I am about to replace my 30 yr old forced warm air heating system. I'm considering adding central ac & had the gas company come out yesterday to give me an estimate. The main plenum (or hot air duct..whatever it's called) is 8"x8" square sheet metal with 7 branch lines (which look like maybe 8" round sheet metal) running in my 44'x24' split ranch. The gas company HVAC tech told me that, while the setup was fine for heating, the ductwork was "maxed out" & he wouldn't add central ac to it. (The first HVAC company that came out didn't mention any such problem but that doesn't mean that they just weren't out for $$$ & would install ac in a marginal system) My question is this:
1.Is the gas company correct in saying I don't have enough duct size to connect a good ac system too it?- If so, short of ripping out the old ducts & starting from scratch, is there a way to overcome the main plenum size problem? (I am fairly handy & was even considering running another main duct from just above the furnace into my attic (short run as I own a split ranch) & then running branches off of this new line into ceiling vents to each room just for ac) Then maybe the HVAC pros could connect a baffle so that some of the air could be diverted into this new trunk line when I run the ac in the summer??? (I live in Mass so our cooling season is only a few months a year)