I have recently installed 2x ceiling extractor fans into our salon, to combat the condensation we are experiencing in these colder months. These are not making much difference however, so I was wondering, can I also install a further In-Line extractor fan, with a beefier Litres/hour rate, on the same ducting path? So in effect I would have 3 fans pulling.
I would suggest you do not do as you suggest (Putting a bigger fan after a smaller fan in the same duct) However you could swap one of the fans for a bigger fan, and put the two smaller fans in series with each other, but I doubt it will do you much good.
I shall explain. An extractor fan does not extract as such, it pulls. It pulls air from an area and sends it along a tube to where ever (Usually outside) It can only pull as much air in as can get into the space it is pulling air from, it is not a vacuum pump.
So if a room has doors and windows and these are all shut there is only a small amount of air getting into the bigger area. A good example is a typical steamed up bathroom. An extractor fan will do what it can, but steam will still linger as the air flow is not that good, however as soon as the bathroom door is opened the steam is gone within seconds, this is because the door is open allowing cleaner air into the room to replace the air which the extractor fan can now remove.
I would suggest you can solve your problem not by bigger fans but by ventilation grilles (or an open door / window) opposite where the extractor fans are. As an experiment, try leaving a door open for a short while and see what happens.
I agree with Mr White, it is down to replacement air, there are heat recovery units, these warm air coming in with air going out, but the main thing is they allow air out so can put more air in.
Some have two impellers pushing air in and out, but some wall mounted versions the heat exchanger is built into the pipe through the wall, and the blow in only and allow pressure in room to push air out.
In my first house has vents in all doors to allow air back to the hot air central heating, the house was too dry, had to put trays of water into air intake to stop getting static shocks. But never seen the door vents in any other house, this house has a cat flap in the door, and with the two fans, bathroom and cooker hood running if not locked closed it will open to let air in to replace that blown out.
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