What is the SEER2 rating of the Lennox MLB018S4S-1P?

The Lennox MLB018S4S-1P is rated at up to 21.5 SEER2 and 12.5 EER2 for cooling and up to 11.2 HSPF2 for heating. The exact figure depends on the indoor unit it is paired with; across its 13 certified matchups SEER2 ranges from 17.6-21.5.

Is the Lennox MLB018S4S-1P good for cold climates?

Yes. At least one certified matchup meets the ENERGY STAR cold-climate criteria, delivering up to 18,000 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 Lennox MLB018S4S-1P cost to run per year?

At its rated efficiency it costs about $372-$1,011 a year in electricity in large U.S. cities, depending on climate and local rates - for example $461 in Phoenix and $846 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 MLB018S4S-1P?

ENERGY STAR lists 13 certified combinations for this outdoor unit. The highest-rated ones use LENNOX MWMC018S4-1P, LENNOX MWMC018S4, LENNOX MWMC018S4-*P.

What refrigerant does the Lennox MLB018S4S-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.

18,000 BTU mini-split heat pump · M series

Lennox MLB018S4S-1P

Below average cooling efficiency and very good heating efficiency for a 18,000 BTU mini-split heat pump, and certified for cold climates.

Ranks #280 of 465 18,000 BTU mini-splits for cooling efficiency, and costs about $421 a year to run in a mixed climate like Atlanta.

SEER2: 21.5 Cooling efficiency over a season
Below average · beats 39%
HSPF2: 11.2 Heating efficiency over a season
Very good · beats 79%
EER2: 12.5 Cooling efficiency on a 95°F day
Average · beats 44%
Heat at 5°F: 18,000 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 18,000 BTU/h at 5°F.
It will heat most of the year - its HSPF2 beats 79% of mini-splits.
You want steady temperatures and quiet running - the compressor varies its speed.
You want a choice of indoor units - 13 certified pairings.

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

Specifications18,000 BTU, R-410A

General
Brand	Lennox
Outdoor unit model	MLB018S4S-1P
Series	M series
Type	Mini-split heat pump
Nominal size	18,000 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	21.5 (range 17.6-21.5)
EER2Efficiency at 95°F outdoors	11.7-12.5
Cooling capacity	15,700-18,000 BTU/h
Heating
HSPF2Seasonal efficiency, higher is better	9.2-11.2
Capacity at 47°F	17,000-19,000 BTU/h
Capacity at 17°F	12,000-15,600 BTU/h
Capacity at 5°F	16,000-18,000 BTU/h
COP at 5°F2.0 = twice as efficient as a space heater	1.75-2.00
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 MWMC018S4-1P at the standard test temperatures, in BTU/h:

Certified matchups13 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.
MWMC018S4-1P LENNOX · cold climate	21.5	12.5	11.2	18,000	207683522
MWMC018S4 LENNOX · cold climate	21.5	12.5	11.2	18,000	210665629
MWMC018S4-*P LENNOX · cold climate	21.5	12.5	11.2	18,000	211034442
MCFB018S4-2P LENNOX · cold climate	20.5	12.5	9.8	16,800	207683529
MCFB018S4-*P LENNOX · cold climate	20.5	12.5	9.8	16,800	211034451
MCFB018S4 LENNOX · cold climate	20.5	12.5	9.8	16,800	210665638
M22A018S4-2P LENNOX · cold climate	20.0	12.5	9.5	16,000	207683533
M22A018S4-*P LENNOX · cold climate	20.0	12.5	9.5	16,000	211034457
M22A018S4 LENNOX · cold climate	20.0	12.5	9.5	16,000	210665644
MMDB018S4-2P LENNOX · cold climate	18.0	11.7	9.2	17,700	207683526
MMDB018S4-*P LENNOX · cold climate	18.0	11.7	9.2	17,700	211034446
MMDB018S4 LENNOX · cold climate	18.0	11.7	9.2	17,700	210665633
MMA018SM4-*P · cold climate	17.6	11.7	9.6	17,000	212348049

Yearly running cost in 10 large cities$372-$1,011

Phoenix, AZ$461/yr
Miami, FL$372/yr
Houston, TX$413/yr
Atlanta, GA$421/yr
Los Angeles, CA$411/yr
New York, NY$1,011/yr
Chicago, IL$822/yr
Denver, CO$684/yr
Seattle, WA$421/yr
Minneapolis, MN$846/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 MLB018S4S-1P?: The Lennox MLB018S4S-1P is rated at up to 21.5 SEER2 and 12.5 EER2 for cooling and up to 11.2 HSPF2 for heating. The exact figure depends on the indoor unit it is paired with; across its 13 certified matchups SEER2 ranges from 17.6-21.5.
Is the Lennox MLB018S4S-1P good for cold climates?: Yes. At least one certified matchup meets the ENERGY STAR cold-climate criteria, delivering up to 18,000 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 Lennox MLB018S4S-1P cost to run per year?: At its rated efficiency it costs about $372-$1,011 a year in electricity in large U.S. cities, depending on climate and local rates - for example $461 in Phoenix and $846 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 MLB018S4S-1P?: ENERGY STAR lists 13 certified combinations for this outdoor unit. The highest-rated ones use LENNOX MWMC018S4-1P, LENNOX MWMC018S4, LENNOX MWMC018S4-*P.
What refrigerant does the Lennox MLB018S4S-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 $458/yrYou save $435/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 MLB018S4S-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: $458
Current system, per year: $893
You save per year: $435
Payback: 15.0 years
Net after 10 years: -$2,154

Cooling $278Heating $180Electricity used: 2,865 kWhSaved vs. a minimum-efficiency heat pump: $229

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 18,000 BTU models

TRUST AIR CONDITIONERS OAH18H/O4S4P · cold climate21.5 SEER2 · 11.3 HSPF2
MDV MOX430-17HFN1-MT0W-L · cold climate21.5 SEER2 · 11.2 HSPF2
Senville SENA/18HF/OQ · cold climate21.5 SEER2 · 11.3 HSPF2
Mitsubishi Electric MUZ-GS18NA21.5 SEER2 · 10.3 HSPF2
MRCOOL O-HH-18-HP-C-230B · cold climate21.5 SEER2 · 11.3 HSPF2
Mitsubishi Electric MUZ-GS18NAH21.5 SEER2 · 10.0 HSPF2
MRCOOL O-HH-18-HP-C-230A · cold climate21.5 SEER2 · 11.3 HSPF2
Fujitsu AOU18RLXFZH · cold climate21.5 SEER2 · 9.6 HSPF2

See all 465 18,000 BTU mini-splits, ranked

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