Heat pump noise

Heat pump noise comes mostly from the outdoor unit: the compressor and the fan. Manufacturers rate outdoor units with a sound rating in A-weighted decibels (dBA) measured under AHRI Standard 270, and you can compare those ratings between models.^{[Source 1]} How loud it sounds at your window also depends on distance, nearby walls, and how fast the unit is running.

How sound is rated

Lennox's sound data sheet describes the AHRI 270 rating as "the overall A-Weighted Sound Power Level, (LWA), dBA (100 Hz to 10,000 Hz)."^{[Source 1]} That is sound power: the total sound the unit emits. What you hear at a given spot is sound pressure, which drops with distance and rises near reflective surfaces. Lennox estimates sound pressure using the AHRI Standard 275 method "with no adjacent reflective surface within 9.8 feet."^{[Source 1]}

Two cautions when comparing numbers:

• Power and pressure are not comparable. A sound power rating of 71 dBA and a sound pressure figure of 55 dBA at 10 feet can describe the same unit.^{[Source 1]} Some manufacturers publish only sound pressure at a set distance, so check which one a number is.
• Speed matters. Variable-speed units have a range, not one number.

NRCan says "most heat pumps have a sound rating of 76 dB or lower," and that "the lower the value, the lower the sound power emitted by the outdoor unit."^{[Source 2]}

Example ratings

From Lennox's expanded sound data for its R-454B heat pumps (October 2026):^{[Source 1]}

Model	AHRI 270 sound rating	Estimated sound pressure at 5 ft	At 10 ft
EL16KP1	71 to 73 dBA, by size	about 59 to 61 dBA	about 53 to 55 dBA
SL22KLV-024 (variable-speed)	58 dBA at minimum speed, 71 at maximum
EL19KPV-060 (variable-speed)	64 dBA at minimum speed, 77 at maximum

Why it is louder in cold weather

Variable-speed heat pumps speed up as the heating load rises. Carrier's 25VNA owner's manual explains: "In winter, the system will operate at higher speeds as it gets colder outside... The higher speed produces a higher sound."^{[Source 4]} The same unit can be near its minimum rating on a mild day and near its maximum on the coldest night.

Normal sounds that are not constant

Some sounds come and go and are part of normal operation:

• Defrost. A "whoosh" at the start and end of a defrost cycle, and the outdoor fan stopping, are normal.^{[Source 4]} See Heat pump defrost cycles.
• Indoor airflow. Ducted heat pumps move more air than furnaces. NRCan notes that "if the heat pump airflow exceeds the capacity of your existing ducting, you may have noise issues or increased fan energy use."^{[Source 2]} See Static pressure.

Grinding, banging, rattling or screeching that is new or getting worse is worth a service call.

Placement

DOE's guidance: "Locate the outdoor unit away from windows and adjacent buildings, and select a heat pump with a lower outdoor sound rating (decibels). You can also reduce noise by mounting the unit on a noise-absorbing base."^{[Source 3]}

Placement also has to meet the manufacturer's clearance, snow and service requirements (What a good heat pump installation looks like), and local noise or setback rules may apply. Check with your city or HOA before choosing a spot near a property line.