Mechanical Heat Recovery Ventilation experiences

hi all new to the forum. i was just wondering about the MHRV, i am going to start my house in the next few weeks which is a storey and a half and was wondering two things 1) What type of floor construction do you need ie. can it be used with timber joists? 2) do i need a heat source ie. central heating. thank you in advance for your help!
 
I installed MHRV in2001. Called the company back because noise transfer from room to room. They put in flexible section in pipes which solved this. I later opened the heat exchanger and found black mould. I removed it to clean it. It was out for a week or two and water was dripping from the vents. When I removed the ceiling openings to dry the ducts the cloths came out covered in black mould. Unless the system is on 24/7 damp air rises into the outlets and condenses. I now have an unused MHRV system as I no longer trust it.