Heat pumps are rising in popularity due to their energy efficiency and ability to provide both heating and cooling. However, when outdoor temperatures drop, supplemental heat becomes crucial for maintaining home comfort. This article details how supplemental heat syncs with heat pumps, explores various types, and outlines strategies for energy savings. Whether you’re considering a new HVAC system or want to boost your current setup, this guide offers everything you need to know about heat pump supplemental heat.
What Is Supplemental Heat In A Heat Pump System?
In heat pump systems, supplemental heat refers to an additional heating source that supports the primary heat pump during especially cold conditions. This add-on heat, often called auxiliary or emergency heat, ensures comfortable indoor temperatures when the heat pump alone cannot meet demand. Supplemental heat is most critical in regions with harsh winters, where outdoor temperatures frequently fall below the efficient threshold of the heat pump.
How Do Heat Pumps Work?
A heat pump moves heat from one place to another. In cooling mode, it removes heat from your home and releases it outside. In heating mode, it extracts heat from the outside air or ground—even at low temperatures—and transfers it indoors. Heat pumps are most efficient when outdoor temperatures are above freezing, but their effectiveness declines as it gets colder. When the outdoor air gets too cold, the system relies on supplemental heat.
Types Of Supplemental Heat For Heat Pumps
There are several common types of supplemental heat sources used with heat pumps:
- Electric Resistance Heaters: The most common option. These heat strips, similar to those in space heaters, are installed inside the air handler.
- Gas Furnaces: Some heat pumps are paired with a gas furnace in a dual-fuel arrangement for powerful backup heating.
- Hydronic Coils: This system uses a boiler and hot water coils to deliver additional heat through the air duct system.
- Oil Furnaces: Rare, but sometimes used in colder climates for extra reliable heating power.
Electric Resistance Supplemental Heat
Electric resistance heat strips are typically built into the air handler. When supplemental heat is needed, electricity passes through metal coils, producing heat that is blown into the home. While this method is simple and effective, it can be expensive to operate compared to the heat pump alone. Heat strips usually activate when:
- Outdoor temperatures drop below the heat pump’s efficient range (around 32°F or lower).
- There is a rapid increase in thermostat setting (e.g., after a power outage or returning from vacation).
- The heat pump is in defrost mode and temporarily cannot provide heat.
Electric resistance heaters serve as the default backup in most American homes with heat pumps.
Dual-Fuel (Hybrid) Heat Pump Systems
Dual-fuel systems pair an electric heat pump with a gas furnace, switching between them for optimal efficiency. The heat pump heats your home until outside temperatures fall below its efficiency point, then the gas furnace activates. This system:
- Combines energy efficiency with powerful backup heating—ideal for colder climates.
- Is managed by a control board that switches automatically based on weather and demand.
- Reduces reliance solely on expensive electric resistance heating.
Homeowners in the northern United States often benefit from dual-fuel heat pump systems.
Hydronic And Oil-Based Supplemental Heat
Some older or custom HVAC setups use hydronic heating coils or oil furnaces for backup. Hydronic coils circulate hot water from a boiler through a heat exchanger inside the air handler, providing moist and efficient heat. Oil furnaces may be used in rural areas where natural gas is unavailable.
- Hydronic coils are efficient and suited for homes with existing hot water heating.
- Oil-based systems are less common but can deliver powerful heat when other options aren’t practical.
When Does Supplemental Heat Turn On?
Supplemental heat activates automatically when the heat pump cannot meet your home’s heating needs alone. Most systems use sensors and thermostats that monitor indoor/outdoor temperatures and system performance. Key situations triggering supplemental heat include:
- Outdoor temperatures falling below 30-35°F (varies by system efficiency).
- Rapid temperature recovery needed indoors.
- Defrost cycles, when the outdoor unit temporarily stops heating to clear ice.
Supplemental Heat Vs. Emergency Heat
The terms auxiliary (or supplemental) heat and emergency heat are often confused. Here’s how they differ:
- Supplemental (Auxiliary) Heat: Activates automatically as needed to assist the heat pump.
- Emergency Heat: Can be manually selected on the thermostat. It shuts off the heat pump and runs only the backup heat source (usually used if the heat pump is malfunctioning).
This distinction is important for homeowners trying to maximize efficiency while maintaining comfort.
How Much Does Supplemental Heat Cost?
Operating costs vary widely depending on the type of supplemental heat and local utility rates. Electric resistance heating is typically much more expensive to run than a heat pump, often two to three times higher. Here’s a cost comparison table of heat pump vs. supplemental heat:
| Heat Source | Estimated Cost Per Million BTUs | Notes |
|---|---|---|
| Heat Pump (Efficient) | $12–$25 | Temperature above 35°F; very efficient |
| Electric Supplemental Heat | $30–$50+ | Can be double or more the cost of heat pump mode |
| Natural Gas Furnace | $9–$20 | Depends on local gas prices |
| Oil Furnace | $20–$35 | Less common, higher cost |
Minimizing time spent on supplemental (especially electric) heat helps keep energy bills low.
Best Practices For Using Heat Pump Supplemental Heat
To maximize efficiency and comfort when supplemental heat is needed, consider these best practices:
- Set a consistent thermostat temperature to avoid sudden demands on the system.
- Program your thermostat to gradually adjust temperatures.
- Keep filters clean and schedule yearly maintenance to ensure peak heat pump performance.
- Seal drafts and improve insulation to reduce overall heating needs.
- If your system allows, use the “auto” setting to let the system decide when to use supplemental heat.
A proactive approach can reduce reliance on backup heat and lower your energy costs.
Location And Climate Impact On Supplemental Heat Use
Homes in colder regions of the United States—such as the Midwest, Northeast, and northern Plains—will see supplemental heat engage more often. In milder regions like the South or Pacific Coast, reliance on supplemental heat is less frequent. Choosing the right type of backup heating and sizing your system accordingly is vital to balancing comfort and cost in your locale.
The Role Of Smart Thermostats
Smart thermostats offer advanced control over when and how supplemental heat is used. Features include:
- Remote monitoring and adjustment via smartphone apps.
- Learning user behavior and optimizing settings.
- Notifications for excessive use of backup heat—helping save energy and identify maintenance issues.
Upgrading to a smart thermostat can improve comfort and energy efficiency by managing supplemental heat more precisely.
Understanding Heat Pump Defrost Cycles
During cold weather, the outdoor unit may develop frost or ice. The system periodically enters a defrost cycle to clear this buildup. While in defrost, the heat pump temporarily heats the outdoor coil, and supplemental heat ensures continued indoor comfort. The process:
- Lasts 5–15 minutes per cycle, depending on conditions.
- Engages the supplemental heater to maintain room temperature.
- May increase energy use mildly, yet it’s necessary for protecting the equipment.
Sizing Supplemental Heat For Your Home
Proper sizing is critical. Too little supplemental heat will leave your home cold; too much can result in unnecessary expense. The ideal approach:
- Work with a professional to calculate your home’s heating load.
- Consider modern heat pump efficiency ratings (HSPF and COP) and local winter extremes.
- Review utility rates and fuel options before installing a dual-fuel or alternative supplemental heat source.
Getting the right size ensures both comfort and optimal energy use.
Energy Efficiency Tips For Heat Pump Supplemental Heat
To save energy and lower heating bills, try these tips:
- Insulate attics, walls, and crawlspaces to reduce heat loss.
- Upgrade old or single-pane windows to double- or triple-pane alternatives.
- Use heavy curtains at night and open them during the day for free solar heat.
- Seal ductwork to prevent warm air leaks.
- Maintain your heat pump—clean coils, unclog drains, and inspect refrigerant levels annually.
Combining these measures reduces the frequency and duration of supplemental heat use.
Comparing Supplemental Heat Options: Pros And Cons
| Supplemental Heat Type | Pros | Cons | Best For |
|---|---|---|---|
| Electric Resistance | Simple installation, no fuel needed | High operating cost | Mild climates, occasional use |
| Gas Furnace (Dual-Fuel) | Efficient, powerful heat | Requires gas hookup, higher upfront cost | Colder climates, high-efficiency homes |
| Hydronic Coils | Efficient, adds humidity | Depends on existing boiler, piping needed | Homes with hydronic systems |
| Oil Furnace | Reliable in off-grid areas | Expensive, fossil fuel reliance | Rural/off-grid homes |
Common Heat Pump Supplemental Heat Problems And Solutions
Frequent Switching To Supplemental Heat
If your system often defaults to supplemental heat, causes could include:
- Undersized or aging heat pump.
- Poor insulation or drafty house.
- Thermostat settings that trigger rapid temperature increases.
Upgrading equipment or improving insulation can address these issues quickly.
High Energy Bills During Cold Months
Excessive use of backup heat usually results in high energy bills. Consider:
- Reviewing thermostat programming for large setpoint swings.
- Scheduling HVAC maintenance to check for malfunctions.
- Exploring dual-fuel options to reduce electric heating costs.
Strategic planning helps control costs in winter.
Supplemental Heat Not Activating
If auxiliary heat does not turn on but is needed, check:
- Thermostat settings and wiring.
- Blown fuses or tripped breakers in the air handler.
- System controls for faults (professional may be required).
Prompt repairs prevent discomfort during cold snaps.
Upgrading Or Adding Supplemental Heat To Existing Heat Pumps
If your home’s heating needs grow, or you’re experiencing frequent supplemental heat use, options include:
- Upgrading to a more efficient, modern heat pump.
- Adding or replacing electric heat strips in the air handler.
- Converting to a dual-fuel system if natural gas is available.
- Integrating smart controls for better management.
Work with a qualified HVAC contractor to evaluate the most cost-effective solution.
Government Incentives And Rebates For Efficient Heat Pump Systems
The U.S. government, through the Department of Energy and local utility programs, offers incentives for high-efficiency heat pumps and dual-fuel systems. Benefits may include:
- Federal tax credits for qualifying ENERGY STAR-certified systems.
- State and utility rebates for energy efficiency upgrades.
- Special low-income programs for weatherization and HVAC improvements.
Check with local energy offices and your installer for current offers when upgrading supplemental heat solutions.
Frequently Asked Questions About Heat Pump Supplemental Heat
How Do I Know If My Heat Pump Is Using Supplemental Heat?
Most programmable thermostats display “AUX” or “EMER” when backup heaters are running. Visible steam from the outdoor unit during defrost is a clue. Increased electric usage is another sign.
Is It Bad For A Heat Pump To Use Supplemental Heat Often?
Frequent use drives up energy costs but doesn’t harm the system. However, repeated reliance could mean your heat pump is undersized or your home is poorly insulated.
Can I Disable Supplemental Heat To Save Money?
Most systems won’t let you turn off auxiliary heat entirely in cold weather, as this risks not heating your home adequately. Instead, optimize insulation and thermostat settings to minimize reliance.
Should I Set My Thermostat Lower To Avoid Supplemental Heat?
Lowering your setpoint reduces demand on backup heating but may compromise comfort. A modest setback (60–65°F at night) can strike a good balance.
What’s The Most Cost-Effective Supplement For My Heat Pump?
In cold climates with natural gas, a dual-fuel system is typically most efficient. In milder climates, electric strips suffice if used sparingly. Hydronic or oil methods suit specialized cases.
Key Takeaways On Heat Pump Supplemental Heat
- Supplemental heat ensures reliability during winter’s coldest periods and is essential for areas with freezing temperatures.
- Most American homes use electric resistance backup, but dual-fuel and hydronic options are available for efficiency and comfort.
- Proper sizing, advanced controls, and insulation improvements are the best ways to minimize costs and maximize comfort.
- Consult a trusted HVAC professional to evaluate and upgrade your system for optimal supplemental heat performance.