With warm weather forecast for the rest of April, heating season here in central Virginia is pretty much over, so here’s a tally of the first winter’s performance of our 3-ton geothermal heating system with cast iron radiators (see welserver.com/WEL0961 for description of the system). Overall, the results were better than I expected, $267 for the whole winter, or about $51/month for the 5-month period Nov-Mar. Although we have solar panels, geo cost is calculated as if I bought all the power from the grid. I’m pretty confident of these numbers, which are based on welserver data. kWh values were calculated from a Hall effect current sensor on the line to the heat pump, and include the flow center and circulation pumps. The sensor was calibrated against an electromechanical residential electric meter using a resistive load (space heater), so if anything the kWh values are probably overestimated by a few percent due to power factor. I did not have the welserver set up in October, but degree-days as well as electric bill was almost the same as November, so I assumed the same kWh. Needless to say, I am very happy with the results. I was hoping to come in under $400, but I never thought it would be closer to $200! If I’d installed a gas boiler instead, I’d be paying $204/year just for the connection, never mind the gas. The only caveat is that this does not include hot water. We did not have a single problem with the system all winter, and we never needed backup heat from the oil-fired boiler. The coldest night was St. Valentine’s day when it dipped to 11°F, and you can see that the radiator temperature was maxing out at about 117°, but even then the system wasn’t running continuously, so it looks like it could have handled a few degrees colder than that. Performance of the loops was outstanding, the absolute lowest EST reading was 45°. Even so, I can think of a few tweaks that might squeeze a little more efficiency from the system. I should probably put a delay relay on one of the ECM circulators just to flush the last few gallons of hot water from the heat exchanger into the radiators at the end of each cycle. Also, when the unit is running at first stage, deltaT for the loop is only 4.5°, so I might save a bit by running just one of the flow center pumps on first stage. The thermostat is currently set to trigger second stage if setpoint isn’t reached within 40 min, but I’m thinking it might be better to just set second stage to come on at a certain outdoor temperature, say 32°, so that it would never come on in milder weather. Also on tap for the summer is even more insulating, e.g., the ceiling joists are only a little over half full of rock wool so that could use some improvement. More importantly, we just signed the contract for another 4 kW of grid-tied solar panels, which should be enough to cover both heat and A/C and will bring us pretty close to being energy self-sufficient and carbon-neutral.