HeatPumpMath Heating cost math that shows its working. https://heatpumpmath.com/ 2026-08-31T00:00:00Z Ashutosh Banerjeebanerjeeashutosh01@gmail.com Computed figures are published under CC BY 4.0. Corrections https://heatpumpmath.com/corrections/ 2026-08-31T00:00:00Z Every error found in the HeatPumpMath model, what it changed, and how it was fixed. Old and new figures are published side by side. Ashutosh Banerjee Research Log https://heatpumpmath.com/research-log/ 2026-08-31T00:00:00Z How the HeatPumpMath model was built and checked, including the sanity checks that caught the summer gas price error. Ashutosh Banerjee Download: Heat Pump Running Cost by State https://heatpumpmath.com/data/ 2026-08-31T00:00:00Z Free CSV and JSON of heating fuel prices and heat pump running cost for all 51 states, from EIA December 2025 to February 2026 data. CC BY 4.0. Ashutosh Banerjee Field Evidence: Measured Heat Pump COP https://heatpumpmath.com/notes/field-evidence/ 2026-08-31T00:00:00Z PNNL measured a median COP of 1.9 at 0 to 5F across 22 instrumented homes. NREL found backup heat outconsuming the compressor at 2 of 12 sites. Ashutosh Banerjee Asking Three Contractors About Balance Point https://heatpumpmath.com/notes/asking-contractors/ 2026-08-31T00:00:00Z Three HVAC contractors asked the same balance point question, a commissioned Manual J load calculation, and what the arithmetic actually returns. Ashutosh Banerjee What people actually pay to heat with a heat pump https://heatpumpmath.com/notes/what-people-actually-pay/ 2026-08-31T00:00:00Z Real winter heating electricity from 32 households, normalised per sq ft per degree day. A 12x spread, with the outliers explained. Ashutosh Banerjee Most heat pump calculators use the wrong gas price https://heatpumpmath.com/notes/wrong-gas-price/ 2026-08-31T00:00:00Z EIA's residential gas price is revenue over volume, so summer runs to twice the winter figure. Pulling the latest month answers winter with summer. Ashutosh Banerjee The 3.5 to 1 rule describes two specific machines https://heatpumpmath.com/notes/three-point-five-rule/ 2026-08-31T00:00:00Z The threshold at which heat pumps beat gas furnaces is not a general law. It is what the equation returns for one particular pairing of equipment. Ashutosh Banerjee Backup heat is where cold climate bills come from https://heatpumpmath.com/notes/backup-heat/ 2026-08-31T00:00:00Z Electric resistance backup runs at COP 1.0. A small share of heat delivered that way pulls seasonal efficiency down far more than people expect. Ashutosh Banerjee