when not in use (or use a switched outlet).

The reason for this is that there is usually much more dust and lint inside a walk-in closet than there is in a kitchen. All the highly inflammable material gets deposited and compacted by the forced cooling air circulation (virtually every MW as a fan) and may lead to a fire even when the microwave oven is not in use at that moment. I've read about at least two such fires in our council newsletter over last five years.

Note that you can't effectively clean the inside of a microwave oven (the inside where the electronics are, not the cavity behind the door where you put the rice) and taking it apart for cleaning is unadvisable at the very least, so caution is the only way to go. If you use a switched outlet, the switch isn't subject to the airflow (or is it a lintflow?) and so it is much more immune to the becoming a fire hazard.

Pavel
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    I'd speculate that the information in your council newsletter was faulty. It's more plausible that it was undisclosed operator error (33:00 instead of 3:30). Do you have any other source of information about this phenomenon? – isherwood Sep 18 '19 at 13:30
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    But microwaves operate in all kinds of different environments with differing levels of dust and lint, and I've never seen a recommendation to unplug it for safety reasons. By the logic of being unable to clean the insides, you'd need to periodically replace any microwave just out of fear of spontaneous combustion, since the amount of dust and lint inside is ever-increasing. A microwave that's been in a kitchen for 10 years might collect more dust than one that's been in a closet for 1 year, but no one says it's unsafe to leave a kitchen microwave plugged in. – Nuclear Hoagie Sep 18 '19 at 15:49
  • @isherwood Nope, just the council newsletter and a lady living in the same building (without her prompt I wouldn't have read the newsletter). The fire apparently started hours after the owners left, but then again the thing could have taken some time before silent smoldering turned into a blaze. – Pavel Sep 18 '19 at 19:50