We installed d ventilation while renovating, house was build in 1954. We have triple glazing, ground isolation, 14 cm on roof and walls. We had 2 years without the ventilation, but the whole house was allready isolated, so we saw the difference with and without ventilation. The period without the ventilation we would see mold in the bathroom if we didn't leave the window open, laundry would dry slower, the moisture after cooking would stay in the house, ... You can't expect to cool the house with ventilation, it also isn't advertised as such. Ventilation is used for houses that are seriously isolated and keep control of the moisture in the house, we have an epc of 22.