I live in a two-story colonial in Virginia built in 1947 that has a two-story addition on the back that was added in 1984. Last year, I had a Carrier Infinity system installed (3 ton A/C, 60k btu 95% furnace). It works great for A/C, but I’m having problems with heating. In a nutshell, the addition is always cold, which is odd since the airflow seems fine and it is better insulated than the rest of the house--it does not get too warm in the summer even though it faces SW and has large windows and skylights. But it is always 4-5 degrees colder than the rest of the house in the winter.
I know the typical zoning setup is to have a zone for each floor, but because of the way the ducting is run in the original house, that is not feasible. (The main supply duct for the original house runs horizontally through the basement, alternating ducts that feed the first floor, second floor, first floor, etc. It could not be zoned without extensive ductwork.)
But because the addition has the same cold problem both in the downstairs family room and the upstairs master bedroom, it seems as though I could zone the addition separately. The supply plenum has two main branches—one feeding the original house, and the other extending into the crawlspace under the addition, and then feeding the supplies on both the first and second floors. This seems to be a simple setup that could be accomodated by two dampers.
Any thoughts on this unorthodox zoning? I requested a Carrier Infinity Zone thermostat with the original installation so I could upgrade later without ditching the $500 thermostat. The installer recommended against zoning this way when it was installed but said he would give me a good rate if I came back and requested it later. The reason the installer recommended against zoning was to give the Infinity system a chance to equalize the temperature by having the fan run on low continuously. This hasn't worked. The old system also resulted in colder temperatures in the addition.