Should Joliet switch to a heat pump?
Joliet is a place where a heat pump genuinely costs more to operate than the alternative. Against a like-for-like gas furnace and AC swap, going electric costs $3,500 more up front here (already netting out a $2,000 tax credit). Unfortunately the electric bill outweighs the gas bill it replaces by about $235 a year here, so the extra spend stays unrecovered. That's Joliet's own climate and rates talking, not a hedge or a caveat.
Joliet's weather, in the numbers that matter
Joliet has a real but manageable winter — 4733 heating degree days a year against a 65°F base — and summers are hot enough that cooling matters as much as heating, at 1089 cooling degree days. The 99% winter design temperature here — the cold snap equipment must be sized for, not the seasonal average — is -4.4°F, against a record low of -10.3°F. That puts the seasonal coefficient of performance at 2.59 for the recommended cold-climate unit. A cold-climate unit is the right call in Joliet — below 25°F design temperature, a standard heat pump leans hard on electric-resistance backup, which erases most of the savings. These numbers come from JOLIET REGIONAL AIRPORT, the closest NOAA station, 1.5 miles out.
The month-to-month numbers for Joliet
Modelled on a typical 2000-square-foot house, the heat pump draws about 4,627 kWh a year to keep it warm, plus cooling, for a combined electric bill near $1,059 a year. Joliet's gas rate of 11.25 per Mcf, applied to the 49 Mcf a year the furnace burns, puts its running cost near $824 a year, against 19.06¢ per kWh for electricity. 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 $7,031 behind.
The other scenario: no gas furnace to begin with
Not every home in Joliet has gas service. Swap the comparison to resistance heat instead of gas, and Joliet's answer improves. About $1,494 a year comes back this way, enough that the 5.4-year payback clears the $8,000 premium comfortably within the equipment's life.
Where Joliet ranks in this dataset
Among 3206 cities, Joliet's winter puts it at rank 997 for severity, while its size puts it at rank 179 for population — 1 in both cases being the extreme. That's the coldest third of the dataset, where climate does most of the work behind this figure.
What to do with this number in Joliet
Joliet, Illinois is home to about 151,837 people, and the figures above are the same ones a local HVAC contractor uses to size and quote a system — this site doesn't guess where a real quote would land, it just tells you whether it's worth asking for one. In Joliet, nothing is lost by holding off until the current equipment genuinely fails.
Ask a local HVAC contractor for a quote before committing either way.
More on how this number was built
Every constant behind this page — the 2.59 seasonal COP, the degree-day corrections, the equipment costs — is documented in the methodology guide. Joliet's -4.4°F design temperature is below the 25°F line, which is why a cold-climate unit is the right call here — see what that changes in the cold-climate unit guide.