A geothermal (ground-source) heat pump doesn't generate heat the way a furnace or electric-resistance heater does — it moves existing heat from the ground into your home, which is why it can deliver more energy as heat than it consumes as electricity. The coefficient of performance (COP) is the single number that captures how efficiently it does this. This calculator computes measured COP from real readings, the theoretical Carnot ceiling from ground and output temperatures, and the dollar savings versus electric resistance heating.

How the Geothermal Heat Pump COP Calculator works

The COP tab uses COP = heat output ÷ work input, converting BTU/hr heat-output readings to kW (1 kW ≈ 3,412 BTU/hr) so both sides of the ratio share units. This is the same definition used by DOE and ENERGY STAR to rate heat pump equipment.

The Theoretical Max tab applies the Carnot formula, COP_carnot = T_hot / (T_hot − T_cold), using absolute temperatures in Kelvin. This is a physics limit, not an equipment rating — it tells you the best any heat pump could theoretically do between your specific ground and output temperatures, regardless of manufacturer or model.

The Savings vs Resistance tab compares your system's electricity use to electric resistance heating, which by definition has COP = 1 (every watt of electricity becomes a watt of heat, with no heat moved from a reservoir). A system at COP = X uses only 1/X the electricity of resistance heating for the same delivered heat.

Inputs and what they mean

Heat output is the rate of usable heat your system delivers — from a manufacturer spec sheet, a rated capacity, or a field measurement. Switch between kW and BTU/hr depending on what your documentation uses.

Work input is the electrical power the compressor and auxiliary equipment draw — this is what shows up on your electric meter, not the heat delivered.

Ground and output temperatures (Theoretical Max tab) should reflect your specific site: ground-loop or groundwater temperature for the source, and the supply temperature your distribution system (radiant floor, forced air, etc.) requires. A smaller gap between the two raises the theoretical ceiling — this is exactly why low-temperature radiant systems pair so well with geothermal heat pumps.

Electricity rate and annual heat demand (Savings tab) should reflect your actual utility rate and your home's estimated annual heating load in kWh — available from a home energy audit or a Manual J load calculation.

Limits and edge cases

Measured COP from a single heat-output/work-input reading is a snapshot, not a seasonal average — real COP varies with ground temperature, load, and defrost cycles over a heating season. For a rating that accounts for this, look for the equipment's published Integrated Energy Efficiency Ratio (IEER) or Heating Seasonal Performance Factor equivalent rather than relying on one measurement.

The Carnot calculation is a hard physics ceiling, not a design target — no real compressor cycle gets close to it, so a low percentage of Carnot (40-60% is normal) does not necessarily indicate a problem. It's most useful for comparing two systems or two temperature scenarios against each other, not as a pass/fail threshold.

The savings estimate assumes your annual heat demand is met entirely by one heating source at a constant COP — it doesn't model backup resistance strips, defrost-cycle losses, or demand charges that some utilities apply. Use it for early-stage comparison, not a final utility bill projection.