Bathroom extractors - advice

[John - plumber]

Hi

I have installed one inline extractor fan above a first floor bathroom shower. The unit is in the loft. It is not as strong as I would like and want to know whether I could add a second incline fan to increase the suction either using a couple of Y connectors (so both fans are sucking the air from the single bathroom vent and then out to the single vent in the roof) or either I can add them one after the other (the run of ducting is less than 3 metres). Would I need any non-return values? Any advice would be welcomed.

 

[JohnD]

What model of fan did you use, and what is its nominal throughput in cubic metres per hour?

 

[John - plumber]

MANROSE MF100T - the extraction rate is c. 240cm3 per min. It is quite a high ceiling hence the reason why I would like to add another fan to the system to increase the draw.

 

[ree]

No, definitely not. Use only one extractor in a bathroom or any other room. Thats my strong opinion FWIW.

You could boost up with a more poweful extractor - hopefully, you dont have a combined light & extractor unit - get rid of it if you do.

Is the present ducting flexi or rigid? Rigid is best by far.

 

[JohnD]

240cu.m is usually plenty for a bathroom, unless perhaps it is a dual-speed fan accidentally left at half-speed, or the duct or grilles are restrictive. Rigid duct is better than the convoluted hose.

Is it a very big bathroom with a big shower? Some photos might spark off ideas.

You can buy an even more powerful ducted fan, though it will cost more. Some will need bigger ducts. The extract grille should be in the ceiling above the shower, as water vapour rises.

You do also need a gap under the bathroom door to allow dry air in to replace what is sucked out.

 

[Deleted 224857]

MANROSE MF100T - the extraction rate is c. 240cm3 per min. It is quite a high ceiling hence the reason why I would like to add another fan to the system to increase the draw.

That is quite a powerful fan.I have same.How big is your bathroom and where is it located.

 

[John - plumber]

The bathroom is probably 4m x 4m but the ceilings are pretty high (the vent is directly above the shower head). I don't really want to ditch the existing fan and replace it with a more powerful one as a do have a second MANROSE MF100T which is currently spare. Therefore, I would like to link them both to the vent in the bathroom and double the extraction rate. Is there any reason why having the two fans connected to the same vent in the bathroom (using a Y connector) would not work? I would then take the two outlet ducts from the fans and connect them into one duct (using a Y connector) going to the one vent in the roof.

 

[JohnD]

still don't understand why that powerful fan is not sufficient for your needs.

Just to check:
Is it running at full speed?
Are grilles unobstructed?
Is there a gap under the bathroom door?
Is the bathroom heated to normal room temperature?
Is the window shut?
How long does the fan run after the shower is finished?
What are the symptoms of the fan being inadequate?

 

[John - plumber]

Thanks John

To answer:

Yes - at full speed
Clear as far as I can tell
There is a gap under the door
Normal room temp
We normally have the window open
We normally leave the fan on for a 10 mins or so after shower
There is a significant build up of condensation on the walls - paint has started to run down.

 

[theprinceofdarkness]

Air ducting should be smooth inside with no sharp transitions or bends (or 'orrible little grills!). Unfortunately Manrose does not really make any of this. Their 4" white plastic pipe is OK, but is only 2' long without any couplers available. Oh and their timers do not run for long enough for a shower.
Domestic ventilation fans are not good at coping with any incoming drafts from the wind and sucking. So its better to put them as close to the inlet grill so they push the air through the ducting, rather then at the far end so they have to suck the air through the ducting.
To answer your question I would put the second fan inline with the first and as close to the inlet grill as is convenient.
Frank

 

[JohnD]

if you shut the window, the fan will be more effective. With the window open, there is a risk that fresh air will come in through the window and be sucked straight out by the fan. Having the door and window shut causes the dry air from under the door to lie under the steamy air, which rises towards the ceiling and the extractor, it really does stratify.

The "T" model has a timer, so try adjusting it upwards. I think the max run-on is 20 minutes. If you set it to come on with the light switch, the fan will keep the bathroom generally fresher and drier, because it will run more often. It is pretty quiet and running cost is tiny.

 

[John - plumber]

Thanks the prince of darkness. When you say put the second fan inline do you mean one after each other (so you have inlet grill, ducting, fan, ducting, fan, ducting, outlet grill) or have them both connected to the inlet grill with a Y connector? - Thanks

 

[cAtLeYx]

How far up the roof is the vent, this should be as close to the ridge as possible to ensure that the duct terminal is in the negative pressure region above the roof. Additional fans will only be as efficient as the diameter of the existing extract duct.