How does a heat pump heat a house?
It moves heat instead of making it. Even cold outdoor air holds some heat, and a heat pump uses refrigerant to carry it inside. In most weather, that takes a lot less electricity than making it with electric heat strips or baseboard heaters.
The catch is the cold. As the temperature drops, the heat pump has to work harder to pull heat in, and it puts out less. Backup heat, usually electric heat strips in the indoor unit, fills the gap. Cold-climate models need that help less often.
How is a gas furnace different?
A furnace makes heat by burning natural gas or propane, so its output doesn't drop when the weather turns cold. The air from the vents also feels hotter than a heat pump's, and some people just prefer that.
A furnace only heats, so it's paired with an AC, or a heat pump, for summer. It needs a gas supply, a vent pipe to carry exhaust outside, and regular checks. The big one is the part that keeps flame and exhaust out of the air you breathe (the heat exchanger).
Which one handles Middle Tennessee winters better?
Neither wins outright. A heat pump is more efficient on most winter days here, and a furnace holds up better in a hard freeze.
Middle Tennessee winters don't really commit. Most days are cool rather than bitter, but nights below freezing are common. The colder it gets, the more a heat pump leans on its backup heat strips, which cost more to run.
Both need electricity, so neither heats the house in a power outage.
Does the choice change how the house cools in summer?
Not much. Both cool the same basic way, with a compressor in an outdoor unit. A heat pump is the air conditioner. With a furnace, a separate AC shares the furnace's blower and ductwork.
Summers here are hot and humid, so size matters. An oversized system cools the house fast and shuts off before it's pulled much moisture out. You end up cool but clammy.
Whichever you choose, we'd want it sized to the house with a load calculation, not matched to the old unit.
What is a dual fuel system?
It's a heat pump and a gas furnace set up as one system. The heat pump does the cooling and, depending on how the switchover is set, much of the heating. When it gets cold enough outside, it switches to the furnace instead of heat strips.
It usually costs more to install than either setup alone. A common rule of thumb: if the house has gas and the AC is due, it's worth pricing.
How can I tell what my house has now?
A few quick looks will tell you, without opening a panel.
- The thermostat. An emergency heat setting or an aux heat light points to a heat pump.
- The indoor unit. A gas furnace has a vent pipe to the roof, a chimney or an outside wall, often white plastic on newer ones. An electric air handler has none. In a crawl space or attic? Skip it. The other checks will tell you.
- Ductwork at the outdoor unit. That's a package unit, everything in one cabinet. Its label says whether it's a heat pump or gas heat with AC.
- The outdoor unit on a mild winter day. If the fan on top spins while the heat is on, in a house with no gas or propane, it's most likely a heat pump. On a very cold day, a heat pump paired with a furnace may sit still.
- Your bills. A gas bill and a gas meter outside mean natural gas. Propane comes from a tank on the property.
See signs of both? You may already have dual fuel.
Why does what's already there usually decide it?
Because keeping what works costs less than starting over. With gas and a furnace in good shape, you can keep gas heat or go dual fuel. If there's no gas at the house, a heat pump is often the simpler choice. Only the gas company can say whether service reaches your street, and at what cost.
The panel and the gas line matter too. A heat pump's backup heat strips need electrical capacity your panel may not have. A new gas furnace needs gas line work sized for it and the other gas appliances in the house.