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      48,000 BTU mini-split heat pump · M series

      Lennox MLB048S4S-1P

      Below average cooling efficiency and very good heating efficiency for a 48,000 BTU mini-split heat pump, and certified for cold climates.

      Ranks #137 of 146 48,000 BTU mini-splits for cooling efficiency, and costs about $1,271 a year to run in a mixed climate like Atlanta.

      SEER2
      17.0 Cooling efficiency over a season
      Below average · beats 2%
      HSPF2
      12.0 Heating efficiency over a season
      Very good · beats 89%
      EER2
      14.0 Cooling efficiency on a 95°F day
      Very good · beats 82%
      Heat at 5°F
      50,000 BTU/h96% of its 47°F output
      Average · beats 59%

      A good fit if…

      • Your winters get properly cold - it is ENERGY STAR cold-climate certified, with 50,000 BTU/h at 5°F.
      • It will heat most of the year - its HSPF2 beats 89% 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

      Specifications48,000 BTU, R-410A
      General
      BrandLennox
      Also sold asSLIMAIR
      Outdoor unit modelMLB048S4S-1P
      SeriesM series
      TypeMini-split heat pump
      Nominal size48,000 BTU
      CompressorVariable-speed units run longer at low powerContinuously variable
      RefrigerantR-410A
      Connected (smart) capableNo
      On the market sinceDecember 18, 2019
      Last certifiedFebruary 20, 2025
      Cooling
      SEER2Seasonal efficiency, higher is better17.0 (range 17.0)
      EER2Efficiency at 95°F outdoors14.0
      Cooling capacity48,000 BTU/h
      Heating
      HSPF2Seasonal efficiency, higher is better12.0
      Capacity at 47°F52,000 BTU/h
      Capacity at 17°F50,000 BTU/h
      Capacity at 5°F50,000 BTU/h
      COP at 5°F2.0 = twice as efficient as a space heater2.02
      ENERGY STAR cold climateYes
      Heating output as it gets colder96% kept at 5°F

      Every heat pump delivers less heat as the outdoor temperature drops. Certified output of its matchup with MMDB048S4-2P at the standard test temperatures, in BTU/h:

      Certified matchups1 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.
      MMDB048S4-2P LENNOX · cold climate17.014.012.050,000205782161
      Same unit, other model numbers1

      These model numbers have exactly the same certified ratings and matchups as the Lennox MLB048S4S-1P: the same equipment under another brand, or a variant code for voltage, colour or market. Everything on this page applies to them.

      Yearly running cost in 10 large cities$1,154-$2,893

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

      Questions6
      What is the SEER2 rating of the Lennox MLB048S4S-1P?
      The Lennox MLB048S4S-1P is rated at up to 17.0 SEER2 and 14.0 EER2 for cooling and up to 12.0 HSPF2 for heating. The exact figure depends on the indoor unit it is paired with.
      Is the Lennox MLB048S4S-1P good for cold climates?
      Yes. At least one certified matchup meets the ENERGY STAR cold-climate criteria, delivering up to 50,000 BTU/h at 5°F with a COP of 2.02, so it is still 2.0 times as efficient as electric resistance heat at that temperature.
      How much does the Lennox MLB048S4S-1P cost to run per year?
      At its rated efficiency it costs about $1,154-$2,893 a year in electricity in large U.S. cities, depending on climate and local rates - for example $1,536 in Phoenix and $2,350 in Minneapolis. The calculator on this page works it out for your city and compares it with your current system.
      Is the Lennox MLB048S4S-1P the same as the SLIMAIR SHC48VH2AG?
      Yes, as far as the certified ratings go. ENERGY STAR lists both model numbers with identical efficiency, capacity and matchups, which means the same outdoor unit sold under a different brand or with a minor variant code (voltage, colour or region). The full list is on this page.
      Which indoor units work with the Lennox MLB048S4S-1P?
      ENERGY STAR lists 1 certified combination for this outdoor unit. The highest-rated one uses LENNOX MMDB048S4-2P.
      What refrigerant does the Lennox MLB048S4S-1P 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 $1,479/yrYou save $1,061/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 MLB048S4S-1P
      3. What it replaces
      4. Price replace the example with your quote
      Heat pump, per year
      $1,479
      Current system, per year
      $2,540
      You save per year
      $1,061
      Payback
      17.0 years
      Net after 10 years
      -$7,388

      Cooling $994Heating $485Electricity used: 9,245 kWhSaved vs. a minimum-efficiency heat pump: $479

      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 February 20, 2025. How we use the data.