What is the SEER2 rating of the Mainline ML12HP115NEX-O?

The Mainline ML12HP115NEX-O is rated at up to 23.2 SEER2 and 12.5 EER2 for cooling and up to 10.4 HSPF2 for heating. The exact figure depends on the indoor unit it is paired with.

Is the Mainline ML12HP115NEX-O good for cold climates?

It is not cold-climate certified: none of its matchups meet the ENERGY STAR cold-climate criteria (a COP of at least 1.75 at 5°F among other limits). In places with frequent sub-zero nights, pick a cold-climate 12,000 BTU model.

How much does the Mainline ML12HP115NEX-O cost to run per year?

At its rated efficiency it costs about $244-$714 a year in electricity in large U.S. cities, depending on climate and local rates - for example $309 in Phoenix and $603 in Minneapolis. The calculator on this page works it out for your city and compares it with your current system.

Is the Mainline ML12HP115NEX-O the same as the SLIMAIR SHC12AE1AG?

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.

Which indoor units work with the Mainline ML12HP115NEX-O?

ENERGY STAR lists 2 certified combinations for this outdoor unit. The highest-rated one uses MAINLINE ML12HP115NEX-I.

12,000 BTU mini-split heat pump · ML Series

Mainline ML12HP115NEX-O

Average cooling and heating efficiency for a 12,000 BTU mini-split heat pump, but not rated for cold climates.

Ranks #226 of 394 12,000 BTU mini-splits for cooling efficiency, and costs about $293 a year to run in a mixed climate like Atlanta.

SEER2: 23.2 Cooling efficiency over a season
Average · beats 67%
HSPF2: 10.4 Heating efficiency over a season
Average · beats 57%
EER2: 12.5 Cooling efficiency on a 95°F day
Average · beats 44%
Heat at 5°F: 7,300 BTU/h61% of its 47°F output
Very good · beats 78%

A good fit if…

You want steady temperatures and quiet running - the compressor varies its speed.

Think twice if…

You often see nights below 0°F - it is not cold-climate certified.

Calculate my running cost

Details

Specifications12,000 BTU, R-454B

General
Brand	Mainline
Also sold as	SLIMAIR, Cooper&Hunter
Outdoor unit model	ML12HP115NEX-O
Series	ML Series
Type	Mini-split heat pump
Nominal size	12,000 BTU
CompressorVariable-speed units run longer at low power	Continuously variable
Refrigerant	R-454B
Connected (smart) capable	No
On the market since	May 20, 2024
Last certified	August 11, 2026
Cooling
SEER2Seasonal efficiency, higher is better	23.2 (range 23.2)
EER2Efficiency at 95°F outdoors	12.5
Cooling capacity	12,000 BTU/h
Heating
HSPF2Seasonal efficiency, higher is better	10.4
Capacity at 47°F	12,000 BTU/h
Capacity at 17°F	10,000 BTU/h
Capacity at 5°F	7,300 BTU/h
COP at 5°F2.0 = twice as efficient as a space heater	2.20
ENERGY STAR cold climate	No

Heating output as it gets colder61% kept at 5°F

Every heat pump delivers less heat as the outdoor temperature drops. Certified output of its matchup with ML12HP115NEX-I at the standard test temperatures, in BTU/h:

Certified matchups2 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.
ML12HP115NEX-I MAINLINE	23.2	12.5	10.4	7,300	217607246
ML12HP115NEX-I MAINLINE	23.2	12.5	10.4	7,300	215864333

Same unit, other model numbers2

These model numbers have exactly the same certified ratings and matchups as the Mainline ML12HP115NEX-O: the same equipment under another brand, or a variant code for voltage, colour or market. Everything on this page applies to them.

SLIMAIR SHC12AE1AG
Cooper&Hunter CH-RES12-115VO

Yearly running cost in 10 large cities$244-$714

Phoenix, AZ$309/yr
Miami, FL$244/yr
Houston, TX$278/yr
Atlanta, GA$293/yr
Los Angeles, CA$287/yr
New York, NY$714/yr
Chicago, IL$582/yr
Denver, CO$486/yr
Seattle, WA$301/yr
Minneapolis, MN$603/yr

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

Questions6

What is the SEER2 rating of the Mainline ML12HP115NEX-O?: The Mainline ML12HP115NEX-O is rated at up to 23.2 SEER2 and 12.5 EER2 for cooling and up to 10.4 HSPF2 for heating. The exact figure depends on the indoor unit it is paired with.
Is the Mainline ML12HP115NEX-O good for cold climates?: It is not cold-climate certified: none of its matchups meet the ENERGY STAR cold-climate criteria (a COP of at least 1.75 at 5°F among other limits). In places with frequent sub-zero nights, pick a cold-climate 12,000 BTU model.
How much does the Mainline ML12HP115NEX-O cost to run per year?: At its rated efficiency it costs about $244-$714 a year in electricity in large U.S. cities, depending on climate and local rates - for example $309 in Phoenix and $603 in Minneapolis. The calculator on this page works it out for your city and compares it with your current system.
Is the Mainline ML12HP115NEX-O the same as the SLIMAIR SHC12AE1AG?: 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.
Which indoor units work with the Mainline ML12HP115NEX-O?: ENERGY STAR lists 2 certified combinations for this outdoor unit. The highest-rated one uses MAINLINE ML12HP115NEX-I.
What refrigerant does the Mainline ML12HP115NEX-O 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 $311/yrYou save $307/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 Mainline ML12HP115NEX-O

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: $311
Current system, per year: $619
You save per year: $307
Payback: 14.6 years
Net after 10 years: -$1,425

Cooling $182Heating $129Electricity used: 1,946 kWhSaved vs. a minimum-efficiency heat pump: $163

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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ZERO ZMSB-12HV110-USHHR2-O23.2 SEER2 · 10.4 HSPF2
Midea MO1ES-H12B-1A23.4 SEER2 · 9.5 HSPF2
ApooDr ASG24-12H220V1B · cold climate23.1 SEER2 · 11.5 HSPF2
Bosch BMS500-AAS012-0CSXRD23.4 SEER2 · 9.5 HSPF2
ComfortStar CPP3-12CD(O) · cold climate23.1 SEER2 · 11.5 HSPF2
CanAir 4C25SCH12H1123.4 SEER2 · 10.4 HSPF2
Continental CDHAS22B-12-O · cold climate23.1 SEER2 · 11.5 HSPF2

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

Source: ENERGY STAR Certified Heat Pumps (U.S. EPA), certification of August 11, 2026. How we use the data.