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      18,000 BTU mini-split heat pump · DIY-series

      MRCOOL DIY-18-HP-C-230C

      Average cooling efficiency and below average heating efficiency for a 18,000 BTU mini-split heat pump, but not rated for cold climates.

      Ranks #173 of 465 18,000 BTU mini-splits for cooling efficiency, and costs about $460 a year to run in a mixed climate like Atlanta.

      SEER2
      22.7 Cooling efficiency over a season
      Average · beats 57%
      HSPF2
      9.8 Heating efficiency over a season
      Below average · beats 33%
      EER2
      12.6 Cooling efficiency on a 95°F day
      Average · beats 52%
      Heat at 5°F
      11,700 BTU/h65% of its 47°F output
      Average · beats 60%

      A good fit if…

      • You want steady temperatures and quiet running - the compressor varies its speed.

      Think twice if…

      • You often see nights below 0°F - it is not cold-climate certified.
      • You mainly need heat - its HSPF2 is below average for mini-splits.
      • You want the newest refrigerant - it uses R-410A, which is being phased down.

      Calculate my running cost

      Details

      Specifications18,000 BTU, R-410A
      General
      BrandMRCOOL
      Outdoor unit modelDIY-18-HP-C-230C
      SeriesDIY-series
      TypeMini-split heat pump
      Nominal size18,000 BTU
      CompressorVariable-speed units run longer at low powerContinuously variable
      RefrigerantR-410A
      Connected (smart) capableNo
      On the market sinceDecember 18, 2019
      Last certifiedJune 29, 2026
      Cooling
      SEER2Seasonal efficiency, higher is better22.7 (range 22.7)
      EER2Efficiency at 95°F outdoors12.6
      Cooling capacity18,000 BTU/h
      Heating
      HSPF2Seasonal efficiency, higher is better9.8
      Capacity at 47°F18,000 BTU/h
      Capacity at 17°F13,800 BTU/h
      Capacity at 5°F11,700 BTU/h
      COP at 5°F2.0 = twice as efficient as a space heater2.05
      ENERGY STAR cold climateNo
      Heating output as it gets colder65% kept at 5°F

      Every heat pump delivers less heat as the outdoor temperature drops. Certified output of its matchup with DIY-18-HP-WMAH-230C25 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.
      DIY-18-HP-WMAH-230C2522.712.69.811,700207339188
      DIY-18-HP-WMAH-230C2522.712.69.811,700207339188
      Yearly running cost in 10 large cities$375-$1,129

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

      Questions5
      What is the SEER2 rating of the MRCOOL DIY-18-HP-C-230C?
      The MRCOOL DIY-18-HP-C-230C is rated at up to 22.7 SEER2 and 12.6 EER2 for cooling and up to 9.8 HSPF2 for heating. The exact figure depends on the indoor unit it is paired with.
      Is the MRCOOL DIY-18-HP-C-230C good for cold climates?
      It is not cold-climate certified: none of its matchups meet the ENERGY STAR cold-climate criteria (a COP of at least 1.75 at 5°F among other limits). In places with frequent sub-zero nights, pick a cold-climate 18,000 BTU model.
      How much does the MRCOOL DIY-18-HP-C-230C cost to run per year?
      At its rated efficiency it costs about $375-$1,129 a year in electricity in large U.S. cities, depending on climate and local rates - for example $479 in Phoenix and $957 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 MRCOOL DIY-18-HP-C-230C?
      ENERGY STAR lists 2 certified combinations for this outdoor unit. The highest-rated one uses DIY-18-HP-WMAH-230C25.
      What refrigerant does the MRCOOL DIY-18-HP-C-230C use?
      It uses R-410A. R-410A is being phased down under the EPA AIM Act, and new systems are moving to R-454B and R-32.

      Running cost and savings

      Pre-filled with this model. Pick your city and what you heat with today; everything else is optional.

      Heat pump $485/yrYou save $443/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 MRCOOL DIY-18-HP-C-230C
      3. What it replaces
      4. Price replace the example with your quote
      Heat pump, per year
      $485
      Current system, per year
      $928
      You save per year
      $443
      Payback
      15.8 years
      Net after 10 years
      -$2,567

      Cooling $279Heating $206Electricity used: 3,030 kWhSaved vs. a minimum-efficiency heat pump: $227

      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 June 29, 2026. How we use the data.