What is the SEER2 rating of the Lennox MLB012S4S-1P?

The Lennox MLB012S4S-1P is rated at up to 25.5 SEER2 and 13.5 EER2 for cooling and up to 10.4 HSPF2 for heating. The exact figure depends on the indoor unit it is paired with; across its 12 certified matchups SEER2 ranges from 19.5-25.5.

Is the Lennox MLB012S4S-1P good for cold climates?

Yes. At least one certified matchup meets the ENERGY STAR cold-climate criteria, delivering up to 12,100 BTU/h at 5°F with a COP of 1.96, so it is still 2.0 times as efficient as electric resistance heat at that temperature.

How much does the Lennox MLB012S4S-1P cost to run per year?

At its rated efficiency it costs about $223-$702 a year in electricity in large U.S. cities, depending on climate and local rates - for example $289 in Phoenix and $598 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 MLB012S4S-1P?

ENERGY STAR lists 12 certified combinations for this outdoor unit. The highest-rated ones use LENNOX MWMC012S4, LENNOX MWMC012S4-1P, LENNOX MWMC012S4-*P.

What refrigerant does the Lennox MLB012S4S-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.

12,000 BTU mini-split heat pump · M series

Lennox MLB012S4S-1P

Very good cooling efficiency and average heating efficiency for a 12,000 BTU mini-split heat pump, and certified for cold climates.

Ranks #78 of 394 12,000 BTU mini-splits for cooling efficiency, and costs about $283 a year to run in a mixed climate like Atlanta.

SEER2: 25.5 Cooling efficiency over a season
Very good · beats 88%
HSPF2: 10.4 Heating efficiency over a season
Average · beats 57%
EER2: 13.5 Cooling efficiency on a 95°F day
Very good · beats 74%
Heat at 5°F: 12,100 BTU/h100% of its 47°F output
Below average · beats 36%

A good fit if…

You want low cooling bills - its SEER2 beats 88% of mini-splits.
Your winters get properly cold - it is ENERGY STAR cold-climate certified, with 12,100 BTU/h at 5°F.
You want steady temperatures and quiet running - the compressor varies its speed.
You want a choice of indoor units - 12 certified pairings.

Think twice if…

You want the newest refrigerant - it uses R-410A, which is being phased down.

Calculate my running cost

Details

Specifications12,000 BTU, R-410A

General
Brand	Lennox
Outdoor unit model	MLB012S4S-1P
Series	M series
Type	Mini-split heat pump
Nominal size	12,000 BTU
CompressorVariable-speed units run longer at low power	Continuously variable
Refrigerant	R-410A
Connected (smart) capable	No
On the market since	December 18, 2019
Last certified	June 13, 2026
Cooling
SEER2Seasonal efficiency, higher is better	25.5 (range 19.5-25.5)
EER2Efficiency at 95°F outdoors	11.7-13.5
Cooling capacity	11,800-12,000 BTU/h
Heating
HSPF2Seasonal efficiency, higher is better	10.0-10.4
Capacity at 47°F	12,000-12,500 BTU/h
Capacity at 17°F	9,600-10,600 BTU/h
Capacity at 5°F	11,300-12,100 BTU/h
COP at 5°F2.0 = twice as efficient as a space heater	1.80-1.96
ENERGY STAR cold climate	Yes

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 MWMC012S4 at the standard test temperatures, in BTU/h:

Certified matchups12 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 unit	SEER2	EER2	HSPF2	Heat @5°F	AHRI ref.
MWMC012S4 LENNOX · cold climate	25.5	13.5	10.4	12,000	210665628
MWMC012S4-1P LENNOX · cold climate	25.5	13.5	10.4	12,000	207683521
MWMC012S4-*P LENNOX · cold climate	25.5	13.5	10.4	12,000	211034441
MFMA012S4-1P LENNOX · cold climate	23.6	13.0	10.0	12,000	207683528
MFMA012S4-*P LENNOX · cold climate	23.6	13.0	10.0	12,000	211034450
MFMA012S4 LENNOX · cold climate	23.6	13.0	10.0	12,000	210665637
M22A012S4-2P LENNOX · cold climate	22.3	12.7	10.2	11,300	207683532
M22A012S4-*P LENNOX · cold climate	22.3	12.7	10.2	11,300	211034456
M22A012S4 LENNOX · cold climate	22.3	12.7	10.2	11,300	210665643
MMDB012S4-2P LENNOX · cold climate	19.5	11.7	10.0	12,100	207683525
MMDB012S4-*P LENNOX · cold climate	19.5	11.7	10.0	12,100	211034445
MMDB012S4 LENNOX · cold climate	19.5	11.7	10.0	12,100	210665632

Yearly running cost in 10 large cities$223-$702

Phoenix, AZ$289/yr
Miami, FL$223/yr
Houston, TX$260/yr
Atlanta, GA$283/yr
Los Angeles, CA$280/yr
New York, NY$702/yr
Chicago, IL$575/yr
Denver, CO$482/yr
Seattle, WA$299/yr
Minneapolis, MN$598/yr

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 MLB012S4S-1P?: The Lennox MLB012S4S-1P is rated at up to 25.5 SEER2 and 13.5 EER2 for cooling and up to 10.4 HSPF2 for heating. The exact figure depends on the indoor unit it is paired with; across its 12 certified matchups SEER2 ranges from 19.5-25.5.
Is the Lennox MLB012S4S-1P good for cold climates?: Yes. At least one certified matchup meets the ENERGY STAR cold-climate criteria, delivering up to 12,100 BTU/h at 5°F with a COP of 1.96, so it is still 2.0 times as efficient as electric resistance heat at that temperature.
How much does the Lennox MLB012S4S-1P cost to run per year?: At its rated efficiency it costs about $223-$702 a year in electricity in large U.S. cities, depending on climate and local rates - for example $289 in Phoenix and $598 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 MLB012S4S-1P?: ENERGY STAR lists 12 certified combinations for this outdoor unit. The highest-rated ones use LENNOX MWMC012S4, LENNOX MWMC012S4-1P, LENNOX MWMC012S4-*P.
What refrigerant does the Lennox MLB012S4S-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 $295/yrYou save $324/yrSee details ↓

1. Where you live

StateCityElectricity ¢ per kWh

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.

Cooling hours full-load hours per yearHeating hours full-load hours per year

2. The heat pump Lennox MLB012S4S-1P

Find a model (fills in the ratings below)

SEER2 cooling efficiencyHSPF2 heating efficiencyCooling capacity BTU/hHeating capacity BTU/h

3. What it replaces

Current heatingFurnace efficiency (AFUE %)Gas price, $/thermCurrent coolingOld AC rating SEER2 (10 ≈ 15+ years old)

4. Price replace the example with your quote

Installed price, $Rebates and incentives, $ utility, state

Heat pump, per year: $295
Current system, per year: $619
You save per year: $324
Payback: 13.9 years
Net after 10 years: -$1,261

Cooling $166Heating $129Electricity used: 1,843 kWhSaved vs. a minimum-efficiency heat pump: $180

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 12,000 BTU models

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MDV MOX330-12HFN1-MW5W-L · cold climate25.5 SEER2 · 10.4 HSPF2
EMI MHSZ112DA · cold climate25.5 SEER2 · 10.4 HSPF2
MRCOOL O-HH-12-HP-C-230A · cold climate25.5 SEER2 · 10.4 HSPF2
DIRECT AIR DIRM-12HXPRO28-1Z · cold climate25.5 SEER2 · 10.4 HSPF2
MRCOOL O-HH-12-HP-C-230B · cold climate25.5 SEER2 · 10.4 HSPF2
ComfortStar CHF12CD(O) · cold climate25.5 SEER2 · 10.4 HSPF2
Multi MFG MSH-12HD-A · cold climate25.5 SEER2 · 10.4 HSPF2

See all 394 12,000 BTU mini-splits, ranked

Source: ENERGY STAR Certified Heat Pumps (U.S. EPA), certification of June 13, 2026. How we use the data.