air extracter problem

[John]

We have two extractors going to a flat roof vent. Both rooms lack a external wall hence the system. There is an extractor in a shower room, then a T-junction I thought damers were to be fitted but there arn't any.. The ventilation then goes to an inline extractor, controlled by the shower room vent.

There is little air coming out at the flat roof but a great deal of kitchen extraction going into the shower room. There is no difference whether the shower room vent is on or no, is over whelmed by the hob extractor.

My feeling is the electrician should have fitted the inline extractor between the T-junction and the shower room not between the junction (where it is could be restriction the airflow) and roof vent with dampers befor both showere and hob extracter's.

I have told them to come back to sort it out but would be grateful of ideas of what they should be doing to sort it out.

[John]

Strike me the problem isnt electrical, but aerodynamic! If both vents have fans at the room end, and the back pressure between the shower roon and the external vent is higher than that in the shower room fan, then the kitchen extract will come into the shower instead.

You could change the system to have an exhaust fan at the roof end? but i would be careful about that. Might be simpler to have two roof vents.

My experience is that the small fans sold for bathrooms are pathetic.

And by the way, has the kitchen extractor got a grease trap?

Good luck anyway with this.

Another John

[marvelus]

Thats what hes got already with the inline fan

Probably

vent axias are good.

[John]

There is a small bathroom fan as well, but the iline one is fitted batwwn th=is and the roof vent with the hob extracter beteen them. Clearly the in line one must be moved to befor the hob extracter with one way vents in front of both to stop back venting?

We looked into 2 but t couudn'tbe done.

[marvelus]

Vent Axia bathroom fans have a shutter on that closes when not in use that would block most air from entering the bathroom via the fan eg:

I think that, without the inline fan, might work better than what you have now.

You said in the 1st post that there was little air coming out at the flat roof vent, is this even when the inline fan is working?

The problem I still see is the bathroom might start venting at the cooker hood if that route gave less resistance than the flat roof vent.