Calculator Inputs
Example Data Table
| Scenario | Heating Load | Gas Efficiency | Geothermal COP | Gas Price | Electric Rate |
|---|---|---|---|---|---|
| Efficient home | 45 MMBtu | 94% | 4.4 | 1.30 per therm | 0.14 per kWh |
| Average home | 60 MMBtu | 92% | 4.1 | 1.45 per therm | 0.16 per kWh |
| High load home | 85 MMBtu | 88% | 3.7 | 1.70 per therm | 0.18 per kWh |
Formula Used
Gas therms used = Heating Load MMBtu × 10 ÷ Gas Efficiency.
Geothermal heating kWh = Heating Load MMBtu × 293.07107 ÷ COP.
Gas annual cost = Gas Therms × Gas Price + Cooling kWh × Electric Rate + Fixed Charges + Maintenance.
Geothermal annual cost = Total Geothermal kWh × Electric Rate + Demand Charges + Maintenance.
Net geothermal cost = Installed Cost × (1 − Incentive %) − Rebate.
Simple payback = Cost Premium ÷ Annual Savings.
Net present value = Present Value of yearly savings − Cost Premium.
Emission savings = Gas system emissions − Geothermal system emissions.
How To Use This Calculator
Enter the annual heating load for the building. Use bills, an audit, or a heat load report when available.
Add the gas system efficiency, local gas price, fixed charge, and yearly service cost.
Enter geothermal COP, electric rate, cooling kWh, auxiliary heat, demand charges, and maintenance.
Add installed costs, incentives, rebates, escalation rates, discount rate, and emission factors.
Press Calculate to show the result below the header and above the form. Use the CSV or PDF buttons to save the result.
Why Compare These Systems?
A geothermal heat pump moves heat instead of burning fuel. That difference changes the cost profile. Natural gas equipment usually has a lower first cost. Geothermal often has lower operating cost when electric rates are fair and the ground loop is sized well.
Energy Inputs Matter
The calculator starts with annual heating load. It then converts that load into fuel use. Gas heating uses therms after efficiency losses. Geothermal heating uses electric energy after dividing the thermal load by COP. A higher COP means less electrical input for the same delivered heat. Cooling fields let you compare a normal air conditioner with the cooling side of the ground source system.
Cost And Payback
Annual cost is not only fuel. Fixed utility fees, demand charges, service plans, and maintenance can move the result. Rebates reduce the geothermal first cost. The tool compares that net first cost with the gas option. Simple payback shows how many years savings need to recover the premium. Net present value discounts future savings, so long projects are judged more fairly.
Emissions View
Emissions depend on the grid and the gas factor. A clean grid can make geothermal very low carbon. A coal heavy grid can reduce that advantage. The input fields are editable, so local data can be used. This makes the comparison more useful than a broad average.
Practical Use
Use conservative values when planning a real project. Heating load should come from bills, a load calculation, or design software. Prices should match current utility tariffs. COP should come from rated equipment data and installer design notes. The result is an estimate, not a final design. It helps screen options, test rate changes, and start better questions with contractors.
Sensitivity Checks
Small changes can shift the answer. Try higher gas prices, lower electric rates, and different COP values. Also test a larger rebate or a bigger service gap. These checks show risk before money is spent. They also show which variable matters most. Many homes save because geothermal avoids combustion losses. Some homes save less because electricity is costly. The best choice depends on climate, load, tariffs, loop cost, and comfort goals. Always compare bids with equal scope and warranty terms.
FAQs
What does COP mean?
COP means coefficient of performance. It shows heat delivered per unit of electricity. A COP of 4 means four units of heat are moved for one unit of electric input.
Why is heating load entered in MMBtu?
MMBtu is common for building heat demand. It also converts cleanly to therms and kWh. One MMBtu equals ten therms or about 293.071 kWh of heat.
Does this replace a contractor design?
No. This calculator gives an estimate for comparison. Final design should use room loads, soil conditions, ductwork, loop design, and equipment ratings.
Why include cooling kWh?
Many homes compare complete comfort systems. Gas handles heating, but cooling still uses electricity. Cooling kWh helps compare total yearly energy cost more fairly.
What is simple payback?
Simple payback estimates how long annual savings take to recover the extra upfront cost. It does not fully include financing, taxes, or resale value.
Why use net present value?
Net present value discounts future savings. It helps compare long term savings against money spent today. A positive value favors the geothermal option.
Can gas be cheaper than geothermal?
Yes. Gas may be cheaper when gas prices are low, electric rates are high, geothermal installation is costly, or the heat pump COP is weak.
Which emission factors should I enter?
Use local utility or government values when possible. Gas emissions use kg CO2e per therm. Grid emissions use kg CO2e per kWh.