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      42,000 BTU mini-split heat pump · KUSUB421A

      LG KUSUB421A

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

      Ranks #54 of 61 42,000 BTU mini-splits for cooling efficiency, and costs about $1,247 a year to run in a mixed climate like Atlanta.

      SEER2
      18.5 Cooling efficiency over a season
      Below average · beats 6%
      HSPF2
      9.5 Heating efficiency over a season
      Below average · beats 24%
      EER2
      11.0 Cooling efficiency on a 95°F day
      Below average · beats 9%
      Heat at 5°F
      36,800 BTU/h80% of its 47°F output
      Below average · beats 20%

      A good fit if…

      • Your winters get properly cold - it is ENERGY STAR cold-climate certified, with 36,800 BTU/h at 5°F.
      • 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.
      • You mainly need heat - its HSPF2 is below average for mini-splits.

      Calculate my running cost

      Details

      Specifications42,000 BTU, R-32
      General
      BrandLG
      Outdoor unit modelKUSUB421A
      SeriesKUSUB421A
      TypeMini-split heat pump
      Nominal size42,000 BTU
      CompressorVariable-speed units run longer at low powerContinuously variable
      RefrigerantR-32
      Connected (smart) capableNo
      On the market sinceApril 30, 2026
      Last certifiedMay 6, 2026
      Cooling
      SEER2Seasonal efficiency, higher is better18.5 (range 18.5)
      EER2Efficiency at 95°F outdoors11.0
      Cooling capacity42,000 BTU/h
      Heating
      HSPF2Seasonal efficiency, higher is better9.5
      Capacity at 47°F46,000 BTU/h
      Capacity at 17°F29,000 BTU/h
      Capacity at 5°F36,800 BTU/h
      COP at 5°F2.0 = twice as efficient as a space heater1.85
      ENERGY STAR cold climateYes
      Heating output as it gets colder80% kept at 5°F

      Every heat pump delivers less heat as the outdoor temperature drops. Certified output of its matchup with KNSLB421A at the standard test temperatures, in BTU/h:

      Certified matchups1 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 unitSEER2EER2HSPF2Heat @5°FAHRI ref.
      KNSLB421A · cold climate18.511.09.536,800218426765
      Yearly running cost in 10 large cities$1,069-$3,019

      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 KUSUB421A?
      The LG KUSUB421A is rated at up to 18.5 SEER2 and 11.0 EER2 for cooling and up to 9.5 HSPF2 for heating. The exact figure depends on the indoor unit it is paired with.
      Is the LG KUSUB421A good for cold climates?
      Yes. At least one certified matchup meets the ENERGY STAR cold-climate criteria, delivering up to 36,800 BTU/h at 5°F with a COP of 1.85, so it is still 1.9 times as efficient as electric resistance heat at that temperature.
      How much does the LG KUSUB421A cost to run per year?
      At its rated efficiency it costs about $1,069-$3,019 a year in electricity in large U.S. cities, depending on climate and local rates - for example $1,340 in Phoenix and $2,539 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 KUSUB421A?
      ENERGY STAR lists 1 certified combination for this outdoor unit. The highest-rated one uses KNSLB421A.
      What refrigerant does the LG KUSUB421A 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 $1,341/yrYou save $890/yrSee details ↓
      1. Where you live
      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.

      2. The heat pump LG KUSUB421A
      3. What it replaces
      4. Price replace the example with your quote
      Heat pump, per year
      $1,341
      Current system, per year
      $2,231
      You save per year
      $890
      Payback
      18.0 years
      Net after 10 years
      -$7,104

      Cooling $799Heating $542Electricity used: 8,384 kWhSaved vs. a minimum-efficiency heat pump: $379

      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.

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

      Source: ENERGY STAR Certified Heat Pumps (U.S. EPA), certification of May 6, 2026. How we use the data.