House Ventilation & Air vent drafts

listermint

Alun wrote: »

When I lived in the Netherlands our house (built in 1986!) had such a system and the only source of fresh air input was small vents built into the windows as far as I remember. Absolutely no issues with condensation, damp etc.

tbf, vastly different climates

Alun

listermint wrote: »

tbf, vastly different climates

Not particularly. Maybe not quite as damp as here, but not "vastly" different by any means.

FitzElla

Alkers wrote: »

Does it not make sense that smaller vents could be used with the CMEV? The constantly running fan will ensure more air is drawn through the vents than a passive system?

For your last bullet - Humidity controlled vent inlets (to replace the OPs wall vents) seems like the most cost-efficient solution here. Is the CMEV one speed the entire time or does it change with humidity etc?

The CMEV is one speed with an on/off boost function, presumably set at a level to meet the min requirements of 0.3 l/s extract per m2 internal floor area.

I agree with your thinking around the smaller vents, but the building regs specifically deal with this set up and specify 7000 mm for each habitable room. Presumably they have done the research to back that up.

listermint

FitzElla wrote: »

The CMEV is one speed with an on/off boost function, presumably set at a level to meet the min requirements of 0.3 l/s extract per m2 internal floor area.

I agree with your thinking around the smaller vents, but the building regs specifically deal with this set up and specify 7000 mm for each habitable room. Presumably they have done the research to back that up.

Ya, but you would also want the gaps underneath each door to be maintained to spec levels too. And those are easily hung wrong or flooring is put in or new doors are added.

FitzElla

listermint wrote: »

Ya, but you would also want the gaps underneath each door to be maintained to spec levels too. And those are easily hung wrong or flooring is put in or new doors are added.

Agreed. But there still doesn't seem to be a solution that complies with the building regs and doesn't involve a massive retrofit.

Alkers

FitzElla wrote: »

The CMEV is one speed with an on/off boost function, presumably set at a level to meet the min requirements of 0.3 l/s extract per m2 internal floor area.

I agree with your thinking around the smaller vents, but the building regs specifically deal with this set up and specify 7000 mm for each habitable room. Presumably they have done the research to back that up.

So why bother with the CMEV if you just need the larger vents in every room in any case?

Alkers

listermint wrote: »

Ya, but you would also want the gaps underneath each door to be maintained to spec levels too. And those are easily hung wrong or flooring is put in or new doors are added.

Aereco specify 2cm air gaps beneath all internal doors

loyatemu

Alkers wrote: »

Aereco specify 2cm air gaps beneath all internal doors

interestingly my 1970s concrete house has air vents above each bedroom door (it also has all the airtightness of a string vest :pac:)

awec

Alkers wrote: »

Does it not make sense that smaller vents could be used with the CMEV? The constantly running fan will ensure more air is drawn through the vents than a passive system?

For your last bullet - Humidity controlled vent inlets (to replace the OPs wall vents) seems like the most cost-efficient solution here. Is the CMEV one speed the entire time or does it change with humidity etc?

We have the system he described but with trickle vents in windows instead of wall vents, so it’s definitely possible.

poker--addict

How do you know if a house is sufficiently ventilated and getting fresh air? Considering a house which is B2 from about 2006. There is a vent at top of windows which can be slid open. There is no heat recovery or mechanical systems generating flow.

No signs of moisture, so it’s more an air quality concern behind the question.

Lumen

The condensation is probably just a consequence of warm, humid, internal air condensing on the vent cover which has been cooled by the air coming in. I wouldn't worry about it particularly.

Lumen

The key issue is whether the house is being over ventilated in certain conditions, e.g. high wind, or whether the drafts are happening whenever the extract system is running.

You can replace the passive vents with unpowered active vents which are humidity sensitive, e.g. from Aereco. I don't know what the impact would be on the central extract though, if it's running continuously.

There are various vent baffle arrangements possible.

Biker1

Under Part F 2019 the minimum equivalent opening for the room vents when using a mechanical extract ventilation system is 2500mm2 and a 10mm gap under all doors is also required.

C. Eastwood

https://www.boards.ie/discussion/comment/118385006#Comment_118385006

poker-addict. Your house was built 2006. The Technical Guidance Document F Ventilation was the applicable Building Regulations 2002 document which should have been complied with. It stated as follows:-

“background ventilation” means ventilation by means of a secure ventilation opening (or openings) consisting of a wall or window ventilator with a controllable ventilation grill and located so as to reduce drafts;

“habitable room” means a room in a dwelling used for living or sleeping purposes but does not include a kitchen having a floor area of less than 6.5 m2;

DWELLINGS

Habitable Rooms

1.5 In a habitable room other than a utility room, a kitchen or a room containing a kitchen, the following provision for ventilation should be adequate:

(a) a ventilation opening suitable for background ventilation having a total area of not less than 6500 mm2.

This could be achieved by a 100 mm dia pipe / hole through the wall = approx 7,500 mm2

It could also be achieved by a trickle vent in the Window frame of size 6,500 mm2.

It is very important that if there is the 100 mm hole through the wall, it must be lined - usually with a PVC duct (pipe) and it is very important that this is sealed at both ends to prevent damp air from the cavity getting in to the Vent duct.

poker--addict

Ok, I guess the vent in windows is sufficient, as long as I keep some of them actually open to allow airflow. They were all closed when i checked them out today. Opened a few now in a way I think should generate some flow and see stale air exhausted. That should be fine?