We've been quoting for MVHR's left right and center these past few weeks and have come to several conclusions: We're confident we can DIY the installation We think we can design the layout of the ducting (for a radial system with semi-rigid ducting) We have no idea why spec's (and therefore costs) being quoted to us vary so immensely (suppliers & units below)     Calculations for Whole Dwelling Ventilation Rates (Table 5.1b) Calc 1 (# rooms) 4 be