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      42,000 BTU mini-split heat pump · SIERRA

      OLMO OS-RMS42-230VO

      Average cooling efficiency and below average heating efficiency for a 42,000 BTU mini-split heat pump, and certified for cold climates.

      Ranks #23 of 61 42,000 BTU mini-splits for cooling efficiency, and costs about $1,212 a year to run in a mixed climate like Atlanta.

      SEER2
      22.0 Cooling efficiency over a season
      Average · beats 48%
      HSPF2
      9.5 Heating efficiency over a season
      Below average · beats 24%
      EER2
      12.0 Cooling efficiency on a 95°F day
      Below average · beats 25%
      Heat at 5°F
      36,000 BTU/h75% of its 47°F output
      Below average · beats 32%

      A good fit if…

      • Your winters get properly cold - it is ENERGY STAR cold-climate certified, with 36,000 BTU/h at 5°F.
      • You want steady temperatures and quiet running - the compressor varies its speed.

      Think twice if…

      • You mainly need heat - its HSPF2 is below average for mini-splits.

      Calculate my running cost

      Details

      Specifications42,000 BTU, R-454B
      General
      BrandOLMO
      Outdoor unit modelOS-RMS42-230VO
      SeriesSIERRA
      TypeMini-split heat pump
      Nominal size42,000 BTU
      CompressorVariable-speed units run longer at low powerContinuously variable
      RefrigerantR-454B
      Connected (smart) capableNo
      On the market sinceSeptember 19, 2025
      Last certifiedJanuary 14, 2026
      Cooling
      SEER2Seasonal efficiency, higher is better22.0 (range 22.0)
      EER2Efficiency at 95°F outdoors12.0
      Cooling capacity42,000 BTU/h
      Heating
      HSPF2Seasonal efficiency, higher is better9.5
      Capacity at 47°F48,000 BTU/h
      Capacity at 17°F28,200 BTU/h
      Capacity at 5°F36,000 BTU/h
      COP at 5°F2.0 = twice as efficient as a space heater1.92
      ENERGY STAR cold climateYes
      Heating output as it gets colder75% 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 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.
      - · cold climate22.012.09.536,000217739003
      Yearly running cost in 10 large cities$907-$3,039

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

      Questions4
      What is the SEER2 rating of the OLMO OS-RMS42-230VO?
      The OLMO OS-RMS42-230VO is rated at up to 22.0 SEER2 and 12.0 EER2 for cooling and up to 9.5 HSPF2 for heating. The exact figure depends on the indoor unit it is paired with.
      Is the OLMO OS-RMS42-230VO good for cold climates?
      Yes. At least one certified matchup meets the ENERGY STAR cold-climate criteria, delivering up to 36,000 BTU/h at 5°F with a COP of 1.92, so it is still 1.9 times as efficient as electric resistance heat at that temperature.
      How much does the OLMO OS-RMS42-230VO cost to run per year?
      At its rated efficiency it costs about $907-$3,039 a year in electricity in large U.S. cities, depending on climate and local rates - for example $1,203 in Phoenix and $2,605 in Minneapolis. The calculator on this page works it out for your city and compares it with your current system.
      What refrigerant does the OLMO OS-RMS42-230VO 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 $1,238/yrYou save $1,026/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 OLMO OS-RMS42-230VO
      3. What it replaces
      4. Price replace the example with your quote
      Heat pump, per year
      $1,238
      Current system, per year
      $2,264
      You save per year
      $1,026
      Payback
      15.6 years
      Net after 10 years
      -$5,741

      Cooling $672Heating $566Electricity used: 7,737 kWhSaved vs. a minimum-efficiency heat pump: $513

      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 42,000 BTU models

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      Source: ENERGY STAR Certified Heat Pumps (U.S. EPA), certification of January 14, 2026. How we use the data.