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      18,000 BTU mini-split heat pump · ML Series

      Mainline ML18HP230GEN-O

      Below average cooling and heating efficiency for a 18,000 BTU mini-split heat pump, and certified for cold climates.

      Ranks #432 of 465 18,000 BTU mini-splits for cooling efficiency, and costs about $467 a year to run in a mixed climate like Atlanta.

      SEER2
      19.2 Cooling efficiency over a season
      Below average · beats 11%
      HSPF2
      9.6 Heating efficiency over a season
      Below average · beats 30%
      EER2
      10.8 Cooling efficiency on a 95°F day
      Below average · beats 7%
      Heat at 5°F
      11,500 BTU/h70% of its 47°F output
      Very good · beats 73%

      A good fit if…

      • Your winters get properly cold - it is ENERGY STAR cold-climate certified, with 11,500 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

      Specifications18,000 BTU, R-454B
      General
      BrandMainline
      Outdoor unit modelML18HP230GEN-O
      SeriesML Series
      TypeMini-split heat pump
      Nominal size18,000 BTU
      CompressorVariable-speed units run longer at low powerContinuously variable
      RefrigerantR-454B
      Connected (smart) capableNo
      On the market sinceNovember 6, 2024
      Last certifiedAugust 11, 2026
      Cooling
      SEER2Seasonal efficiency, higher is better19.2 (range 19.2)
      EER2Efficiency at 95°F outdoors10.8
      Cooling capacity18,000 BTU/h
      Heating
      HSPF2Seasonal efficiency, higher is better9.6
      Capacity at 47°F16,400 BTU/h
      Capacity at 17°F14,000 BTU/h
      Capacity at 5°F11,500 BTU/h
      COP at 5°F2.0 = twice as efficient as a space heater2.14
      ENERGY STAR cold climateYes
      Heating output as it gets colder70% kept at 5°F

      Every heat pump delivers less heat as the outdoor temperature drops. Certified output of its matchup with ML18HP230GEN-I 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 unitSEER2EER2HSPF2Heat @5°FAHRI ref.
      ML18HP230GEN-I MAINLINE · cold climate19.210.89.611,500217970332
      ML18HP230GEN-I MAINLINE · cold climate19.210.89.611,500217970309
      Yearly running cost in 10 large cities$439-$1,098

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

      Questions5
      What is the SEER2 rating of the Mainline ML18HP230GEN-O?
      The Mainline ML18HP230GEN-O is rated at up to 19.2 SEER2 and 10.8 EER2 for cooling and up to 9.6 HSPF2 for heating. The exact figure depends on the indoor unit it is paired with.
      Is the Mainline ML18HP230GEN-O good for cold climates?
      Yes. At least one certified matchup meets the ENERGY STAR cold-climate criteria, delivering up to 11,500 BTU/h at 5°F with a COP of 2.14, so it is still 2.1 times as efficient as electric resistance heat at that temperature.
      How much does the Mainline ML18HP230GEN-O cost to run per year?
      At its rated efficiency it costs about $439-$1,098 a year in electricity in large U.S. cities, depending on climate and local rates - for example $531 in Phoenix and $909 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 Mainline ML18HP230GEN-O?
      ENERGY STAR lists 2 certified combinations for this outdoor unit. The highest-rated one uses MAINLINE ML18HP230GEN-I.
      What refrigerant does the Mainline ML18HP230GEN-O use?
      It uses R-454B.

      Running cost and savings

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

      Heat pump $521/yrYou save $381/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 Mainline ML18HP230GEN-O
      3. What it replaces
      4. Price replace the example with your quote
      Heat pump, per year
      $521
      Current system, per year
      $902
      You save per year
      $381
      Payback
      18.4 years
      Net after 10 years
      -$3,194

      Cooling $330Heating $191Electricity used: 3,258 kWhSaved vs. a minimum-efficiency heat pump: $167

      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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      Source: ENERGY STAR Certified Heat Pumps (U.S. EPA), certification of August 11, 2026. How we use the data.