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      18,000 BTU mini-split heat pump · WindFree - Max heat (RAC)

      Lennox MWMD018S6-1P

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

      Ranks #349 of 465 18,000 BTU mini-splits for cooling efficiency, and costs about $514 a year to run in a mixed climate like Atlanta.

      SEER2
      21.0 Cooling efficiency over a season
      Below average · beats 30%
      HSPF2
      9.7 Heating efficiency over a season
      Below average · beats 31%
      EER2
      13.2 Cooling efficiency on a 95°F day
      Average · beats 69%
      Heat at 5°F
      14,300 BTU/h72% of its 47°F output
      Average · beats 60%

      A good fit if…

      • Your winters get properly cold - it is ENERGY STAR cold-climate certified, with 14,300 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.
      • You mainly need heat - its HSPF2 is below average for mini-splits.

      Calculate my running cost

      Details

      Specifications18,000 BTU, R-32
      General
      BrandLennox
      Outdoor unit modelMWMD018S6-1P
      SeriesWindFree - Max heat (RAC)
      TypeMini-split heat pump
      Nominal size18,000 BTU
      CompressorVariable-speed units run longer at low powerContinuously variable
      RefrigerantR-32
      Connected (smart) capableNo
      On the market sinceJuly 23, 2024
      Last certifiedApril 17, 2026
      Cooling
      SEER2Seasonal efficiency, higher is better21.0 (range 21.0)
      EER2Efficiency at 95°F outdoors13.2
      Cooling capacity18,500 BTU/h
      Heating
      HSPF2Seasonal efficiency, higher is better9.7
      Capacity at 47°F20,000 BTU/h
      Capacity at 17°F17,500 BTU/h
      Capacity at 5°F14,300 BTU/h
      COP at 5°F2.0 = twice as efficient as a space heater2.05
      ENERGY STAR cold climateYes
      Heating output as it gets colder72% kept at 5°F

      Every heat pump delivers less heat as the outdoor temperature drops. Certified output of its matchup with MWLD018S6S-1P 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.
      MWLD018S6S-1P LENNOX · cold climate21.013.29.714,300215810010
      MWPD018S6S-1P LENNOX · cold climate21.013.29.714,300215810015
      Yearly running cost in 10 large cities$416-$1,265

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

      Questions5
      What is the SEER2 rating of the Lennox MWMD018S6-1P?
      The Lennox MWMD018S6-1P is rated at up to 21.0 SEER2 and 13.2 EER2 for cooling and up to 9.7 HSPF2 for heating. The exact figure depends on the indoor unit it is paired with.
      Is the Lennox MWMD018S6-1P good for cold climates?
      Yes. At least one certified matchup meets the ENERGY STAR cold-climate criteria, delivering up to 14,300 BTU/h at 5°F with a COP of 2.05, so it is still 2.1 times as efficient as electric resistance heat at that temperature.
      How much does the Lennox MWMD018S6-1P cost to run per year?
      At its rated efficiency it costs about $416-$1,265 a year in electricity in large U.S. cities, depending on climate and local rates - for example $534 in Phoenix and $1,073 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 Lennox MWMD018S6-1P?
      ENERGY STAR lists 2 certified combinations for this outdoor unit. The highest-rated ones use LENNOX MWLD018S6S-1P, LENNOX MWPD018S6S-1P.
      What refrigerant does the Lennox MWMD018S6-1P use?
      It uses 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 $541/yrYou save $437/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 Lennox MWMD018S6-1P
      3. What it replaces
      4. Price replace the example with your quote
      Heat pump, per year
      $541
      Current system, per year
      $978
      You save per year
      $437
      Payback
      16.0 years
      Net after 10 years
      -$2,626

      Cooling $310Heating $231Electricity used: 3,381 kWhSaved vs. a minimum-efficiency heat pump: $213

      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 April 17, 2026. How we use the data.