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      36,000 BTU mini-split heat pump · MMLD Mini-Split

      Lennox MMLD036S6S-1P

      Average cooling and heating efficiency for a 36,000 BTU mini-split heat pump, and certified for cold climates.

      Ranks #82 of 205 36,000 BTU mini-splits for cooling efficiency, and costs about $946 a year to run in a mixed climate like Atlanta.

      SEER2
      22.0 Cooling efficiency over a season
      Average · beats 48%
      HSPF2
      10.6 Heating efficiency over a season
      Average · beats 65%
      EER2
      13.5 Cooling efficiency on a 95°F day
      Very good · beats 74%
      Heat at 5°F
      40,000 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 40,000 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

      Specifications36,000 BTU, R-32
      General
      BrandLennox
      Outdoor unit modelMMLD036S6S-1P
      SeriesMMLD Mini-Split
      TypeMini-split heat pump
      Nominal size36,000 BTU
      CompressorVariable-speed units run longer at low powerContinuously variable
      RefrigerantR-32
      Connected (smart) capableNo
      On the market sinceAugust 30, 2024
      Last certifiedApril 27, 2026
      Cooling
      SEER2Seasonal efficiency, higher is better22.0 (range 18.7-22.0)
      EER2Efficiency at 95°F outdoors12.0-13.5
      Cooling capacity33,000-36,000 BTU/h
      Heating
      HSPF2Seasonal efficiency, higher is better9.0-10.6
      Capacity at 47°F40,000 BTU/h
      Capacity at 17°F26,600-30,600 BTU/h
      Capacity at 5°F36,000-40,000 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 M33D036S6-1P 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.
      M33D036S6-1P LENNOX · cold climate22.013.510.640,000218214251
      MDDD036S6-1P LENNOX · cold climate20.012.89.840,000215810032
      MWXD036S6-1P LENNOX · cold climate20.012.09.036,000218214258
      MMD036S6-1P LENNOX · cold climate18.712.09.540,000216581334
      Yearly running cost in 10 large cities$773-$2,321

      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 MMLD036S6S-1P?
      The Lennox MMLD036S6S-1P is rated at up to 22.0 SEER2 and 13.5 EER2 for cooling and up to 10.6 HSPF2 for heating. The exact figure depends on the indoor unit it is paired with; across its 4 certified matchups SEER2 ranges from 18.7-22.0.
      Is the Lennox MMLD036S6S-1P good for cold climates?
      Yes. At least one certified matchup meets the ENERGY STAR cold-climate criteria, delivering up to 40,000 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 MMLD036S6S-1P cost to run per year?
      At its rated efficiency it costs about $773-$2,321 a year in electricity in large U.S. cities, depending on climate and local rates - for example $988 in Phoenix and $1,966 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 MMLD036S6S-1P?
      ENERGY STAR lists 4 certified combinations for this outdoor unit. The highest-rated ones use LENNOX M33D036S6-1P, LENNOX MDDD036S6-1P, LENNOX MWXD036S6-1P.
      What refrigerant does the Lennox MMLD036S6S-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 $999/yrYou save $923/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 MMLD036S6S-1P
      3. What it replaces
      4. Price replace the example with your quote
      Heat pump, per year
      $999
      Current system, per year
      $1,922
      You save per year
      $923
      Payback
      14.6 years
      Net after 10 years
      -$4,269

      Cooling $576Heating $423Electricity used: 6,242 kWhSaved vs. a minimum-efficiency heat pump: $485

      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.