I have a mostly commercial industrial background, but have installed a few full systems in residential applications. We are currently bidding on installing new HVAC system as retrofit. The home is 2 story, and the first floor system air handler will be installed under house in crawl. Other contractors have recommended to the customer that the return be installed inside the wall. I honestly don't understand how this can be done without compromising the integrity of the wall and or structure. Do you drill holes in board at bottom of wall, or cut the whole board and them re-support? I honestly would have thought installing the return in the floor would be better. Any experienced suggestions would be great, Thanks to all!