I have a 3 T unit serving about 1600 square feet of leaky old stone house. Although there was an energy audit and blower door test, my system seems to have been generally designed according to a rule of thumb, like "old stone houses around 1600 sqft require a 3T system." I got 3 quotes from installers, and all of them took the energy audit information and propsed a 3T system. This winter, we spent a nearly all of our time below 40 degrees cycling between 2nd stage and auxiliary electric heat. Our electric bills were large. We have been going back and forth with our installer for several months on a fix. W purged the loop - no improvement. They came out and did another energy audit - blower door, IR photos, etc. - and came up with a large winter ACH number - almost 2 and an 85,000 BTU/hr heat loss. Yes - our house leaks. So now, instead of a 3T system, they would like to upsize us to a 5T and have asked us to pay for additional loop, which is going to be expensive on our particular piece of property. Does this seem crazy to anyone else out there? Yes, our house leaks, but we have spent significant money tightening things up since the first audit, with little effect on the ACH number. We plan on doing more to tighten up the building in the future. I see people on here with 3T-4T units serving 3,000 sqft of old house. I'm trying to figure out if the 5T proposal for 1600sqft makes sense in ANY context. They would also like to size the loop field at 6T for a 5T unit - an addition of 2T of loop. I've looked at the load calculations and they seem to make sense - although I'm not an expert. I'm also a little worried about the system's ability to cool the house in the summer. With the 3T unit last summer, we struggled to cool the second floor because the first floor has thick stone walls and is always cool (i.e. the A/C doesn't often run). If I make the unit larger, won't this exacerbate the problem? Help! Need some feedback!!