As I mentioned before, I'm in the process of getting quotes for a new central air system. I already have forced hot air heat and with a coil installed, and am trying to decide between bids.

One bid is for a York Latitude 4-ton unit with a SEER of 13 for $4250. Another is for a Trane XB13 48000 BTU unit with a SEER of 13 for $5026. A third is for a Trane XLi 48000 BTU unit with a SEER of 14 for $5803. I'm still waiting on a fourth bid.

Do I understand correctly that 48,000 BTU is the same as 4 tons? If so, they're all recommending the same size unit. None of them provided me with Manual J calculations, and only one of them (the lower-end Trane estimate) went through the house looking at rooms. I believe they all estimated from the size of my furnace, the square footage of my house, the age of my home (100 years), the height of the ceilings (9 feet), and their knowledge of the climate conditions in this area.

I know that you all can't give me a hard answer on this, but I'm going to describe my house to see if the 4-ton unit seems reasonable. I tried using the calculation program someone recommended here, but didn't really understand it.

My house is a semi-detached unit, the east side of a two-family house. There are seven windows facing north (three of them double-paned Low-E windows with good insulation, the rest old and drafty, but hopefully soon to be replaced). None of these windows are shaded by trees. There are 10 windows that face east, three of the good windows and the rest old, none of them shaded by trees. There are six windows facing south, all old, all shaded by old trees. The house gets full sun in the morning, but is in shade throughout the afternoon.

The house is about 2300 square feet on three floors, with an attic above the third floor and an unfinished basement. There are 9-foot ceilings throughout. There's some insulation in the walls of the first floor and in the attic, but the house is fairly drafty.

We have a family of three, do only light cooking in the summer, and when we entertain in the summer, it's outside.

I live in New England, near Boston. The average summer temperature is around 80, though it gets nearer to 90 pretty frequently. Humidity is the big problem, though. Average summer humidity is about 70%, but often gets to 90%.

I've read the information about not getting too large a unit, as it won't be able to remove humidity properly, so I'm concerned about that. I've asked all the contractors who gave me estimates to provide the Manual J information, but two admitted frankly that they didn't do it and one is hemming and hawing. I know the recommendation here would be to find someone else, but I have no idea who to choose. The estimates I have so far are from Home Depot, from the single recommendation I was able to get from friends, and from the HVAC person I used to install my furnace (liked them a lot, and the other contractors have all commented that they did an excellent job). I suppose I could pick some contractor at random from the phone book, but hate to do that.

I very much appreciate any information you can give me.