What is the SEER2 rating of the LG KUSXA421A?

The LG KUSXA421A is rated at up to 21.5 SEER2 and 13.5 EER2 for cooling and up to 10.8 HSPF2 for heating. The exact figure depends on the indoor unit it is paired with; across its 2 certified matchups SEER2 ranges from 18.8-21.5.

Is the LG KUSXA421A good for cold climates?

Yes. At least one certified matchup meets the ENERGY STAR cold-climate criteria, delivering up to 43,500 BTU/h at 5°F with a COP of 2.20, so it is still 2.2 times as efficient as electric resistance heat at that temperature.

How much does the LG KUSXA421A cost to run per year?

At its rated efficiency it costs about $922-$2,740 a year in electricity in large U.S. cities, depending on climate and local rates - for example $1,175 in Phoenix and $2,318 in Minneapolis. The calculator on this page works it out for your city and compares it with your current system.

Which indoor units work with the LG KUSXA421A?

ENERGY STAR lists 2 certified combinations for this outdoor unit. The highest-rated ones use KNSCB421A, KNSJB421A.

42,000 BTU mini-split heat pump · KUSXA421A

LG KUSXA421A

Below average cooling efficiency and very good heating efficiency for a 42,000 BTU mini-split heat pump, and certified for cold climates.

Ranks #29 of 61 42,000 BTU mini-splits for cooling efficiency, and costs about $1,119 a year to run in a mixed climate like Atlanta.

SEER2: 21.5 Cooling efficiency over a season
Below average · beats 39%
HSPF2: 10.8 Heating efficiency over a season
Very good · beats 71%
EER2: 13.5 Cooling efficiency on a 95°F day
Very good · beats 74%
Heat at 5°F: 43,500 BTU/h91% of its 47°F output
Very good · beats 78%

A good fit if…

Your winters get properly cold - it is ENERGY STAR cold-climate certified, with 43,500 BTU/h at 5°F.
It will heat most of the year - its HSPF2 beats 71% of mini-splits.
You want steady temperatures and quiet running - the compressor varies its speed.

Think twice if…

Cooling cost matters most - its SEER2 is below average for mini-splits.

Calculate my running cost

Details

Specifications42,000 BTU, R-32

General
Brand	LG
Outdoor unit model	KUSXA421A
Series	KUSXA421A
Type	Mini-split heat pump
Nominal size	42,000 BTU
CompressorVariable-speed units run longer at low power	Continuously variable
Refrigerant	R-32
Connected (smart) capable	No
On the market since	April 14, 2026
Last certified	April 17, 2026
Cooling
SEER2Seasonal efficiency, higher is better	21.5 (range 18.8-21.5)
EER2Efficiency at 95°F outdoors	12.6-13.5
Cooling capacity	42,000 BTU/h
Heating
HSPF2Seasonal efficiency, higher is better	9.4-10.8
Capacity at 47°F	48,000 BTU/h
Capacity at 17°F	28,600-30,800 BTU/h
Capacity at 5°F	42,500-43,500 BTU/h
COP at 5°F2.0 = twice as efficient as a space heater	2.08-2.20
ENERGY STAR cold climate	Yes

Heating output as it gets colder91% kept at 5°F

Every heat pump delivers less heat as the outdoor temperature drops. Certified output of its matchup with KNSCB421A at the standard test temperatures, in BTU/h:

Certified matchups2 indoor units

The same outdoor unit scores differently with each indoor unit. Ask your installer for the AHRI reference number of the exact system you are quoted.

Indoor unit	SEER2	EER2	HSPF2	Heat @5°F	AHRI ref.
KNSCB421A · cold climate	21.5	13.5	10.8	43,500	214837930
KNSJB421A · cold climate	18.8	12.6	9.4	42,500	214837932

Yearly running cost in 10 large cities$922-$2,740

Phoenix, AZ$1,175/yr
Miami, FL$922/yr
Houston, TX$1,055/yr
Atlanta, GA$1,119/yr
Los Angeles, CA$1,101/yr
New York, NY$2,740/yr
Chicago, IL$2,237/yr
Denver, CO$1,870/yr
Seattle, WA$1,157/yr
Minneapolis, MN$2,318/yr

At each state's average electricity price and the city's typical heating and cooling hours.

Questions5

What is the SEER2 rating of the LG KUSXA421A?: The LG KUSXA421A is rated at up to 21.5 SEER2 and 13.5 EER2 for cooling and up to 10.8 HSPF2 for heating. The exact figure depends on the indoor unit it is paired with; across its 2 certified matchups SEER2 ranges from 18.8-21.5.
Is the LG KUSXA421A good for cold climates?: Yes. At least one certified matchup meets the ENERGY STAR cold-climate criteria, delivering up to 43,500 BTU/h at 5°F with a COP of 2.20, so it is still 2.2 times as efficient as electric resistance heat at that temperature.
How much does the LG KUSXA421A cost to run per year?: At its rated efficiency it costs about $922-$2,740 a year in electricity in large U.S. cities, depending on climate and local rates - for example $1,175 in Phoenix and $2,318 in Minneapolis. The calculator on this page works it out for your city and compares it with your current system.
Which indoor units work with the LG KUSXA421A?: ENERGY STAR lists 2 certified combinations for this outdoor unit. The highest-rated ones use KNSCB421A, KNSJB421A.
What refrigerant does the LG KUSXA421A use?: It uses R-32.

Running cost and savings

Pre-filled with this model. Pick your city and what you heat with today; everything else is optional.

Heat pump $1,185/yrYou save $1,078/yrSee details ↓

1. Where you live

StateCityElectricity ¢ per kWh

Adjust heating and cooling hours

Filled in from your city's climate. Change them if you run the system much more or less than usual.

Cooling hours full-load hours per yearHeating hours full-load hours per year

2. The heat pump LG KUSXA421A

Find a model (fills in the ratings below)

SEER2 cooling efficiencyHSPF2 heating efficiencyCooling capacity BTU/hHeating capacity BTU/h

3. What it replaces

Current heatingFurnace efficiency (AFUE %)Gas price, $/thermCurrent coolingOld AC rating SEER2 (10 ≈ 15+ years old)

4. Price replace the example with your quote

Installed price, $Rebates and incentives, $ utility, state

Heat pump, per year: $1,185
Current system, per year: $2,264
You save per year: $1,078
Payback: 14.8 years
Net after 10 years: -$5,216

Cooling $688Heating $498Electricity used: 7,409 kWhSaved vs. a minimum-efficiency heat pump: $565

Estimates use the unit's rated SEER2 and HSPF2, full-load hours derived from NOAA 1991-2020 degree days, average residential electricity prices from the U.S. EIA (12 months to July 2026) and fuel prices from EIA (2025 for natural gas, week of 2026-10-05 for propane and heating oil). Very cold days that need backup heat are not modelled. Federal minimum for comparison: 14.3 SEER2 / 7.5 HSPF2.

Similar 42,000 BTU models

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Mitsubishi Electric MXZ-SM42NLHZ · cold climate21.5 SEER2 · 11.1 HSPF2
AproDr AM6OG-48HFN1 · cold climate21.3 SEER2 · 10.6 HSPF2
Mitsubishi Electric MXZ-SM42NAMHZ2 · cold climate21.5 SEER2 · 11.1 HSPF2
Panasonic CU - 6YM48CBUC · cold climate21.3 SEER2 · 10.6 HSPF2
MRCOOL DIY-MULTI6-48HP230D-O · cold climate21.8 SEER2 · 10.5 HSPF2
InfinityLiving EZ-48Z-M5B · cold climate21.8 SEER2 · 10.5 HSPF2
Mitsubishi Electric PUZ-AK42NL21.0 SEER2 · 10.1 HSPF2

See all 61 42,000 BTU mini-splits, ranked

Source: ENERGY STAR Certified Heat Pumps (U.S. EPA), certification of April 17, 2026. How we use the data.