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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.

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    A floor level fan will also collect more dust and pet hair. – Chloe Oct 25 '17 at 16:46
  • yes, you can go "backwards", w/ air intake on/near the ceiling, otherwise its effectiveness will be lowered. – dandavis Oct 25 '17 at 21:31
  • In my country it is not because of elecricity safety laws. Any electric socket or device must be mounted at least 1 meter above floor (Or more) – Piro says Reinstate Monica Oct 26 '17 at 6:16
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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.

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    Dry steam is superheated steam, that is at higher temperature than boiling point at its current pressure. Wet steam contains some liquid phase, it's not a gas but an aerosol - which is what gives it cloudy appearance. In the bathroom there can be no steam other than wet. If we agree to call this water-air mixture "steam" at all, it's definitely the wet kind. Depending on how wet it is, it can be heavier than air, as steam 100% wet is liquid water. – Agent_L Oct 25 '17 at 16:26
  • if you have steam from your bath, you need to turn the water heater WAY down ;) – dandavis Oct 26 '17 at 2:17
  • Just to add on the intention of the extractor fan- in house with forced ventilation the bathroom fans might be used as part of the ventilation system. Air is usually drawn out of baths and and kitchen and drawn in wither through inlets in windows or walls, or through special a dedicated pipeline for example when using an heat exchange unit on the way to recover exhaust air heat – Rsf Oct 26 '17 at 7:39
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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.

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