New extractor fan not very effective

[cornflakegirl]

We're redoing our bathroom and have had an extractor fan / light fitted above the shower. It doesn't seem to be doing very much - the windows and mirror are still getting misted up during a 5 minute shower in the way that they did before it was fitted. We have done the test with a square of toilet paper, and it stayed up. The flow rate is supposed to be 23l/s, so well above the minimum requirement.

Are we just expecting too much? I think we're going to have to keep having the window open while we shower to clear the steam - is that normal?

We have the extractor fan in the light above the shower and there is still a certain amount of steaming up going on on the mirror. Ours is a good one when I put a bit of toilet paper near it it gets sucked up out of my hand.

I said this to dh as I thought every bit of steam would whirl up into the extractor but he said it was ok.

Yeah, I expected some steam, and that the extractor would clear that as it continues to run. But I couldn't see any difference from the amount we got with no extractor!

Get a heated mirror so it doesn't steam up and just leave the fan on for a bit to clear steam afterwards if you want it clear, or open the window if you wanted to be more green about it

Yeah, opening the window is fine as a workaround - it worked well before - but I'm a bit cheesed off to have paid to have a fan installed and for it not to make any noticeable difference! We've got the installer coming back to check whether they're working properly, but if he just does the paper test and says they're fine, then I want to have some idea of whether I'm being fobbed off.

The fan is just to stop things getting mouldy not to keep the air clear all the time. As the volume of steamy air produced by a shower is probably a strong breeze you wouldn't want around you during a shower.
The fan should run on for a while after a shower to clear out any raised humidity.
The walls and ceiling should meet a certain level of insulation to prevent mould forming in the presence of normal levels of heating and ventilation

I measured our bathroom, and it's around 13 cubic metres - so 13,000 litres. At 23l/s it should clear in around 10 minutes, but it took around 30 minutes to clear after my normal length shower this morning. (Mirror and windows were steamed up, but room wasn't particularly steamy. I wiped down the walls of the shower and the window.)

I'm wondering if the issue is the configuration of the room. The shower is next to the door, so maybe the airflow just goes from the door to the fan, and doesn't circulate enough in the rest of the room?

show us a pic, please. Some fans are very ineffectual.

Where does it vent to? Out of a hole in the wall? Through a duct? Does it go via the loft? How long is the duct?

23 litres per second is about 80 cubic metres per hour (the way I usually measure it) which is typical of a small 100mm diameter fan, but insufficient for a room that has steamy showers.

It's the size I'd use in a WC or a bathroom with no shower. Just about enough in a warm, well-insulated bathroom when you have a bath if it runs from the time you enter (before turning the taps on) to the time you leave (after emptying the bath, brushing your teeth and cutting your toenails) but preferably with a run-on timer.

It's a Xpelair Airline ALL100T

It vents through probably 2m of duct (length of the bathroom) to a hole in the outside wall. The duct joins with the duct from the adjacent (currently being installed) shower room at the vent.

I was wondering if it was just too underpowered. But the electrician just tells us that it's well above the 15l/s minimum.

I can't see that exact model. Is it like www.xpelair.co.uk/product/airline-100t-inline-extract-fan

You say "The duct joins with the duct from the adjacent (currently being installed) shower room at the vent."

Can you photograph or draw this please? Maybe the duct is not free-flowing. Have a look to see if it blows outside the house through its grille. On a cold day you should be able to see steam from the shower in the cold air.

If you are ducting two rooms through one duct you may do better with a more powerful one.

Does the duct run in the loft?

I see it is rated at 85 cu.m/hr in free air, which IMO is too low for a shower room (and 40dbA for noise).

We'll have a think about the duct layout, but I would go for something like this which has twice the power, and a noise level of only 24dB(A). it is a better quality one with a ball-bearing motor, and, being 100mm diameter, will fit your existing ducting, and designed to go in the loft or similar position. For minimum noise, mount it on a board isolated from the loft timbers with a piece of rubber mat or carpet underlay.

Or www.tlc-direct.co.uk/Products/SLTD250T.html this or this extra-quiet oneat three times the power.

Sadly, they are more expensive than the one you've got, but if your existing one is unsatisfactory, I think you should consider them.

try this calculator

www.tlc-direct.co.uk/Technical/Ventilation/Ventilation4.html

and see if it helps

The building regulations figures are IMO far too small.

Thank you. Will take a look and reply later.

The calculator seems to be working on the assumption that all the air needs to be processed in 3 mins. Is that a usual assumption? It feels fast.

I think it's this one - has the light inbuilt.
[https://www.xpelair.co.uk/product/airline-led-100t-inline-extract-fan]

Sorry, clearly forgotten how to do clicky links.

Left hand side is for current bathroom, right for new bathroom, vent to outside far middle.

That layout makes the duct much longer. Presumably there are non-return valves in the flexible ducts, otherwise steam would blow from one room into the other.

Do the ducts poke out under the eaves? Or through a special roof tile?

Yeah, I was surprised by the layout. We're guessing it's for convenience of being able to attach the fan motors to beams whilst still having headspace to work.

Valves aren't in place yet but will be.

Duct comes out of a hole in the outside wall, having come back down through the ceiling near the soil stack.

it might be that the length of the ducting is obstructing the flow. Length and bends reduce the flow. It's worse with a weedy fan, which I think yours is.

If you know an experienced plumber, see if he will run the duct more neatly for you in rigid pipe (it is almost the same as soil pipe, so easy for a plumber) which catches less dust and fluff and is much smoother than convoluted hose and runs in straight lines.

I would have lifted all the insiulation out of the way while working, and perhaps laid new when finished. Your loft is not very neat. The old yellow fibreglass sheds irritant dust and fibres, which are a great problem for me. New stuff treated with Ecose is brown, and does not shed.

Thanks PigletJohn, we'll look into that.