Cold Climate Backup Heat Options: Strips, Dual Fuel, and the Balance Point

Use this guide as a source-backed frame for understanding backup heat behind a cold climate heat pump. The central idea is the balance point, the temperature below which a heat pump needs help, and the two main ways homes provide that help. Every figure comes from a page fetched on 2026-08-24, and each section lists the source that supports it.

Why Backup Heat Exists: The Balance Point

Backup heat exists because a heat pump loses ground as it gets colder. The Building America Solution Center states that when outdoor temperatures are below the balance point, the heat pump cannot fully meet the home's heating needs without a backup heat source. The balance point is the temperature where the heat pump's output stops keeping up with the home's heat loss.

The Department of Energy building science training module lists the balance point temperature as a core concept in cold climate heat pump sizing, alongside heat pump cycling. This is not a fringe idea. It is one of the named topics in how cold climate systems are sized and selected.

Read this as the reason the rest of the page matters. A home in a cold climate will spend some hours below its balance point, and during those hours the heat pump needs a second heat source. The two common sources, electric resistance and a dual-fuel furnace, are the subject of the next sections. Where the balance point falls depends on the home and the equipment, so this guide does not assign a single universal temperature to it.

How Cold Weather Reduces Heat Pump Capacity

The balance point is a symptom of a physical fact. The Department of Energy reports that the heating capacity and efficiency of conventional air-source heat pumps decrease significantly as the outdoor temperature drops. As the same source puts it, supplemental electric resistance heat must be used, decreasing the heating performance. That is the mechanism that pulls a home below its balance point on cold nights.

Cold climate heat pumps are the class of equipment built to push that limit lower. ENERGY STAR requires cold climate units to hold a percent of heating capacity at 5 degrees Fahrenheit at 70 percent or more of that at 47 degrees Fahrenheit, and to meet a coefficient of performance at 5 degrees Fahrenheit of at least 1.75. Those thresholds describe how much capacity and efficiency a certified cold climate unit keeps when it is cold.

The Department of Energy has also documented equipment going further. It describes a cold climate prototype able to operate down to minus 13 degrees Fahrenheit while utilizing no supplemental resistance heat, and reports up to 70 percent energy savings in comparison to electric resistance heat. Read those as documented figures for specific equipment, not as a promise for every model. The general lesson holds. Colder air means less heat pump capacity, and the amount retained is what decides how much backup heat a home actually calls on.

Electric Resistance Strips as Backup

The most common backup is electric resistance heat, the strip or auxiliary elements in the air handler. The Building America Solution Center is direct about its economics, describing electric resistance auxiliary heating as an inefficient and typically expensive form of heat, which should be minimized. That does not mean it has no place. It means the goal is to lean on it as little as possible.

A useful trait of electric resistance backup is that it works alongside the heat pump. The Department of Energy notes, in its cold climate prototype work, that conventional air-source heat pumps require supplemental electric resistance heat as capacity falls, which is a picture of the heat pump and the strips both contributing during cold hours rather than the heat pump shutting off. That simultaneous operation is what lets a home hold temperature when the heat pump alone would fall short below the balance point.

The sourced takeaway is a balance. Electric resistance strips are simple and can supplement the heat pump directly, but the same evidence flags them as an inefficient and typically expensive form of heat to minimize. That tension is exactly why the design aim is a low balance point and controls that keep the strips off until they are truly needed.

Dual-Fuel Furnace Backup and Switchover

The other main option is a dual-fuel system, which pairs the heat pump with a gas furnace. Carrier describes it as automatically switching between the heat pump and the gas furnace based on outdoor temperatures, and states that when outdoor temperatures drop too low for the heat pump to efficiently extract heat, the system automatically switches to the gas furnace. The heat pump handles mild weather and the furnace takes over when it is cold.

The switchover happens at a set temperature. Carrier reports that a dual fuel system typically switches from the electric heat pump to the gas furnace when outdoor temperatures drop to between 35 and 40 degrees Fahrenheit, and that this switch-over point, known as the balance point, can be adjusted by an HVAC technician based on local climate and energy rates. That adjustability is what lets the switchover be tuned to a specific home.

Dual fuel differs from electric resistance in one important way. The Building America Solution Center notes that in dual fuel systems using natural gas, the heat pump does not operate alongside the backup heat, unlike electric resistance systems where simultaneous operation occurs. So the sourced contrast is clear. Electric resistance can supplement the heat pump at the same time, while a dual-fuel furnace generally replaces it below the switchover temperature.

When Backup Is Needed and How to Choose

Backup is needed for the hours a home spends below its balance point. The Building America Solution Center defines that condition directly, noting that below the balance point the heat pump cannot fully meet the home's heating needs without a backup heat source, and the Department of Energy adds that conventional air-source heat pump capacity and efficiency decrease significantly as it gets colder. Together those explain why colder climates lean on backup more.

The choice between electric resistance and dual fuel follows from the sourced contrasts. Electric resistance is simple and can supplement the heat pump at the same time, but the Building America Solution Center flags it as an inefficient and typically expensive form of heat to minimize. Dual fuel adds a gas furnace that Carrier says takes over at a switchover point commonly between 35 and 40 degrees Fahrenheit, adjustable by a technician, and the Building America Solution Center notes the furnace generally runs instead of the heat pump rather than alongside it.

Equipment class also shapes the answer. ENERGY STAR certified cold climate heat pumps must keep at least 70 percent of their 47 degree capacity at 5 degrees Fahrenheit and meet a coefficient of performance of at least 1.75 at that temperature, and the Department of Energy has documented prototypes operating down to minus 13 degrees Fahrenheit with no supplemental resistance heat. A unit that holds more capacity when cold spends fewer hours below its balance point, which reduces how hard the backup has to work.

This is also the editorial guardrail. The guide can organize sourced facts about the balance point, cold-weather capacity, electric resistance, and dual fuel, but it cannot pick a home's balance point or backup type from a distance. When a proposal does not state the design temperature, the expected balance point, or the backup strategy, the honest step is to mark those as open questions rather than assume the backup is sized right.