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      36,000 BTU mini-split heat pump · M series

      Lennox MLB036S4S-2P

      Below average cooling efficiency and very good heating efficiency for a 36,000 BTU mini-split heat pump, and certified for cold climates.

      Ranks #179 of 205 36,000 BTU mini-splits for cooling efficiency, and costs about $966 a year to run in a mixed climate like Atlanta.

      SEER2
      19.4 Cooling efficiency over a season
      Below average · beats 11%
      HSPF2
      11.0 Heating efficiency over a season
      Very good · beats 75%
      EER2
      9.5 Cooling efficiency on a 95°F day
      Below average · beats 3%
      Heat at 5°F
      40,000 BTU/h100% of its 47°F output
      Below average · beats 37%

      A good fit if…

      • Your winters get properly cold - it is ENERGY STAR cold-climate certified, with 40,000 BTU/h at 5°F.
      • It will heat most of the year - its HSPF2 beats 75% of mini-splits.
      • 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 want the newest refrigerant - it uses R-410A, which is being phased down.

      Calculate my running cost

      Details

      Specifications36,000 BTU, R-410A
      General
      BrandLennox
      Outdoor unit modelMLB036S4S-2P
      SeriesM series
      TypeMini-split heat pump
      Nominal size36,000 BTU
      CompressorVariable-speed units run longer at low powerContinuously variable
      RefrigerantR-410A
      Connected (smart) capableNo
      On the market sinceDecember 18, 2019
      Last certifiedMay 28, 2026
      Cooling
      SEER2Seasonal efficiency, higher is better19.4 (range 16.5-19.4)
      EER2Efficiency at 95°F outdoors8.8-9.5
      Cooling capacity36,000 BTU/h
      Heating
      HSPF2Seasonal efficiency, higher is better10.0-11.0
      Capacity at 47°F39,000-42,000 BTU/h
      Capacity at 17°F32,000-33,400 BTU/h
      Capacity at 5°F36,000-40,000 BTU/h
      COP at 5°F2.0 = twice as efficient as a space heater1.75-1.98
      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 M33C036S4-*P at the standard test temperatures, in BTU/h:

      Certified matchups6 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.
      M33C036S4-*P LENNOX · cold climate19.49.510.540,000211034459
      M33C036S4 LENNOX · cold climate19.49.510.540,000210665646
      MCFA036S4-*P LENNOX · cold climate17.68.810.036,600211034453
      MCFA036S4 LENNOX · cold climate17.68.810.036,600210665640
      MMDB036S4-*P LENNOX · cold climate16.59.011.036,000211034448
      MMDB036S4 LENNOX · cold climate16.59.011.036,000210665635
      Yearly running cost in 10 large cities$872-$2,304

      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 MLB036S4S-2P?
      The Lennox MLB036S4S-2P is rated at up to 19.4 SEER2 and 9.5 EER2 for cooling and up to 11.0 HSPF2 for heating. The exact figure depends on the indoor unit it is paired with; across its 6 certified matchups SEER2 ranges from 16.5-19.4.
      Is the Lennox MLB036S4S-2P 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 1.98, so it is still 2.0 times as efficient as electric resistance heat at that temperature.
      How much does the Lennox MLB036S4S-2P cost to run per year?
      At its rated efficiency it costs about $872-$2,304 a year in electricity in large U.S. cities, depending on climate and local rates - for example $1,071 in Phoenix and $1,922 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 MLB036S4S-2P?
      ENERGY STAR lists 6 certified combinations for this outdoor unit. The highest-rated ones use LENNOX M33C036S4-*P, LENNOX M33C036S4, LENNOX MCFA036S4-*P.
      What refrigerant does the Lennox MLB036S4S-2P 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 $1,060/yrYou save $861/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 MLB036S4S-2P
      3. What it replaces
      4. Price replace the example with your quote
      Heat pump, per year
      $1,060
      Current system, per year
      $1,922
      You save per year
      $861
      Payback
      15.7 years
      Net after 10 years
      -$4,888

      Cooling $653Heating $407Electricity used: 6,628 kWhSaved vs. a minimum-efficiency heat pump: $423

      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 May 28, 2026. How we use the data.