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      18,000 BTU mini-split heat pump · Z4S Series

      ZERO Z4SOV-18HDMB-USHH

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

      Ranks #343 of 465 18,000 BTU mini-splits for cooling efficiency, and costs about $509 a year to run in a mixed climate like Atlanta.

      SEER2
      21.0 Cooling efficiency over a season
      Below average · beats 30%
      HSPF2
      10.0 Heating efficiency over a season
      Average · beats 43%
      EER2
      13.0 Cooling efficiency on a 95°F day
      Average · beats 62%
      Heat at 5°F
      18,000 BTU/h90% of its 47°F output
      Average · beats 48%

      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…

      • Cooling cost matters most - its SEER2 is below average for mini-splits.

      Calculate my running cost

      Details

      Specifications18,000 BTU, R-454B
      General
      BrandZERO
      Also sold asAI AIR CONDITIONING, ComfortStar, TRUST AIR CONDITIONERS, Mitsutomo, SLIMAIR, Elios, DuraSTAR, Wells, PerfectAire, KEEN Home, Convectair, Cadet
      Outdoor unit modelZ4SOV-18HDMB-USHH
      SeriesZ4S 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 sinceSeptember 10, 2025
      Last certifiedMay 28, 2026
      Cooling
      SEER2Seasonal efficiency, higher is better21.0 (range 20.0-21.0)
      EER2Efficiency at 95°F outdoors13.0
      Cooling capacity19,000 BTU/h
      Heating
      HSPF2Seasonal efficiency, higher is better10.0
      Capacity at 47°F20,000 BTU/h
      Capacity at 17°F20,000 BTU/h
      Capacity at 5°F18,000 BTU/h
      COP at 5°F2.0 = twice as efficient as a space heater2.00
      ENERGY STAR cold climateYes
      Heating output as it gets colder90% kept at 5°F

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

      Certified matchups3 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.
      - · cold climate21.013.010.018,000217752799
      - · cold climate20.513.010.018,000217752801
      - · cold climate20.013.010.018,000217752800
      Same unit, other model numbers14

      These model numbers have exactly the same certified ratings and matchups as the ZERO Z4SOV-18HDMB-USHH: 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$427-$1,239

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

      Questions5
      What is the SEER2 rating of the ZERO Z4SOV-18HDMB-USHH?
      The ZERO Z4SOV-18HDMB-USHH is rated at up to 21.0 SEER2 and 13.0 EER2 for cooling and up to 10.0 HSPF2 for heating. The exact figure depends on the indoor unit it is paired with; across its 3 certified matchups SEER2 ranges from 20.0-21.0.
      Is the ZERO Z4SOV-18HDMB-USHH 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 2.00, so it is still 2.0 times as efficient as electric resistance heat at that temperature.
      How much does the ZERO Z4SOV-18HDMB-USHH cost to run per year?
      At its rated efficiency it costs about $427-$1,239 a year in electricity in large U.S. cities, depending on climate and local rates - for example $540 in Phoenix and $1,046 in Minneapolis. The calculator on this page works it out for your city and compares it with your current system.
      Is the ZERO Z4SOV-18HDMB-USHH the same as the AI AIR CONDITIONING A3MO23-18N2-M1H?
      Yes, as far as the certified ratings go. ENERGY STAR lists 15 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.
      What refrigerant does the ZERO Z4SOV-18HDMB-USHH 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 $542/yrYou save $454/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 ZERO Z4SOV-18HDMB-USHH
      3. What it replaces
      4. Price replace the example with your quote
      Heat pump, per year
      $542
      Current system, per year
      $996
      You save per year
      $454
      Payback
      15.4 years
      Net after 10 years
      -$2,464

      Cooling $318Heating $224Electricity used: 3,390 kWhSaved vs. a minimum-efficiency heat pump: $224

      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 May 28, 2026. How we use the data.