Geothermal Heat Pump Sizing Calculator
A geothermal (ground-source) heat pump exchanges heat with the relatively stable underground temperature rather than variable outdoor air, delivering high efficiency for both heating and cooling -- but the ground loop, not the heat pump unit itself, is usually the biggest cost driver of the installation. This calculator takes a building heating/cooling load in BTU/hr and a ground loop length per ton (ft/ton) to size the required heat pump capacity in tons and the required ground loop length in feet, giving you a planning-level estimate of system scale before a site-specific geotechnical assessment. It pairs naturally with our Geothermal Direct-Use Heating Calculator for the hydrothermal-resource side of geothermal heating, and our Home Energy Audit Calculator for the load-calculation side that feeds this sizing.
A professional Manual J load calculation gives the most accurate figure for your specific building. As a rough reference, a typical mid-size (2,000-2,500 sq ft) U.S. home often falls in the 36,000-60,000 BTU/hr range, though insulation quality, climate, and window area cause significant variation.
Vertical closed-loop systems typically require 150-300 feet of loop per ton of capacity, depending on soil thermal conductivity and local climate -- sandy or rocky soil generally requires more loop length than moist clay soil, which conducts heat more efficiently.
building heating/cooling load (BTU/hr) ÷ 12,000
required heat pump capacity (tons) × ground loop length per ton (ft/ton)
This is a simplified planning-level estimate. Actual system sizing should be based on a professional Manual J (or equivalent) load calculation and a site-specific geotechnical assessment of soil thermal properties -- consult a qualified HVAC contractor or geothermal installer before finalizing system design.
Results update live as you type. For planning and field-check estimates — always verify against applicable standards and equipment ratings.
How we calculate this →Ground loop length -- not the heat pump unit itself -- is usually the biggest cost driver in a residential geothermal system, and it depends heavily on local soil conditions. A 5-ton system (serving a typical mid-size home) needs roughly 1,000 feet of ground loop at 200 ft/ton, but the same system could need anywhere from 750 to 1,500 feet depending on whether the soil is dense, moist clay (efficient heat transfer, less loop needed) or dry, sandy soil (poor heat transfer, more loop needed) -- which is exactly why a site-specific soil assessment matters so much for accurate system cost estimates.
How geothermal heat pump sizing is calculated
This calculator sizes a residential geothermal (ground-source) heat pump system from the building heating/cooling load and a ground loop length per ton, producing the required heat pump capacity in tons and the required ground loop length in feet. Two quantities tie the calculation together.
Required Heat Pump Capacity (tons) = Building Heating/Cooling Load (BTU/hr) ÷ 12,000. One ton of heat pump capacity equals 12,000 BTU/hr -- a unit originally derived from the cooling effect of melting one ton of ice over 24 hours and still the standard sizing unit throughout the HVAC industry -- so dividing the building load by 12,000 converts BTU/hr into tons of required capacity. At the default 60,000 BTU/hr, that is 60,000 ÷ 12,000 = 5.0 tons.
Required Ground Loop Length (feet) = Required Heat Pump Capacity (tons) × Ground Loop Length per Ton (ft/ton). Multiplying the required capacity in tons by the loop length needed per ton gives the total ground loop length the system requires. At the defaults (5.0 tons and 200 ft/ton), that is 5.0 × 200 = 1,000 feet.
Two notes on the model. First, the ground loop length per ton is the single most consequential input, and it varies substantially with soil thermal conductivity and local climate -- vertical closed-loop systems typically require 150-300 feet per ton, with moist, dense clay soil at the lower end (efficient heat transfer) and dry, sandy, or rocky soil at the higher end (poor heat transfer), so a site-specific geotechnical assessment is essential for accurate loop sizing and the editable field lets you substitute a project-specific figure. Second, this calculator covers capacity and loop-length sizing only and does not model the heat pump unit selection (which depends on entering water temperature, flow rate, and manufacturer performance data), the choice between vertical and horizontal loop configurations (vertical loops use deep boreholes on smaller lots; horizontal loops use shallower trenches across more land), auxiliary or supplemental heating for extreme conditions, or installed cost -- all of which a full system design would include. For the load-calculation side that feeds this sizing, see the Home Energy Audit Calculator; for the hydrothermal-resource side of geothermal heating (using a geothermal fluid directly rather than a ground-source heat pump), see the Geothermal Direct-Use Heating Calculator. Data sources: Heat pump capacity unit definition (1 ton = 12,000 BTU/hr) from standard HVAC engineering references (ASHRAE Handbook); vertical closed-loop ground loop length ranges (150-300 ft/ton) and soil thermal conductivity variation from International Ground Source Heat Pump Association (IGSHPA) and DOE (Department of Energy) geothermal heat pump design guidelines; residential building load ranges from ACCA Manual J methodology and DOE residential building energy analysis. Verification: with defaults (60,000 BTU/hr, 200 ft/ton), Required Heat Pump Capacity = 5.0 tons, Required Ground Loop Length = 1,000 feet.