HVAC options - two installers, different approaches
We are looking at getting a new HVAC system. We currently have a 10 SEER Carrier system that is roughly 10 years old. Ever since we have lived in the house (6 years) we have lived with a problem of air flow on the third floor (three story townhouse). When it gets warm in the summer (90+ degrees) we can't get the third floor to 77 degrees, at that point the AC runs constantly during the day. We have lived with it in the past, but now have a 7.5 year old and really want to regulate the temperature better on the third floor. Really, though, none of our vents (even the one coming right off the current air handler) would blow your hair back.
Our home is not open concept, the top and bottom floors have about 4 rooms each, and the second floor has three. By exterior dimension the home is about 2300 hundred square feet. (a little over 700 per floor).
We have talked with two different HVAC companies about the issue. The first suggested a Carrier Infinity 15 SEER system with a 3 ton variable speed air handler. He also talked about installing some directors in the vents to see if we could get some better flow on the third floor.
The second company suggested a 17 SEER Lennox system (he has some rebates right now that make it he same price as a 15 SEER, and the price is the same as the first installer) but recommended a 3.5 ton variable speed air handler to see if we could get better air flow that way. He also recommended trying (with a piece of cardboard at first) blocking the return on the first floor to see if that would help pull more air out the third floor return and better flow (if that worked he recommended partially sealing part of the 2nd floor return so that the third floor return would pull in more air). He said he recommended the 3.5 ton because of the number of registers we had (20).
So we called the first company back to ask for a quote on a 3.5 ton air handler, and he told he wouldn't do it, because it would cause back flow to the compressor that would shorten its lifetime and was a bad idea.
So the question is what should we do? I am no HVAC expert but I'm not sure who to believe here and would like some other opinions.