Heat pump vs furnace in Peoria County, Illinois

What winter here does to a heat pump

Winter is the long season here, eight months of it, October through May, against four months of cooling. So the machine you pick is mostly a bet on how it handles cold, not heat. And the cold here is real cold. The overnight low averages 20°F across December, January and February, and that's below both marks that matter for a heat pump: the 40°F mark where its output starts falling short of its rating, and the 35°F mark where it often needs backup heat to make up the difference.

About 125 nights a year here drop to freezing or below, roughly half the nights heat runs at all. Every one of those nights is below both marks. A standard heat pump on those nights is working below its rated capacity and likely leaning on backup heat to keep the house warm. That's not a rare edge case here. That's about half the winter.

The deep cold, 0°F or below, only hits about 8 nights a year. So the furnace-only extreme is rare. But the moderate cold that still drags a heat pump below its rating, the freezing and just-below-freezing nights, is common. That's the part of this climate a heat pump has to answer for, not the 8 coldest nights but the 125 cold ones.

There's a real counter to this. Cold-climate heat pumps, the ones that carry the ENERGY STAR Cold Climate mark, are built and tested to keep most of their capacity down to 5°F, and field tests of prototype cold-climate units found backup heat covered only a small share of the heat needed between 0°F and 35°F, with the system running on backup alone rarely happening above 0°F. So the cold itself isn't disqualifying. A heat pump built for it can mostly handle a winter like this one. A standard heat pump, the kind built to the federal minimum, is the one that struggles here.

What it costs to run, and what's already in the walls

Run the numbers at Illinois's own prices and gas wins. A gas furnace makes the same heat for $1.33 per 100,000 Btu against $2.12 for a heat pump, at least 37 percent less. That heat pump figure already assumes a unit built to the federal minimum, running at its full seasonal rating, with nothing added for backup heat. On the roughly 125 nights a year here below freezing, a standard heat pump would lean on backup heat or lose capacity, so its real cost on those nights runs higher than that number, not lower.

Most homes here are already set up for gas. Utility gas heats 68.1% of homes in the county, about two in three. Electricity heats about one in four. If your house is one of the two in three already piped for gas, a furnace runs on the fuel the house and the neighborhood are already built around. If you're in the one in four on electric heat, or building new, that math doesn't apply the same way, and the heat pump's other case, no gas line, no combustion in the house, one system for heat and cooling both, carries more weight.

A furnace only heats. For four months a year here, June through September, it does nothing, and you need a separate air conditioner. A heat pump covers both jobs with one system. That's not a cost argument, it's a simplicity one: one piece of equipment, one maintenance schedule, instead of two.

So the honest split is this. If your house already runs on gas and you want the cheaper fuel to run through a winter with 125 freezing nights a year, a furnace is the straightforward choice, paired with a central AC for summer. If you want one system for both seasons, no gas line, and you're willing to pay more to run it, or to put the difference toward a cold-climate model built to hold its output at 5°F, a heat pump is the one built for a winter like this.

Sources: NOAA nClimDiv · NOAA 1991–2020 seasonal normals · Census ACS 2020–2024 · EIA SEDS 2024 · 10 CFR 430.32 · PNNL Building America guide · PNNL-37127 field study · ENERGY STAR product criteria