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      6,000 BTU mini-split heat pump · ML Series

      Mainline ML06HP230NEXH-O

      Very good cooling efficiency and excellent heating efficiency for a 6,000 BTU mini-split heat pump, and certified for cold climates.

      Ranks #31 of 42 6,000 BTU mini-splits for cooling efficiency, and costs about $134 a year to run in a mixed climate like Atlanta.

      SEER2
      25.3 Cooling efficiency over a season
      Very good · beats 86%
      HSPF2
      14.6 Heating efficiency over a season
      Excellent · beats 99%
      EER2
      16.0 Cooling efficiency on a 95°F day
      Excellent · beats 96%
      Heat at 5°F
      8,100 BTU/h107% of its 47°F output
      Excellent · beats 93%

      A good fit if…

      • You want low cooling bills - its SEER2 beats 86% of mini-splits.
      • Your winters get properly cold - it is ENERGY STAR cold-climate certified, with 8,100 BTU/h at 5°F.
      • It will heat most of the year - its HSPF2 beats 99% 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

      Specifications6,000 BTU, R-454B
      General
      BrandMainline
      Outdoor unit modelML06HP230NEXH-O
      SeriesML Series
      TypeMini-split heat pump
      Nominal size6,000 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 better25.3 (range 21.4-25.3)
      EER2Efficiency at 95°F outdoors14.4-16.0
      Cooling capacity6,000-6,500 BTU/h
      Heating
      HSPF2Seasonal efficiency, higher is better12.0-14.6
      Capacity at 47°F7,000-8,000 BTU/h
      Capacity at 17°F7,000-8,000 BTU/h
      Capacity at 5°F7,500-8,100 BTU/h
      COP at 5°F2.0 = twice as efficient as a space heater2.30-2.40
      ENERGY STAR cold climateYes
      Heating output as it gets colder107% kept at 5°F

      Every heat pump delivers less heat as the outdoor temperature drops. Certified output of its matchup with ML06HP230NEX-I at the standard test temperatures, in BTU/h:

      Certified matchups6 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.
      ML06HP230NEX-I MAINLINE · cold climate25.316.014.67,500217607251
      ML06HP230NEX-I MAINLINE · cold climate25.316.014.67,500215864338
      ML06HP2301WYCAS-I MAINLINE · cold climate22.015.012.08,100217607299
      ML06HP2301WYCAS-I MAINLINE · cold climate22.015.012.08,100215864386
      ML06HP230LSDUC-I MAINLINE · cold climate21.414.413.87,800217607286
      ML06HP230LSDUC-I MAINLINE · cold climate21.414.413.87,800215864373
      Yearly running cost in 10 large cities$121-$321

      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 ML06HP230NEXH-O?
      The Mainline ML06HP230NEXH-O is rated at up to 25.3 SEER2 and 16.0 EER2 for cooling and up to 14.6 HSPF2 for heating. The exact figure depends on the indoor unit it is paired with; across its 6 certified matchups SEER2 ranges from 21.4-25.3.
      Is the Mainline ML06HP230NEXH-O good for cold climates?
      Yes. At least one certified matchup meets the ENERGY STAR cold-climate criteria, delivering up to 8,100 BTU/h at 5°F with a COP of 2.40, so it is still 2.4 times as efficient as electric resistance heat at that temperature.
      How much does the Mainline ML06HP230NEXH-O cost to run per year?
      At its rated efficiency it costs about $121-$321 a year in electricity in large U.S. cities, depending on climate and local rates - for example $149 in Phoenix and $268 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 ML06HP230NEXH-O?
      ENERGY STAR lists 6 certified combinations for this outdoor unit. The highest-rated ones use MAINLINE ML06HP230NEX-I, MAINLINE ML06HP2301WYCAS-I, MAINLINE ML06HP230LSDUC-I.
      What refrigerant does the Mainline ML06HP230NEXH-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 $147/yrYou save $203/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 ML06HP230NEXH-O
      3. What it replaces
      4. Price replace the example with your quote
      Heat pump, per year
      $147
      Current system, per year
      $350
      You save per year
      $203
      Payback
      12.3 years
      Net after 10 years
      -$473

      Cooling $90Heating $57Electricity used: 920 kWhSaved vs. a minimum-efficiency heat pump: $123

      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 6,000 BTU models

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