Mechanical heat recovery ventilation system

Smaller halls and landings often wont have outlets.

Installed a PIV in the landing and the heating coil generated a lot of moisture in the attic as it was at the unit end, not at the point where the duct enters the plasterboard of the landing. There are different models so watch out for this if installing. Worked great otherwise but it's a 400w heater so you'll have bills...!! Did keep the kitchen smells downstairs though.

In the end I took it out due to moisture issue and attic has been dry since. Retrofitted a Zehnder Comfoair 350 for the upstairs only and the bedroom air quality is massively improved. 3 x bedrooms and 2 x wetrooms covered. It's slightly audible as the lowest setting expects to do a whole house so velocity is a bit higher than it would otherwise be but if you can sleep in a hotel room ok it's no worse than that.

You can always crack open a window but over the course of a night, this may not be desired / possible so air quality decreases over time. I've 2 x F7 filters on the unit and an air quality sensor in my bedroom.

I'm a B1 but no air tightness done - I've Z profiles in the passive air vents still and not blocked them up yet (these cut down sound but narrow the air passage significantly). Ideally you'd do air tightness first as air will start flowing in different ways. Not seen any issues after 18 months and no lingering damp in wet rooms after showers etc.

Doing downstairs would be a significant challenge though as a retrofit but was the next step in the plan....

Both should but PIV tend to underperform. Go with cMEVs, but do your research and plan well if you get irritated by noise, as cause some can be noisy.

Likely yes they will

sensorpush - Robin Clevet used it in a recent youtube video on his channel to test a new build house. About the size of a box of matches, battery lasts a year, bluetooth and just sync your phone / app with it every 2 weeks or more often. Mine is in my attic (see below) after the condensation issue I had with the PIV unit. There is a gateway device you can also buy to internet connect the sensorpush but it's hard to find in stock. Get one and move it around daily to measure different rooms.

MVHR have two types - Enthalpy models can cause problems with moisture but I doubt you have that type. Yours is too high, not too low!

Do you have any commissioning paperwork for the MVHR? Flow rates etc? Be good to see if its balanced or not? You're on the right track.

How do you dry your clothes, how many showers are active / day - you also have humans adding to moisture, how many bodies vs what is the floor area of your house? Opening windows in the morning is a good idea, having some data on humidity will help too. Cooking / extract, opening windows after showers, ventilating bedrooms with fresh air in the morning should all help. Be good to identify rooms with highest levels of moisture and what times it builds up.

What is your heating type? Any gas heating? Just wondering where all the moisture is coming from? The humidity measuring will be interesting. I'd guess it's the bedroom and not the wardrobe that's the issue, solve it there, the wardrobes should be ok. You're just missing humidity data to help trace the severity and cyclical timing of the issue.

It is a nice idea to have a valve in a large wardrobe, but I am sure it not essential, would rather be a fun advanced DIY project. You prob dont have enough flow into your bedroom. How much is the valve open? Post a pic or a measurement.