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      15,000 BTU mini-split heat pump · ML Series

      Mainline ML15HP230NEXH-O

      Average cooling and heating efficiency for a 15,000 BTU mini-split heat pump, and certified for cold climates.

      Ranks #17 of 62 15,000 BTU mini-splits for cooling efficiency, and costs about $386 a year to run in a mixed climate like Atlanta.

      SEER2
      22.7 Cooling efficiency over a season
      Average · beats 57%
      HSPF2
      10.2 Heating efficiency over a season
      Average · beats 53%
      EER2
      14.0 Cooling efficiency on a 95°F day
      Very good · beats 82%
      Heat at 5°F
      18,000 BTU/h116% of its 47°F output
      Below average · beats 34%

      A good fit if…

      • Your winters get properly cold - it is ENERGY STAR cold-climate certified, with 18,000 BTU/h at 5°F.
      • 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

      Specifications15,000 BTU, R-454B
      General
      BrandMainline
      Also sold asElios
      Outdoor unit modelML15HP230NEXH-O
      SeriesML Series
      TypeMini-split heat pump
      Nominal size15,000 BTU
      CompressorVariable-speed units run longer at low powerContinuously variable
      RefrigerantR-454B
      Connected (smart) capableNo
      On the market sinceFebruary 6, 2026
      Last certifiedAugust 11, 2026
      Cooling
      SEER2Seasonal efficiency, higher is better22.7 (range 22.7)
      EER2Efficiency at 95°F outdoors14.0
      Cooling capacity15,500 BTU/h
      Heating
      HSPF2Seasonal efficiency, higher is better10.2
      Capacity at 47°F15,500 BTU/h
      Capacity at 17°F14,400 BTU/h
      Capacity at 5°F18,000 BTU/h
      COP at 5°F2.0 = twice as efficient as a space heater1.95
      ENERGY STAR cold climateYes
      Heating output as it gets colder116% kept at 5°F

      Every heat pump delivers less heat as the outdoor temperature drops. Certified output of its matchup with ML15HP230NEX-I 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.
      ML15HP230NEX-I MAINLINE · cold climate22.714.010.218,000218082866
      Same unit, other model numbers1

      These model numbers have exactly the same certified ratings and matchups as the Mainline ML15HP230NEXH-O: the same equipment under another brand, or a variant code for voltage, colour or market. Everything on this page applies to them.

      Yearly running cost in 10 large cities$322-$940

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

      Questions6
      What is the SEER2 rating of the Mainline ML15HP230NEXH-O?
      The Mainline ML15HP230NEXH-O is rated at up to 22.7 SEER2 and 14.0 EER2 for cooling and up to 10.2 HSPF2 for heating. The exact figure depends on the indoor unit it is paired with.
      Is the Mainline ML15HP230NEXH-O good for cold climates?
      Yes. At least one certified matchup meets the ENERGY STAR cold-climate criteria, delivering up to 18,000 BTU/h at 5°F with a COP of 1.95, so it is still 2.0 times as efficient as electric resistance heat at that temperature.
      How much does the Mainline ML15HP230NEXH-O cost to run per year?
      At its rated efficiency it costs about $322-$940 a year in electricity in large U.S. cities, depending on climate and local rates - for example $408 in Phoenix and $794 in Minneapolis. The calculator on this page works it out for your city and compares it with your current system.
      Is the Mainline ML15HP230NEXH-O the same as the Elios ESHMA15C2AN1?
      Yes, as far as the certified ratings go. ENERGY STAR lists both model numbers with identical efficiency, capacity and matchups, which means the same outdoor unit sold under a different brand or with a minor variant code (voltage, colour or region). The full list is on this page.
      Which indoor units work with the Mainline ML15HP230NEXH-O?
      ENERGY STAR lists 1 certified combination for this outdoor unit. The highest-rated one uses MAINLINE ML15HP230NEX-I.
      What refrigerant does the Mainline ML15HP230NEXH-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 $411/yrYou save $389/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 ML15HP230NEXH-O
      3. What it replaces
      4. Price replace the example with your quote
      Heat pump, per year
      $411
      Current system, per year
      $799
      You save per year
      $389
      Payback
      15.4 years
      Net after 10 years
      -$2,113

      Cooling $240Heating $170Electricity used: 2,566 kWhSaved vs. a minimum-efficiency heat pump: $202

      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.