One of the final significant jobs I had to do before we moved in was connect up and commission the MVHR.  All the radial ductwork and individual plenums had been fitted at first fix, however I had left installing and connecting the actual unit until the loft has been insulated, as I didn't want to risk pipe connections being damaged.   The day before we were due to move in, the insulation contractor having laid all the loft insulation, I spent a couple of hours in the loft space above