Hello there, I am in the process of installing a HRV in my house ,and have been searching for any info available . I read an artical where they used thin-walled pvc for attic ducting. Is this an accepable practice ? Also do you need to install backdraft dampers at every room exhaust register . Or would one at the house exhaust do the trick ? This is a full ducted system no other hvac is installed in the house .

Just had a new HVAC system (4 ton) installed by a national brand dealer. It's a downflow, airhandler is in a closet in the house, newly installed ductwork runs through the crawlspace underneath. There is a major (2 ft. dia.?) supply trunk down the center of the crawlspace, all roooms are fed off of that via 6" insulated metal duct. Supply trunk and 6"duct are wrapped in foil faced insulation. Question 1. Should the ductwork be suspended from the overhead? The way it is now, the feeders are suspended but the main trunk is laying in the dirt. Question 2. The air filter at the handler is 20x25 (500 sq.in.) but the air return intake grill at the wall is only 35x10 (350 sq.in.). There were no restrictions on the size of the grill, so the final size and configuration were at the discretion of the installer. Is it likely this reduced cross section will hamper the airflow? Thanks in advance.