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      36,000 BTU mini-split heat pump · M5O Series

      MDV M5OX631-36HFN10-M1X-D

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

      Ranks #39 of 205 36,000 BTU mini-splits for cooling efficiency, and costs about $835 a year to run in a mixed climate like Atlanta.

      SEER2
      23.0 Cooling efficiency over a season
      Average · beats 62%
      HSPF2
      11.3 Heating efficiency over a season
      Very good · beats 81%
      EER2
      13.0 Cooling efficiency on a 95°F day
      Average · beats 62%
      Heat at 5°F
      38,000 BTU/h100% of its 47°F output
      Average · beats 48%

      A good fit if…

      • Your winters get properly cold - it is ENERGY STAR cold-climate certified, with 38,000 BTU/h at 5°F.
      • It will heat most of the year - its HSPF2 beats 81% of mini-splits.
      • 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-454B
      General
      BrandMDV
      Also sold asMainline
      Outdoor unit modelM5OX631-36HFN10-M1X-D
      SeriesM5O Series
      TypeMini-split heat pump
      Nominal size36,000 BTU
      CompressorVariable-speed units run longer at low powerContinuously variable
      RefrigerantR-454B
      Connected (smart) capableNo
      On the market sinceNovember 1, 2015
      Last certifiedMay 6, 2026
      Cooling
      SEER2Seasonal efficiency, higher is better23.0 (range 19.4-23.0)
      EER2Efficiency at 95°F outdoors12.0-13.0
      Cooling capacity36,000 BTU/h
      Heating
      HSPF2Seasonal efficiency, higher is better10.4-11.3
      Capacity at 47°F36,000 BTU/h
      Capacity at 17°F38,000-38,500 BTU/h
      Capacity at 5°F36,000-38,000 BTU/h
      COP at 5°F2.0 = twice as efficient as a space heater1.90-2.00
      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 best matchup 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.
      - · cold climate23.013.010.736,000214861875
      - · cold climate21.512.211.337,000214861890
      - · cold climate21.212.510.637,000214861877
      - · cold climate20.512.110.937,400214861892
      - · cold climate19.412.010.438,000214861876
      - · cold climate19.412.010.438,000214861891
      Same unit, other model numbers2

      These model numbers have exactly the same certified ratings and matchups as the MDV M5OX631-36HFN10-M1X-D: 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$736-$2,004

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

      Questions5
      What is the SEER2 rating of the MDV M5OX631-36HFN10-M1X-D?
      The MDV M5OX631-36HFN10-M1X-D is rated at up to 23.0 SEER2 and 13.0 EER2 for cooling and up to 11.3 HSPF2 for heating. The exact figure depends on the indoor unit it is paired with; across its 6 certified matchups SEER2 ranges from 19.4-23.0.
      Is the MDV M5OX631-36HFN10-M1X-D good for cold climates?
      Yes. At least one certified matchup meets the ENERGY STAR cold-climate criteria, delivering up to 38,000 BTU/h at 5°F with a COP of 2.00, so it is still 2.0 times as efficient as electric resistance heat at that temperature.
      How much does the MDV M5OX631-36HFN10-M1X-D cost to run per year?
      At its rated efficiency it costs about $736-$2,004 a year in electricity in large U.S. cities, depending on climate and local rates - for example $912 in Phoenix and $1,678 in Minneapolis. The calculator on this page works it out for your city and compares it with your current system.
      Is the MDV M5OX631-36HFN10-M1X-D the same as the MDV M5OX631-36HFN10-M1XD-D?
      Yes, as far as the certified ratings go. ENERGY STAR lists 3 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.
      What refrigerant does the MDV M5OX631-36HFN10-M1X-D use?
      It uses R-454B.

      Running cost and savings

      Pre-filled with this model. Pick your city and what you heat with today; everything else is optional.

      Heat pump $908/yrYou save $948/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 MDV M5OX631-36HFN10-M1X-D
      3. What it replaces
      4. Price replace the example with your quote
      Heat pump, per year
      $908
      Current system, per year
      $1,856
      You save per year
      $948
      Payback
      14.2 years
      Net after 10 years
      -$4,015

      Cooling $551Heating $357Electricity used: 5,674 kWhSaved vs. a minimum-efficiency heat pump: $516

      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.

      Similar 36,000 BTU models

      See all 205 36,000 BTU mini-splits, ranked

      Source: ENERGY STAR Certified Heat Pumps (U.S. EPA), certification of May 6, 2026. How we use the data.