Two inline fans into one duct

I`m looking at using two inline fan kits: http://www.screwfix.com/app/sfd/cat/pro.jsp?tsF057&id 061 to ventilate a bathroom and utility room that are next to each other (both have no other forms of ventilation or windows). What I was wondering because space is tight getting to the outside wall is if I could join the two 100mm ducts into each other using a 'T-piece' or similar like the one here: http://www.tlc-direct.co.uk/Products/BG4T.html Is this permisible (it must be otherwise they wouldn`t sell a T-piece right?). If one fan was on & sucking air through to the outside, would some of it not end up going the other duct and end up in the other room or do the fans have some inbuilt 'non return' for reverse air flow?
John
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You can get backdraft shutters that are supposed to act as one way valves. I have seen them in the RS components catalogue. Perhaps two outlets, each with a backdraft shutter would be good. Single fan with two suctions would mean only half the flow rate from each, which might be a bit disappointing in clearing the room.
Also don't forget to try to keep the ducts warm, insulated over the top, to avoid condensation dripping back when it is cold outside. Also run the ducting slightly downhill to the outside if possible.
Good Luck, Eric
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But what if the ducting from each separate fan has a one way flap-valve ("baffle"??) before the ducts come together at the T or Y junction?
John Forbes
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Will you ever run both together ?
If they're only ever used in isolation, then just use two backdraft shutters, one between each fan and the Y or T.
If they're used together, then run two separate ducts (which isn't that hard, especially with rectangular duct - most of the work is always in making the holes. If you try to join the two ducts with the T, then unless the flow is perfectly balanced (strictly the pressure) one of the fans will provide minimal flow or may even reverse. If you can arrange identical ducting, then you might get away with it.
Again, if there's a risk of the wind causing a pressure difference across the two rooms, fit backdraft filters. You'll also need the filters if one fan will be run on its own.
A better option is to use one fan on the shared duct and put the T on the inlet side. Use an adjustable grille (or the pipe length and diameter) to balance the flow as needed. Use a pair of backdraft shutters again, if there's any chance of wind-blown drafts between the two rooms.
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Its also a strange fact that best flow is from anrrow inlet, big ehaust, so I'd want to have a BIG pipe after the Y, and as others have said, run one fan off either switch. Probly need a relay.
I'd suse a big fan big pipe and twin smaller diameter inlets to it.
....
No I wouldn't. I'd take it on the chin and use two setups. :-)
In teh ned, its easier.
Andy Dingley wrote:

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