HRV Sizing?

[rsspencer]

Dear helpful kind souls,

I'm trying to double check the size of an HRV the local guy is going to be installing for me. I trust him, but want to understand and verify as size does matter and makes big difference in price.

Anyway, for the main level house it has 24,600 cuft (high ceilings) which I figure means I need 144 cfm for .35 changes/hr. right so far?

The HRV's all have cfm graphs for different speeds and static pressures.
Without the ducts in place and a gauge, how do I know what the static pressure will be? Is there a general rule of thumb? I think the installer said he was estimating .5w.c. Or do I need to actually figure out duct runs and calculate it somehow?

FWIW, the duct ports of the HRV are 6" and 7" so he is planning on running same sized metal ducts with lots of turns and runs upto 60' with 3-4 90's before getting back to the trunk line.

Thanks for the wisdom and instruction.

[rsspencer]

[beenthere]

The duct would be sized the same as for a furnace or air handler to deliver X CFM at X static pressure..