You probably think of backup heat as something the installer simply includes by default, a small add-on bundled into the air handler without much thought. However, backup heat is its own distinct cold-climate specification — one that shapes both your comfort on the coldest mornings and the size of your January electric bill.
Most homeowners running a heat pump in a cold climate will rely on backup heat at some point each winter. The question is what kind, how much, and how it is controlled.
Heat pump backup heat is supplemental heating that activates when the heat pump alone cannot meet demand — during deep cold, defrost cycles, or rapid recovery. The two common configurations are electric resistance strips and dual-fuel systems that pair the heat pump with a gas or propane furnace.
Why Backup Heat Is A Separate Spec Decision
Backup heat sizing is not the same conversation as cold-climate heat pump sizing, and it is not the same as defrost behavior either. It deserves its own line on the equipment proposal.
A correctly sized heat pump can still need backup at the design temperature — the 99% winter figure for your location. That said, the amount of backup you actually need depends on how much of the building load the heat pump covers on its own.
This is why a Manual J load calculation matters here. If you have not run one, our guide to defrost cycle sizing explains how cold-weather behavior interacts with capacity, and the two posts together give you the full cold-climate picture.
What Are Electric Resistance Strips?
Electric resistance strips — also called heat strips or strip heat — are coils of resistance wire installed in the air handler. When the thermostat calls for supplemental heat, the strips energize and warm the air directly.
Electric resistance strips deliver heat at a COP of roughly 1.0, meaning one unit of electricity produces one unit of heat. A cold-climate heat pump, by contrast, often delivers a COP of 2.0 to 3.0 even in freezing weather, so strip heat is always the more expensive way to produce a given amount of warmth.
Strips are inexpensive to install and require no fuel line, no combustion venting, and no second appliance. For that reason they are the default backup in most all-electric heat pump installations.
The drawback is operating cost. Because strips convert electricity to heat at a COP near 1.0, every hour they run costs roughly two to three times what the heat pump would have cost for the same output.
What Is A Dual-Fuel Configuration?
A dual-fuel system pairs the heat pump with a gas or propane furnace, sharing the same ductwork. The heat pump handles mild and moderate weather, and the furnace takes over below a set changeover temperature.
A dual-fuel heat pump uses a furnace as backup instead of electric strips. A control board switches from heat pump to furnace at a programmed balance point, typically between 25°F and 35°F, so the system always runs whichever heat source is cheaper at that outdoor temperature.
Dual-fuel is most attractive for homes that already have a serviceable gas furnace or an existing propane tank. Replacing only the outdoor condenser and adding controls is far cheaper than a full furnace removal.
Keep in mind that dual-fuel keeps a combustion appliance in the home. For households pursuing full electrification — and the rebate paths described in our whole-home electrification ROI breakdown — that is a meaningful trade-off.
Comparing The Two Configurations
The right choice depends on your fuel prices, your climate, and your electrification goals. The table below summarizes the practical differences.
| Factor | Electric Strips | Dual-Fuel |
|---|---|---|
| Install cost | Low — coils in the air handler | Higher — furnace plus control board |
| Operating cost of backup | High — COP near 1.0 | Varies with gas or propane price |
| Combustion in home | None | Yes — venting required |
| Electrification fit | Full all-electric path | Retains fossil fuel |
| Best fit | New construction, no existing furnace | Existing functional gas furnace |
All of these factors add up to a single question — which backup source is cheaper to run during the hours you actually need it. In much of the Northeast, where electric rates are high and the HEEHRA program favors all-electric retrofits, the math is rarely simple.
How To Size Backup Heat
Backup heat should cover the gap between the heat pump's capacity at design temperature and the building's total heat loss. Oversizing strips is a common and costly error.
To size backup heat, subtract the heat pump's rated capacity at your design temperature from the home's Manual J heat loss. The difference, expressed in BTU/hr, is the backup load. Strip heat is then specified in kilowatts, where one kilowatt delivers roughly 3,412 BTU/hr.
Many installers default to 10 kW or 15 kW strip kits regardless of the actual gap. That oversizing inflates electrical service requirements and tempts the control logic to call for strip heat more often than necessary.
Controlling When Backup Runs
The single biggest driver of backup operating cost is the control strategy, not the hardware. A heat pump that hands off to backup too early wastes money every cold day.
The balance point is the outdoor temperature at which the heat pump's capacity exactly matches the home's heat loss. Below it, backup heat is genuinely needed. A well-configured thermostat locks out strip heat above the balance point so the heat pump carries the full load whenever it can.
Be aware that many thermostats ship with aggressive default settings that energize backup heat during normal recovery, such as a morning setback. Configuring an outdoor temperature lockout is the most effective single adjustment for cutting winter cost.
For dual-fuel systems, the changeover temperature plays the same role. Setting it by economic balance point — where furnace cost per BTU equals heat pump cost per BTU — rather than a fixed default keeps the system on the cheaper source.
Which Configuration Fits Your Home?
If you are building new or removing fossil fuel entirely, electric strips paired with a properly sized cold-climate heat pump are the straightforward path. The strips run rarely if the balance point is set well.
If you have a recent, efficient gas furnace and live in a region with cheap natural gas, dual-fuel can lower winter operating cost — at the cost of keeping combustion in the home. Households weighing rebates should review our rebate stacking application order guide, since some incentive programs reward all-electric configurations specifically.
Backup heat is a spec line, not an afterthought. Ask your contractor for the heat pump's capacity at your design temperature, the calculated backup load, and the proposed balance point in writing before you sign.
Whichever configuration you choose, the controls determine the bill. A modest strip kit with a smart lockout will almost always cost less to run than an oversized one left on factory defaults.
Frequently Asked Questions
Do all cold-climate heat pumps need backup heat?
Most do, though the amount varies. Even a well-sized cold-climate heat pump may fall short of the building load at the 99% winter design temperature, and backup covers that gap. Backup also bridges defrost cycles, when the outdoor coil briefly reverses to shed ice. Some tightly built, well-insulated homes with generously sized equipment need backup only a handful of hours per year.
Is dual-fuel cheaper to run than electric strips?
It depends entirely on local fuel prices. Where natural gas is inexpensive and electricity is costly — much of the Midwest and parts of the Northeast — dual-fuel backup can cost less per BTU than resistance strips. Where electric rates are moderate or gas is delivered as propane, the advantage shrinks or disappears. Run the comparison with your actual utility rates rather than relying on a regional rule of thumb.
Does HEEHRA cover dual-fuel systems?
HEEHRA is state-administered, and eligibility rules vary state to state. The program is structured around electrification, so all-electric heat pump configurations are generally the clearest fit. Some state implementations may treat dual-fuel differently or exclude it. Check your state energy office's HEEHRA rollout details, and see our coverage of the program's state-by-state status before assuming a dual-fuel install qualifies.
How much electric strip heat should I install?
Only enough to cover the gap between the heat pump's capacity at design temperature and the home's Manual J heat loss. That figure, converted from BTU/hr to kilowatts at roughly 3,412 BTU/hr per kilowatt, is your target. Many installs default to 10 kW or 15 kW kits that exceed the real need, which raises electrical service costs and encourages unnecessary strip operation.
What thermostat setting cuts backup heat cost the most?
An outdoor temperature lockout. This setting prevents electric strips from energizing above the system's balance point, forcing the heat pump to carry the full load whenever it is capable. Many thermostats ship with defaults that call backup heat during ordinary morning recovery. Configuring the lockout to match your calculated balance point is the most effective single change for lowering winter operating cost.
Plan Your Backup Heat Before You Buy
Backup heat sizing belongs on the proposal next to the heat pump model number, not buried in the install. The configuration you pick and the balance point you set will follow you through every cold-climate winter.
If you are still narrowing down equipment, pair this with our cold-climate heat pump sizing guide and confirm your design-temperature capacity first. A contractor who can show you the load math is worth more than one quoting the cheapest strip kit.
This article is for informational purposes and is not financial, tax, legal, or medical advice. Consult a licensed professional — a CPA, elder-law attorney, HVAC contractor, or your state energy office — before acting.