We’re adding a much-needed continuous ventilation system (dMEV type) to our 80s terrace.
As per building regulations we’re adding 1 background ventilator (aka “hole in the wall”) per bedroom and 2 more downstairs, so 5 total. The regs specify they should have at least 4000mm² equivalent area. We’d like acoustic damping as we live in a city centre.
I’ve been Googling around and found the following 2 models. They’re both tubular so they need a core drill through the wall.
I’m a little surprised they’re over £100 each for what is basically a plastic tube with some acoustic foam inside…
Can anyone point me to another product, or share their experience with installing acoustic ventilators in general?
Building regulations come and go and you are under no obligation to meet current regulations in an ‘80s building unless you are doing major works.
Do all rooms normally have their doors closed? If so 4000mm2 is not going to get you the ventilation you feel obliged to have but will get you full cooling effect in each room. Conversely if all the doors are open you will get the prescribed ventilation and spread the cooling to the rest of the house.
Of course you can counter the cooling by increasing your heating and thus heating bill.
How is the house heated at present? How about cooking. Your actual ventilation requirement can be calculated by the number of oxygen consuming items (human, animal and combustion) taking oxygen from your internal air and replacing it with water vapour and carbon dioxide. CO2 being the most urgent to combat.
Electric heating and cooking don’t create CO2, at least not inside your house. Balance flue heaters don’t either.
Gas cookers and old style boilers do.
According to Passivhaus requirements you need:
The overall ventilation rate,
30 m3/h of fresh air supply per person.
The fresh air requirement for each habitable room;
bedrooms should have 20 m3/h of fresh air supply per person. At night we need a little less fresh air, compared to when we are awake and active.
The fresh air requirement for living spaces depend on their use, size and overheating risk.
The extract requirements
Kitchen: 46 m3/h | 60 m3/h in boost mode
Bathroom or shower room: 31 m3/h | 40 m3/h in boost mode
Utility, WC or storage: 15 m3/h | 20 m3/h in boost mode
The room requirements are not in addition to the personal requirements. They are guidelines for distribution. Of course you may get some of that unintentionally through poor airtightness. Have you had an airtightness test done?
Noted, I assumed (incorrectly?) that they’d be the minimum standard I should be aiming for. Are you making the case that building regulations are excessive on their ventilation requirements, or just that I’m not bound by them?
Mostly closed, yes. Why not? Isn’t this the purpose of the 10mm² undercut? Perhaps my thinking’s wrong here, but a 760mm × 10mm undercut is a 7600mm² area which exceeds 4000mm². (Not actually sure I can directly compare actual area with effective area.)
Are you saying that the 4000mm² is too small a ventilator, or that door undercuts are ineffective, or something else?
Yes indeed, that’s the plan. During the assessment we measured 2000ppm CO₂ after a few minutes of 4 people sitting in the open plan living room. We purged it and closed the windows and quickly saw the same level. We have a problem! Hence this ventilation plan. (We’ve ruled out MVHR for at least the next 5 years.)
Currently a gas boiler, to be replaced with a heat pump within 12 months. We replaced the gas hob with induction this year shortly after that USA report about childhood asthma :\
Thanks! That’s helpful and conveniently, it tallies with the overall ventilation rate I calculated from the building regulations (90 vs 93 m³/h).
The per-room requirements basically work out too, so it looks like I’m adding about the right ventilation in the right place for 3 people in our layout.
We will soon, once we’ve replaced the extremely leaky warped uPVC windows and repaired the ceiling around the new air tight loft hatch.
Back to your first point,
What’s your concern about the 4000mm² ventilators + closed doors, what am I missing?
If you have the appropriate undercuts you can ignore the intro to my post. I’m glad that you have investigated properly and are not just blindly following the regulations.
My house doesn’t (yet) have the undercuts. I have had MVHR (and an induction hob) since 2006 but have had all doors open or ajar for most of that time. Now I have older teenagers at home they keep themselves shut in their rooms. They complain about the summer heat and generally upset the ventilation plan. I tell them that if they are too hot they should open their doors but it seems there is a “law” that I wasn’t familiar with saying that their doors should be shut at all times. I ignore the “law” when they aren’t home. The doors are solid oak and I have been putting off the task of cutting them ever since it became necessary.
Returning to your home, you need the house as airtight as possible to get best results from the eventual MVHR but you are busy putting holes in walls. It seems that your temporary solution is contrary to your long term plan. Could you find another solution? I have to confess that I don’t know what it might be. How about ducting the supply and extract to the quiet side of the house and then re-using the ducts when you fit MVHR?
My concern about the use of current regulations is that there seems to be a disconnect between the heating and ventilation requirements. Remember that houses built to current regulations will still need retrofitting to meet ZEB or even nZEB standards.
Please share with me your method of measuring CO2. I am blindly assuming that my internal air is fine, based on Passivhaus regulations (as interpreted by Green Building Store) but it would be nice to see it for myself.
Sorry for the dreadfully slow response. The original CO₂ measurements were from a hand-held device that the retrofit assessor brought with them. But off the back of that, I’ve now installed a Flamefast CO2M which is proving very interesting, especially in the night.
Thanks for sharing. The monitors look interesting but unfortunately aren’t compatible with my current setup. I monitor temperature in each room and VOCs & humidity in 2. My MVHR also reports instantaneous extract air temperature and humidity, which are averages for the whole house. Unfortunately it doesn’t store historic data.
Co2 meters can be wildly inaccurate. I have three and the only one I trust is the Air gradient unit that I built with the help of Eco home lab. I have put them together in the same location at the same time and monitored the readouts. All will come down to atmospheric 425-450ppm. However, the two cheap units quickly produce excessively high readings ~2x that of the Air Gradient unit even when there is no activity in a room. These monitors are in good agreement for temperature ±0.5℃, humidity ±15 (7 different devices), CO2 is the least reliable and any activity = rapid rise in readings.
Most CO2 meters, particularly cheap ones, don’t measure CO2 but gaseous carbon, and derive CO2 by attributing a “typical” proportion of that carbon to CO2, so if you have some other carbon source in your room the alleged CO2 level will rise. In most modern homes there are significant levels of VOCs that raise the carbon level.
Both CO2 and VOCs need venting so the net result is still useful but inaccurate.