'A' rated house but gaping vent holes

It only covers the bathrooms. All other rooms have the typical hole in the wall - so have ventilation but cold draughts.

I have a 2018 built bungalow, sliding sash windows all round and regular wall vents.

I think our air tightness was about 4.5 when we did it.

The condensation in the windows is terrible in cold weather, particularly in the bedrooms. The windows are timber and we’re starting to see some mould forming on the window frames.

Have a guy coming next week to look at putting in an mhrv system, he said it would do a full room exchange about every 2 hours, I’m guessing this will go a long way towards solving the condensation issue.

Block em up.

A car if left parked up for months will get mouldy and moist inside, as it has no vents! But if you're using your car, getting in and out of it, driving it, and using heater then a car NEVER moulds up while in use, and neither would his house if he blocked the vents, as people come and go, air gets in regardless, heating is on, windows are open.

I'd block them, not a permanent job, but in cold weather, block em.

You're going to always have some level of condensation with warm air hitting cold surfaces and vice versa, even with vents and open windows. In my experience it's the Irish winter which is wet and with big differences in outside and inside temps when heating is on. Ventilation is good for CO2 levels and smells etc but from what I've seen it won't stop some level of condensation, unless your house has no cold external surfaces.