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I am fitting a new shower to a downstairs bathroom (the room previously only have toilet & sink) and need to fit an extractor fan. The room borders onto an enclosed porch (uPVC doors & windows with sloped tiled roof above).

I could fit the fan near the ceiling and put the ducting through the wall into the porch then vertically through the roof to exit via a chimney in the tiled roof. This is the expensive and more invasive option.

What I would like to know is if it's possible/practical is to fit the extractor to just above the skirting board and have the duct go round the floor of the porch. I understand that hot air rises etc, but what I don't know is whether that really makes much difference if the fan can replace the air in the room sufficiently quickly.

Phil Peace
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2 Answers2

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First off, you misunderstand the intention of the extractor fan. It is not to remove hot air. It is to remove moisture from the air, and that's done to help protect against mold and mildew buildup. This is particularly important in bathrooms where the door is usually left shut.

(It still helps with open door bathrooms too but in those cases the moisture will dissipate into the rest of the house on its own if a fan isn't used so it's less of a concern.)

Typically the moisture will be in the form of steam and will tend to want to rise to the ceiling. In the "door shut" scenario the air will be coming in through the base of the door - so putting the fan on the floor won't really help remove any moisture.

The Evil Greebo
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First, agreed with Evil Greebo, fan needs to be in ceiling to remove moisture. That said, Check your local mechanical codes, but the ductwork post fan can run vertically downwards. Bends, especially 90’s, are detrimental to flow, so plan a path that reduces or eliminates them. You may be able to run vertically downward inside your framed wall then out parallel to the joists under enclosed patio, for aesthetic invisibility of ducts. Furthermore due to stack effect downward or horizontal venting of bathrooms also helps to conserve energy. If this were for a gas appliance you would need to consult your codes, but this would likely not be an option.

Keil
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