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Our strata gave us permission to install an exhaust fan with 4x 250W heating bulbs into our bathroom. We are on the top floor and the roof cavity above us is the cieling for the building. There are no firewalls in the cieling.

I've been told by a friend who's a licensed electrician that these items can be a big fire hazard, as if something catches fire in the bathrooom and the fan is on, the fire will be sucked straight into the roof cavity.

What are the chances of this happening? I can't imagine there's much in the bathroom that could catch fire...

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3 Answers 3

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I would worry more about the heating bulbs starting a fire themselves.

Secondly I would worry about mold, if your not exhausting your warm moist bathroom air properly.

I'm not sure about an exhaust fan sucking fire into the roof cavity, I guess it could happen. I would think the fire would have to be fairly large for this to happen, in which case the fan is probably the least of your concerns.

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Aside from the kitchen, I would say the bathroom is one of the most likely places for things to catch fire. You have:

  1. Water and electricity (never a great combination).

  2. Curling irons and hair dryers (often cheaply made & get very hot)

  3. Lots of flammable things (paint, wallpaper, drywall, cabinets, towels, etc.)

  4. Things that go boom (hair spray, air fresheners, other aerosols)

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But... most of those things go boom when you're in the room. Not nearly as bad as old rags in the garage, or a defective water heater. –  Bryce Aug 10 '12 at 5:46

As far as I am aware it is not normally too much of a concern as long as the bathroom is on the top floor of the house (and the air is exhausted to the outside). It can be a big problem if the bathroom is underneath another habitable room as the celling would form part of the fire protection of the room above in that case. Or if the air is being extracted somewhere it could get back into a habitable space (as it would carry toxic smoke into that area), but as this is damp air you probably are just going to extract it straight to the outside. However it does depend somewhat on the design/construction of the building and local building codes.

It is possible to buy devices to close off the extract point if a fire occurs. These include fire cuffs and wraps that will crush the duct work in the event of a fire, and grilles and vents with built in fire dampers (that will close the vent if it gets hot). It is essential to use these devices if your ventilation system penetrates a fire rated part of the building, in order to maintain the safety of the building. If you are in any doubt, I would recommend fitting safety devices suitably rated to maintain the same fire protection that you had before you started (e.g if you make a hole in some plaster board, fit a damper/cuff that is rated at least as good as the plasterboard). Make sure you follow the installation instructions fully.

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