# Geothermal direct use and ground-source heat pumps: Correlation Prices it moves with, and why Source page: https://www.materialinsights.org/energy/e_geo_direct/correlation/ Geothermal direct use and ground-source heat pumps cost mainly the heat pump unit, ground loops or wells, and installation. Running costs follow electricity tariffs, and demand rises when gas or oil heating is expensive or restricted. Price index **US PPI: heat pumps** index (BLS base period =100) · monthly, Dec 2009 to Sep 2026 #### What its price moves with Selected link ##### Geothermal direct use and ground-source heat pumps and Heat pumps, air conditioning and refrigeration Monthly changes 0.28 weak correlation 12-month changes 0.63 moderate correlation Last 5 years 0.18 monthly changes Lead or lag none No clear lead or lag Price function, Dec 2009 to Sep 2026 Geothermal direct use and ground-source heat pumps ≈ 6.45 × (Heat pumps, air conditioning and refrigeration)^0.55 R² 0.96 On this fit, a 10% higher heat pumps, air conditioning and refrigeration price goes with a 5.3% higher geothermal direct use and ground-source heat pumps price over the long run. Units: index (BLS base period =100) and index. Chart: Geothermal direct use and ground-source heat pumps and Heat pumps, air conditioning and refrigeration prices rebased to 100 at Dec 2009, log scale Both prices rebased to 100 at Dec 2009, on a log scale so equal percentage moves look the same size. Chart: Geothermal direct use and ground-source heat pumps price against Heat pumps, air conditioning and refrigeration price, monthly, log scales, with fitted line Each dot is one month; paler dots are older (2009), darker dots recent (2026); the ringed dot is the latest month. The dashed line is the fitted price function. Both axes are logarithmic. Energy [HP Heat pumps, air conditioning and refrigeration](https://www.materialinsights.org/energy/e_heat_pumps/)Shared industry 0.28 Ground-source units are a type of heat pump made by the same industry as air conditioners. The US indices move together moderately: monthly changes correlate at 0.28 and yearly changes at 0.63. weak co-movement month to month · 202 months Show charts Commodity [Cu Copper](https://www.materialinsights.org/commodities/copper/)Main input 0.13 Compressor motors, heat exchangers and pipes use copper. The US heat pump index shows little monthly link with copper, at 0.13,, rising to 0.27 over the last five years, still a weak link. little or none co-movement month to month · 202 months Show charts Chemical [HDPE High-density polyethylene](https://www.materialinsights.org/chemicals/hdpe/)Loop input 0.04 Ground loops are long runs of HDPE pipe buried in trenches or boreholes. The resin proxy and heat pump index show a weak link, with yearly changes correlating at 0.23. little or none co-movement month to month · 202 months Show charts Energy [Gas Natural gas](https://www.materialinsights.org/energy/natural_gas/)Rival source −0.10 Gas boilers are the main rival for heating, so high gas prices raise demand for heat pumps. The indices show this only over a year, with 12-month changes correlating at 0.42. little or none co-movement month to month · 202 months Show charts Energy [Bld Energy in buildings](https://www.materialinsights.org/energy/e_buildings/)Running cost 0.03 Heat pumps run on electricity, so power tariffs decide running costs and payback. The US electricity price and heat pump index show a weak yearly link at 0.29. Cheap power speeds payback. little or none co-movement month to month · 201 months Show charts Chemical [HFC Fluorochemicals and refrigerants](https://www.materialinsights.org/chemicals/fluoro_intermediates/)Working fluid −0.00 Most heat pumps use fluorinated refrigerants, which face phase-down rules. The US fluorochemical proxy and heat pump index show a weak link, with yearly changes correlating at 0.23. New refrigerants cost more. little or none co-movement month to month · 202 months Show charts How to read these numbers **Correlation of monthly changes** (the number in the coloured pill) compares how much each price moved, month by month, since 2006 or the first month both series exist. It runs from −1 to +1: near +1 the two usually rise and fall in the same months, near 0 there is no link, and a negative number means they tend to move in opposite directions. Above 0.7 is strong, 0.4 to 0.7 moderate, 0.2 to 0.4 weak. **12-month changes** compare year-on-year moves, which shows whether two prices share the same cycles even when the month-to-month noise differs. **Price function** is a straight-line fit of the two prices on logarithmic scales: price ≈ k × (partner price)^β. β is how much this price moves, in per cent, for a 1% move in the partner over the whole period, and R² is the share of the variation the fit explains. Two prices that both drift up with inflation can fit well without any real link, so read it together with the monthly correlation. **Lead or lag** checks whether the monthly correlation is clearly higher when one price is shifted by 1 to 6 months. Correlation is not cause. The reasons on each card explain the economic link; the numbers show how strongly it has shown up in prices. Proxy series are US producer price indexes or related prices and can blur the real link. Data: World Bank Commodity Price Data (Pink Sheet), October 2026; US Bureau of Labor Statistics producer price indexes, IMF primary commodity prices and US EIA prices via FRED, Federal Reserve Bank of St. Louis, retrieved November 2026. Calculations by this site. ## Other sections - [Summary](https://www.materialinsights.org/energy/e_geo_direct/index.md) - [Overview](https://www.materialinsights.org/energy/e_geo_direct/overview/index.md) - [Efficiency](https://www.materialinsights.org/energy/e_geo_direct/efficiency/index.md) - [Techniques](https://www.materialinsights.org/energy/e_geo_direct/techniques/index.md) - [Resources and labour](https://www.materialinsights.org/energy/e_geo_direct/resources/index.md) - [Impact on the biosphere](https://www.materialinsights.org/energy/e_geo_direct/biosphere/index.md) - [Relationships](https://www.materialinsights.org/energy/e_geo_direct/links/index.md)