Ventilation of shower / bathroom - what would you do?

[SirLancelot]

Hi all,

Got a bit of a tricky situation, and would appreciate input from forum members.

(Ventilation seems to be an area, which is often overlooked, given its importance)



Pics included.

Room: Wash basin, toilet, shower cubicle (No bathtub).

Room - Dimensions = 1.81m long by 1.74m wide by 2.53m tall


Exhaust ducting = 100mm diameter by 300mm long.

I used this to do the calculation - but I have no idea if it is out of date - or is wrong. It suggests that I absolutely need a 120mm fan. Don't know how seriously to take it.

So -


1. Clearly it would be very easy just to put in another 100mm/ 4inch fan, but there must be a
reason that a larger one is suggested? Would it really make a significant difference?


2. If a more powerful/bigger extractor is needed, what might be the simplest solution here? Is there a way to couple a larger fan say 120mm/ 5" fan, to this 100cm existing tube, and have it work out okay? (I'm hoping to avoid replacing the exhaust tube with a larger diameter one).


3.What brand of fan/extractor would you recommend?


4.Any thoughts or alternatives you might care to suggest or that come to mind?

My thanks to all that contribute

SirLancelot

 

[Burnerman]

I have a similar sized bathroom and I use a 4" fan too.....but I'm meticulous about using a squeegie to dry the shower walls every time.
I use a Manrose Gold fan, with timer - and it runs for maybe 20 mins after switching off. Sometimes I let it run for longer.
Looking at your wires there, there could be two lives, which you will need for the timer fan - one switched, one not.
John

 

[^woody^]

Why do you think that you need a bigger diameter fan?

It's all down to air changes and efficiency. A 100mm centrifugal fan is more efficient than the same diameter axial fan for instance.

 

[theprinceofdarkness]

I hope that some air can get into your shower room or it will implode.
Frank

 

[Nige F]

4 inch is fine - clean the duct and make sure that one way flap is free to move

 

[Joe Malone]

Install a Vectaire MF100C centrifugal fan and avoid cheap axial fans. Also, and this is critical, get it wired to run continuously on trickle speed with the boost speed wired to the lighting circuit, running timers and humidistat switches are a complete waste of time and you want to be dealing with air changes in the property over a 24 hour period not just switching the fan on when you shower or bathe.

 

[SirLancelot]

ooops,

Made a mistake.

Room is not a bathroom. Room has toilet, wash basin and shower cubicle only.

Bathroom - supposedly - 6 air changes per. hour req.

For a shower room - its 15-20 according to vent-axia's website??
Quite the difference.

A. I just need to know where the official rates are published, so I can take a look for myself?

B. Has anybody heard of Schneider-electric:

I found one of their premium fans - the GSSTFAN4TH (page 28) : Here

Does anybody have any experience with this unit. It can move about 32 l/s - double the 15l/s in AD-Part F.

Thanks.

 

[SirLancelot]

UPDATE - What I have found - Zone 3 - Wall mounted extractor fan.

I an amateur diy student. This does not represent professional advice - I'm just exploring the subject - hoping for others to provide some input and share their knowledge.

Door undercut regs - 7600mm2 gap beneath doors required (so if door is a standard 760cm wide door, a 10mm gap underneath is sufficient). Or a door grille that covers the same area as a minimum. This is to promote good ventilation throughout a domestic dwelling.

UK Part F building regulations: Planning Portal - Approved Document F - Ventilation

Table 5.1a: Bathroom - minimum extract rate (Intermittent Extract) = 15l/s.

Table 5.2a (Segment 4) - Controls - Intermittent Extract : "In a room with no openable window (i.e. an internal room) the fan shall have a 15 minute overrun."

This is the building Regs minimum - and does not seem to account for shower use/room size and many other important factors.

Alternatively, the Chartered Institute of Building Services Engineers - provide a ventilation guide - which gives a very different approach. Funny thing is, many extractor fan manufacturers reference those values on their websites:

CIBSE GUIDE B 2005: Glossary | Polypipe Ventilation

Recommended Air Change Rates (Page 2):
http://www.nuaire.co.uk/media/79314/nuaire_commercial_useful_info.pdf

Air Changes Per. Hour (ACH) Table:
http://www.vent-axia.com/files/Ventilation Design Guidelines 2.pdf

So - Contradictions all round.

CISBE - Suggest that for a room with a shower - the Air in a room should be changed 15 times per. hour (min).

Part F Regs - Seem only to provide a minimum extraction rate of 15 l/s - regardless of size of room (and assumes bathrooms to include showers too - if I am right).

The purpose of a bathroom/shower extractor fan is to effectively remove the unwanted air/moisture from the room, so that the moisture does not settle into the fabric of the house i.e cause damp/ condensation/ mould.

For us newbies - Example:

Try sucking air through a straw, whilst, (after a few seconds) squeezing the other end. All of a sudden, it becomes a lot harder, and you don't shift much air through the straw. Same principle here. There has to be enough air coming in, to replace the air you're trying to shift. Hence Door gap, vent in door, or simply leave the door ajar slightly - will allow the fan to do its job.

Axial vs Centrifugal: High resistance situations (fan has to create more 'push') because of long ducting, ducting with many bends or if the duct often faces strong wind - centrifugal is appropriate. If you have a short duct, and the exit port is unlikely to face direct wind - and axial should do the job.

Calculation: H x W x L (meters) of room. Multiply by recommended air change per. hour rate. Divide result by 3.6 and you will get the recommended extract rate your fan should have (in litres per second - l/s).

Conclusion - So if I follow building regs - all I need is a fan with an extract rate of 15 l/s. But if I follow the CIBSE recommended air change rates - i should get a 32 l/s extractor fan, i.e more than double. I'm going for a fan with a Humidistat built in - so that it will only switch off, once the moisture is down to a sufficient level. After all - that is the main purpose of a shower room fan in the first place.

I will be going for the Schneider-electric premium GSSTFAN4TH. I can find no reviews on it, so we shall see how it goes.

Comments welcome / suggested corrections welcome.

Leo

 

[Joe Malone]

Hardly worth the effort of researching really considering you've chosen to fit a cheap £18 fan. Wait to see how long it is before you start having problems with the humidistat switch. You should avoid them like the plague and especially cheap and nasty Schneider fans. I've also advised you that centrifugal fans are essential for ceiling mounted locations and this advice is based on pragmatic experience. I have to ask why you bothered seeking advice in the first place since you simply think this issue is about the volume of air any given fan can move. It isn't, but please come back and tell us when your humidistat switch fails.

 

[SirLancelot]

Hardly worth the effort of researching really considering you've chosen to fit a cheap £18 fan. Wait to see how long it is before you start having problems with the humidistat switch. You should avoid them like the plague and especially cheap and nasty Schneider fans. I've also advised you that centrifugal fans are essential for ceiling mounted locations and this advice is based on pragmatic experience. I have to ask why you bothered seeking advice in the first place since you simply think this issue is about the volume of air any given fan can move. It isn't, but please come back and tell us when your humidistat switch fails.

Hi Joe,

Your advice was spot on. I am having problems with the humidistat already.

The reason I chugged ahead with all this research is that I'm one of those people that like to breakdown a situation into its basics, and gain new knowledge and competencies along the way. I wanted the knowledge/understanding too.

Why did I go for the Schneidier axial? Quite simply, the axial was a few quid, while the cost of the centrifugal would stretch us at the moment.

I am sending the faulty Schneider back and purchasing a centrifugal, as soon as I receive word that I passed my job interview (hopefully within a week).

Joe, could you please help broaden my knowledge. I will be following your advice.

Would you mind sharing what your experience has shown you and why (axial vs centrifugal):

Why is the centrifugal better over the axial?

What discoveries/experiences brought you to this conclusion?

If I have it on continuous trickle with boost, how can I manage/reduce the heat loss throughout the fans active lifetime?

You mention that this scenario is not simply 'about the volume of air the fan can move'. Please help fill in the blanks for me.

I really appreciate any time you are willing to give, to help increase my understanding and knowledge.

Thanks again,

SirLancelot

 

[SirLancelot]

Hi Joe,

Would genuinely appreciate any input/advice you can provide.

SirLancelot

 

[OwainDIYer]

Part of the problem may be the trickle vent on the window is almost directly below the fan. This will cause a 'short circuit' of airflow in through the trickle vent and out through the fan, bypassing the shower area completely.

You might find an improvement if you close the vent and leave the fan running relying on makeup air through under door ventilation from the rest of the house.

Or put a (safety extra low voltage) fan above the shower

 

[Joe Malone]

Hi SirL,

Sorry but not logged in for a while. I am a Chartered Building Consultant and a Chartered Building Engineer. My expertise is in damp investigation and building defect analysis and I have been teaching damp investigation since 2006 and also do a great deal of expert witness work in this area. I have also managed maintenance across tens of thousands of properties so I also have pragmatic experience of what works and what doesn't when it comes to ventilation. Humidistats are a joke, they always fail prematurely, often simply because the extractor draws contaminants towards the extractor that then tends to clog up the humidistat sensor, this is a basic design flaw as far as I'm concerned but I know from bitter experience that they're just downright unreliable.

Install a cheap noisy fan and residents will understandably turn it off because the noise is too intrusive so this is one reason for specifying something that is silent on trickle speed. I don't like cheap axial fans and would never install one, they are a false economy in my book. I've always specified centrifugal because you don't always know whether the contractor will be installing in the wall or ceiling, the centrifugal fans covers all eventualities and can move air through a length of duct in a loft space, an axial fan won't. I always carry out a simple test when I'm checking existing extractor fans, it's not very scientific but it's a useful gauge... I simply put a sheet of A4 paper over a fan running on trickle speed and if it won't hold the paper to the fan then the chances are that it simply isn't moving enough air.

Moving onto more technical issues relating to condensation damp... It is important to keep the property warm so ventilation should be carefully managed to prevent transient condensation. There are single room heat recovery fans available, PIV systems (That should be avoided), Passifyer vents, and whole house MVHR systems. Heat recovery fans or MVHR are the best options but most of us do not want to spend the sorts of money involved with installing these measures so we are left with doing the best we can with standard centrifugal extractor fans. To spread heat losses over a 24 hour period, which in turn helps prevent issues of transient condensation, you should wire fans to run continuously at trickle speed with boost speed wired to the bathroom lighting circuit for those times when you are showering or bathing. Moreover, a good basic centrifugal fan is incredibly reliable and once installed you can simply forget about it. The maxim that you buy cheap you buy twice is never more appropriate that when referring to cheap extractor fans.

 

[Joe Malone]

Part of the problem may be the trickle vent on the window is almost directly below the fan. This will cause a 'short circuit' of airflow in through the trickle vent and out through the fan, bypassing the shower area completely.

You might find an improvement if you close the vent and leave the fan running relying on makeup air through under door ventilation from the rest of the house.

Or put a (safety extra low voltage) fan above the shower

Yes, this is a problem, if there is a trickle vent in the same room then it should be closed or it will indeed short circuit the extraction process. Fans are meant to draw air from other rooms and not from the room they are located in.

 

[Joe Malone]

With regards to reducing heat losses then hopefully you'll have understood that installing a single room HRF is your best and most cost effective option for doing this but they're circa £200.00

Also interestingly, the heat recovery rate is roughly halved when running at boost speed. The internal heat exchangers are far more efficient when the air flow is trickled across the plates rather than boosted. I have a continuous running single room heat recovery fan installed in my bathroom that on trickle speed recovers around 70% of the heat that would otherwise be lost with a standard extractor.