Illinois Heating

Heat pump vs furnace in Knox County, Illinois

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Which costs less to run in Knox County?

A gray outdoor condenser unit with a top-mounted fan sits on a concrete pad beside a dark blue horizontal lap-sided wall, lit from above at night.

Heat pump

To heat your home here$2.12per 100,000 Btu

A beige sheet-metal furnace with ducting and a metal flue stands in a basement corner with dark blue painted walls, a concrete floor, and a bare hanging light bulb overhead.

Furnace

To heat your home here$1.33per 100,000 Btu

At Illinois's gas and electricity prices, a gas furnace makes the same heat as a heat pump for at least 37% less.

Btu stands for British thermal unit, the standard measure of heat energy.

Where does a heat pump shine?

  • Heats and cools in one system

    Winter and summer are covered by the same outdoor unit. That's one machine to service instead of two.

    Living room with a beige sofa holding navy and light blue cushions under a large window overlooking green trees and white hydrangeas, a wooden coffee table with a woven tray, potted plant and candle, a navy bookcase at right, and a striped armchair in the foreground.

  • Steady, even comfort

    Instead of short bursts of heat, it keeps a gentle, steady output going. The house stays at one comfortable temperature.

    A golden retriever sleeps on a patterned rug beside a navy wingback chair with a knit throw and open book, next to a lit floor lamp, a side table with a mug and small plant, gray built-in shelving, and a window showing snow outside.

  • No gas line, nothing burning in the house

    It moves heat instead of making it from fire. That means no combustion, no flue and no gas bill for heat.

    A kitchen with navy blue cabinets, white marble-look counters and backsplash, a stainless steel kettle on a black cooktop under a range hood, a potted plant, bowl of lemons, wooden utensils and cutting board, and a light blue mug on a foreground island beside a sink.

Where does a furnace shine?

  • Strong, steady heat in hard cold

    Nights in Knox County average 18°F through December, January and February. A furnace burns gas to make heat, so it keeps putting out the same full blast of warm air no matter how far the temperature drops.

    A dark blue two-story house with a white-trimmed covered porch at dusk, with lit windows, a small lit tree, lanterns along a shoveled walkway, and deep snow on the roof and yard.

  • Runs on the gas most homes here already use

    Most homes in Knox County already have gas line run to them, since gas heats 67.4% of occupied homes here. If yours is one of them, a furnace just hooks into what's already there.

    A row of attached townhouses with brick and painted facades, front stoops with black metal railings, and exterior gas meters, beside a sidewalk with patchy snow and bare trees.

  • Pairs with any central AC

    Most central air systems are built around a furnace. The two share the blower, the ducts and the thermostat.

    A bronze-toned floor register vent set in a hardwood floor near a white baseboard, with a sheer curtain lifting above it, a woven jute rug in the foreground and a blue throw at right.

Can a heat pump keep up here

Winter here is long and it gets properly cold. Heat runs about eight months a year, October through May, and the overnight low averages 18°F across December, January and February. About 135 nights a year dip to freezing or below, and about 11 of those get down to 0°F or colder.

A standard heat pump starts losing ground before it gets anywhere near that cold. Below 40°F its heat output falls short of its rated capacity. Below about 35°F it typically needs backup heat to make up the difference. The average winter low here is under both marks, and every single one of those 135 freezing nights is too.

That doesn't mean a heat pump leaves you cold. It means it isn't carrying the house alone on those nights, something else is helping. Field testing on cold-climate heat pumps backs this up: in occupied homes over two winters, backup heat covered only a small share of the load between 0°F and 35°F, and the system running on backup alone was rare even above 0°F. So the backup is a helper, not the main event, if the equipment is sized and chosen right.

If a heat pump is the plan, the one to look for carries the ENERGY STAR Cold Climate mark. To earn it, a heat pump has to produce at least 1.75 units of heat per unit of electricity at 5°F and hold onto at least 70 percent of its 47°F capacity at that temperature, checked by outside testing. That's the version built for a winter like this one, not the federal minimum.

Snow-covered dark steps with white railings lead to a navy front door on a light blue clapboard house, with a snow shovel leaning beside the door.

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

Run the numbers at Illinois prices and gas wins. A furnace makes the same 100,000 Btu of heat for $1.33. A heat pump at the federal minimum makes it for $2.12, without even counting what backup heat adds on the coldest nights. Over eight months of heating, that gap is the whole story on operating cost.

It also matches what's already sitting in most houses here. Utility gas heats about two in three homes in Knox County, 67.4 percent. Electric heat is the setup in about one in five, 21.8 percent. A furnace replacement is usually a swap for what the house already has, gas line and venting included. A heat pump, if the house was never set up for one, is a bigger change to make.

A furnace only does one job. It heats the house for those eight months and sits idle the other four, since it has no cooling function at all, so it still needs a separate AC system alongside it. A heat pump heats and cools from the same equipment, which is worth something if the central air is also due for replacement. That's the real trade: a furnace that costs less to run and fits what's already there, against a heat pump that costs more to run here but replaces two systems with one, if it's a cold-climate model sized for this winter.

Half the houses in Knox County were built in 1957 or earlier, so for a lot of homes here, whether the ductwork, gas line and electrical panel are already set up for either choice is worth checking before deciding, not assumed.

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

A row of two-story wood-sided houses in dark blue and light blue with covered porches, flanked by brick houses, with snow on the roofs, icicles along the eaves, and a plowed snowbank along the street.

Common questions about heat pumps and furnaces

  • Can a heat pump heat a house through an Illinois winter?

    It can, but not alone on the coldest nights. About 135 nights a year here fall at or below freezing, and a standard heat pump's output drops below 40°F and keeps dropping into the teens. On the roughly 11 nights a year that reach 0°F, it needs backup heat to keep up.

  • Do I need backup heat with a heat pump here?

    Yes, for most of the winter nights here. The average overnight low in December, January and February is 18°F, well below the 35°F mark where a standard heat pump starts to lean on backup heat. A cold-climate model built to the ENERGY STAR spec holds more of its capacity down to 5°F, but Knox County still sees nights colder than that.

  • Can I keep my furnace and add a heat pump?

    Yes, and in Knox County that combination has a real job to do. A heat pump falls short of its rated heat below 40°F and often leans on backup heat below about 35°F, and the overnight low here averages 18°F across December, January and February. Keeping the furnace as backup means it only has to carry the hardest nights, while the heat pump handles the rest.

  • Is a heat pump cheaper to run than a furnace in Knox County?

    No, a gas furnace runs cheaper here. At Illinois's average prices, a furnace makes the same heat for $1.33 per 100,000 Btu against $2.12 for a heat pump, both figures at each machine's federal minimum efficiency. Gas already heats two in three homes in Knox County, which is part of why that price gap holds locally.

A person's arm in a light blue shirt reaches to adjust a round thermostat on a dark blue wall above a light switch plate, with a tool bag in the foreground and a living room visible through a doorway.

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