OK:
The WHF for the apt to attic; you need MUA into the apts, or you create a negative pressure situation which can be dangerous or a nuisance. (Pilot lights going out, etc)
A good HVAC guy may be able to help you; or try a 'factory guy' from the WHF Mfg thru th supply house.
Now, if you force all the air into the attic, the AF has to be sized (and on) to pull it out of the attic, or the WHF will not operate efficiently.
John
