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      24,000 BTU mini-split heat pump · MMLD Mini-Split

      Lennox MMLD024S6S-1P

      Average cooling and heating efficiency for a 24,000 BTU mini-split heat pump, and certified for cold climates.

      Ranks #191 of 430 24,000 BTU mini-splits for cooling efficiency, and costs about $653 a year to run in a mixed climate like Atlanta.

      SEER2
      22.0 Cooling efficiency over a season
      Average · beats 48%
      HSPF2
      10.2 Heating efficiency over a season
      Average · beats 53%
      EER2
      13.0 Cooling efficiency on a 95°F day
      Average · beats 62%
      Heat at 5°F
      27,000 BTU/h100% of its 47°F output
      Below average · beats 9%

      A good fit if…

      • Your winters get properly cold - it is ENERGY STAR cold-climate certified, with 27,000 BTU/h at 5°F.
      • You want steady temperatures and quiet running - the compressor varies its speed.

      Think twice if…

      • Nothing stands out - its ratings have no weak spot for its class.

      Calculate my running cost

      Details

      Specifications24,000 BTU, R-32
      General
      BrandLennox
      Outdoor unit modelMMLD024S6S-1P
      SeriesMMLD Mini-Split
      TypeMini-split heat pump
      Nominal size24,000 BTU
      CompressorVariable-speed units run longer at low powerContinuously variable
      RefrigerantR-32
      Connected (smart) capableNo
      On the market sinceAugust 2, 2024
      Last certifiedApril 27, 2026
      Cooling
      SEER2Seasonal efficiency, higher is better22.0 (range 17.3-22.0)
      EER2Efficiency at 95°F outdoors11.7-13.0
      Cooling capacity23,000-24,000 BTU/h
      Heating
      HSPF2Seasonal efficiency, higher is better8.8-10.2
      Capacity at 47°F27,000 BTU/h
      Capacity at 17°F15,700-21,600 BTU/h
      Capacity at 5°F24,200-27,000 BTU/h
      COP at 5°F2.0 = twice as efficient as a space heater1.80
      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 M33D024S6-1P 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.
      M33D024S6-1P LENNOX · cold climate22.013.010.227,000215810028
      MWXD024S6-1P LENNOX · cold climate20.012.09.524,600218214256
      MDDD024S6-1P LENNOX · cold climate18.012.09.527,000215810029
      MMD024S6-1P LENNOX · cold climate17.311.78.824,200216581332
      Yearly running cost in 10 large cities$516-$1,614

      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 MMLD024S6S-1P?
      The Lennox MMLD024S6S-1P is rated at up to 22.0 SEER2 and 13.0 EER2 for cooling and up to 10.2 HSPF2 for heating. The exact figure depends on the indoor unit it is paired with; across its 4 certified matchups SEER2 ranges from 17.3-22.0.
      Is the Lennox MMLD024S6S-1P good for cold climates?
      Yes. At least one certified matchup meets the ENERGY STAR cold-climate criteria, delivering up to 27,000 BTU/h at 5°F with a COP of 1.80, so it is still 1.8 times as efficient as electric resistance heat at that temperature.
      How much does the Lennox MMLD024S6S-1P cost to run per year?
      At its rated efficiency it costs about $516-$1,614 a year in electricity in large U.S. cities, depending on climate and local rates - for example $669 in Phoenix and $1,374 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 MMLD024S6S-1P?
      ENERGY STAR lists 4 certified combinations for this outdoor unit. The highest-rated ones use LENNOX M33D024S6-1P, LENNOX MWXD024S6-1P, LENNOX MDDD024S6-1P.
      What refrigerant does the Lennox MMLD024S6S-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 $680/yrYou save $606/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 MMLD024S6S-1P
      3. What it replaces
      4. Price replace the example with your quote
      Heat pump, per year
      $680
      Current system, per year
      $1,287
      You save per year
      $606
      Payback
      14.8 years
      Net after 10 years
      -$2,939

      Cooling $384Heating $296Electricity used: 4,253 kWhSaved vs. a minimum-efficiency heat pump: $313

      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 27, 2026. How we use the data.