Bathroom extractor fan advice needed

4 May 2012
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United Kingdom
Hi All,
I have a problem with mold in my bathroom and want to install an extractor fan to remove excess moisture.

My household has 3 young adults, 2 middle aged adults and one child together with one main bathroom and an en-suite in the master bedroom.

As you can imagine, having younger adults, the main bathroom is in constant use, showering, bathing, grooming and general preening. Whilst this is all good, there is no ventilation apart from a small window. The main bathroom is small measuring approx 1.8m wide x 1.8m deep and 2.4m high.

The high use and lack of ventilation has led to a constant battle with mold despite using Zinsiser Perma White anti mold paint.

My next approach is to install an in-line extractor fan in the loft and vent the exhaust out via a 100mm hole drilled in the wall. I have already purchased an inline mixed flow fan with 100mm inlet size and switched timer. This fan has a variable run on time up to 20mins and an extraction rate of either 160 or 240 cubic meter per hour.

I have a couple of questions which I hope others can help answer as follows:-
- What is the best location for the extraction vent in the bathroom? I understand the best position is in the ceiling over the bath/shower furthest from the fresh air inlet. However the house has a very shallow pitched roof which makes access to the area above the bath/shower tricky. As an an alternative, can I mount the extraction vent high up on the bathroom wall? This position will lead to a much shorter route to the in-line fan (1m vs 2.5m), but the inlet will be nearer the fresh air inlet, possibly leading to less moisture extraction. Will the high extraction rates of the inline-fan overcome this problem?
- Do I need to use insulated ducting or is standard PVC ducting OK? As mentioned the in-line fan and ducting will be in the loft directly above the bathroom and landing. I could cover the ducting with fiberglass loft insulation to protect it from condensation.

For safety I will be using an electrician to wire in the fan and its switched live timer circuit.

All info welcome.
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How come you're not going out through wall.

Insulated ducting isn't important, but as moisture will collect in the pvc ducting, and that type of ducting slow the air flow down, you want to get aluminium ducting from wickes that can be angles downwards slightly, and will take any moisture that collects to the outside. I think that on that size room, positioning isn't so desperate, but get it as close to the furthest point as you can.
How come you're not going out through wall.

Sorry for not being clear, I will try and explain a bit better.

I am going out through an external wall, however as the bathroom is directly above a conservatory I cant get access from outside for a core drill.
Instead the plan for the external vent is slightly to the side of the bathroom where I can stand on a flat roof extension and drill the hole. The vent hole then goes into an airing cupboard adjacent to the bathroom.

From the airing cupboard I have 2 choices:-
  • A) I could create an extractor vent hole directly in the wall between the cupboard and bathroom, this is the easiest and shortest route.
  • B) I could go further and make the extractor hole in the bathroom ceiling. As mentioned this is more tricky due to poor access in the loft.
The shortest route is option A) above needing about 1.5 m of ducting and option B) needs about 3m of ducting. In both cases the inline fan will be mounted somewhere in the middle of the ducting.

My worry is that with option A) the extractor vent is not in the optimal position but would the shorter run of ducting and power of the in-line fan overcome this?
Best position is opposite side of room to door, 300mm in from a corner or wall. You don't need to insulate the duct as the fan will be extracting any condensation within it.

It should be wired to the light with a 15 minute overrun, or to a humidistat.
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Either option will be fine. It doesn't need to be in the loft, but an inline fan is more deigned for a long run, not a short one, so if it's only a metre going though the cupboard, then you may strugle to get an inline fan into that run. If you made the run through the cupboard as smooth as possible with aluminium ducting, then I'd use a normal wall mounted fan rather than an inline one. Remember to mae sure you have a fall on the ducting whichever route you use.
A wall fan, unless low voltage, has to be positioned according to electrical zones in a bathroom.

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