HVAC Rated
    Menu

      12,000 BTU mini-split heat pump · ML Series

      Mainline ML12HP230NEXH-O

      Very good cooling and heating efficiency for a 12,000 BTU mini-split heat pump, and certified for cold climates.

      Ranks #104 of 394 12,000 BTU mini-splits for cooling efficiency, and costs about $266 a year to run in a mixed climate like Atlanta.

      SEER2
      25.0 Cooling efficiency over a season
      Very good · beats 83%
      HSPF2
      11.6 Heating efficiency over a season
      Very good · beats 86%
      EER2
      12.5 Cooling efficiency on a 95°F day
      Average · beats 44%
      Heat at 5°F
      12,000 BTU/h94% of its 47°F output
      Average · beats 48%

      A good fit if…

      • You want low cooling bills - its SEER2 beats 83% of mini-splits.
      • Your winters get properly cold - it is ENERGY STAR cold-climate certified, with 12,000 BTU/h at 5°F.
      • It will heat most of the year - its HSPF2 beats 86% of mini-splits.
      • You want steady temperatures and quiet running - the compressor varies its speed.

      Think twice if…

      • Nothing stands out - its ratings have no weak spot for its class.

      Calculate my running cost

      Details

      Specifications12,000 BTU, R-454B
      General
      BrandMainline
      Outdoor unit modelML12HP230NEXH-O
      SeriesML Series
      TypeMini-split heat pump
      Nominal size12,000 BTU
      CompressorVariable-speed units run longer at low powerContinuously variable
      RefrigerantR-454B
      Connected (smart) capableNo
      On the market sinceMay 20, 2024
      Last certifiedAugust 11, 2026
      Cooling
      SEER2Seasonal efficiency, higher is better25.0 (range 20.0-25.0)
      EER2Efficiency at 95°F outdoors12.0-13.2
      Cooling capacity12,000 BTU/h
      Heating
      HSPF2Seasonal efficiency, higher is better10.0-11.6
      Capacity at 47°F12,000-12,500 BTU/h
      Capacity at 17°F9,600-12,000 BTU/h
      Capacity at 5°F11,300-12,000 BTU/h
      COP at 5°F2.0 = twice as efficient as a space heater1.80-2.00
      ENERGY STAR cold climateYes
      Heating output as it gets colder94% kept at 5°F

      Every heat pump delivers less heat as the outdoor temperature drops. Certified output of its matchup with ML12HP230CON-I at the standard test temperatures, in BTU/h:

      Certified matchups12 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.
      ML12HP230CON-I MAINLINE · cold climate25.012.510.511,300217607295
      ML12HP230CON-I MAINLINE · cold climate25.012.510.511,300215864382
      ML12HP230NEX-I MAINLINE · cold climate24.013.210.511,500217607253
      ML12HP230NEX-I MAINLINE · cold climate24.013.210.511,500215864340
      ML12HP2301WYCAS-I MAINLINE · cold climate23.013.010.011,500217607301
      ML12HP2301WYCAS-I MAINLINE · cold climate23.013.010.011,500215864388
      ML12HP230STDCAS-I MAINLINE · cold climate22.212.511.611,500217607283
      ML12HP230STDCAS-I MAINLINE · cold climate22.212.511.611,500215864370
      ML12HP230HSDUC-I MAINLINE · cold climate20.012.010.612,000217607291
      ML12HP230HSDUC-I MAINLINE · cold climate20.012.010.612,000215864378
      ML12HP230LSDUC-I MAINLINE · cold climate20.012.010.011,800217607288
      ML12HP230LSDUC-I MAINLINE · cold climate20.012.010.011,800215864375
      Yearly running cost in 10 large cities$226-$644

      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 ML12HP230NEXH-O?
      The Mainline ML12HP230NEXH-O is rated at up to 25.0 SEER2 and 12.5 EER2 for cooling and up to 11.6 HSPF2 for heating. The exact figure depends on the indoor unit it is paired with; across its 12 certified matchups SEER2 ranges from 20.0-25.0.
      Is the Mainline ML12HP230NEXH-O good for cold climates?
      Yes. At least one certified matchup meets the ENERGY STAR cold-climate criteria, delivering up to 12,000 BTU/h at 5°F with a COP of 2.00, so it is still 2.0 times as efficient as electric resistance heat at that temperature.
      How much does the Mainline ML12HP230NEXH-O cost to run per year?
      At its rated efficiency it costs about $226-$644 a year in electricity in large U.S. cities, depending on climate and local rates - for example $284 in Phoenix and $542 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 ML12HP230NEXH-O?
      ENERGY STAR lists 12 certified combinations for this outdoor unit. The highest-rated ones use MAINLINE ML12HP230CON-I, MAINLINE ML12HP230NEX-I, MAINLINE ML12HP2301WYCAS-I.
      What refrigerant does the Mainline ML12HP230NEXH-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 $285/yrYou save $334/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 ML12HP230NEXH-O
      3. What it replaces
      4. Price replace the example with your quote
      Heat pump, per year
      $285
      Current system, per year
      $619
      You save per year
      $334
      Payback
      13.5 years
      Net after 10 years
      -$1,161

      Cooling $169Heating $116Electricity used: 1,780 kWhSaved vs. a minimum-efficiency heat pump: $190

      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 12,000 BTU models

      See all 394 12,000 BTU mini-splits, ranked

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