My old HVAC system suffered damage due to a lightning strike. I called up a local service co. and they sold me on a Trane split-system that was slightly oversized compared to what we had. The new equipment went into the same space and they adapted the existing duct work.
On the second or third day of work, one of the installers offered to add a new return and he said it would be free. I wasn't sure why it was necessary, but I figured he must know what he's doing and he's doing it for free, so why not? He cut a big return about 14x18" low in the wall directly behind the HVAC, opening up the plenum box to the living space so that intake air feeds right into the bottom of the air handler, just "ahead" of where the filter is mounted.
It seems to me this modification will severely unbalance the pressure throughout the house. Was this a sensible thing to do? If so, why?
- Previous air filter was 16x25x1 new one is 20x22x1
- 2-story single-zone house with thermostat upstairs
- HVAC is centrally located in a closet downstairs
- Ducted registers and returns in every room (no returns in 2 bathrooms)
- In-ceiling ducting downstairs, floor registers and wall returns upstairs
- High vaulted ceilings upstairs
- Temperature difference between up/downstairs can reach 11F (chest height)
- Location is Southern Missouri, heating with heat pump Oct-Apr
- No dampers or other seasonal adjustment practices
- My assessment of the home's insulation is poor-to-very-poor