We recently moved into our house and had central HVAC installed to replace the old forced air furnace. Unfortunately, the return is in the living room near the TV, and it's very noisy when the system is running. Some of the noise comes from the furnace being located just behind that wall, but the main problem is the loud sucking noise from the return, and we'd like to reduce it if we can.
Our house is a single story of appx 1200 sq ft, the furnace is a Rheem RGPN-05NAUER (3-ton), and the return opening measures 8x24" or 192 sq in. There is no actual duct for the return; the furnace sits on a raised, enclosed platform in the closet appx 17" above the floor, and the return opening feeds directly into that open space, which measures 48x50" or 2400 sq in. The system cools well, but the living room and its adjacent room (both up front with no door between) tend to be a little cooler than the rest of the house.
From what I've read, it looks like the return opening is too small regardless of noise or cooling concerns, and I expect that having it enlarged would help reduce the sucking noise. I'm debating whether to bring the contractor back (he took a couple other shortcuts) or call in someone else, but is there some sort of formula or general rule for sizing the return opening? Alternatively, would a second opening be acceptable or advisable? It would be in an adjacent room up front or in the dining room just beyond (all share walls with that closet).
Also, I'm curious as to whether the return arrangement with that open space under the furnace is okay, as opposed to having an actual duct from the return opening to the furnace. I don't think it would cost a lot to have one installed but I'd rather not spend the money if it's unnecessary.
I'm not interested in DIY, I just want to get a handle on things before I proceed. I expect I've already made mistakes by not being better informed.