Bathroom extractor fan - Effectiveness

[Dambo]

I installed a shower extractor fan with a built-in light a couple of weeks ago. The customer rang me yesterday to say he doesn't think it's being very effective. The fan is installed in the attic space above the bathroom and is about a meter away from the ceiling cut out with the external grille being only about a meter away on the other side, with no bends in the ducting. The fan should have an extraction rate 85m

 

[Sidewinder]

Yes you measure the air velocity at the inlet grille at in the plane of the opening.

This will give you the velocity in m/s.

You then calcuate the area of the opening in m^2 and multiply the both this gives you the volumetric flow rate in m^3/s, you then multiply this by 3600 to get m^3/hr.

Trouble is your instrument must be small in relation to the area of the opening so you are looking at a hot wire anemometer really.

Mark does them, will set you back about

 

[bluetobits]

you could always measure bathroom size, light a smoke pellet and see if it clears at a rate of 7 cubic meters in 5 mins. :coat

 

[Sidewinder]

bluey,

Not fussed on that method myself too many variables!

Position, you, movement, doors opening & closing etc.

May work though?

 

[bluetobits]

bluey,Not fussed on that method myself too many variables!

Position, you, movement, doors opening & closing etc.

May work though?

I think your method is definitely the one to go with mate

 

[Sidewinder]

It's the method used for testing extraction systems for compliance with COSHH regulations.

So it is spot on, however, you also use the smoke method for clearance, but for that you would fill the room with smoke then turn on the extactor and check the clearance time on the "sealed" room.

Could be difficult with a domestic bathroom.

You would need to allow the room to fill and the smoke to evenly mix, then turn on the extract start the time and then stop it when the last of the smoke was gone.

A bit qualatative rather than quantitative really.

You would as you say then compare the clearance time against the volume of the room.

Thing is you woun't know IF all the air has been changed, only that the visible smoke is gone.

---------- AUTO MERGE Post added at 13:22 ---------- Previous post was at 13:21 ----------

Forgot, to say, not dissing your post, just commenting and trying to be a bit constructive!

 

[bluetobits]

I understand completely, no offense taken.

 

[Sidewinder]

OK cool!

Cheers.

Just about to have my traditional glass of port & start putting the xmas decs up with the kids, xmas music on stereo!

 

[PC Electrics]

You could always set up a home made pitot tube in the air flow using some small bore copper pipe or similar and a manometer using some clear tubing & water. Any half decent text book on Fluid Mechanics from the library will help you do the calculations.

On the other hand, you could just fit a decent fan in the first place. Most of those fan-lites are cr@p.

Fit one of these instead:

http://www.screwfix.com/prods/41379/Heating-Cooling/Extractor-Fans/Manrose-Chrome-White-35W-In-Line-Centrifugal-Shower-Fan-Kit

and seperate downlights:

http://www.screwfix.com/prods/93450/Lighting-Lamps/Internal-Lighting/Bathroom-Lighting/Bathroom-Downlights/Halolite-Fixed-Round-Polished-Chrome-240V-Mains-Voltage-Bathroom-Downlight

 

[Sidewinder]

PC,

That would work, inclined tube would be better, would take some doing to get it accurate mind!

Both in the making and the maths!

Fair play good shout!

 

[Evans Electric]

Must say that most of the fans that form part of the Shower /fan/light kits are carp.

About as powerful as a fish phart !!

 

[dave2]

I have one of these fans fitted in my shower en-suite room and it works perfectly well. The room is about 10m3 and when showering you can see the water vapour dissappearing up the duct. The total length of the ducting is about 3.5m.

What I will say is that I need to have it on over run for at least 5 minutes after the light has been turned off.

Dave

 

[Tooold]

I'v got a fan light above the shower works really well but its an in line centrifugal so really sucks it out. Standard one not up to it for our bathroom

 

[Doc Hudson]

Have you got large enough gaps to allow air into the room such that the fan can extract. If the room is relatively draft free, the fan will be trying to create a vacuum. Some new builds require a 10mm gap under to door for this purpose on rooms with no other ventilation.

Doc H.

 

[Sidewinder]

Doc,

Exactly in line with my comment on make up air!

 

[Dave Buchan]

I come across a similar problem like this quite frequently when mainly asked to address condensation and mould issues and the effectivness of air extraction within properties.

I generally leave temperature/RH dataloggers in the problematic bathrooms for a week or two, so I can then evaluate the data and see exactly how long it's actually taking to remove the excess water vapour from the air that the occupant is generating.

The efficiency of the fan will ultimately be decided on the lifestyle of the individual using it though, (you can have an extraction rate of 85m

 

[SPECIAL LOCATION]

I have a customer who doesn't like leaving the fan ON...

Only like it on while they are using the bathroom...

They can't grasp the concept that the moisture is still in the air after you have switched the shower off!!!!headbangheadbang

 

[Evans Electric]

I,ve had a load of customers much the same and including my regular builder , they insist I turn the timer down to the minimum , which , as you say defeats the point of the overrun drawing out as much moisture as possible . Still its up to them, doesn't bother me , just find it daft. :C

 

[batty]

I,ve had a load of customers much the same and including my regular builder , they insist I turn the timer down to the minimum , which , as you say defeats the point of the overrun drawing out as much moisture as possible . Still its up to them, doesn't bother me , just find it daft. :C

Don't mention builders thats as bad as mentioning the Germans.

 

[PC Electrics]

I,ve had a load of customers much the same and including my regular builder , they insist I turn the timer down to the minimum , which , as you say defeats the point of the overrun drawing out as much moisture as possible . Still its up to them, doesn't bother me , just find it daft. :C

This is often because people don't like the noise at night after they've been to the loo. That's why I fit the fan I linked to above, because it's very quiet.