St. Charles, IL: the heat pump payback math
Here in St. Charles, the honest answer is that a heat pump raises your annual running cost. Swap a failed furnace and AC for a heat pump rather than buying like-for-like, and the extra cost here runs $3,500 after a $2,000 federal tax credit. Unfortunately the electric bill outweighs the gas bill it replaces by about $295 a year here, so the extra spend stays unrecovered. There's no spin on that: St. Charles's numbers say wait.
The climate behind St. Charles's payback figure
5064 heating degree days pile up here every year, so St. Charles has a cold winter that leans hard on heating equipment; the cooling side runs to 915 cooling degree days, where summers add a moderate cooling load. -7.1°F is the figure equipment gets sized against here — the 99th-percentile cold snap, not an average day — with a record low of -14.1°F on file. Worked through the model, that's a seasonal COP of 2.53 on the cold-climate unit fit for this climate. Below the 25°F line where a standard machine starts leaning on resistance backup, St. Charles sits firmly in cold-climate territory, so that's the class of unit priced here. Climate figures trace to the nearest NOAA station, DUPAGE AIRPORT, 3.3 miles from St. Charles.
What it actually costs to run, year to year
Modelled on a typical 2000-square-foot house, the heat pump draws about 5,068 kWh a year to keep it warm, plus cooling, for a combined electric bill near $1,115 a year. The gas furnace it replaces burns roughly 53 Mcf a year at 11.25 per Mcf here, for a running cost near $819 a year (electricity here runs 19.06¢/kWh). Looked at as a full purchase rather than an incremental one, payback here is longer than the 15-year equipment life, leaving the 15-year total $7,930 behind.
Electric resistance heat in St. Charles, compared
Gas isn't universal in St. Charles — many houses run on electric heat already. Swap the comparison to resistance heat instead of gas, and St. Charles's answer improves. About $1,555 a year comes back this way, enough that the 5.1-year payback clears the $8,000 premium comfortably within the equipment's life.
St. Charles against the rest of the country
Ranked against the other 3206 cities covered, St. Charles comes in at 632 for heating severity — 1 would be the coldest place in the dataset — and 1227 by population, where 1 is largest. That's the coldest third of the dataset, where climate does most of the work behind this figure.
Next step for 33,482 people in St. Charles
About 33,482 people live in St. Charles, Illinois, and every number on this page is what a contractor would actually work from when quoting a system here — the point isn't to replace that quote, it's to tell you whether to bother asking for one. Here, there's no cost penalty to waiting until your current furnace or AC actually needs replacing.
Line up a few local HVAC quotes before you decide.
Reading further on this page's numbers
Nothing above is a black box: the methodology guide shows the full arithmetic behind St. Charles's 2.53 seasonal COP and payback figure. St. Charles's -7.1°F design temperature falls on the cold side of the 25°F cutoff the cold-climate unit guide walks through.