Best inline extractor fan to replace this?

[Andy.T]

I'm looking at replacing an underperforming 4" inline fan (a Silavent Vitalis 100) for my bathroom.

We've shortened the run of ducting and removed some bends and it has a fairly good supply of air from under the bathroom door but it's still not cutting the mustard. It's rated at (I believe) 187m3h and I've been looking at one of these which is rated at 250m3h or possibly the 5" which is rated at 380m3h.

Are those Soler and Palau's the sort of fans I should be looking at in terms of reliability and performance? Or are there better makes/models?

I'd like it to be quiet if possible as its close to a bedroom. I don't mind spending a bit more to have something that will definitely keep the room from steaming up.

And yes, I'm going to be putting back the insulation (removed for the change of fan and lights) and upgrading it too which should help a little I guess.

Thanks,

Andy

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• Andy.T
• 3 Jan 2015
• 2

 

[ericmark]

To remove moisture the replacement air must be dry and warm. If I take readings today as an example.

My office 38% humidity at 21.8°C and outside 77% humidity at 4.8°C so due points are 9.4°C in my house and 0.2°C outside.

So air drawn from my office would tend to dry out the bathroom as long as bathroom was above 4.8°C and from outside would dry out bathroom if over 0.2°C.

However go to my father-in-laws house and humidity in the house sits at around 70% so far more air is required to dry his bathroom and air temperatures need to be far higher.

Although he leaves door open to bathroom the whole house is so well sealed he runs a very real risk of fumes if he uses his open flue gas room heater.

Step one must be look at the replacement air. Draft proofing often means there is very little replacement air available.

Today more and more the only way is a heat recovery unit which is drawing in much drier air from outside and warming it with air leaving but these are also in their infancy I was reading other day installation instructions saying could be mounted at any angle. Clearly you will get condensation and so that's not strictly true water must be able to run out.

Years ago my parents had single glazed windows in metal frames with a tray at the bottom and hole to outside each side of tray. This was a great de-humidifier any moisture would condense on window and run outside. And all doors including main doors to outside were poor fitting so loads of ventilation. Clearly we don't want to return to those days but you do have to consider how dry the replacement air is. Drawing air from loft space could help likely it is dryer.

Fit fan other way around so it's pumping in dry air from outside and likely bathroom will dry out. Clearly not what is wanted as damp air now sent to rest of the house.

I don't clearly know your house but likely larger fan will not help. Once I got a humidity meter I realised the problem summer is far worse than winter in winter outside air is rather dry as it's so cold summer outside air can have more moisture in it than inside air. In July best results are around 50% humidity and inside and outside air nearly the same. So if you have a problem in winter and not summer then some where likely vents to outside are blocked. Often cavity wall insulation block vents also found stuffed full of paper.

 

[Andy.T]

Thanks for that Eric, I can get a hygrometer I guess, but I don't believe we have a more general problem with humidity in the house. We don't really get condensation on windows etc. and we make sure we don't leave wet washing about the place etc. It just seems to be a particular problem in the bathroom (long hot baths! ).

The problem is worse in winter than summer and I always took this to be just down to the bathroom being that bit colder in the winter, even with the heating on (it's a bit of a suntrap in the summer).

I just figured that if I could get the air moving enough then it will remove the warm damp air before it has a chance to condense on the (relatively) colder walls and ceiling.

Do you guys really think that a more powerful fan wouldn't achieve this?

Thanks,

Andy

 

[JohnW2]

I just figured that if I could get the air moving enough then it will remove the warm damp air before it has a chance to condense on the (relatively) colder walls and ceiling. ... Do you guys really think that a more powerful fan wouldn't achieve this?

That is obviously true, provided that the damp air is replaced by less damp air. I have to say that I am not as pessimistic as eric. I would have thought that, even in summer, outside air is likely to usually be appreciably dryer than the air in a bathroom immediately after a bath or shower.

Kind Regards, John

 

[Andy.T]

Thanks for that John, and do you have any experience of those inline fans, or any others that you could recommend as being good performers/reliable?

 

[bernardgreen]

If only it was as simple as fitting a more powerful fan.

No matter how powerful the fan is there will be areas in the room where the air is not going to moved by the extraction fan.

The main air flow will be from wherever the replacement air enters the room directly to the extractor fan. The areas away from this air flow will tend to be static air and therefore steam / water vapour in those areas will not be extracted and will condense on walls and ceiling. Corners between walls and ceiling are where static air is most likely to occur,

A ceiling fan that moves the air around the room will reduce the amount of static air.

Containing the steam within a shower cubicle with the extractor sucking air and steam from the cubicle will reduce the amount of steam that reaches the areas of static air. ( but the replacement air entering the cubicle will create cold draughts on the person in the cubicle )

 

[JohnW2]

Thanks for that John, and do you have any experience of those inline fans, or any others that you could recommend as being good performers/reliable?

You're welcome. I have a couple of in-line fans, which work fine, but I don't even recall what make they are, so can't really help with recommendations - other probably can. I would have thought that you wouldn't go far wrong by going for one of the major reputable brands (e.g. Manrose and Xpelair) - and avoiding anything particularly cheap!

Kind Regards, John

 

[JohnW2]

No matter how powerful the fan is there will be areas in the room where the air is not going to moved by the extraction fan. ... The main air flow will be from wherever the replacement air enters the room directly to the extractor fan. The areas away from this air flow will tend to be static air and therefore steam / water vapour in those areas will not be extracted and will condense on walls and ceiling. Corners between walls and ceiling are where static air is most likely to occur,

That is clearly all true. However, as you go on to say, if one has an adequately powerful fan extracting from a point close to where the moisture/steam is being generated, much of it will get extracted before it has a chance to get into those 'static areas'.

The ideal would probably be to have multiple extracting vents - but that is not practical in a domestic environment.

It's interesting that a few decades ago very few people had bathroom extractors and we didn't hear a lot of fuss about condensation on bathroom walls. If/when it arose, people wiped it off! What I understand less is why it seems to result in major mould problems in some houses, yet not in many others.

Kind Regards, John

 

[bernardgreen]

The ideal would probably be to have multiple extracting vents - but that is not practical in a domestic environment.

Multiple vents for replacement air and located in the areas of otherwise static air would stir the air around more than a single vent under the door.

 

[JohnW2]

Multiple vents for replacement air and located in the areas of otherwise static air would stir the air around more than a single vent under the door.

True - but very clever design would probably then be required to get a reasonable balance of the 'impedances' of the various possible air paths.

Kind Regards, John

 

[Andy.T]

Thanks again guys, see a rough plan of the bathroom below and a pic of the intake (the green circle on the plan)...

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• Andy.T
• 3 Jan 2015
• 1

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• Andy.T
• 3 Jan 2015
• 1

It's actually a pretty small room (only about 7 feet cubed) and the position of the fan intake is pretty good (being the complete opposite corner of the room to the gap under the door).

Am I really kidding myself to think that a more powerful fan (that S&P 5 inch one is more than twice as powerful as my current one) and some tweaks to the ducting (for example starting with a gentle 45 degree solid piece of ducting from the inlet and moving the fan to the side of the rafter rather than the bottom as it is currently to reduce bends) will help?

 

[JohnD]

To remove moisture the replacement air must be dry and warm.

That's not true. Cold air holds much less water vapour than warm air. The humidity reading is stated as RH - Relative Humidity - which is the amount of water vapour that the air contains compared to the amount that it could hold at that temperature.

A cubic metre of hot dry air in the Sahara contains a lot more water than a metre of cold wet air in Manchester. Even though the Manchester air has a higher RH.

Anyway, a bathroom fan usually sucks in air from the rest of the house through the gap under the bathroom door. That encourages stratification, where the warm air and water vapour (water vapour is lighter than air) rise upwards towards the ceiling, where the fan sucks it out. The cooler dry air replaces it from floor level, preferably without mixing. This works much better if the window and door are closed.

 

[Andy.T]

This works much better if the window and door are closed.

Yep I always have the window and door closed and so the air is always being drawn in at the lowest, furthest spot.

 

[ericmark]

To remove moisture the replacement air must be dry and warm.

That's not true. Cold air holds much less water vapour than warm air. The humidity reading is stated as RH - Relative Humidity - which is the amount of water vapour that the air contains compared to the amount that it could hold at that temperature.

This is of course true I realise now I spelt dew wrong when I quoted dew points but I have noted with my house the relative humidity will raise and fall a lot but dew point relativity static.

A cubic metre of hot dry air in the Sahara contains a lot more water than a metre of cold wet air in Manchester. Even though the Manchester air has a higher RH.

No so sure on that. If true then the amount of water running from the AC units would be rather high. However in Hassi R'Mel where I lived back in 1980 - 82 there was hardly any condensate from the AC units. Move into the Atlas mountains yes there was loads of water and there was a big problem with it freezing in the AC which then stopped AC from working but in the Sahara there was no such problem.

Anyway, a bathroom fan usually sucks in air from the rest of the house through the gap under the bathroom door. That encourages stratification, where the warm air and water vapour (water vapour is lighter than air) rise upwards towards the ceiling, where the fan sucks it out. The cooler dry air replaces it from floor level, preferably without mixing. This works much better if the window and door are closed.

I still maintain best way to dehumidify a bathroom is single glazed windows with catchment trays directing water outside.

What we want is of course removal of water without removing heat. A heat recovery unit is clearly the best method but failing that then there needs to be a balance between air sent outside and moisture removed.

The water clinging to walls, shower curtains, and tray will take some time to evaporate into the atmosphere in the bathroom and main point is fan should not stop until this water has been absorbed.

There will be an exception to every rule but in the main a fan shifting twice as much air will leave more moisture in the bathroom as one running twice as long.

Quality of the replacement air is important and I am sure everyone has tried opening a window which should allow the bathroom to dry however because the bathroom becomes so cold it does not work.

I remember fitting a humidity controlled extractor to my fathers bed room when he had a shower in the corner of the bed room and the fan seemed at first as if it would never stop. It would often run for 3/4 hour specially in the summer and as a result he would switch it off on the isolator.

Since you have a window clearly using the light switch to activate fan is useless as you may not use the light every time you use the room. So by using a pneumatic timed button plus the timer built into the fan it will run for around 1/2 hour after each push. I expect the extra time will do far more than extra fast air exchange and cause less drafts. The 15 minutes in Part F is minimum there is nothing to stop you increasing that time.

 

[EFLImpudence]

What I understand less is why it seems to result in major mould problems in some houses, yet not in many others.

I look after several flats and it really is down to the inhabitants.
Some never let moisture out; that is they keep it in - so it condenses on the cooler parts.
The same flat can either be mould ridden or spotless.

The rest of the OP's house may be very humid; this will appear in the bathroom, fan or not.
In the past, houses were draughty and continually ventilated.
Nowadays they are virtually completely sealed.

Leave a sopping cloth in the car overnight and see what happens.