Heat Pump Systems

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Homeowner Summary

A heat pump is an air conditioner that can run in reverse. In summer it moves heat out of your home just like a traditional AC. In winter it reverses the process and moves heat from outdoor air into your home. This makes heat pumps remarkably efficient: for every dollar of electricity they consume, they can deliver two to three dollars worth of heating energy, because they move heat rather than generate it.

Modern heat pumps work effectively in much colder climates than older models could handle. Cold-climate heat pumps can maintain full heating capacity down to 5 degrees F (-15 degrees C) and continue operating below 0 degrees F (-18 degrees C). However, all air-source heat pumps lose efficiency as outdoor temperatures drop, and most systems include auxiliary electric resistance heat strips or are paired with a gas furnace (dual-fuel system) for extremely cold conditions.

Ground-source (geothermal) heat pumps are the most efficient type, using the stable temperature of the earth rather than outdoor air as their heat exchange medium. They cost significantly more to install but deliver 3-5x the energy they consume and last longer than air-source systems.

Heat pumps are increasingly popular due to their efficiency, ability to both heat and cool, and favorable tax incentives. A well-maintained air-source heat pump lasts about 15 years; ground-source systems can last 20-25 years for the indoor components and 50+ years for the ground loop.

How It Works

A heat pump uses the same refrigeration cycle as an air conditioner but adds a reversing valve that switches the direction of refrigerant flow. In cooling mode, the outdoor coil is the condenser (releases heat) and the indoor coil is the evaporator (absorbs heat). In heating mode, the reversing valve swaps these roles: the outdoor coil becomes the evaporator (absorbs heat from outdoor air, even in cold weather) and the indoor coil becomes the condenser (releases heat into your home).

Defrost cycle: In heating mode, moisture from outdoor air can freeze on the outdoor coil. The system periodically runs a defrost cycle, temporarily switching to cooling mode and energizing the outdoor fan off while the hot refrigerant melts the ice. This is normal and lasts 1-10 minutes. You may see steam rising from the outdoor unit.

Auxiliary/emergency heat: When outdoor temperatures drop below the heat pump's effective range, or during defrost cycles, electric resistance heat strips activate to supplement. "Auxiliary heat" (AUX) means the heat pump is running with supplemental help. "Emergency heat" (EM HEAT) bypasses the heat pump entirely and runs only on resistance heat; this is inefficient and should only be used if the heat pump fails.

Ground-source systems: Instead of exchanging heat with outdoor air, a ground-source heat pump circulates fluid through a loop of pipe buried underground (horizontal trenches at 4-6 feet, or vertical boreholes at 150-300 feet). Ground temperature stays a relatively constant 45-60 degrees F year-round, making the system efficient regardless of outdoor air temperature.

Maintenance Guide

DIY (Homeowner)

Change the air filter every 1-3 months (heat pumps run year-round, so filters get dirtier faster)
Keep the outdoor unit clear: 24 inches of clearance, remove leaves, snow, and ice accumulation
Do not block defrost drainage: ensure the base of the outdoor unit can drain freely
Check thermostat settings: avoid large temperature setbacks that trigger expensive auxiliary heat
Inspect the outdoor unit after storms for debris or damage
Clean the outdoor coil with a gentle hose rinse each spring and fall

Professional

All standard AC maintenance procedures (see air-conditioning article) plus:
Verify reversing valve operation in both heating and cooling modes
Check defrost control board and defrost termination/initiation sensors
Test auxiliary heat strips: amp draw per stage, sequencer operation, high-limit switches
Measure heating performance: supply air temperature, coefficient of performance
Check refrigerant charge in both modes (heating mode superheat and subcooling differ from cooling)
Inspect and test check valves or bi-flow TXVs
For ground-source: check loop pressure (typically 15-30 psi), flow rate, entering/leaving water temperatures, antifreeze concentration

Warning Signs

Heat pump running constantly without maintaining temperature
AUX or EM HEAT indicator on continuously (except during extreme cold)
Outdoor unit completely encased in ice (defrost failure)
Significant difference between heating and cooling performance
Higher than expected electric bills during heating season
Unusual noises: hissing at the reversing valve, grinding, or banging
Cold air blowing from vents during heating mode
Water leaking at the indoor unit

When to Replace vs Repair

Compressor failure on a system over 10 years old: strong candidate for replacement
Reversing valve failure: $800-$1,500 repair; worth it if the system is under 8 years old
Auxiliary heat running excessively on a system sized correctly: may indicate refrigerant loss or compressor wear; evaluate repair vs replacement based on age
Ground-source indoor unit: replace at 20-25 years; the ground loop typically outlasts multiple indoor units
50% rule applies: repair cost exceeding 50% of replacement cost favors a new system
Technology jump: if upgrading from a single-stage to an inverter-driven heat pump, the comfort and efficiency improvement is substantial

Pro Detail

Specifications & Sizing

SEER2/EER2: Cooling efficiency (same as AC ratings). Federal minimums: SEER2 14.3 (North) / SEER2 15.2 (South).
HSPF2 (Heating Seasonal Performance Factor): Measures heating efficiency over a season. Federal minimum: HSPF2 7.5. Energy Star: HSPF2 8.1+. Higher is better. HSPF2 is roughly 4.7% lower than equivalent HSPF.
COP (Coefficient of Performance): Ratio of heat output to electrical input at a specific condition. COP of 3.0 means 3 kW of heat per 1 kW of electricity. Air-source at 47 degrees F: COP 3.0-4.5. At 17 degrees F: COP 2.0-3.0. Ground-source: COP 3.5-5.0.
Sizing: Manual J load calculation. Heat pumps should be sized for cooling load in mixed climates; auxiliary heat covers the heating gap. In heating-dominant climates, cold-climate heat pumps may be sized for heating load.
Cold-climate heat pumps (ccHP): Rated to maintain capacity down to 5 degrees F. Inverter-driven compressors vary speed for better performance across a wider temperature range. Look for NEEP (Northeast Energy Efficiency Partnerships) cold-climate specifications.
Balance point: The outdoor temperature at which heat pump output equals the building's heat loss. Below this point, auxiliary heat supplements. Typically 25-35 degrees F for standard heat pumps; 5-15 degrees F for cold-climate models.
Dual-fuel systems: Heat pump paired with a gas furnace. The switchover point is set based on local energy prices (gas vs electricity). Typically switches to gas at 30-40 degrees F outdoor temperature. Requires a dual-fuel thermostat or control board.

Common Failure Modes

| Component | Failure Mode | Typical Age | Repair Cost | |-----------|-------------|-------------|-------------| | Compressor | Same as AC, plus liquid slugging from reversing valve issues | 10-15 years | $1,500-$3,000 | | Reversing valve | Stuck midway, internal leak (heats in cool mode, cools in heat mode) | 8-15 years | $800-$1,500 | | Defrost control board | No defrost initiation, continuous defrost | 7-12 years | $200-$500 | | Defrost sensors | Inaccurate temperature reading causing ice buildup | 5-10 years | $100-$300 | | Auxiliary heat strips | Element burnout, sequencer failure | 10-15 years | $200-$600 | | Check valve/bi-flow TXV | Stuck, causing poor performance in one mode | 8-15 years | $300-$700 | | Accumulator | Internal breakdown, restricting refrigerant | 10-15 years | $400-$800 |

Diagnostic Procedures

Not heating: Verify thermostat is in heat mode and calling (O/B terminal energized correctly, varies by brand: Honeywell energizes O in cooling, Rheem energizes O in heating). Check reversing valve solenoid voltage. Listen for reversing valve shifting. If no shift, check solenoid coil resistance (typically 10-50 ohms).
Stuck in defrost: Check defrost control board, defrost termination sensor (opens at ~70 degrees F coil temp), and defrost initiation sensor. Verify time/temperature or demand defrost parameters. Check for failed reversing valve solenoid.
Excessive auxiliary heat use: Measure heat pump heating capacity vs building load. Check refrigerant charge (heating mode: measure subcooling at indoor coil and superheat at outdoor coil). Verify outdoor coil is clean. Check for restricted airflow. Confirm balance point setting is correct.
Ice on outdoor unit: Normal during heating: light frost that periodically defrosts. Abnormal: solid ice encasement. Check defrost system, outdoor fan motor, refrigerant charge (low charge = low coil temps = excessive icing). Verify drain path is clear beneath the unit.
Ground-source low performance: Check loop fluid temperature differential (entering vs leaving water temp; should be 10-15 degrees F in heating, 10-15 degrees F in cooling). Low delta-T may indicate loop circulation issues or degraded ground heat exchange. Check loop pump operation, antifreeze concentration, and loop pressure.

Code & Compliance

Same electrical and refrigerant codes as AC systems
Heat pump installations often require a heat loss/gain calculation to verify sizing
Dual-fuel systems must comply with both gas and electrical codes
Ground-source installations may require environmental permits for drilling/trenching
Federal tax credits: 30% of cost (up to $2,000) for qualifying heat pumps under the Inflation Reduction Act (through 2032)
Many utilities offer heat pump rebates; amounts vary by region and utility
Some jurisdictions now require or incentivize heat pumps for new construction

Cost Guide

| Service | Cost Range | Notes | |---------|-----------|-------| | Annual tune-up | $100-$200 | Should cover both heating and cooling checks | | Reversing valve replacement | $800-$1,500 | Complex repair; includes refrigerant recovery | | Defrost board replacement | $200-$500 | Parts + labor | | Auxiliary heat strip set | $200-$600 | Depends on kW rating | | Compressor replacement | $1,500-$3,000 | May warrant system replacement | | Air-source heat pump replacement | $4,000-$8,000 | Standard efficiency; includes installation | | Cold-climate heat pump | $5,000-$10,000 | Inverter-driven; premium equipment | | Ground-source heat pump | $15,000-$30,000 | Includes ground loop; long-term ROI strong | | Dual-fuel system (HP + furnace) | $6,000-$12,000 | Combined equipment and installation |

Note: Federal tax credits and utility rebates can reduce out-of-pocket costs by $2,000-$8,000 for qualifying heat pump installations.

Energy Impact

Heat pumps are the most efficient heating technology available for most homes:

COP 3.0 means 300% efficient: $1 of electricity produces $3 of heat (vs $0.95 for a 95% furnace)
At current national average energy prices ($0.15/kWh electricity, $1.20/therm gas), heat pumps are cost-competitive with gas furnaces in moderate climates and increasingly competitive in cold climates with cold-climate models
Dual-fuel systems optimize cost by running the heat pump when it is cheaper than gas and switching to gas when temperatures drop below the economic balance point
Ground-source systems achieve COP 3.5-5.0 year-round, delivering the lowest operating costs of any HVAC technology
Inverter-driven heat pumps maintain high efficiency across a wide range of conditions by varying compressor speed rather than cycling on/off

Annual energy cost comparison (2,000 sq ft home, Zone 4):

Gas furnace (95% AFUE): ~$900/year heating
Air-source heat pump (HSPF 10): ~$750/year heating
Ground-source heat pump (COP 4.0): ~$500/year heating

Shipshape Integration

SAM provides comprehensive heat pump monitoring that accounts for the unique dual-mode operation of these systems:

Dual-mode performance tracking: SAM monitors efficiency in both heating and cooling modes independently, establishing baselines and detecting performance degradation in either mode.
Auxiliary heat monitoring: SAM tracks when auxiliary heat activates and correlates it with outdoor temperature. If AUX heat runs at temperatures well above the expected balance point, SAM alerts to potential heat pump issues (low refrigerant, defrost problems, reversing valve failure).
Defrost cycle analysis: SAM monitors defrost frequency and duration. Abnormally frequent or prolonged defrost cycles indicate developing problems before they cause a complete ice-over.
Energy monitoring: Because heat pumps run year-round, SAM tracks energy consumption across seasons, detecting seasonal efficiency trends and year-over-year degradation.
Filter reminders: Adjusted for year-round operation. Heat pump filters need more frequent changes than furnace-only systems because the blower runs in both heating and cooling seasons.
Equipment age and lifecycle: SAM tracks heat pump age against the 15-year expected lifespan and factors in repair history, efficiency trends, and technology improvements when recommending replacement timing.
Home Health Score: Heat pump condition impacts both the heating and cooling components of the Home Health Score. Systems with declining performance, excessive auxiliary heat use, or approaching end-of-life are flagged for dealer attention.
Dealer intelligence: Service recommendations include mode-specific diagnostic data, helping technicians arrive prepared with the right approach for heating-mode vs cooling-mode issues.