Selv fan not enough

[johnashby]

Fitted a selv fan for a customer who has a tiny bathroom but it's not clearly any steam at all. It's well ducked outside and the fan runs fine.
Is there anything I can try to help him?
I understand natural air flow might help from even the bathroom door being slightly open but there must be a better way for circulation?

 

[Richard-the-Ninth]

Hold a piece of toilet paper to the fan, will it hold it? (If not the fan is going the wrong way or the vent/pipe is blocked, don't forget to look outside, check any grille is not covered in lint.)

A lot of people don't realise that a bathroom fan can only suck out so much air, it can not create a vacuum. (Some forget that) in which case as you said, make sure when in use the bathroom door is open slightly and or there is at least 15mm gap under the door

 

[binky]

Some fans can be set for high or low speeds, might be worth a quick read if the instructions, like I always do...

 

[kerching]

Open bathroom door
Switch on fan
Hold calibrated bog paper against fan
If it sticks then shut the door. If it then falls off it’s a makeup air/vacuum issue
The rest is by extrapolation of previous data

 

[Murdoch]

Is the gap under the door 6 mm minimum?

How long is the duct run?

 

[SPECIAL LOCATION]

Fitted a selv fan for a customer who has a tiny bathroom but it's not clearly any steam at all. It's well ducked outside and the fan runs fine.
Is there anything I can try to help him?
I understand natural air flow might help from even the bathroom door being slightly open but there must be a better way for circulation?

From my experience there are four typically issues;
(1) Fan not strong enough.
(2) Duct too long.
(3) Unable to allow equivalent amount of air into the room at the same rate that you are trying to extract.
(4) Fan not running for a long enough duration after the room has been used. (building regs recommend 15mins run-on for bathrooms without an opening window.)

When you say "well ducted", Do you mean its a longer run through a loft void rather than just a core-drill hole through the wall?
Most axial fans are only sufficient for a direct through the wall sort of duct length, e.g. less than 500mm long.

For longer duct runs you generally need a centrifugal fan that can push air further. (same principal as trying to blow through a drinking straw -vs- blowing through a hose pipe. need more force!)

Have a look at the spec of the fan for what rate of volume of air it can move..
Decent centrifugal fans can move double or triple the volume of cheaper axial fans.

Sufficient air flow is not optional, it is essential. otherwise the air will not move..
(Just as if one end of a drinking straw is partially blocked it will restrict or stop any flow).

Consider a 100mm vent-duct area is 7855 square mm, (or 78sqr cm)..
A 760mm door would need 10.3mm gap at the bottom to allow the same amount of air movement.

Also thick pile carpets on the outside of the door will also restrict air flow when the door is shut.

 

[UNG]

I always find that quick read of the fans spec is a good start, the m³/hr they will move can be really poor on some fans especially the so called "quiet" ones throw in a longish duct and / or a lack of air replacement and the end result is a poorly ventilated bathroom

 

[johnashby]

I always find that quick read of the fans spec is a good start, the m³/hr they will move can be really poor on some fans especially the so called "quiet" ones throw in a longish duct and / or a lack of air replacement and the end result is a poorly ventilated bathroom

Thanks for the solid advice, this fan has no speed control only time period setting once switched off.
I think it's the lack of natural ventilation the duct is short and it's straight goes through plasterboard and 1 brick outdoors.

 

[Murdoch]

Thanks for the solid advice, this fan has no speed control only time period setting once switched off.
I think it's the lack of natural ventilation the duct is short and it's straight goes through plasterboard and 1 brick outdoors.

I would recommend you shorten the door to improve airflow

 

[UNG]

I would recommend you shorten the door to improve airflow

Or install an air vent into the door

 

[tommytank]

The main criterion of a fan is to remove the humid air after a shower. this can take up to 15 minuets. if you want to remove the steam out of the bathroom as you are showering you would need a fan the size of a jet engine.