Well the Zehneder ComfoQ is all fitted and commissioned and has been running 3 months now, and unfortunately my initial concerns about having the master bedroom too cold and too draughty remain - it was warmer and more comfortable before so clearly not getting the full benefits here.

I'm generally sensitive to slight draughts (including warm ones) and feel really cold ??? compared to the average human so my people aren't going to notice it at all (spouse definitely doesn't). I wear a sweater or hoodie most of summer.

The master bedroom supply valve *feels* like it shoots air diagonally down towards the bed instead of (or as well as) across the ceiling. My arms need to be fully tucked up under blankets and duvet all night when they didn't before, which is a nuisance when you are trying to hold a book and it's no different now the weather is a bit warmer outside. I also notice the draught direction on walking into the room.

The supply air valve air temperature feels too low - but this might not so matter if it wasn't pointed at me.

The lounge at times also has the same thing happening towards the sofa although the temperature is OK and it's only noticeable some of the time.

Everything was well fitted and insulated and avoided the typical mistakes of trying to put the MVHR in the loft (it's downstairs and attic ducting is well insulated). It's a Zehneder so very efficient and nice and quiet, loft above is well insulated and there's EWI but no solar gain in bedroom or lounge and it's an old house. The airtight vapour membrane on the loft floor got taken out pre-MVHR (condensation was running down the walls because windows don't have air vents), and looking at the ducting up there I can't see how we can really get another put down. The supply valves have been carefully planned for addressing the areas we had conversation/ventilation issues ("dead space") while being far enough away from bed and sofa.

Solutions I can see now are:
1. Set MVHR temperature profile to warm, which I did this morning but won't fix the draught sensation

2. directional supply valves to avoid blowing air right at me (it would need to be adjustable so that air can still get to the corner of the room but maybe 30-40 degrees of the 360 degrees blocked from the outlet of the supply valve

3. adjusting the flow rate to lower it, which to keep things balanced means either increasing it in other bedrooms or reducing the extract rate in bathroom and kitchen (which I'm reluctant to do) .
This might not be ideal since both the problem rooms have only 1 supply valve and are the largest rooms, and that's the only downstairs supply valve (other beds are not currently used but also don't have the draught effect).

The master bed also has a raised ceiling so a large volume of fresh air is needed. Passivehaus good practice guide recommends starting at 30 m³/h for double rooms. I think I need to dig out my commissioning details for current settings.

What is the actual temperature in the bedroom and in the rooms/corridors that are adjacent? And what is the temperature of the air coming out of the MVHR terminal? You can use a thread (or length of wool) on the end of a stick to see where air is actually flowing. Or smoke of course. What do your supply valves actually look like and where are they mounted - particularly in the bedroom and lounge (photos might help)? Some actual flow numbers might help as well.

I sometimes think I can feel the airflow in bed but I'm pretty sure I can't, so there may be an element of that. It does sound like you're on the sensitive end of the spectrum for temperature; my wife sometimes gets the opposite and more common hot flushes at night, while I stay tucked in. I practice 'sleep hygiene' nowadays so I don't read in bed.

You could maybe fake up a directional vent by taping some paper to the vent with sellotape? Then you would know whether that solved your problem.

I'm not sure why the height of the bedroom ceiling should matter? It's the number of people in the room that determines the amount of CO2 produced. We have a CO2 meter in ours to keep an eye on it. If we turn the whole house ventilation rate down to 50 m³/hr then the CO2 gets up to around 1000 ppm but at 125 m³/hr its 500-600 ppm.

Posted By: Doubting_ThomasCan you post a photo or link to the type of outlet that you have?
From memory you can get different types, including directional ones as you suggest. I think the term is Coanda supply, although this search term seems to bring up just as much variation.

That would be a good starting point.
Coanda Effect vents are designed so that the supply air 'sticks' to the ceiling.
- Wall mounted ones tend to be directional, sending a 'beam' of air along the ceiling, potentially for a long distance. If that air hasn't diffused by the time it reaches the other side of the room it will hit the far wall and may cause a draft. Your directional vales, @stonecold, may or not use the Coanda effect - sounds like they are wall mounted?
- Ceiling mounted Coanda Effect vents diffuse the air in all directions, so are unlikely to cause cool drafts unless they are placed too close to a wall or other obstruction; indeed they are designed specifically to minimise the risk of drafts.

What size outlets? Maybe a larger size and larger bore supply hose a metre or so before it will reduce the velocity of the incoming air and feel less draughty.

Maybe you can bodge/test the current outlets with some masking taped on cardboard cowelling in order to see if a directional outlet vent is likely to improve things.

Posted By: djhApropos of nothing I just noticed an interesting page about ventialtion athttps://madinde.com/stossluften-shock-ventilation-in-germany" rel="nofollow" >https://madinde.com/stossluften-shock-ventilation-in-germany

It is, indeed a German obsession. The trouble is, most Germans don't follow the 'rules' of Stoßlüften, so their latest energy efficient homes are underperforming by between 15 to 35%.

It's a major factor preventing Germany from achieving its energy efficiency targets: https://www.politico.eu/article/germanys-energy-efficiency-open-windows-ventilation/

Posted By: djhWe have a CO2 meter in ours to keep an eye on it. If we turn the whole house ventilation rate down to 50 m³/hr then the CO2 gets up to around 1000 ppm but at 125 m³/hr its 500-600 ppm.

I have never thought to measure the CO2 level in our house, thinking now I should. When looking for a tester or measuring instrument my go-to supplier is test-meter. Had a look and the range is vast priced from £75 to £750.
Anyone got any recommendations. I would like data logging of sorts but don't want to spend silly money.

https://www.amazon.co.uk/gp/product/B079L5VD7P/

Michael de Podesta did a lot of experimenting using this one to log to a SD card

https://protonsforbreakfast.wordpress.com/2024/01/12/estimating-the-rate-of-air-changes-in-a-dwelling/

The 'industry standard' amongst passivhaus folk is Aranet 4 Pro, which uses NDIR sensors. However it still costs at least £175.

Reading this review convinced me to go for an Inkbird IAM-T1 which apparently uses the same sensors and is significantly cheaper:

https://breathesafeair.com/inkbird-iam-t1-review/

I found a seller on e-bay who offered me a discount, so I got one for something like £56. The only concession is that the data is only stored on the device for 30 days so you have to back-up via Bluetooth to your phone. I've set a monthly reminder to do that so that I don't have to leave Bluetooth on all the time.

Guess different people see different points for CO2 monitoring, hence the different instruments available!

If someone's using it long term to alert them to tweak their ventilation up and down, they need a different detector from if they're taking a one-off check that everything is set up ok.

My interest was in using CO2 as a tracer gas to do a one-off look-see of how airtight the house is. Needs a few hours of logging (onto a SD card is fine). But still on the to do list.

I use humidity as my indicator to tweak ventilation rate, because my house doesn't buffer moisture all that much, and this detects ventilation needed from laundry/cooking/showers as well as from breathing. Can see this wouldn't work if the house materials were the kind that would absorb many days of moisture.

Our local carbon footprint club uses the envisense ones as loan units. Easy operation, logging capability, not too expensive and reasonably sturdy.