My house is a small two bedroom with a study, 97 sqm, and HRV installed 5 vents, every room + study.
Dvs came around and said one vent will be enough, personally i dont think so.
Nice work chim, will be interesting to see what you think, i checked my windows last nite and we had a tiny bit of condesation on them, but nothing major, mind you its been really cold and we have had the heater blasting.