Passive vent in through soffit?

KungPao

Hi,

New windows on the way (old ones had trickle vents, new ones won't, house built 2004) and looking at options for ventilation.

A bit of a busy road out front, and wondered, perhaps a mad idea, but is it possible to have ceiling mounted vents in a bedroom, with ducting in the attic (a few metres max), and terminating at the soffit at rear of house? Instead of through a wall which will be closer to noise - built in wardrobe in the way. As intake only. I plan to have dMEV vents installed in the en-suite and bathroom for continous extraction.

If not, I may go with the old hole in the wall, with acoustic vents at 127mm, but looking to keep noise down to an absolute minimum, so if ceiling to soffit at the rear is possible, even better.

I know extracting out through the soffit is not exactly great due to the moist air being sucked back in to the attic, but is my idea possible?

MicktheMan

I would install something like a centralised mechanical extract ventilation system (cMEV) rather than passive vents.

KungPao

Cheers Mick.

If I have cMEV in the en-suite and bathroom (1st floor), don't I need intakes in the bedrooms though? House it a bit leaky no doubt, but with new 3G windows with no trickle vents, and planned upgrades (insulated PB and fill any gaps along the way), I think I'd need some air in?

MicktheMan

I don't know your house for sure but unless it is exceptional there will be plenty of air leakage through the building fabric to allow the ventilation system be effective.

You could have the house tested for air tightness once your upgrade works are complete and that would determine without doubt where you're at.

You can also try this simple test in the bedrooms (dry rooms); close all windows, en-suite doors etc. Now open the (bedroom) door fully and give it a decent push closed letting it go half way. If it slams closed and doesn't bounce back open then you have likely fabric leakage sufficient not to need any vents in the room for air intake. If the door bounces open and doesn't slam shut try the test again except this time open a window in the room a bit. If it slams shut this time then you will likely need a passive vent.

KungPao

MicktheMan wrote: »

I don't know your house for sure but unless it is exceptional there will be plenty of air leakage through the building fabric to allow the ventilation system be effective.

You could have the house tested for air tightness once your upgrade works are complete and that would determine without doubt where you're at.

You can also try this simple test in the bedrooms (dry rooms); close all windows, en-suite doors etc. Now open the (bedroom) door fully and give it a decent push closed letting it go half way. If it slams closed and doesn't bounce back open then you have likely fabric leakage sufficient not to need any vents in the room for air intake. If the door bounces open and doesn't slam shut try the test again except this time open a window in the room a bit. If it slams shut this time then you will likely need a passive vent.

Thanks again, Mick. Appreciate that.

KungPao

Could I just add to this. If I get MEV upstairs, but discover I do indeed need some passive vents in the dry rooms, is the soffit vent idea possible or is it against regs or something?

I can't find much online on intake at soffits, mostly extract.

A simple vent on the ceiling ducted to a soffit vent. I mean a PIV pumps attic air in, so I can't think why my idea would be a non-starter. I suppose over-ventilation is a risk, but it won't be facing prevailing winds, and could maybe incorporate some baffles like those "black hole" vents.

Any thoughts?

Right image sums up what I'm talking about, but as intake:
https://derickl1yuax.cloudfront.net/uploads/d6d44ec6/ckeditor_assets/pictures/42/content_options.jpg

whizbang

The static pressure in your house will mean those vents will always be exhaust.

KungPao

whizbang wrote: »

The static pressure in your house will mean those vents will always be exhaust.

Won’t the continuous MEV be creating a negative pressure so my proposed vents would always be intake?

whizbang

Apologies, I didn't realise you were using MEV.