Two numbers behind one setting
A dual fuel system pairs a heat pump with a gas furnace. The thermostat uses an outdoor sensor to decide which one heats the house. The temperature where it changes over is the switchover point, and you choose it.
Bluffline Memphis Heat Pumps sets it with you on every dual fuel installation, because the right answer depends on what you care about most.
The balance point
Every heat pump has a balance point: the outdoor temperature where its heat output equals the house’s heat loss. Above it, the heat pump keeps up alone. Below it, it falls behind and needs help. In a typical Memphis house with a correctly sized heat pump, the balance point lands somewhere in the 20s or low 30s.
The economic switchover
The economic switchover is the temperature where heat from the heat pump starts to cost more than heat from gas. It depends on your gas price, your electric price, the furnace’s efficiency and how the heat pump’s efficiency falls as it gets colder.
What MLGW’s rates say
On MLGW’s typical rates, gas in a 95 percent furnace costs about $6.30 per million BTU of delivered heat. A heat pump costs about $10.20 on a mild day and $14.30 on a cold one.
What that means for the setting
Gas is cheaper at every outdoor temperature on a normal month. So there is no economic switchover in the usual sense: from a cost view alone, gas should do all the heating. The heat pump earns its place through cooling, comfort and as a second heat source.
When gas spikes
MLGW’s purchased gas adjustment changes monthly. In February 2026 it pushed gas to about $12.20 per million BTU, above the heat pump’s mild-day cost. In a month like that, the heat pump is the cheaper heat on mild days, and a lower switchover saves money. The gas versus heat pump guide has the full comparison.
Three ways to set it
Most settings fall into one of three patterns:
| Approach | Typical setting | What you get |
|---|---|---|
| Comfort first | About 35 degrees | Steady, quiet heat pump heat on mild days; gas on cold ones; small extra cost on normal rates |
| Cost first | 45 to 50 degrees | Gas carries nearly all of winter; heat pump mainly cools |
| Flexible | 30 to 40, adjusted by season | Lower when gas is expensive, higher when it is cheap |
Why comfort-first is popular
Heat pump air leaves the registers in the 90s and runs in long, even cycles. Furnace air is hotter and comes in shorter bursts. Many people find the heat pump steadier on a 45-degree day, and the cost difference over a mild-day season is modest.
Never below the balance point
Whatever you choose, the switchover shouldn’t sit below the balance point. If it does, the heat pump runs on cold mornings when it can’t keep up, and the house drifts below the setpoint before gas takes over.
How the thermostat makes the handoff
A dual fuel thermostat reads an outdoor temperature sensor, either a wired sensor on the north wall or one built into the outdoor unit’s communicating controls.
What happens at the switchover
- Above the setting, a call for heat runs the heat pump.
- Below it, the thermostat locks the heat pump out and runs the furnace.
- During defrost, many systems briefly fire the furnace so cold air doesn’t blow from the registers.
- At the changeover, a short delay keeps the two from running together.
The heat pump’s coil sits above the furnace in the same air stream, so the two never heat at the same time. Furnace heat would push the coil’s refrigerant pressure too high.
Recovery from setbacks
If you set the temperature back overnight, a big morning recovery can make some thermostats bring the furnace on early even above the switchover. Smaller setbacks, or the thermostat’s recovery settings, keep the heat pump working. The thermostat setup guide covers those menus.
Finding your balance point
The load calculation gives the house’s heat loss at Shelby County’s 20-degree design temperature. The heat pump’s published performance data gives its output at different outdoor temperatures. Where the two lines cross is the balance point.
What moves it
- A bigger heat pump lowers the balance point.
- Better insulation and windows lower the house’s heat loss and the balance point with it.
- Leaky ducts in a crawlspace or attic raise it.
Ask for the balance point on your start-up sheet, so you know the floor under any setting. The sizing guide explains how the load calculation works.
Outside MLGW territory
In Olive Branch, Southaven and across the river, power and gas come from different suppliers, and the per-BTU numbers change.
Where gas costs more relative to electricity than it does on MLGW, an economic switchover can appear in the 30s or 40s. We work it from your own bills.
A Germantown example
Take a 1984 two-story in Germantown with an eight-year-old gas furnace and a new 3.5-ton heat pump on top of it, the kind of job on our Germantown page.
The load calculation puts the house’s heat loss at the 20-degree design temperature within reach of the heat pump plus a margin, and its balance point lands in the high 20s.
What the owners chose
- Comfort first: the heat pump runs down to 35 degrees, comfortably above the balance point.
- Gas below 35: the furnace carries the cold mornings and the few hard freezes.
- A note on the thermostat menu showing where the setting lives, so it can drop to 30 in a high-gas winter.
What it costs them
On normal MLGW rates the comfort-first setting costs a little more over a winter than letting gas do everything, because mild days are when most heating hours happen in Memphis. The owners judged the steadier heat worth it.
A cost-first household in the same house would set 45 or 50 and accept furnace-style heat. Neither choice is wrong; they are two answers to the same question about what matters more on a 45-degree morning.
Changing it yourself
Most dual fuel thermostats keep the switchover in an installer or equipment menu, sometimes called the heat pump lockout or the dual fuel changeover. It is a single number. We show you where it is at start-up and write the setting on the start-up sheet.
When to revisit it
- When gas runs high for a season, lower it a few degrees.
- When gas is cheap again, raise it back.
- If mornings feel cold, check that it isn’t below the balance point.
Emergency heat on dual fuel
On a dual fuel system the emergency heat setting usually runs the furnace alone, not electric strips. Use it if the outdoor unit fails. The aux and emergency heat guide explains the difference on strip-heat systems.
The short version
Set the switchover where you like the heat, not lower than the balance point, and move it when gas prices move.
The Memphis buying guide covers the rest of the decision, and the cost page has the typical ranges for adding a heat pump to a furnace.