Ducted Heat Pump Sizing: How To Choose The Right Size For Your Home

The tempting approach is to look at the size of the existing furnace or central air conditioner and purchase a heat pump with the same nominal capacity. Another common shortcut is to calculate a certain number of Btu per square foot and select the nearest equipment size.

Neither approach is a reliable substitute for a proper load calculation.

A ducted heat pump has to satisfy two different requirements: cooling demand during the summer and heating demand during the winter. Those loads can be very different, and heat-pump heating capacity also changes as outdoor temperature changes.

That makes heat-pump sizing more complicated than simply asking whether a house needs a 2-ton, 3-ton, 4-ton or 5-ton system.

A properly sized ducted heat pump should be selected by considering:

• the home’s heating load;
• the home’s cooling load;
• the outdoor design temperatures;
• the heat pump’s capacity at relevant outdoor temperatures;
• the duct system’s airflow capability;
• the home’s insulation and air leakage;
• the number, size and orientation of windows;
• the building’s floor area and geometry;
• indoor design conditions;
• auxiliary or backup heat;
• the equipment’s modulation or staging;
• and the actual matched indoor and outdoor equipment.

This guide explains how those factors fit together and how a homeowner can evaluate a ducted heat-pump sizing proposal.

Why Ducted Heat Pump Sizing Is Different From Picking A Furnace Size

A furnace primarily has one job: provide heating.

A central air conditioner primarily has one job: provide cooling.

A ducted heat pump has to do both.

In addition, the heat pump’s heating output is not constant across all outdoor temperatures.

For example, a particular heat pump might have one heating capacity at 47°F, another at 17°F and another at 5°F. The exact values vary by model.

Therefore, the nameplate tonnage does not tell the entire story.

A system advertised as a 3-ton heat pump should not automatically be assumed to deliver 36,000 Btu/h of heating at every outdoor temperature.

What Does “Ton” Mean In Heat Pump Sizing?

In residential HVAC terminology, one ton of nominal cooling capacity corresponds to approximately 12,000 Btu/h.

These are nominal cooling capacities, not guarantees of actual delivered capacity under every operating condition.

Modern variable-capacity equipment can also modulate over a range, meaning the compressor does not necessarily operate continuously at the nominal maximum capacity.

Cooling Capacity And Heating Capacity Are Different

One of the most important concepts in heat-pump sizing is that the cooling tonnage cannot be treated as the heating capacity.

Suppose a heat pump is nominally rated as a 3-ton system.

Its nominal cooling capacity might be approximately 36,000 Btu/h.

But its heating capacity could vary substantially with outdoor temperature and operating conditions.

This is why homeowners should ask for the manufacturer’s performance data rather than relying only on the nominal tonnage.

The First Step: Calculate The Building Load

The starting point should be the house, not the equipment.

A heating-load calculation estimates how much heat the building loses at the selected outdoor design condition.

A cooling-load calculation estimates how much heat must be removed during the selected cooling design condition.

For residential HVAC work in the United States, Manual J is the widely recognized residential load-calculation methodology used to estimate these loads.

The result is not simply a number based on floor area.

The calculation considers the building envelope and operating conditions.

What Goes Into A Heating Load?

Heat leaves a house through several mechanisms.

Important contributors include:

• heat transfer through exterior walls;
• heat transfer through the roof or ceiling;
• heat transfer through floors;
• heat loss through windows;
• heat loss through exterior doors;
• air infiltration;
• ventilation requirements;
• thermal bridges and other envelope characteristics.

The heating load therefore depends on far more than the home’s square footage.

What Goes Into A Cooling Load?

Cooling load has additional components.

The system must remove both sensible heat and latent heat under appropriate conditions.

Heat gains can come from:

• solar radiation through windows;
• outdoor heat transfer;
• infiltration;
• people;
• lighting;
• appliances;
• electronics;
• ventilation air.

Humidity also matters because removing moisture requires latent cooling capacity.

This is one reason a house can have a relatively modest heating load but still require significant cooling capacity during hot, sunny weather.

Why Square-Foot Rules Can Produce The Wrong Size

A common shortcut is something like:

House size × assumed Btu per square foot = required equipment size.

The problem is that houses with identical floor areas can have dramatically different loads.

Consider two hypothetical 2,000-square-foot houses.

House A might have:

• excellent insulation;
• high-performance windows;
• limited air leakage;
• moderate solar exposure.

House B might have:

• poor insulation;
• older windows;
• significant infiltration;
• large west-facing glass areas.

Their heating and cooling loads could be very different even though their floor areas are identical.

Square footage is useful information, but it is not a complete sizing calculation.

Heating Design Temperature Matters

Once the building load is known, the outdoor design temperature becomes important.

A heat pump needs to provide sufficient heating capacity under the conditions for which the system is designed.

The design temperature varies by geographic location and is not simply the lowest temperature ever recorded.

This distinction matters because designing equipment around an extreme historical temperature could produce a very different result from designing around an accepted heating design condition.

Why The 47°F Rating Is Not Enough

Heat pumps are commonly associated with performance data at standardized outdoor conditions such as 47°F.

That temperature is useful for comparing equipment, but it may not represent the conditions that create the greatest heating demand in a particular home.

If a location experiences substantial periods below 32°F, the homeowner should examine performance at lower temperatures.

For cold-climate applications, even lower-temperature performance becomes particularly important.

The correct question is therefore:

How much heating capacity does this particular heat pump provide at the outdoor temperatures relevant to my home?

rather than:

How many tons is the heat pump?

Heat Pump Capacity Changes With Outdoor Temperature

Air-source heat pumps extract heat from outdoor air.

As outdoor conditions become colder, the refrigeration system generally has to operate under more difficult conditions and less heat is available to extract.

As a result, heating capacity and efficiency can change.

The change is equipment-specific.

Some systems are designed to maintain substantial heating capacity at low outdoor temperatures, while others experience a larger reduction in capacity.

This is why manufacturer performance tables are important when selecting a system.

Heating Capacity Should Be Compared Against The Heating Load

Imagine, purely as an example, that a home’s calculated design heating load is 42,000 Btu/h.

A heat pump should not be selected simply because its nominal size says 3.5 tons.

The designer should determine the actual heating capacity of the proposed system at the relevant outdoor design condition.

If the heat pump provides less than the building load at that temperature, the difference must be addressed through:

• additional heat-pump capacity;
• supplemental electric heat;
• a dual-fuel furnace;
• or another appropriate heating strategy.

The system’s control strategy should be understood before the equipment is purchased.

What Is Heat Pump Balance Point?

The balance point is the outdoor condition at which the building’s heating requirement and the heat pump’s available heating capacity are approximately equal.

Above that point, the heat pump may have enough capacity to meet the building load under the modeled conditions.

Below that point, additional heat may be required if the building load exceeds the heat pump’s capacity.

The concept is particularly useful for understanding auxiliary heat and dual-fuel operation.

It should not be confused with a fixed temperature at which every heat pump must stop operating.

What Is The Difference Between Balance Point And Changeover Temperature?

These terms describe different concepts.

Balance point: a relationship between building heating load and available heat-pump capacity.

Changeover temperature: a control setting at which a dual-fuel system changes from heat-pump operation to furnace operation.

A dual-fuel system may change over before the theoretical balance point for reasons involving operating cost, comfort, equipment protection, control strategy or other design considerations.

How Oversizing A Ducted Heat Pump Can Cause Problems

It is easy to assume that bigger equipment is safer.

That is not necessarily true.

Oversizing can create problems, particularly for cooling operation.

A system that satisfies the cooling thermostat very quickly may have insufficient operating time for effective moisture removal under some conditions.

Potential consequences can include:

• short cycling;
• reduced humidity control;
• uneven temperatures;
• more frequent starts and stops;
• reduced comfort;
• inefficient operation.

Variable-capacity systems can reduce some of these problems because they can modulate down to lower output levels, but the minimum capacity and control behavior still matter.

Why Oversizing Is Especially Important In Mild Weather

Consider a spring or autumn day.

The house might require only a small amount of heating or cooling.

If the heat pump can reduce its output sufficiently, it can operate for longer periods at lower capacity.

If its minimum capacity is still substantially greater than the building load, the system may cycle more frequently.

Therefore, homeowners should examine not only the maximum capacity but also the minimum modulation range for variable-capacity equipment.

Can A Variable-Speed Heat Pump Be Oversized?

Yes.

Variable-speed or variable-capacity equipment gives the system more flexibility, but it does not make sizing irrelevant.

A variable-capacity heat pump still has a minimum and maximum operating range.

If the building load is below the system’s minimum sustainable output for long periods, cycling can still occur.

Proper design remains important.

Why Undersizing Can Also Be A Problem

Undersizing creates a different set of issues.

If the heat pump cannot provide enough heating capacity at low outdoor temperatures, the system may rely heavily on auxiliary heat.

In an all-electric system, that can mean increased use of electric resistance heating.

In a dual-fuel system, it may result in more frequent furnace operation.

Potential consequences include:

• higher operating costs under some conditions;
• reduced heating capacity;
• greater auxiliary-heat use;
• comfort problems;
• longer recovery times.

The objective is therefore not simply to avoid undersizing by buying the largest available system.

The objective is to match equipment capacity to the building and control strategy.

Cooling Load Can Create A Different Sizing Constraint

Suppose a house has a relatively high winter heating load but a comparatively modest summer cooling load.

A heat pump selected purely around the heating requirement could be too large for the cooling requirement.

This creates a design challenge.

Possible solutions can include:

• selecting equipment with a wide modulation range;
• using appropriate supplemental heat;
• using a different equipment configuration;
• improving the building envelope;
• considering a dual-fuel system;
• selecting equipment based on the actual certified performance of the system.

This is one reason variable-capacity heat pumps can be useful in applications where heating and cooling loads differ substantially.

Heating Load Vs Cooling Load

How Ductwork Affects Heat Pump Sizing

Even a correctly sized heat pump can perform poorly if the duct system cannot move the required amount of air.

The duct system has to support the airflow required by the selected indoor unit.

Important factors include:

• supply-duct dimensions;
• return-duct dimensions;
• filter size;
• register restrictions;
• duct leakage;
• flex-duct installation quality;
• static pressure;
• blower capability.

If the duct system is severely restrictive, simply increasing equipment capacity does not solve the underlying problem.

Why Return Air Is Particularly Important

A ducted HVAC system needs a sufficient return-air pathway.

Imagine trying to push a large volume of air through a system while the return side is severely restricted.

The blower may have to operate against greater resistance.

This can affect airflow, noise and system performance.

A heat-pump installation should therefore consider both supply and return air.

Static Pressure And Heat Pump Sizing

Static pressure describes resistance to airflow within the duct system and equipment.

A contractor can measure total external static pressure and compare it with the equipment manufacturer’s requirements or allowable limits.

High static pressure can indicate restrictions such as:

• undersized ducts;
• undersized return grilles;
• restrictive filters;
• closed dampers;
• poorly designed transitions;
• undersized coils;
• other airflow restrictions.

Static-pressure testing is therefore useful during commissioning of a ducted heat-pump installation.

How Insulation Changes Heat Pump Sizing

Improving insulation can reduce the heating and cooling loads of a house.

For example, adding attic insulation can reduce heat loss during winter and heat gain during summer.

Air sealing can also reduce infiltration.

This means the required HVAC capacity can change after building-envelope improvements.

For a major renovation, it can therefore make sense to perform the load calculation after the planned envelope improvements have been incorporated into the design assumptions.

Windows Have A Major Effect On Cooling Load

Two houses with identical floor areas can have very different cooling loads because of their windows.

Window area, orientation, glazing characteristics, shading and solar exposure can all affect heat gain.

A house with large west-facing windows can experience substantial afternoon solar gain.

This is one reason a square-foot rule can miss important characteristics of a particular building.

Air Leakage Also Matters

Infiltration occurs when outdoor air enters a building through cracks, openings and other unintended pathways.

In cold weather, that outdoor air can increase the heating load.

During hot and humid weather, infiltration can increase the cooling and latent loads.

Air sealing can therefore improve comfort while also reducing HVAC demand.

Should You Size The Heat Pump For The Coldest Possible Temperature?

Not necessarily.

The system should be designed around the appropriate building design conditions and the actual performance of the equipment.

Designing solely around an exceptionally rare temperature can lead to a system that is oversized for much of the year.

On the other hand, ignoring legitimate low-temperature heating requirements can cause excessive auxiliary-heat operation.

The solution is to evaluate the complete load and performance profile.

Cold Climate Heat Pumps Require Additional Attention

In colder regions, the low-temperature performance of the heat pump becomes particularly important.

A cold-climate system should be evaluated using its certified performance at low outdoor temperatures rather than simply assuming that a conventional heat pump will behave the same way.

ENERGY STAR’s cold-climate criteria include specific low-temperature performance requirements, making certified performance data useful when comparing qualifying equipment.

How Auxiliary Heat Changes The Sizing Decision

Some homeowners assume that the heat pump must independently provide 100% of the home’s design heating load.

That is not always the design objective.

A system can be designed so that the heat pump provides most of the heating demand while auxiliary heat handles the remaining load under particular conditions.

For example, an all-electric system might use resistance heat below a particular operating condition.

A dual-fuel system might use the gas furnace instead.

The important question is:

What percentage of the heating load will the heat pump provide, and under what conditions will backup heat operate?

Auxiliary Heat Should Not Be Used To Hide Poor Sizing

Backup heat is a legitimate design feature.

But a contractor should be able to explain why it is included and how often it is expected to operate under the design conditions.

If a heat pump is dramatically undersized and relies heavily on resistance heat, the homeowner may experience substantially different operating costs than expected.

The proposed system should therefore be evaluated as a complete heating strategy rather than by looking only at the heat pump’s nameplate.

What Is Staging?

A staged heat pump can operate at different capacity levels rather than simply operating at full output whenever there is a call for heating or cooling.

A two-stage system typically has discrete capacity stages.

A variable-capacity system can provide a broader range of operation.

The exact modulation range depends on the equipment.

Staging can help the system match changing building loads more closely.

Single-Stage Vs Two-Stage Vs Variable-Capacity

Can A 4-Ton Heat Pump Be Better Than A 3-Ton Heat Pump?

The answer depends on the house and the equipment.

If the calculated load requires a capacity close to the 3-ton system’s capabilities, installing a 4-ton system merely because it has more capacity may create cooling-side problems.

If the 3-ton system cannot meet the required heating load at the design temperature, however, a 4-ton system or a different model may be appropriate.

The correct comparison is therefore not:

3 tons vs 4 tons.

It is:

Which equipment configuration provides the required heating and cooling capacity across the relevant operating conditions?

Why Model Numbers Matter

Two heat pumps with the same nominal tonnage can have different performance characteristics.

They may differ in:

• compressor technology;
• maximum heating capacity;
• low-temperature performance;
• minimum modulation;
• SEER2;
• HSPF2;
• noise;
• control architecture;
• refrigerant;
• indoor-unit compatibility.

That is why a quote should contain complete indoor and outdoor model numbers.

Matched Systems Matter

The outdoor unit should be evaluated with the specific indoor equipment with which it will operate.

Changing the indoor coil or air handler can change the certified performance of the combination.

For this reason, homeowners should not assume that any air handler can be paired with any outdoor heat pump simply because the physical dimensions appear compatible.

AHRI directory information can be used to verify certified matched-system performance for applicable equipment combinations.

What If The Contractor Says “We Always Install This Size”?

Ask for the load calculation.

A contractor may have extensive experience with similar houses, but a standard equipment size is not a substitute for evaluating the actual building.

Two houses on the same street can have different:

• insulation;
• windows;
• orientation;
• air leakage;
• occupancy;
• additions;
• duct systems;
• renovation histories.

The correct equipment size should follow the building analysis.

What Information Should You Give The Contractor?

To obtain a useful sizing calculation, provide accurate information about:

• conditioned floor area;
• number of floors;
• ceiling heights;
• construction type;
• insulation levels;
• window dimensions;
• window orientation;
• window type;
• door dimensions;
• attic conditions;
• crawlspace or basement conditions;
• existing ductwork;
• air-sealing improvements;
• planned renovations;
• occupancy.

How To Read A Heat Pump Performance Table

When reviewing manufacturer data, look for the heating capacity at several outdoor temperatures.

For example, a table might contain performance information around:

• 47°F;
• 35°F;
• 17°F;
• 5°F;
• or other tested conditions.

The exact test points vary by equipment and certification program.

You should compare the available heating capacity against the calculated building load at corresponding conditions.

This is much more informative than comparing nominal tonnage alone.

Example: Why Nominal Tonnage Can Mislead

Consider a hypothetical home with a design heating load of 38,000 Btu/h.

Two nominally similar heat pumps are being considered.

System A provides strong heating capacity at moderate outdoor temperatures but loses more capacity as temperatures fall.

System B has a similar nominal cooling size but maintains more heating capacity at lower outdoor temperatures.

Even though the two systems may look similar on a basic product listing, their suitability for the house can be different.

This is why the actual performance data should be examined.

Heat Pump Sizing And Home Improvements

If you plan to replace windows, improve attic insulation, seal major air leaks or remodel the building envelope, tell the HVAC designer.

A load calculation based entirely on the existing building condition may not represent the building after the improvements are completed.

The opposite is also true.

If the house has major envelope deficiencies that will not be corrected, those conditions need to be included in the design.

Should Every Room Have Its Own Load Calculation?

For a properly designed ducted system, room-by-room load calculations can be useful because they help determine how much air each space needs.

The system then has to distribute that airflow through appropriately sized supply and return pathways.

This becomes particularly important in houses with:

• large additions;
• multiple floors;
• large glass areas;
• open-plan spaces;
• rooms over garages;
• rooms with unusual solar exposure.

Why Room Balance Matters

A correctly sized outdoor heat pump cannot compensate for poorly distributed airflow.

If one bedroom receives too little supply air while another receives too much, occupants may experience different temperatures even though the central equipment is operating correctly.

Balancing dampers, supply-register selection, return pathways and duct design therefore matter as much as the outdoor-unit capacity.

Ducted Heat Pump Sizing Checklist

1. Calculate the home’s heating load.
2. Calculate the home’s cooling load.
3. Determine the appropriate outdoor design temperatures.
4. Review existing insulation and air leakage.
5. Evaluate windows and solar exposure.
6. Inspect the existing duct system.
7. Evaluate return-air capacity.
8. Measure or evaluate static pressure where appropriate.
9. Identify the required indoor airflow.
10. Compare actual heat-pump heating capacity at low temperatures.
11. Check minimum and maximum modulation.
12. Determine auxiliary-heat requirements.
13. Verify indoor/outdoor equipment compatibility.
14. Check electrical requirements.
15. Review thermostat and control compatibility.
16. Verify certified performance of the matched system.
17. Compare the proposal with at least one alternative where practical.

What A Good Heat Pump Sizing Proposal Should Show

A detailed proposal should ideally identify:

• design heating load;
• design cooling load;
• design outdoor temperatures;
• selected heat-pump model;
• indoor-unit model;
• heating capacity at relevant temperatures;
• cooling capacity;
• SEER2;
• HSPF2;
• auxiliary heat size;
• duct modifications;
• airflow assumptions;
• electrical requirements;
• control system;
• refrigerant type;
• installation and commissioning scope.

If the proposal provides only a tonnage and a price, ask for additional technical information before comparing the bids.

Common Ducted Heat Pump Sizing Mistakes

Mistake 1: Matching The Existing AC

The old AC may have been oversized, undersized or selected using outdated assumptions.

Mistake 2: Matching The Existing Furnace

Furnace capacity does not directly determine heat-pump capacity.

Mistake 3: Using Square Footage Alone

Floor area does not capture insulation, windows, infiltration and solar gain.

Mistake 4: Ignoring Low-Temperature Capacity

A heat pump’s heating performance at moderate outdoor temperatures does not automatically describe its performance during cold weather.

Mistake 5: Ignoring Minimum Capacity

Maximum capacity is not the only important number for variable-capacity equipment.

Mistake 6: Ignoring The Duct System

Equipment capacity and airflow capability have to work together.

Mistake 7: Assuming Auxiliary Heat Is Free

Electric resistance backup consumes electricity directly and can materially increase electrical demand when it operates.

Mistake 8: Choosing The Largest System Available

Oversizing can create cooling, humidity and cycling problems.

Mistake 9: Comparing Only Efficiency Ratings

Efficiency ratings are important, but capacity, controls, duct compatibility and low-temperature performance also matter.

Frequently Asked Questions

1. How do I know what size ducted heat pump I need?

The proper starting point is a heating and cooling load calculation, normally using an accepted residential method such as Manual J. The equipment is then selected based on actual heating and cooling performance.

2. How many tons of heat pump do I need for a 2,000-square-foot house?

There is no reliable answer based on square footage alone. Two 2,000-square-foot homes can have substantially different heating and cooling loads.

3. Can I use the same size heat pump as my AC?

Not automatically. The cooling load may justify a particular nominal size, while heating capacity at low outdoor temperatures may require a different equipment configuration.

4. Should my heat pump be the same size as my furnace?

No. Furnace capacity and heat-pump capacity are selected using different performance characteristics and should be based on the home’s calculated loads.

5. Is a bigger heat pump better?

Not necessarily. Oversizing can cause problems such as short cycling and reduced humidity control, particularly when the equipment cannot modulate sufficiently low.

6. Is an undersized heat pump always bad?

Not necessarily. Some systems are intentionally designed with supplemental or backup heat. The important question is whether the overall heating strategy meets the home’s requirements efficiently and comfortably.

7. What is the most important heat-pump sizing number?

There is no single number. The building load and the equipment’s actual capacity at relevant outdoor temperatures must be considered together.

8. What temperature should I use for heat-pump sizing?

The appropriate design temperature depends on the home’s location and accepted design conditions. It should not simply be the lowest temperature ever recorded.

9. Why does heat-pump capacity decrease in cold weather?

Air-source heat pumps obtain heat from outdoor air. As outdoor conditions become colder, the refrigeration system generally has less thermal energy available to extract and operates under different pressure and temperature conditions.

10. Does a cold-climate heat pump need to be oversized?

Not automatically. Cold-climate equipment should be selected based on the building load and its certified low-temperature performance.

11. What is the balance point of a heat pump?

It is the condition where the heat pump’s available heating capacity approximately equals the building’s heating load. Below that condition, supplemental heat may be required depending on the system design.

12. Can a heat pump be oversized for cooling but undersized for heating?

Yes. Heating and cooling loads are different, and equipment capacity changes with operating conditions. This is one reason system selection requires more than a single nominal capacity number.

13. Does variable-speed equipment eliminate sizing problems?

No. Variable-capacity equipment provides a wider operating range, but it still has minimum and maximum capacities and must be matched to the building.

14. How does ductwork affect heat-pump sizing?

The duct system must be capable of moving the airflow required by the indoor equipment. Restrictions can cause high static pressure and poor comfort even when the outdoor unit is correctly sized.

15. Should I replace my ducts when installing a heat pump?

Not necessarily. Existing ducts can often be reused if they are appropriately sized, sealed, insulated and capable of supporting the required airflow.

16. What happens if the heat pump is too large?

Potential problems include short cycling, reduced moisture removal, temperature swings and less efficient operation during low-load conditions.

17. What happens if the heat pump is too small?

The system may rely more heavily on auxiliary heat or another backup source, particularly during cold weather.

18. Should I use electric resistance heat as backup?

It can be appropriate for an all-electric system, but the size and expected operating frequency should be considered because resistance heat can create significant electrical demand.

19. Can I keep my gas furnace as backup?

Yes. A properly integrated heat pump and furnace can form a dual-fuel system.

20. What should I ask my HVAC contractor about sizing?

Ask for the calculated heating and cooling loads, design temperatures, proposed equipment models, heating capacity at relevant outdoor temperatures, auxiliary-heat strategy and duct-system assessment.

21. Does insulation affect heat-pump size?

Yes. Better insulation and air sealing generally reduce the heating and cooling loads of a building.

22. Do windows affect heat-pump size?

Yes. Window area, orientation, glazing and solar exposure can significantly influence cooling load and can also affect heating load.

23. Does a bigger house always need a bigger heat pump?

Larger buildings generally require more capacity, but floor area alone does not determine the required equipment size.

24. Can two houses of the same size need different heat pumps?

Absolutely. Construction, insulation, windows, air leakage, orientation and climate can all change the required capacity.

25. Should I choose the heat pump before calculating the load?

No. The building load should guide the equipment selection.

Final Takeaway

Correct ducted heat-pump sizing is not about finding the biggest system that will fit the house or matching the tonnage of an old air conditioner.

The process starts with the building.

A proper design determines the heating and cooling loads, establishes the relevant outdoor design conditions and then compares those requirements with the actual performance of available heat pumps.

For heating, the most important additional consideration is that heat-pump capacity changes with outdoor temperature. A system that appears adequate at a moderate test condition may provide substantially different capacity during colder weather.

For cooling, oversizing can create its own problems, particularly where humidity control and minimum operating capacity are concerned.

The duct system must also be considered. Supply airflow, return-air capacity, static pressure, filter restrictions and duct leakage can all affect how effectively the selected equipment performs in the real house.

Finally, the homeowner should understand the backup strategy. An all-electric system may use resistance heat, while a dual-fuel system may retain a gas furnace. Neither strategy should be treated as an afterthought.

The best sizing proposal is therefore not simply a statement such as “3-ton heat pump.”

It is a documented relationship between:

• the building’s heating load;
• the building’s cooling load;
• the heat pump’s actual capacity;
• the outdoor temperature;
• the duct system;
• the controls;
• and the backup-heating strategy.

For a broader examination of ducted heat-pump systems and equipment selection, see:

Best Ducted Heat Pumps In The USA