Bathroom condensation - extractor fan calculation

[Graham.mead]

Howdo,

Just a quick question about fans!

I've been plagued with condensation problems from my bathroom mainly due to vapour from the batch condensing on the windows and outside facing wall.

I'm trying to work out what volume extraction rate fan I should install in the bathroom. I know that you should calculate the volume of the room and then multiply this by the number of air changes per hour to get a throughput rate.

My main problem is that some sites say 3 per hour whilst others e.g

talk about 20 per hour!! This obviously has a sevenfold impact on how many cubic metres per hour is required and hence the fan.

What do you guys/gals out there recommend

TIA Graham

[fred]

In article , [e-mail] writes

Scottish regs say: Bathroom or shower-room (with or without a WC): mechanical extraction capable of 15 litres/sec (intermittent)

English: Mechanical extract ventilation capable of extracting at a rate not less than

15 l/sec which may be operated intermittently or PSV. Rapid ventilation by opening window.

With no mention of air changes.

My own is crap (replacement awaits bathroom refurb) but I do have it on a one hour delay which is adequate.

Does that help?

[kdband]

Just happen to have a copy of the approved plans for my extension to hand and they specify :-

"Install mechanical ventilation to bathroom & wc to extract at a min rate of 15l/s switched with light & with min 15 minutes overrun."

The latter is the bit I know I'm going to hate when someone uses the loo in the middle of the night and a noisy fan kicks in for 15 minutes. Anybody know whether there is such a thing as a silent fan ? Any noise seems loud at 3am!

[G.W. Walker]

Can you fit a switched supply to the fan so that it can be overridden at night..?

[Tim Morley]

I use a vent-axia 4" fan with a humidistat built in (great as kids used to forget to put fan on if having a shower plus did not want coming on in middle of night with lights), plus a pull switch (momentery) on the ceiling for those scary Sunday morning moments after a curry!

[fred]

In article , G.W. Walker writes

That should work, better still a timed supply to the fan, off at midnight, on at 7?

[Mike]

On this great day..4 May 2005 08:55:15 -0700, [e-mail] wrote:

>

[Lobster]

On first reading of that I thought you were referring to your own personal criteria for assessing the required power of fan for your bathroom...

David

[Dave]

[e-mail] wrote: ... snipped

I've used 2 pull cords: one operates the room downlighters, the other operates the fan and the shower light. It's quite pleasant to have just the shower light on when having a shower; the main lights are on a dimmer outside (above) the door so it can be turned down before turning on the lights in the middle of the night; the separate pull switches avoid the annoying "fan in the night" syndrome. It also means you don't need all the lights on for a shower during daylight.

Dave S

[Martin Angove]

Install a fan with a humidity sensor and ignore the "switched live" input. Set the sensor correctly and it'll come on a few minutes after you start to run a bath and go off when the room is sufficiently aired. It will not come on in the middle of the night when someone goes to the loo. As for noise, some manufactures are better than others and I believe the group's opinion is that duct-mounted fans are better in this respect than the hole-in-the-wall type.

They're a fraction more expensive than simple timed models and need to be mounted as high up as possible. They can also be a problem when there is very high humidity generally, such as you might get before a Summer thunderstorm, but they are usually easily adjustable. So long as there's a good seal around the fan and the duct and there is no air "short circuit" you should be ok.

Having had both sorts I'd never now fit anything else in a bathroom. The question that then needs asking is whether the ventilation is required simply for use of the loo. My understanding was that it was required to control humidity and for no other reason.

Hwyl!

M.

[Martin Angove]

Aah, I've done something similar and all my mates think I'm daft. At last I can tell them I'm not the only one!

We have 5*50W halogens in the bathroom which I have run from two transformers. Inside the bathroom is a standard pullcord, outside the bathroom is a light switch. With the outside switch "off" (it looks like it's off but is actually wired L2 so is on) the pullcord turns all the downlighters on or off. With the outside switch "on" (see above) only the two lights above the sink and the loo work. Brilliant in the middle of the night as there's still enough light to read by, but you aren't blinded.

Night blindness is a problem in our house due to large piles of things about the place. Often toys, but also bits of old computer or 3-year-old magazines :-)

Hwyl!

M.

[Martyn Pollard]

I'm in the market for a bathroom extractor fan and wonder if its worth paying a bit extra and getting a heat recovery unit. BES sell a baxi ec25h @ =A3188.30(13687) that has a built in humidity sensor. A bit of googling reveals there is another model EC25P which has a PIR to start the fan.

Its probably one of those novelty factor devices that has an very long, if ever payback period.

[Martin Angove]

It really depends on your heating strategy I suppose, it'll probably only make a real difference if you have a highly insulated, draght-proofed house. Having said that, don't forget that a mid-quality

4" humidity fan is going to be £30 or £40 anyway, so £190 doesn't seem quite so bad (effectively £160).

I considered one not because of the cost-saving, but because I hate draughts in the bathroom. The one thing such a device *should* do is eliminate draughts, or at least make them less noticeable, because there is no "through flow" of air from, for example, under the bathroom door to the extractor. Instead the air enters and exits at the hole in the wall and is warmed to boot.

Apart from the cost (we were seriously short of cash at the time) the main thing that put me off was that the smallest units are 6" IIRC, and I had enough trouble core-drilling 4"! I hired a Hilti and did four 4" holes in one day, three of them through the original house walls of brick-brick-concrete render. It was a mighty undertaking.

Hwyl!

M.

[TheScullster]

Graham

Did all this last year and would suggest:

Get Vent Axia fan calculator brochure. This alerts you to other important considerations not just those to do with Vent Axia products. E.g. the easiest way in the world to duct a fan is with crinkly hose, but, check how much this de-rates the fan based on hose length, numbers of bends etc. If you look at the cheapo shed packaged items (fan and hose, maybe light as well) you will see that the fan is rated at a reasonable throughput in free air, but drops to perhaps half this if the full length of supplied hose is used! Rigid duct is therefore recommended - plastic or galvanised.

Decide on number of air changes - plenty of suggestions for this already I see.

Consider best position for vapour outlet - near toilet/shower/bath and best position for discharge to outside.

Look at duct route through ceiling and establish length of straight and number of bends.

Check with Vent Axia brochure what effect this will have on fan performance for a given fan/duct combination.

Adjust duct and fan size to give throughput acceptable to you.

I still think there is some mileage in paying premium for Xpelair or Vent Axia stuff. Other users claimed decent life expectancy for these last year, when I did mine. Would hate to go to all the trouble and have to replace the fan unit after 1-2 years.

Consider mounting fan on absorbent pads to minimise hum and putting flexible connections either side of fan.

Once happy with fan and duct arrangement, consider controls - timer, humidistat, switching etc to suit.

HTH

Phil

[John Stumbles]

Sometimes it would be nice to have it come on after someone has used the loo. The problem is how to control it. Any suggestions? (Hint: this is a splendid opportunity for the wags in this group to make hilarious quips about motion sensors :-)

[John Stumbles]

Is that a momentary version of a 'standard' sort of ceiling-mounted bathroom light pull switch? If so, where did you get it?

[Owain]

[bigcat]

galvanised.

performance

I hate bathroom fans. If you dont have a window and must have one,

1. pick a large low speed unit, 9" or 12" rather than 6". This will reduce noise.
2. forget 4"ers, theyre just a waste of time.
3. Use rubber washers at every mounting point you can to reduce noise.

It seems silly to use noisy annoying energy consuming fans when nature will do the airshifting for you.

1. if you have a window, use it! Fit a lock that allows you to lock it securely a half inch open. Silent, zero energy.
2. If no window, fit 2 tubes not 1, have the outlet ends pointing opposite directions. No fan needed. It is fair to say you either need larger ducting, or else to have them open for longer since the flow rate is lower.

A humidistatic dehumidifier will avoid you throwing all that heat out, and dehumidifes the whole house. And enables you to dump the tumble dryer too.

NT

[Martin Angove]

A PIR wouldn't be difficult to wire up, but then you're back to the problem of it coming on every time someone used the bathroom. A Methane sensor would be fun, but probably impractical.

Try Owain's suggestion instead (somewhere else in this thread) of a momentary action pull-switch in the bathroom, or if that doesn't suit, a momentary action rocker switch or similar outside the bathroom.

The humidistat fans I've fitted all also have the switched-live input and a timer so they can be used in this way with no modification.

Hwyl!

M.

[Huge]

Float switch in the cistern?

Microswitch on the loo roll holder?

Timer on the light? (If you're in there more than 'n' minutes, it's probably a #2, therefore run the fan for 'y' minutes).

Sounds like a good project for a Third Year Undergraduate Electronics course (or more likely these days, a PhD.)