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

      Bosch BMS500-AAS018-1CSXHD

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

      Ranks #292 of 465 18,000 BTU mini-splits for cooling efficiency, and costs about $412 a year to run in a mixed climate like Atlanta.

      SEER2
      21.4 Cooling efficiency over a season
      Below average · beats 36%
      HSPF2
      12.3 Heating efficiency over a season
      Excellent · beats 92%
      EER2
      12.5 Cooling efficiency on a 95°F day
      Average · beats 44%
      Heat at 5°F
      18,000 BTU/h100% 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.
      • It will heat most of the year - its HSPF2 beats 92% of mini-splits.
      • 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
      BrandBosch
      Outdoor unit modelBMS500-AAS018-1CSXHD
      SeriesBMS 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 sinceMarch 18, 2024
      Last certifiedMay 28, 2026
      Cooling
      SEER2Seasonal efficiency, higher is better21.4 (range 18.0-21.4)
      EER2Efficiency at 95°F outdoors12.0-12.5
      Cooling capacity16,000-18,000 BTU/h
      Heating
      HSPF2Seasonal efficiency, higher is better10.5-12.3
      Capacity at 47°F18,000-20,000 BTU/h
      Capacity at 17°F14,500-18,000 BTU/h
      Capacity at 5°F17,000-18,000 BTU/h
      COP at 5°F2.0 = twice as efficient as a space heater1.89-2.00
      ENERGY STAR cold climateYes
      Heating output as it gets colder100% kept at 5°F

      Every heat pump delivers less heat as the outdoor temperature drops. Certified output of its matchup with BMS500-AAU018-1AHWXD at the standard test temperatures, in BTU/h:

      Certified matchups4 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.
      BMS500-AAU018-1AHWXD BOSCH · cold climate21.412.511.018,000215223286
      BMS500-AAU018-1AHZXD BOSCH · cold climate20.612.512.217,500215223287
      BMS500-AAU018-1AHCXD BOSCH · cold climate20.012.512.317,000215223288
      BMS500-AAU018-1AHDXD BOSCH · cold climate18.012.010.518,000215223289
      Yearly running cost in 10 large cities$373-$980

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

      Questions5
      What is the SEER2 rating of the Bosch BMS500-AAS018-1CSXHD?
      The Bosch BMS500-AAS018-1CSXHD is rated at up to 21.4 SEER2 and 12.5 EER2 for cooling and up to 12.3 HSPF2 for heating. The exact figure depends on the indoor unit it is paired with; across its 4 certified matchups SEER2 ranges from 18.0-21.4.
      Is the Bosch BMS500-AAS018-1CSXHD 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 Bosch BMS500-AAS018-1CSXHD cost to run per year?
      At its rated efficiency it costs about $373-$980 a year in electricity in large U.S. cities, depending on climate and local rates - for example $457 in Phoenix and $817 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 Bosch BMS500-AAS018-1CSXHD?
      ENERGY STAR lists 4 certified combinations for this outdoor unit. The highest-rated ones use BOSCH BMS500-AAU018-1AHWXD, BOSCH BMS500-AAU018-1AHZXD, BOSCH BMS500-AAU018-1AHCXD.
      What refrigerant does the Bosch BMS500-AAS018-1CSXHD 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 $453/yrYou save $457/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 Bosch BMS500-AAS018-1CSXHD
      3. What it replaces
      4. Price replace the example with your quote
      Heat pump, per year
      $453
      Current system, per year
      $909
      You save per year
      $457
      Payback
      14.2 years
      Net after 10 years
      -$1,933

      Cooling $280Heating $173Electricity used: 2,829 kWhSaved vs. a minimum-efficiency heat pump: $250

      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.