PIV unit in a 27sqm flat overkill?

ic

It looks like your bathroom doesn't have an external wall - is the extractor fan ceiling mounted, and do you know where its venting to?  Nearly always developers install cheap axial fans to get a tick from building control - however they're not always appropriate and are just inefficient under-powered noise makers.  If your fan is trying to push air along a pipe of a couple of metres or more to one of the outside walls, which might also then have a vent cover that has flaps to prevent back draught blocking the flow, it probably isn't up to the job and is failing to actually extract anything.  You should look into a centrifugal fan - these are designed to push air a long way (whereas axial fans can really only deal with a short run, say through the immediate wall). 

You can get models that fit on the wall or ceiling in the room, or an inline model that can be installed in the loft space (with the benefit of reducing the noise you hear).  These are larger than axial models, but have way more umph to shift air the distance.  As already recommended you should also get a model with humidistat so that it runs on higher power whilst the room is damp, before dropping to a trickle vent speed the rest of the time.

Example: https://www.screwfix.com/p/vent-axia-427479-100mm-4-centrifugal-bathroom-extractor-fan-with-humidistat-timer-white-240v/81214

hang3r

Grenage said:

What temperature do you keep the flat?

I heat it up to 18-20C when I'm in (mostly a few hours in the morning and late evening). For the night and during the day the heating is off, so temperature drops to 11-14C.

Emmia said:

If you replace your bathroom fan, get one with a humidistat which will turn the fan on if the moisture level goes over a certain point - I'd actually try this before a dehumidifier or the PIV.

Incidentally is the loft space demised to your flat? If it isn't you shouldn't be putting things up there like PIVs

Makes sense to start with the bathroom. Though, so far I haven't dried any washed clothes. Once I do, the bathroom fan is unlikely to help the flat to stay dry. There isn't really space to dry them in the bathroom.

I believe the lease mentions that you can use it as long as you don't make any structural changes. I can see the previous tenant put up some boards on the joists, stored some knick-knacks and even installed a small shelf.

ThisIsWeird said:

Then look at your temp control. I presume you have heating at normal, comfy levels during 'living' times? And then what overnight and when you are out? I presumed turned down or even off? How well insulated is your flat - how quickly does it respond to a heat demand? What type of CH system is it?

How many of you are in the flat? I ask 'cos you'll need their general agreement for the following...

Two ways - ventilate it away as described above, or buy a dehumidifier. But who the heck wants a dehumidifier if it ain't actually needed?

Yep 18-20C when I'm in, and switch the heating off when I'm away or sleeping which can drop to 11-14C. Double glazed windows, ceiling has insulation above it in the loft, external walls are plasterboard with cavity to wood and then brick on outside. Electric heating only, so a 1.6kw oil-filled electric radiator mounted under bedroom window.

Just myself in the flat.

A dehumidifier seems preferable compared to what you described about keeping windows open. Seems less hassle, and a dehumidifier is cheaper to run than an electric radiator for reheating the room after having windows open all day.

ic said:

It looks like your bathroom doesn't have an external wall - is the extractor fan ceiling mounted, and do you know where its venting to?  Nearly always developers install cheap axial fans to get a tick from building control - however they're not always appropriate and are just inefficient under-powered noise makers.  If your fan is trying to push air along a pipe of a couple of metres or more to one of the outside walls, which might also then have a vent cover that has flaps to prevent back draught blocking the flow, it probably isn't up to the job and is failing to actually extract anything.  You should look into a centrifugal fan - these are designed to push air a long way (whereas axial fans can really only deal with a short run, say through the immediate wall). 

One of the bathroom walls is external, but the fan is mounted on a different wall (close to the ceiling). I had a quick look in the loft a few days ago, and I could see there was some ducting coming out where the fan is likely to be located and it appears to be connecting first to some kind of 'Y' splitter (which I believe has an unused connection closed off) and then more ducting leading to the edge of the loft. Will need to get a bit closer next time.

ThisIsWeird

hang3r said:

Grenage said:

What temperature do you keep the flat?

I heat it up to 18-20C when I'm in (mostly a few hours in the morning and late evening). For the night and during the day the heating is off, so temperature drops to 11-14C.

Emmia said:

If you replace your bathroom fan, get one with a humidistat which will turn the fan on if the moisture level goes over a certain point - I'd actually try this before a dehumidifier or the PIV.

Incidentally is the loft space demised to your flat? If it isn't you shouldn't be putting things up there like PIVs

Makes sense to start with the bathroom. Though, so far I haven't dried any washed clothes. Once I do, the bathroom fan is unlikely to help the flat to stay dry. There isn't really space to dry them in the bathroom.

I believe the lease mentions that you can use it as long as you don't make any structural changes. I can see the previous tenant put up some boards on the joists, stored some knick-knacks and even installed a small shelf.

ThisIsWeird said:

Then look at your temp control. I presume you have heating at normal, comfy levels during 'living' times? And then what overnight and when you are out? I presumed turned down or even off? How well insulated is your flat - how quickly does it respond to a heat demand? What type of CH system is it?

How many of you are in the flat? I ask 'cos you'll need their general agreement for the following...

Two ways - ventilate it away as described above, or buy a dehumidifier. But who the heck wants a dehumidifier if it ain't actually needed?

Yep 18-20C when I'm in, and switch the heating off when I'm away or sleeping which can drop to 11-14C. Double glazed windows, ceiling has insulation above it in the loft, external walls are plasterboard with cavity to wood and then brick on outside. Electric heating only, so a 1.6kw oil-filled electric radiator mounted under bedroom window.

Just myself in the flat.

A dehumidifier seems preferable compared to what you described about keeping windows open. Seems less hassle, and a dehumidifier is cheaper to run than an electric radiator for reheating the room after having windows open all day.

ic said:

It looks like your bathroom doesn't have an external wall - is the extractor fan ceiling mounted, and do you know where its venting to?  Nearly always developers install cheap axial fans to get a tick from building control - however they're not always appropriate and are just inefficient under-powered noise makers.  If your fan is trying to push air along a pipe of a couple of metres or more to one of the outside walls, which might also then have a vent cover that has flaps to prevent back draught blocking the flow, it probably isn't up to the job and is failing to actually extract anything.  You should look into a centrifugal fan - these are designed to push air a long way (whereas axial fans can really only deal with a short run, say through the immediate wall). 

One of the bathroom walls is external, but the fan is mounted on a different wall (close to the ceiling). I had a quick look in the loft a few days ago, and I could see there was some ducting coming out where the fan is likely to be located and it appears to be connecting first to some kind of 'Y' splitter (which I believe has an unused connection closed off) and then more ducting leading to the edge of the loft. Will need to get a bit closer next time.

If your flat is well insulated, as it appears to be, then it won't struggle to bring the temp up as and when required - you've already said you turn the heating off overnight and when not in use, so I'm only suggesting going one wee step further - ventilate properly, when it doesn't affect you.
Give it a bash for a few days and nights.
Enjoy your dry windows :-)

Emmia

@hang3r

Makes sense to start with the bathroom. Though, so far I haven't dried any washed clothes. Once I do, the bathroom fan is unlikely to help the flat to stay dry. There isn't really space to dry them in the bathroom..

I think you underestimate these fans, we have them in both of our two windowless bathrooms. Prior to their installation both rooms had mould issues (and there were mould issues elsewhere in the flat) due to showering/bathing/life as the original fans were cheap and rubbish.

We used to run our dehumidifier daily, it's a Meaco 20L suitable (allegedly) for a 3 bed house, and we We live in a 2 bed flat. But despite this, mould appeared... There was less mould, but I still had to tackle it in a few places and our humidity sensor, indicated the humidity was at around 85% - 90% if we didn't run the dehumidifier.

One of the old fans died,  and the other started to sound ropey, so we replaced both with our current fans with the humidistat. The new fans, ran pretty much constantly for a week or so (mostly at the quieter low level) and the humidity dropped to around 60% in that time. The humidity now hovers around that level if we don't use the dehumidifier - this includes when we have clothes drying indoors. We rarely get the dehumidifier out now.

We also don't open the windows overnight, as we're ground floor in London and I think that's a security risk, and frankly for years we couldn't anyway as the windows were either painted shut, or the opening/closing mechanism was broken/dodgy.

This is why I think you should try the fan first, before a PIV or a separate dehumidifier which is a faff to get out, move around etc.

ic

ic said:

It looks like your bathroom doesn't have an external wall - is the extractor fan ceiling mounted, and do you know where its venting to?  Nearly always developers install cheap axial fans to get a tick from building control - however they're not always appropriate and are just inefficient under-powered noise makers.  If your fan is trying to push air along a pipe of a couple of metres or more to one of the outside walls, which might also then have a vent cover that has flaps to prevent back draught blocking the flow, it probably isn't up to the job and is failing to actually extract anything.  You should look into a centrifugal fan - these are designed to push air a long way (whereas axial fans can really only deal with a short run, say through the immediate wall). 

One of the bathroom walls is external, but the fan is mounted on a different wall (close to the ceiling). I had a quick look in the loft a few days ago, and I could see there was some ducting coming out where the fan is likely to be located and it appears to be connecting first to some kind of 'Y' splitter (which I believe has an unused connection closed off) and then more ducting leading to the edge of the loft. Will need to get a bit closer next time.

Sounds like the pipe run has a few twists and turns, as well as a possible deadleg. That will cripple what an axial fan can do - they're really only good for a straight run, with that length allowed getting significantly shorter with each turn.

In my home I have a cat litter tray under the stairs, vented by a 5m run of duct. I originally tried an xpelair axial fan, but there was no draught from the outside vent, and it smelled inside. I replaced with the centrifugal fan I linked earlier and it resolved the issue. I even added a pir so that it'd run at a higher speed after the cat used the tray, the pir triggering the light switch timer on the fan. Now we have zero smell in the house. 

Albermarle

Sounds like the pipe run has a few twists and turns, as well as a possible deadleg. That will cripple what an axial fan can do - they're really only good for a straight run, with that length allowed getting significantly shorter with each turn.

Plus if it is in the loft and that is used for storage etc, it is easy for the duct to be pushed out of a straight line, crushed etc . if you are not careful.

hang3r

ThisIsWeird said:

If your flat is well insulated, as it appears to be, then it won't struggle to bring the temp up as and when required - you've already said you turn the heating off overnight and when not in use, so I'm only suggesting going one wee step further - ventilate properly, when it doesn't affect you.
Give it a bash for a few days and nights.
Enjoy your dry windows :-)

Fair enough, certainly worth a go. As a temporary solution if nothing else. Thanks.

Emmia said:

I think you underestimate these fans, we have them in both of our two windowless bathrooms. Prior to their installation both rooms had mould issues (and there were mould issues elsewhere in the flat) due to showering/bathing/life as the original fans were cheap and rubbish.

We used to run our dehumidifier daily, it's a Meaco 20L suitable (allegedly) for a 3 bed house, and we We live in a 2 bed flat. But despite this, mould appeared... There was less mould, but I still had to tackle it in a few places and our humidity sensor, indicated the humidity was at around 85% - 90% if we didn't run the dehumidifier.

One of the old fans died,  and the other started to sound ropey, so we replaced both with our current fans with the humidistat. The new fans, ran pretty much constantly for a week or so (mostly at the quieter low level) and the humidity dropped to around 60% in that time. The humidity now hovers around that level if we don't use the dehumidifier - this includes when we have clothes drying indoors. We rarely get the dehumidifier out now.

We also don't open the windows overnight, as we're ground floor in London and I think that's a security risk, and frankly for years we couldn't anyway as the windows were either painted shut, or the opening/closing mechanism was broken/dodgy.

This is why I think you should try the fan first, before a PIV or a separate dehumidifier which is a faff to get out, move around etc.

Thank you for elaborating. That does sound more promising. Do you normally leave your bathroom doors open or closed?

ic said:

ic said:

It looks like your bathroom doesn't have an external wall - is the extractor fan ceiling mounted, and do you know where its venting to?  Nearly always developers install cheap axial fans to get a tick from building control - however they're not always appropriate and are just inefficient under-powered noise makers.  If your fan is trying to push air along a pipe of a couple of metres or more to one of the outside walls, which might also then have a vent cover that has flaps to prevent back draught blocking the flow, it probably isn't up to the job and is failing to actually extract anything.  You should look into a centrifugal fan - these are designed to push air a long way (whereas axial fans can really only deal with a short run, say through the immediate wall). 

One of the bathroom walls is external, but the fan is mounted on a different wall (close to the ceiling). I had a quick look in the loft a few days ago, and I could see there was some ducting coming out where the fan is likely to be located and it appears to be connecting first to some kind of 'Y' splitter (which I believe has an unused connection closed off) and then more ducting leading to the edge of the loft. Will need to get a bit closer next time.

Sounds like the pipe run has a few twists and turns, as well as a possible deadleg. That will cripple what an axial fan can do - they're really only good for a straight run, with that length allowed getting significantly shorter with each turn.

In my home I have a cat litter tray under the stairs, vented by a 5m run of duct. I originally tried an xpelair axial fan, but there was no draught from the outside vent, and it smelled inside. I replaced with the centrifugal fan I linked earlier and it resolved the issue. I even added a pir so that it'd run at a higher speed after the cat used the tray, the pir triggering the light switch timer on the fan. Now we have zero smell in the house. 

Ok. So, axial fans are clearly out. But which one would be better - a centrifugal one mounted in the bathroom wall to replace the old one. Or, an inline one mounted in the loft?

One one hand, the inline ones are much more powerful. But, on the other hand, they don't appear to come with a humidistat (checked the well-rated ones from tornado, manrose and vent-axia).

Emmia

hang3r said:

Emmia said:

I think you underestimate these fans, we have them in both of our two windowless bathrooms. Prior to their installation both rooms had mould issues (and there were mould issues elsewhere in the flat) due to showering/bathing/life as the original fans were cheap and rubbish.

We used to run our dehumidifier daily, it's a Meaco 20L suitable (allegedly) for a 3 bed house, and we live in a 2 bed flat. But despite this, mould appeared... There was less mould, but I still had to tackle it in a few places and our humidity sensor, indicated the humidity was at around 85% - 90% if we didn't run the dehumidifier.

One of the old fans died,  and the other started to sound ropey, so we replaced both with our current fans with the humidistat. The new fans, ran pretty much constantly for a week or so (mostly at the quieter low level) and the humidity dropped to around 60% in that time. The humidity now hovers around that level if we don't use the dehumidifier - this includes when we have clothes drying indoors. We rarely get the dehumidifier out now.

We also don't open the windows overnight, as we're ground floor in London and I think that's a security risk, and frankly for years we couldn't anyway as the windows were either painted shut, or the opening/closing mechanism was broken/dodgy.

This is why I think you should try the fan first, before a PIV or a separate dehumidifier which is a faff to get out, move around etc.

Thank you for elaborating. That does sound more promising. Do you normally leave your bathroom doors open or closed?

 

We leave the doors open except when showering/bathing so the fans do help to  dehumidify the whole flat - they run automatically day or night (at a low level) if the humidity level triggers them, bumping up (if they're running, or starting up if they're not) when the lights are switched on in the bathroom 

hang3r

Emmia said:

We leave the doors open except when showering/bathing so the fans do help to  dehumidify the whole flat - they run automatically day or night (at a low level) if the humidity level triggers them, bumping up (if they're running, or starting up if they're not) when the lights are switched on in the bathroom 

That makes sense. Just out of curiousity, do you know the model of your fans? And can you hear them when they're at low level and you are near the bathroom?

Mine being a small studio flat, I'm always near the bathroom, so would like to avoid unnecessary noise as much as possible.

Emmia

hang3r said:

Emmia said:

We leave the doors open except when showering/bathing so the fans do help to  dehumidify the whole flat - they run automatically day or night (at a low level) if the humidity level triggers them, bumping up (if they're running, or starting up if they're not) when the lights are switched on in the bathroom 

That makes sense. Just out of curiousity, do you know the model of your fans? And can you hear them when they're at low level and you are near the bathroom?

Mine being a small studio flat, I'm always near the bathroom, so would like to avoid unnecessary noise as much as possible.

I'm not sure of the exact model, as they've been in for ~7years, however they're very similar to this one in looks / spec terms.

https://www.screwfix.com/p/vent-axia-479087-100mm-4-axial-bathroom-extractor-fan-with-humidistat-timer-white-240v/617gy

If they come on in the night at the low level I don't notice them...  Judging by your floor plan and despite the fact our flat is bigger, I think I sleep at roughly the same distance from the bathroom that you do.

Ours are wall mounted onto an external wall.