Two inline fans, one vent to outside...

[theflyingpig]

I've got two inline fans extracting from two bathrooms. They share a roof vent. I've put non returns into the pipe work between each fan and the Tee.... But, what's gonna happen if both fans run simultaneously??

Both fans will be on manual pull switches. Is there a way of wiring these to prevent both being able to run simultaneously?

Thanks

 

[Harry Bloomfield]

I've got two inline fans extracting from two bathrooms. They share a roof vent. I've put non returns into the pipe work between each fan and the Tee.... But, what's gonna happen if both fans run simultaneously??

Assuming they are a similar power, both non returns will open and both will share the roof vent. A Y will be better than a T.

 

[Jon c]

If both are running they will both be less effective than with only one running, you can only get a certain volume of air through a 100mm vent hole (assuming the roof vent is a 100mm vent)! Also I would imagine the fan motors would be stressed more as they effectively would have a restriction in the outwards flow. If not possible to put another roof vent in, it might be a better option to use one fan with a Y piece for both bathrooms, so it would come on when either pull switch is used.

 

[Harry Bloomfield]

If not possible to put another roof vent in, it might be a better option to use one fan with a Y piece for both bathrooms, so it would come on when either pull switch is used.

That would cut the extraction by half, to each room, a poorer solution than the two fans, which will only conflict in being both on, sometimes.

 

[Jon c]

That would cut the extraction by half, to each room, a poorer solution than the two fans, which will only conflict in being both on, sometimes.

Thats a fair point but I would imagine a powerful inline unit would be more than sufficient. The way I see it unless the two fans have a very similar length of ducting to the Y point, (assuming they have the same airflow l/s in the first place) one will overpower the other and cause problems. Even then both will struggle. Having the Y point right at the exterior vent would help with this, still a non ideal setup. Also I have seen the 'non return valves' mentioned, they really aren't airtight so you'd still get potentially unwanted air transfer between bathrooms. I realise neither is really an ideal solution but there's only so much you can do sometimes

 

[brig001]

Buy or borrow an anemometer. I got this one and just held it at the inlet of each fan with one on, other on and both on. In my case with rigid ducting and a Y piece, there was only a slight reduction when both were running

Brian

https://www.amazon.co.uk/gp/aw/d/B0876SNWW4?psc=1&ref=ppx_pop_mob_b_asin_title

 

[jj4091]

Simple way to check airflow would be to hold a sheet of A4 paper over the input of each fan & see if there is a change in vacuum as each fan is switched on.

 

[robinbanks]

No need for an anemometer if a crude "is there blow-through from another fan" is all that is required; Run one fan and place a lit candle next to the other, blow out the candle and watch the smoke movement

Personally I don't think there will be an issue if the external vent cover isn't particularly restrictive. Don't worry about motors getting stressed if they're both running; it's less blowback than they'd experience on a windy day

 

[brig001]

Incense sticks are good too, but I wanted to buy an anemometer