I don't think they are mandated. I've had air scores lower than 3 in houses before and nobody has ever came along and forced me to have one. There's no mechanism to, unless the bco is very switched on. Besides isnt it mechanical ventilation which is in the regs not nessecarily mvhr? What's all this Dmev stuff you hear about?
You're in the m&e business can we trust your impartiality here 🤣 I'm just saying I've lived with one in an airtight house and without one in a house with a score less than 3. Its just my personal opinion, nice to have but windows also work. Are @ToughButterCup and @nod nuts too?