Hello, we would like to finalize our decision which contractor to go with for geothermal installation in our home but there are still a few things hanging in the air that we would really appreciate some independent views on. We are retrofitting an existing home in Maryland (4000 sqft on 2 levels + basement) with the Waterfurnace Synergy 3D. We plan to use the existing ducts for cooling, but we plan to install radiant floor heating as the only heating source. Manual J calculations seem to point to a 5T unit to satisfy the heating load (the cooling load is only around 35,000 BTU). The first question we have is about the loop size. One proposal we got promised 160' of vertical 1.25'' loop per ton. Another contractor noted that based on a software that takes into consideration the location-specific factors, he would only install about 600' of 1.25'' loop total. We live in an area with solid rock about 40' below surface and average temperature of 56F. We understand from reading this forum that loops should not be sized by a rule of thumb, but we've seen too many mentions of the 150-200' per ton before not to be a little worried. A software can be wrong too... Of course the lower cost of the shorter loop is very tempting, but we want to do this right. Could anyone let us know whether the shorter loop makes any sense? One of the reasons we are worried is because another contractor mentioned that using radiant floor heating should be actually paired with a loop sized for a 6T unit. That really confuses us because we thought radiant floor heating was more efficient than forced air heating. The second question relates to duct sizes. For cooling, we want to have three rooms of the house on a separate zone from the rest of the house. We would like to create this zone using the three existing 7'' round ducts and just branch them off in the basement from the main supply. On one side, we are being told that additional ducts would need to be added between the basement and the second floor because the three existing ones together are not sufficient for the 5T unit output even when the unit runs in the lower stage, and thus we would be damaging the unit whenever the small zone calls alone if we did not add more ducts. On the other side, we hear that this is not a problem when a Waterfurnace zone controller with a variable speed fan is used. Could someone please shed some light into this for us? Any insights would be greatly appreciated. Thanks a lot for reading this.