HVAC Rated
    Menu

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

      Mainline ML18HP230CALH-O

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

      Ranks #18 of 465 18,000 BTU mini-splits for cooling efficiency.

      SEER2
      25.6 Cooling efficiency over a season
      Excellent · beats 90%
      HSPF2
      - Heating efficiency over a season
      EER2
      15.0 Cooling efficiency on a 95°F day
      Excellent · beats 91%
      Heat at 5°F
      22,600 BTU/h113% of its 47°F output
      Very good · beats 89%

      A good fit if…

      • You want low cooling bills - its SEER2 beats 90% of mini-splits.
      • Your winters get properly cold - it is ENERGY STAR cold-climate certified, with 22,600 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

      Specifications18,000 BTU, R-454B
      General
      BrandMainline
      Also sold asComfort-Aire, KERR, Kerr Kapstone
      Outdoor unit modelML18HP230CALH-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 sinceMay 20, 2024
      Last certifiedAugust 11, 2026
      Cooling
      SEER2Seasonal efficiency, higher is better25.6 (range 25.6)
      EER2Efficiency at 95°F outdoors15.0
      Cooling capacity18,000 BTU/h
      Heating
      HSPF2Seasonal efficiency, higher is better-
      Capacity at 47°F20,000 BTU/h
      Capacity at 17°F19,300 BTU/h
      Capacity at 5°F22,600 BTU/h
      COP at 5°F2.0 = twice as efficient as a space heater2.34
      ENERGY STAR cold climateYes
      Heating output as it gets colder113% kept at 5°F

      Every heat pump delivers less heat as the outdoor temperature drops. Certified output of its matchup with ML18HP230CALH-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.
      ML18HP230CALH-I MAINLINE · cold climate25.615.0-22,600217607260
      ML18HP230CALH-I MAINLINE · cold climate25.615.0-22,600215864347
      Same unit, other model numbers2

      These model numbers have exactly the same certified ratings and matchups as the Mainline ML18HP230CALH-O: the same equipment under another brand, or a variant code for voltage, colour or market. Everything on this page applies to them.

      Questions5
      What is the SEER2 rating of the Mainline ML18HP230CALH-O?
      The Mainline ML18HP230CALH-O is rated at up to 25.6 SEER2 and 15.0 EER2 for cooling and up to - HSPF2 for heating. The exact figure depends on the indoor unit it is paired with.
      Is the Mainline ML18HP230CALH-O good for cold climates?
      Yes. At least one certified matchup meets the ENERGY STAR cold-climate criteria, delivering up to 22,600 BTU/h at 5°F with a COP of 2.34, so it is still 2.3 times as efficient as electric resistance heat at that temperature.
      Is the Mainline ML18HP230CALH-O the same as the Comfort-Aire A-ZHP18SA-1?
      Yes, as far as the certified ratings go. ENERGY STAR lists 3 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 ML18HP230CALH-O?
      ENERGY STAR lists 2 certified combinations for this outdoor unit. The highest-rated one uses MAINLINE ML18HP230CALH-I.
      What refrigerant does the Mainline ML18HP230CALH-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 $496/yrYou save $464/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 ML18HP230CALH-O
      3. What it replaces
      4. Price replace the example with your quote
      Heat pump, per year
      $496
      Current system, per year
      $961
      You save per year
      $464
      Payback
      15.1 years
      Net after 10 years
      -$2,355

      Cooling $248Heating $249Electricity used: 3,102 kWhSaved vs. a minimum-efficiency heat pump: $245

      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 18,000 BTU models

      See all 465 18,000 BTU mini-splits, ranked

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