2 extractor fans, one outlet pipe

[pilsbury]

Some way off, but mulling this over. I will have a downstairs bog and utility room adjacent to each other. Both these have a wall shared with the garage. I was going to run the extractor fan pipe work for both in the garage to an outside wall.

To save 2 of those flappy vent things on the outside wall, I was going to join both extractor pipes into one to outlet vent.

But I don’t want the bog smells being blown into the utility instead of out the vent.

How could I work this, or am I asking for anyone using the utility room to get the full force of something unpleasant.

 

[endecotp]

Search for "back draught shutter" or similar.

You could also consider a single inline fan, downstream of where the two ducts join. Not sure how easily you could wire that up.

 

[John D v2.0]

That isn't going to go well even with a shutter! They are mostly to stop draughts from outside. Unless you've no sense of smell.
One dodgy way round it would be to extract from the utility into the toilet at low rate and toilet to outside at high rate. Or extract from both with a single fan as above.
Wiring to make it come on with either light you would need two double pole switches if you can get hold of them, or relays.

 

[noseall]

Don't attempt it. Just go for two holes, its simpler. We duct a lot of our fans through the roof.

 

[pilsbury]

Hmmm, sounds like 2 vent outlets might be a safe option.

 

[rssteve]

Also if running through the garage you will need to box it in fire board or use metal duct work.