R asked in Home & GardenMaintenance & Repairs · 1 month ago

If an Exhaust Fan 'Burns Out' Will That  Cause a Fire?

I am wondering what might theoretically happen if one left a bathroom exhaust fan on for an extended period (say, several days/nights)?

I would hope if it wore out it would just sieze and die---harmlessly. But I'm thinking the most likely reason for dying would be something internal wearing out or overheating, starting a fire🔥😲.

When you think about it, these fans run for thousands of hours over the years, with the usual cause for replacement being that they've either worn somewhat, making them too noisy, or they never did draw air out very well, finally spurring the homeowner to replace them with something better. 

So, *don't leave one running and go away for a week?  (To keep household air from becoming stale.)

9 Answers

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  • 1 month ago

    No, safety standards for such things (like UL or CSA) would require that manufacturers PROVE that the design is "adequately" safe to be left running for WEEKS at a time, including with a "locked-rotor test" in some cases. Many building/electrical/fire codes prohibit installation of appliances that are not "listed and labeled" for safety.

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  • Anonymous
    1 month ago

    Nope. that is a metal motor suspended in a metal bracket with nothing that burns near it so if it dies, it dies,   If it is not exchanging the air good enough for you, that is because the bathroom door is closed and the apartment window is tightly shut so open it a bit(even 1/8 inch)will let in fresh air into the apartment and out up the fan pipe to the atmosphere.  That is how it works best.  If not a window or veranda door then the hallway door.

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  • Kate
    Lv 7
    1 month ago

    If they are not cleaned out regularly, the dust and grime will build up in them and seize the motor (could also start a fire). They can also overheat if left on too long.

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  • 1 month ago

    My house is designed with a bath style fan running 24/7 to provide continuous fresh air.

    Never heard of one causing a fire, usually the failure is ultimately the winding overheating and burning a small point "open" allowing no current to flow. Often the winding overheating is a result of the rotor getting bound in place, without the blade turning high "inrush" current continues to flow and cooks the winding.

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  • 1 month ago

    those things are good for months of use so overnight isn't likely to cause any harm at all. and when they do die, it is usually a quiet death ... they just stop working

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  • elhigh
    Lv 7
    1 month ago

    In my experience the likelihood of a consumer-level electric motor failing causing a fire are next to zero. Not zero, because there's always the chance, but I have never encountered a fire caused directly by a motor, and I work in HVAC where there are lots of motor failures.

    A burned out motor generally just means that some part of the motor overheated which caused the failure, possibly a heat-related failure, not necessarily that there was an actual fire as such. Insulation burned through, a bearing overheated and seized, something like that. When this kind of thing happens the usual end result is that when insulation does finally burn through, that causes a strong enough short circuit to throw the breaker, and there you are with the power disconnected and things slowly cooling off.

    Where I work we have exhaust fans that run for months nonstop.  No joke, no exaggeration: months.  Some are bigger than what you're talking about but some are exactly like the unit you're describing.  They bear up under the use with no difficulty.  It's been a few years since I had to replace a failed exhaust fan motor, they're pretty durable actually.

    There's always a risk, but that's life. As risks go, this isn't one you need to lose any sleep over at all.

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  • 1 month ago

    The devices are made so that a fire is not likely, properly installed. But, few are installed per what they call properly. There are instructions. Like the house insulation is stuffed tight around and over them because they do not furnish an expensive insulated box. So, you have to get up in the attic and look at it and see if there is a fire hazard. Then you get to decide how close you put your insulation and how much normal heat loss is acceptable. Most people are oblivious to such things.

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  • Anonymous
    1 month ago

    Those fans are self cooling.  You have to run it for a very long time for them to get hot.  Many kitchen exhaust fans run for months without any issues. 

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  • Anonymous
    1 month ago

    In theory it can, but if it shorts it will usually blow the fuse. it is normally faulty wiring that causes the problems, not the unit itself.

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