Auxiliary heat is one of the most misunderstood parts of a ducted heat-pump system. Homeowners sometimes assume that if auxiliary heat turns on, the heat pump has failed or was incorrectly sized. In reality, auxiliary heat can be a normal and intentional part of a properly designed heat-pump system.
A ducted heat pump can provide efficient heating by extracting thermal energy from outdoor air. However, the amount of heat available from outdoor air and the heat pump’s ability to transfer that heat change as outdoor temperature falls. The building’s heat loss also increases as the outdoor temperature becomes colder.
At some point, the heat pump may not be able to provide enough heating capacity by itself. The system can then use a supplemental heat source.
That supplemental source is commonly called auxiliary heat or aux heat.
Understanding auxiliary heat is important because it affects:
- Winter comfort
- Electricity consumption
- System sizing
- Thermostat operation
- Electrical-service requirements
- Heat-pump control strategy
- Backup-heating decisions
This guide explains how auxiliary heat works in ducted heat-pump systems, when it operates, how electric resistance heat differs from emergency heat, why auxiliary heat can become expensive, and how homeowners should evaluate the backup-heating strategy before purchasing a system.
Quick Answer: What Is Auxiliary Heat?
| Term | Meaning | Typical Purpose |
|---|---|---|
| Heat pump | Primary heating equipment that transfers heat from outside to inside | Normal heating operation |
| Auxiliary heat | Supplemental heat that assists the heat pump | Additional capacity when the heat pump cannot fully satisfy demand |
| Electric resistance heat | Electrical energy converted directly into heat | Common auxiliary heat source in ducted systems |
| Emergency heat | A control mode intended to use backup heat without normal heat-pump operation | Manual or fault-related backup operation |
| Dual fuel | Heat pump combined with a combustion furnace | Uses different heating sources according to system controls |
| Defrost heat | Supplemental heating used during certain outdoor-coil defrost conditions | Helps maintain indoor comfort during defrost |
How A Ducted Heat Pump Heats A Home
A ducted air-source heat pump uses a refrigeration cycle to move heat between the outdoor and indoor environments.
During heating mode, the outdoor coil acts as the evaporator and extracts thermal energy from outdoor air. The refrigerant carries that energy through the system, while the compressor raises the refrigerant pressure and temperature.
The indoor coil then releases heat into the indoor air stream.
The blower moves that conditioned air through the supply ducts and into the rooms.
Even when outdoor air feels extremely cold to a person, it still contains thermal energy. The heat pump can extract some of that energy when operating conditions permit.
However, the colder the outdoor air becomes, the more difficult the heat-transfer process becomes and the heating capacity of the system generally declines.
Why Auxiliary Heat Is Needed
There are two curves that matter during winter:
- The building heating-load curve
- The heat-pump capacity curve
The building’s heat requirement generally increases as outdoor temperature falls.
At the same time, an air-source heat pump generally loses heating capacity as outdoor temperature falls.
Eventually, the building may require more heat than the heat pump can supply.
When that occurs, the control system can activate auxiliary heat.
For example, consider a hypothetical house:
| Outdoor Temperature | Building Heating Load | Heat Pump Capacity | Additional Heat Required |
|---|---|---|---|
| 40°F | 20,000 BTU/h | 36,000 BTU/h | 0 |
| 30°F | 25,000 BTU/h | 34,000 BTU/h | 0 |
| 20°F | 30,000 BTU/h | 31,000 BTU/h | 0 |
| 10°F | 35,000 BTU/h | 27,000 BTU/h | 8,000 BTU/h |
| 0°F | 42,000 BTU/h | 23,000 BTU/h | 19,000 BTU/h |
The figures above are illustrative and do not represent the performance of a particular heat pump.
This is the basic reason auxiliary heat exists.
Does Auxiliary Heat Mean The Heat Pump Is Broken?
No.
Auxiliary heat can be completely normal.
A system may activate auxiliary heat because:
- Outdoor temperature has fallen substantially
- The building heating load has increased
- The thermostat is recovering from a large temperature setback
- The heat pump is temporarily in defrost mode
- The heat pump cannot increase capacity quickly enough
- The system has been intentionally designed with supplemental heat
However, auxiliary heat that operates unusually often or for long periods can indicate a sizing, controls, airflow, equipment or mechanical problem.
The operating pattern matters.
Auxiliary Heat Versus Emergency Heat
These terms are frequently confused.
Auxiliary Heat
Auxiliary heat is normally controlled automatically by the thermostat or heat-pump control system.
The heat pump can continue operating while supplemental heat provides additional capacity.
Emergency Heat
Emergency heat is a user-selectable operating mode on many heat-pump thermostats.
When emergency heat is selected, the system is generally instructed to use the backup heat source instead of normal heat-pump heating.
The exact control behavior depends on the equipment and thermostat.
Emergency heat is intended primarily for situations where the heat pump should not operate, such as certain equipment failures or when instructed by a service professional.
Should You Turn On Emergency Heat During Very Cold Weather?
Usually, you should not manually switch to emergency heat simply because the weather is cold.
A properly configured heat-pump system should automatically manage normal heat-pump operation and auxiliary heat according to its controls.
Emergency heat is not simply a “stronger” heat-pump setting.
If the heat pump is operating normally, manually selecting emergency heat can unnecessarily disable the primary heat source and cause the backup system to provide most or all of the heating.
Electric Resistance Auxiliary Heat
Electric resistance heat is one of the most common forms of auxiliary heat in ducted heat-pump systems.
An electric resistance element produces heat when electrical current passes through a resistive material.
The process is straightforward:
Electrical energy → resistance element → thermal energy → indoor air
Unlike a heat pump, resistance heating does not move heat from outdoors. It directly converts electrical energy into heat.
Why Electric Resistance Heat Can Be Expensive
A heat pump can produce several units of heat for each unit of electrical energy consumed when operating under favorable conditions because it is transferring existing thermal energy rather than creating all of the heat from electricity.
Electric resistance heat, by comparison, has approximately a one-to-one relationship between electrical energy input and thermal energy output at the point of use.
For example, a 10-kW resistance heater consumes approximately 10 kW while operating at full output.
Its thermal output is approximately:
10 kW × 3,412 BTU/h per kW ≈ 34,120 BTU/h
This is useful backup capacity, but it can consume electricity rapidly if operated for long periods.
How Much Electricity Does Auxiliary Heat Use?
The answer depends primarily on the size and runtime of the auxiliary heater.
Consider a hypothetical 10-kW auxiliary heater:
- Power = 10 kW
- Runtime = 1 hour
- Energy consumption = 10 kWh
If electricity costs $0.20/kWh, one hour would cost approximately:
10 kWh × $0.20 = $2.00
At $0.30/kWh:
10 kWh × $0.30 = $3.00
These are simplified examples. Actual system operation can involve multiple heat stages, cycling and simultaneous heat-pump operation.
Why A Small Amount Of Auxiliary Heat Can Have A Large Effect On Electricity Use
Suppose the heat pump normally consumes 3 kW while operating.
If a 10-kW resistance stage activates simultaneously, total electrical demand could temporarily approach:
3 kW + 10 kW = 13 kW
This does not mean the auxiliary heater will always operate simultaneously with the heat pump or at full output. Actual behavior depends on the equipment and controls.
Nevertheless, this illustrates why homeowners should understand the size and staging of electric auxiliary heat.
Auxiliary Heat Staging
Many ducted systems can use multiple stages of auxiliary resistance heat.
For example:
| Stage | Illustrative Heater Size | Approximate Heat Output |
|---|---|---|
| Stage 1 | 5 kW | 17,060 BTU/h |
| Stage 2 | 5 kW additional | 17,060 BTU/h additional |
| Total | 10 kW | 34,120 BTU/h |
Illustrative values only.
Staging allows the control system to use only the amount of supplemental heat needed rather than immediately activating the entire heater bank.
Heat Pump + Furnace: Dual-Fuel Auxiliary Heat
Not every ducted heat pump uses electric resistance as its backup.
A heat pump can be paired with a gas, propane or oil furnace in a dual-fuel configuration.
In this arrangement, the heat pump and furnace share the heating responsibility according to system controls.
The system might use the heat pump under one set of outdoor conditions and the furnace under another.
The exact changeover temperature is not universal.
It depends on factors such as:
- Heat-pump capacity
- Heat-pump efficiency
- Fuel cost
- Electricity cost
- Furnace efficiency
- Outdoor temperature
- Building load
- Control strategy
Auxiliary Heat During Defrost
Defrost is another situation in which supplemental heat can be useful.
During heating operation, frost can accumulate on the outdoor coil under suitable temperature and humidity conditions.
The heat pump periodically reverses its refrigeration cycle to remove that frost.
During this process, the system temporarily directs heat toward the outdoor coil rather than delivering all available heat to the house.
Indoor auxiliary heat may therefore operate during some defrost cycles to reduce the impact on indoor comfort.
Why A Heat Pump May Blow Cooler Air During Defrost
Homeowners sometimes notice that the air coming from supply registers feels less warm during defrost.
This can be normal.
The system’s operating mode has temporarily changed to remove frost from the outdoor coil.
Depending on the equipment, controls and auxiliary heat configuration, supplemental heat may be used to reduce the sensation of cool air indoors.
A brief change in supply-air temperature does not automatically indicate a malfunction.
Auxiliary Heat During Thermostat Recovery
Large thermostat setbacks can also cause auxiliary heat to activate.
For example, suppose a homeowner lowers the indoor temperature overnight and then raises the thermostat several degrees shortly before waking.
The heat pump may determine that recovering the temperature rapidly requires supplemental heat.
Whether this happens depends on the thermostat and system controls.
For heat pumps, moderate setbacks can sometimes be preferable to large, rapid recovery demands, particularly when resistance auxiliary heat is expensive.
Why Auxiliary Heat May Appear After A Large Temperature Increase
Imagine the indoor temperature is 64°F and the thermostat is raised to 72°F.
The system suddenly has a large temperature-recovery target.
If the heat pump cannot satisfy the recovery requirement within the control logic, the thermostat may call for auxiliary heat.
This is not necessarily a sign that the heat pump cannot maintain 72°F.
It may simply be responding to the rapid recovery request.
Does Setting The Thermostat Higher Make The Heat Pump Heat Faster?
Not necessarily.
Raising the thermostat several degrees above the desired temperature generally does not make the heat pump operate at an arbitrarily higher heating capacity.
Depending on the system, the thermostat may instead call for auxiliary heat.
Therefore, setting the thermostat much higher than the desired temperature can sometimes increase auxiliary-heat use without providing the expected proportional increase in heat-pump output.
Heat Pump Capacity And Auxiliary Heat
The amount of auxiliary heat required depends strongly on the difference between:
Building heating load − available heat-pump capacity
For example:
- Building load = 40,000 BTU/h
- Heat-pump capacity = 32,000 BTU/h
The theoretical shortfall is:
40,000 − 32,000 = 8,000 BTU/h
Auxiliary heat would need to provide approximately that additional capacity under the assumed condition.
Actual control operation is more complicated because equipment output, building load and outdoor conditions continuously change.
Why Oversizing The Auxiliary Heater Is Not Necessarily Better
It may seem logical to install a very large resistance heater so that the house can be heated quickly.
However, larger resistance heaters can require larger electrical circuits, wiring, breakers and potentially greater electrical-service capacity.
The design should therefore consider the actual heating load and backup strategy rather than simply maximizing auxiliary-heater capacity.
Electrical Requirements For Electric Auxiliary Heat
Electric resistance heat can represent a substantial electrical load.
For example:
| Auxiliary Heater | Approximate Full-Load Current At 240 V |
|---|---|
| 5 kW | 20.8 A |
| 7.5 kW | 31.3 A |
| 10 kW | 41.7 A |
| 15 kW | 62.5 A |
These are simplified current calculations using:
Current = Power ÷ Voltage
Actual circuit and conductor requirements must be determined according to the equipment specifications and applicable electrical codes.
A large auxiliary heater can therefore be an important consideration when replacing a conventional HVAC system with a ducted heat pump.
Can An Existing Electrical Panel Support Auxiliary Heat?
It depends on the home’s electrical service and existing loads.
A heat-pump installation may require evaluation of:
- Service rating
- Available breaker spaces
- Existing electrical loads
- Heat-pump circuit requirements
- Air-handler circuit requirements
- Auxiliary-heater circuit requirements
- Local electrical-code requirements
An installer should perform the appropriate electrical load assessment rather than assuming that an existing panel can accommodate a large resistance-heating package.
Heat Pump Auxiliary Heat And Operating Cost
Auxiliary heat can substantially change winter operating cost because resistance heat has a different energy-use profile from heat-pump operation.
Consider a simplified example.
A heat pump produces 30,000 BTU/h with a COP of 3.
The approximate electrical input required is:
30,000 ÷ 3 = 10,000 BTU/h electrical input
Since 1 kWh contains approximately 3,412 BTU:
10,000 ÷ 3,412 ≈ 2.93 kW
A 30,000-BTU/h resistance heater would require approximately:
30,000 ÷ 3,412 ≈ 8.8 kW
Again, these are simplified calculations intended to illustrate the difference between heat-pump and resistance heating. Actual performance varies with operating conditions.
When Auxiliary Heat Is Normal
Some auxiliary-heat operation can be expected when:
- Outdoor temperatures approach or fall below the system’s balance point
- The building experiences an unusually high heating load
- The system is recovering from a substantial thermostat setback
- The heat pump enters defrost
- The heat pump cannot increase output quickly enough to satisfy demand
The exact operating pattern varies by system.
When Frequent Auxiliary Heat May Indicate A Problem
Frequent auxiliary heat deserves investigation when it occurs under conditions where the heat pump should normally be able to provide the required heating.
Possible causes include:
- Incorrect equipment sizing
- Low refrigerant charge
- Restricted airflow
- Dirty air filter
- Dirty indoor coil
- Outdoor coil blockage
- Faulty sensors
- Incorrect thermostat configuration
- Control-wiring problems
- Faulty reversing valve
- Compressor problems
- Defrost-control problems
- Duct leakage
- Excessive building heat loss
Homeowners should not assume that auxiliary heat itself is the problem. The objective is to determine why it is being called.
Auxiliary Heat And Airflow
Airflow is especially important in ducted systems.
The heat pump and electric auxiliary heater both depend on the air handler and duct system to move air through the home.
If airflow is too low, the system may have difficulty transferring its available heating capacity into the occupied spaces.
Potential causes include:
- High-MERV restrictive filters
- Dirty filters
- Undersized return ducts
- Undersized supply ducts
- Closed registers
- Improperly sized blower
- Dirty indoor coil
- Excessive static pressure
Therefore, auxiliary-heat troubleshooting should include airflow and static-pressure evaluation where appropriate.
Auxiliary Heat And Duct Leakage
If a substantial portion of heated air escapes through leaking ducts, the heat pump has to operate longer to deliver the required amount of useful heat to the occupied spaces.
In extreme cases, duct leakage can contribute to inadequate comfort and increased auxiliary-heat operation.
Duct sealing and insulation should therefore be considered as part of a whole-system evaluation.
Should You Turn Off Auxiliary Heat?
In most systems, homeowners should not disable auxiliary heat without understanding the consequences.
Auxiliary heat is an intentional component of the system’s control strategy.
Disabling it can potentially cause the home to lose temperature during conditions in which the heat pump cannot meet the load.
If auxiliary heat appears to be operating excessively, the better approach is to investigate the cause rather than simply defeating the control.
How Thermostats Control Auxiliary Heat
Modern heat-pump thermostats can use several pieces of information to determine when supplemental heat is appropriate.
Depending on the system, controls may consider:
- Indoor temperature
- Thermostat setpoint
- Rate of temperature recovery
- Outdoor temperature
- Heat-pump operating status
- Defrost status
- Compressor staging
- Auxiliary-heat staging
The control logic varies considerably between equipment manufacturers and thermostat models.
Therefore, thermostat compatibility should be verified when installing a new ducted heat pump.
Smart Thermostats And Auxiliary Heat
A smart thermostat can provide useful scheduling and control features, but compatibility is critical.
Some heat-pump systems use proprietary communication between the thermostat and HVAC equipment.
Others use conventional low-voltage control signals.
A thermostat that works with a conventional furnace or air conditioner is not automatically compatible with every modern heat pump.
Before replacement, verify:
- Heat-pump compatibility
- Number of heating and cooling stages
- Auxiliary-heat control
- Emergency-heat control
- Outdoor-temperature sensing
- Communication requirements
- Manufacturer-specific control requirements
Outdoor Temperature Lockouts
Some heat-pump control systems can use outdoor-temperature thresholds to control auxiliary heat.
For example, a control strategy might prevent electric resistance heat from operating under mild outdoor conditions unless there is a particular need for it.
The actual thresholds should be selected based on the equipment, climate and system design rather than using a universal temperature value.
Why There Is No Universal “Aux Heat Temperature”
You may hear statements such as:
“Auxiliary heat always comes on below 35°F.”
That is not a universal rule.
Different heat pumps have different capacity curves.
Different homes have different heating loads.
Different thermostats use different algorithms.
Consequently, auxiliary heat may operate at very different outdoor temperatures in different installations.
How To Reduce Unnecessary Auxiliary Heat Use
Homeowners can reduce unnecessary auxiliary-heat operation by maintaining the system properly and avoiding conditions that cause unnecessary recovery demands.
- Keep filters clean
- Keep outdoor coils unobstructed
- Do not repeatedly make large thermostat setbacks
- Maintain proper airflow
- Keep supply and return registers unobstructed
- Have the system serviced according to manufacturer recommendations
- Investigate unusual auxiliary-heat operation
- Verify thermostat configuration
For persistent problems, a qualified HVAC technician should evaluate the equipment.
How Auxiliary Heat Affects Heat-Pump Sizing
Auxiliary heat should be considered during equipment selection rather than after installation.
A contractor should be able to explain:
- The calculated heating load
- The heat pump’s capacity at design conditions
- The expected balance point
- The auxiliary-heat capacity
- The expected operating strategy
- The electrical requirements
This provides a clearer picture of how the system will perform during extreme winter conditions.
Should A Heat Pump Cover 100% Of The Heating Load?
Not necessarily.
Some systems are designed to provide nearly all of the heating load with the heat pump.
Others intentionally use supplemental heat for the coldest portion of the heating season.
Both approaches can be valid depending on the home’s climate, equipment and economics.
The important point is that the design should be deliberate.
Heat Pump + Resistance Heat Versus Dual Fuel
| Feature | Heat Pump + Electric Resistance | Heat Pump + Furnace |
|---|---|---|
| Primary heating | Heat pump | Heat pump |
| Backup/supplemental heat | Electric resistance | Gas, propane or oil furnace |
| Additional electrical demand | Can be substantial when resistance stages operate | Usually lower than large resistance elements for backup heating |
| Combustion equipment | No | Yes |
| Electrical-service considerations | Important for resistance heater size | Generally different because furnace supplies backup heat |
| Control complexity | Depends on heat-pump and thermostat | Requires dual-fuel control strategy |
Neither configuration should be selected from a generic rule. Local energy prices, existing equipment, climate and electrical infrastructure all matter.
Questions To Ask Before Buying A Ducted Heat Pump
- What type of auxiliary heat will this system use?
- How many kilowatts of electric resistance heat are included?
- How is auxiliary heat staged?
- At what conditions is auxiliary heat expected to operate?
- What is the heat pump’s heating capacity at the local design temperature?
- What is the system’s capacity at 17°F?
- What is its capacity at 5°F if relevant?
- What is the calculated heating load of the home?
- What is the expected balance point?
- Can the existing electrical service support the auxiliary heater?
- Will the thermostat control auxiliary heat correctly?
- Will auxiliary heat operate during defrost?
- How will airflow be measured after installation?
- What happens if the heat pump cannot maintain the setpoint?
Common Auxiliary-Heat Mistakes
1. Assuming Aux Heat Means Failure
Auxiliary heat can be normal system operation.
2. Using Emergency Heat As Normal Heating
Emergency heat is generally intended as a backup operating mode rather than the normal way to heat the home.
3. Ignoring Resistance-Heater Size
A large electric heater can create a substantial electrical load.
4. Ignoring The Building Load
Auxiliary heat requirements make more sense when the building heating load and heat-pump capacity are known.
5. Blaming The Heat Pump Without Checking Airflow
Restricted airflow can reduce system performance and contribute to comfort problems.
6. Making Large Thermostat Setbacks
Large temperature recoveries can trigger auxiliary heat depending on the thermostat and system controls.
7. Disabling Auxiliary Heat Without Diagnosis
Turning off supplemental heat can create comfort and safety problems during conditions where the heat pump cannot meet the load.
Auxiliary Heat Installation Checklist
| Item | What To Verify |
|---|---|
| Heat-pump capacity | Capacity at relevant outdoor temperatures |
| Heating load | Proper load calculation |
| Auxiliary heater | Type and total capacity |
| Staging | Correct control of backup stages |
| Electrical service | Service and circuit capacity |
| Thermostat | Compatible heat-pump and auxiliary-heat control |
| Defrost | Correct supplemental-heat behavior |
| Airflow | Required airflow achieved |
| Static pressure | Within equipment specifications |
| Commissioning | Controls and heating operation verified |
Frequently Asked Questions
1. What is auxiliary heat on a ducted heat pump?
Auxiliary heat is supplemental heating that assists the heat pump when additional heating capacity is needed.
2. Is auxiliary heat normal?
Yes. Some auxiliary-heat operation can be a normal part of a properly designed heat-pump system.
3. Is auxiliary heat the same as emergency heat?
No. Auxiliary heat is normally automatic supplemental heating, while emergency heat is a backup operating mode that generally prevents normal heat-pump operation.
4. What is the most common auxiliary heat source?
Electric resistance heating is common in ducted heat-pump systems, although dual-fuel systems can use a furnace as the backup heat source.
5. Why does auxiliary heat cost more?
Electric resistance heat directly converts electricity into heat and can consume substantial electrical power compared with a heat pump operating at a favorable COP.
6. Does auxiliary heat mean my heat pump is undersized?
Not automatically. Supplemental heat can be intentionally included in the system design.
7. Why does auxiliary heat come on during defrost?
During defrost, the heat pump temporarily changes operation to remove frost from the outdoor coil. Supplemental heat can help maintain indoor comfort during that period.
8. Can auxiliary heat operate above freezing?
Yes. It can operate above freezing depending on the thermostat settings, temperature-recovery demand, heat-pump capacity and control strategy.
9. Does every heat pump have auxiliary heat?
Not every configuration uses the same type of supplemental heat. Some systems rely on auxiliary electric heat, while others use dual-fuel equipment or other backup strategies.
10. Should I turn on emergency heat when temperatures fall below freezing?
Normally, no. The system should generally manage normal heat-pump and auxiliary operation automatically. Emergency heat is intended for backup situations.
11. Can I turn auxiliary heat off?
It is generally better not to disable it without understanding the system design. If it operates excessively, investigate the cause.
12. Why does auxiliary heat activate after I raise the thermostat?
A large temperature-recovery demand can cause some thermostats to request supplemental heat.
13. Does lowering the thermostat at night save money with a heat pump?
It can, but very large setbacks may trigger auxiliary heat during recovery. The optimal strategy depends on the system and controls.
14. How can I tell if auxiliary heat is running?
Many thermostats display “AUX,” “Aux Heat” or a similar indicator when supplemental heating is active.
15. How much power does electric auxiliary heat use?
It depends on the installed heater. A 10-kW heater, for example, consumes approximately 10 kWh for each hour it operates at full output.
16. Can auxiliary heat run at the same time as the heat pump?
Yes, depending on the equipment and control strategy. Some systems use supplemental heat while the heat pump continues operating.
17. What is dual-fuel heating?
Dual-fuel heating combines a heat pump with a combustion furnace and uses controls to determine which heat source should operate under particular conditions.
18. Does a dual-fuel system have electric auxiliary heat?
It depends on the equipment configuration. Some systems use a furnace as the primary backup while others may also include electric supplemental heat.
19. Can frequent auxiliary heat indicate a problem?
Yes. If it operates much more frequently than expected, the system should be checked for sizing, airflow, refrigerant, controls, equipment or building-envelope problems.
20. Can a dirty filter cause auxiliary heat to operate?
A severely restricted filter can reduce airflow and system performance. If the heat pump cannot satisfy demand effectively, auxiliary heat may operate more frequently.
21. Does duct leakage increase auxiliary-heat use?
Significant duct leakage can reduce the amount of heat reaching conditioned spaces and increase system runtime, potentially contributing to supplemental-heat operation.
22. How large should auxiliary electric heat be?
It should be selected based on the building load, heat-pump capacity, electrical service and system design rather than a universal rule.
23. Does auxiliary heat reduce heat-pump efficiency?
When electric resistance heat operates, total system electricity consumption can increase substantially. The effect depends on how much auxiliary heat is used.
24. Is resistance auxiliary heat dangerous?
Electric resistance heaters are common HVAC components, but they require correct installation, electrical protection, airflow and maintenance. Electrical work should follow applicable codes and manufacturer requirements.
25. What should I ask an installer about auxiliary heat?
Ask about the type and size of supplemental heat, expected operating conditions, staging, electrical requirements, thermostat compatibility, balance point and commissioning procedure.
Final Takeaway
Auxiliary heat is not automatically a sign that a ducted heat pump is failing.
It exists because a home’s heating requirement and a heat pump’s available capacity change with outdoor temperature.
A well-designed system should have a clear strategy for dealing with the difference between building heating load and heat-pump capacity.
Before purchasing a ducted heat pump, understand:
- The calculated heating load of the home
- The heat pump’s capacity at relevant outdoor temperatures
- The expected balance point
- The type of auxiliary heat
- The size and staging of electric resistance heaters, if used
- The electrical-service requirements
- The thermostat and control strategy
- The system’s defrost behavior
- The ductwork and airflow requirements
The goal should not necessarily be to eliminate auxiliary heat completely. Instead, the system should be designed so that the heat pump provides the majority of appropriate heating demand while supplemental heat operates when the system genuinely requires additional capacity or when the control strategy intentionally calls for it.
For the commercial comparison of complete ducted systems, see Best Ducted Heat Pumps In The USA.
About the Author
ManBearPig is a part-man, part-bear, part-pig creature and a full-time expert on global warming—mostly because he has personally experienced the consequences of being extremely, extremely, super cereal.
When he isn’t roaming the wilderness, terrorizing unsuspecting humans, or demanding that people take climate change seriously, ManBearPig studies rising temperatures, melting ice, extreme weather, carbon emissions, and other inconvenient signs that the planet may not be particularly happy with us.
His research philosophy is simple:
“I’m super cereal.”
ManBearPig believes climate change is too important to discuss without facts—and too ridiculous to discuss without a little humor. Through this website, he explores global warming, climate science, environmental changes, energy, and the strange ways humans respond when their own planet starts sending them warning signals.
He has no university degree, no laboratory, and absolutely no intention of becoming a respectable academic.
But he does have hooves, claws, a snout, and an unusually strong opinion about melting ice.