Hello, Allow me to apologize in advance for the very long post. I am brand new to geothermal. I am located in the central part of SC. I own a 3000 square foot historic home with minimal insulation. 1800 sq ft downstairs and 1200 upstairs. We have around 10" of blown cellulose in the attic and 6" batts underneath the house in the crawlspace. External walls have only been insulated when the exterior siding needed replacing which allowed me access to install batts with vapor barrier. Otherwise, there is no wall insulation. I am planning on adding additional cellulose in the attic this summer. We recently had all the ductwork replaced as well as both hvac systems. The installer put in a closed loop system with four 250' long trenches 6' deep. The loops ran out on the bottom of the trenches and returned at 4' deep. The upstairs now has a 3 ton Waterfurnace 5 series split unit (500A11). It has performed well since it was installed at the beginning of December 2021. It runs mostly in stage 1. Two weeks later the downstairs unit was finished. It is a 3 ton Waterfurnace 5 Series outdoor package unit (506A11). Since it was installed, the unit has been running on the auxiliary heat about 1/3 of the time. I kept questioning this and finally after I got an outrageous power bill, the installer came out and installed an outdoor sensor and programmed the unit not to use the heat strips until the outside temp reaches 10° - which should happen once every five years or so here. Since the heat strips were disabled, the unit has struggled to heat the downstairs. The last three nights it was 27, 28, and 30 degrees respectively. Running in stage 2, the unit was not able to reach the 70 degrees set on the thermostat until the late afternoon. We also have an 8 degree difference between the first rooms in the duct run and the last 2 rooms in the duct run. One other odd thing is the waterlines as they exit the ground under the house are actually about 70' or so from this unit itself so they are lying on top of the ground in tube type insulation for about 70' til they reach the unit. (Upstairs unit has the pipes coming up underneath the unit like they should be.) My installer doesn't think this makes a difference. The installer did run a program to determine the size of the units needed. He knew we had an under insulated historic house and that we will not be adding any wall insulation and added that info into the program. How can we need the same size unit for the upstairs and the downstairs? From the symphony program I can tell that the loop temperatures for the upstairs unit is typically 9 degrees warmer than the other loops. The trenches were filled with the air temperature being around 65 degrees for the upstairs unit and the dirt was dry but the other unit 2 weeks later had a much colder temperature of around 39 degrees and the soil was wet for those trenches when they were filled. Could that still have an impact 45 days later? Also, I've noticed the supply air temperatures for the upstairs unit are usually 10-15 degrees warmer than the other unit. I'm hoping to get some suggestions and education from you guys. My installer has said that worst case scenario we can increase the outdoor packaged unit to a 4 ton and that would necessitate adding an additional 200' trench. He wants us to wait until a cooling season cranks up to make that decision. But if the 3 ton unit isn't capable of heating the space when the temps fall below 35 or so, what does it matter if it can cool the space?