"low" extractor fan ..........

[MDJ]

Does hot air really rise? - https://physics.stackexchange.com/questions/6329/does-hot-air-really-rise

very interesting

 

[AJshep]

@Murdoch personally id go for a "Continuous" MEV fan something like a Greenwood Airvac CV2GIP, and just check you have a 9mm undercuts under the doors to allow airflow.
The trouble with intermittent fans is that when you delve into Part F and do the calculations it works out that these types of fans require so much background ventilation it usually almost impossible to achieve in a double glazed property.
Most houses just havent got enough windows to put enough trickle vents into to acheive the required background ventilation.

 

[Chris1234]

You can get replacement roof tiles that have a vent in then that attaches to an extractor.

 

[Deleted account]

A customer called me regarding a new bathroom she had just got fitted in the loft.
Building control was involved and they wouldn't sign it off until an extractor was fitted.

Long story short the easiest and only option without major redoing of the bathroom was to fit extractor aprox 3 ft from floor to go into a crawl loft space then out through eaves.

I contacted building control to see if they would accept that. They did and works competed and signed off.

 

[Marvo]

Wonder why building regs says ceiling level then?

Stale air tends to be warmer than fresh air so it rises. Hence extraction or return air is generally taken out at ceiling level.

Extracting from a lower level won't usually have a profoundly negative effect as long as there's nobody going to be sitting in close proximity in which case it might be a bit draughty.

 

[johnduffell]

high up as possible, it's simple physics. Unless the fan is so powerful it's causing a general draught in the room it will be like draining a header tank by punching a hole through it half way up.
we have a lower fan approx eye level due to sloping wall/roof higher up, and the air stratifies, so you can see clear air below eye level but above eye level is clouds of fog.
We are going to move to ceiling above the shower, extract into an HRV before it has a chance to spread.