I'm looking for advice for when it comes to future proofing my home, since I'm about to have some building work done (an interior wall down, kitchen & living room gutted and redecorated). I'm trying to make my home a bit more efficient if possible, but also recognise that I need decent air flow. I have a 1980s detached brick house with cavity wall insulation, good loft insulation, double glazing, concrete floor, gas central heating. Most downstairs windows have trickle vents, upstairs does not.
With trickle vents closed and windows closed, the house tends to hold onto heat quite well. During the recent storms I found a few gaps around windows where wind could come through, so I will seal those soon. The trickle vents work well when open, but also seem to seal well when closed.
I don't have any issues with condensation downstairs, but the air in the house can become quite stale in winter and smells from cooking, etc tend to linger for a long time. Upstairs I get a little bit of mould at the very top of the outside walls - presumably where the top of the wall meets the roof and cool air is circulating into the loft from outside and cooling this part of the wall and ceiling. Usually I can wipe these areas once or twice a year which keeps any mould away, but this again suggests to me that airflow is probably an issue. This is less of an issue in my upstairs bathrooms as they have extraction fans which run for a decent amount of time after use, but here I feel like I am venting lots of hot air alongside any moisture, which feels wasteful.
I also recently got my hands on a co2/humidity/temperature monitor, which confirms to me that humidity in the house is fine, but co2 levels can get a little high (up to 2000ppm at their peak for a few hours in the evening).
So, in short I think I need to increase air flow throughout the house, but try to reduce heat loss if possible.
I am a little confused by the available options. So far I've been made aware of MVHR, d-MVHR and PIV. Whole house MVHR is probably going to be quite expensive and destructive. I don't see where I could get vents to my ground floor, for example. Presumably only installing on the first floor (from the loft - which would be easy) is a bit pointless. d-MVHR seems like it would be much easier to install bit by bit, although I am worried that some of the units might be noisy. Is there d-MVHR that would work well for a bathroom or kitchen? PIV is clearly the easiest to install, but would it help much?
I would appreciate any help or advice offered. Thanks!