What is the SEER2 rating of the Mainline ML12HP230NEX-O?

The Mainline ML12HP230NEX-O is rated at up to 24.6 SEER2 and 12.7 EER2 for cooling and up to 11.5 HSPF2 for heating. The exact figure depends on the indoor unit it is paired with; across its 12 certified matchups SEER2 ranges from 19.0-24.6.

Is the Mainline ML12HP230NEX-O good for cold climates?

Yes. At least one certified matchup meets the ENERGY STAR cold-climate criteria, delivering up to 8,900 BTU/h at 5°F with a COP of 2.50, so it is still 2.5 times as efficient as electric resistance heat at that temperature.

How much does the Mainline ML12HP230NEX-O cost to run per year?

At its rated efficiency it costs about $230-$650 a year in electricity in large U.S. cities, depending on climate and local rates - for example $288 in Phoenix and $547 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 Mainline ML12HP230NEX-O?

ENERGY STAR lists 12 certified combinations for this outdoor unit. The highest-rated ones use MAINLINE ML12HP230CON-I, MAINLINE ML12HP230NEX-I, MAINLINE ML12HP2301WYCAS-I.

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

Mainline ML12HP230NEX-O

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

Ranks #131 of 394 12,000 BTU mini-splits for cooling efficiency, and costs about $269 a year to run in a mixed climate like Atlanta.

SEER2: 24.6 Cooling efficiency over a season
Very good · beats 80%
HSPF2: 11.5 Heating efficiency over a season
Very good · beats 84%
EER2: 12.7 Cooling efficiency on a 95°F day
Average · beats 54%
Heat at 5°F: 8,900 BTU/h74% of its 47°F output
Excellent · beats 97%

A good fit if…

You want low cooling bills - its SEER2 beats 80% of mini-splits.
Your winters get properly cold - it is ENERGY STAR cold-climate certified, with 8,900 BTU/h at 5°F.
It will heat most of the year - its HSPF2 beats 84% 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

Specifications12,000 BTU, R-454B

General
Brand	Mainline
Outdoor unit model	ML12HP230NEX-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	24.6 (range 19.0-24.6)
EER2Efficiency at 95°F outdoors	11.7-12.7
Cooling capacity	11,500-12,000 BTU/h
Heating
HSPF2Seasonal efficiency, higher is better	10.0-11.5
Capacity at 47°F	12,000 BTU/h
Capacity at 17°F	8,500-10,400 BTU/h
Capacity at 5°F	8,400-8,900 BTU/h
COP at 5°F2.0 = twice as efficient as a space heater	2.25-2.50
ENERGY STAR cold climate	Yes

Heating output as it gets colder74% kept at 5°F

Every heat pump delivers less heat as the outdoor temperature drops. Certified output of its matchup with ML12HP230CON-I 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.
ML12HP230CON-I MAINLINE · cold climate	24.6	12.7	11.0	8,900	217607275
ML12HP230CON-I MAINLINE · cold climate	24.6	12.7	11.0	8,900	215864362
ML12HP230NEX-I MAINLINE · cold climate	23.1	12.2	11.5	8,600	217607248
ML12HP230NEX-I MAINLINE · cold climate	23.1	12.2	11.5	8,600	215864335
ML12HP2301WYCAS-I MAINLINE · cold climate	22.1	12.3	10.0	8,600	217607280
ML12HP2301WYCAS-I MAINLINE · cold climate	22.1	12.3	10.0	8,600	215864367
ML12HP230STDCAS-I MAINLINE · cold climate	21.1	12.5	10.4	8,400	217607264
ML12HP230STDCAS-I MAINLINE · cold climate	21.1	12.5	10.4	8,400	215864351
ML12HP230HSDUC-I MAINLINE · cold climate	19.5	12.0	10.5	8,900	217607271
ML12HP230HSDUC-I MAINLINE · cold climate	19.5	12.0	10.5	8,900	215864358
ML12HP230LSDUC-I MAINLINE · cold climate	19.0	11.7	10.2	8,800	217607268
ML12HP230LSDUC-I MAINLINE · cold climate	19.0	11.7	10.2	8,800	215864355

Yearly running cost in 10 large cities$230-$650

Phoenix, AZ$288/yr
Miami, FL$230/yr
Houston, TX$259/yr
Atlanta, GA$269/yr
Los Angeles, CA$263/yr
New York, NY$650/yr
Chicago, IL$530/yr
Denver, CO$442/yr
Seattle, WA$272/yr
Minneapolis, MN$547/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 Mainline ML12HP230NEX-O?: The Mainline ML12HP230NEX-O is rated at up to 24.6 SEER2 and 12.7 EER2 for cooling and up to 11.5 HSPF2 for heating. The exact figure depends on the indoor unit it is paired with; across its 12 certified matchups SEER2 ranges from 19.0-24.6.
Is the Mainline ML12HP230NEX-O good for cold climates?: Yes. At least one certified matchup meets the ENERGY STAR cold-climate criteria, delivering up to 8,900 BTU/h at 5°F with a COP of 2.50, so it is still 2.5 times as efficient as electric resistance heat at that temperature.
How much does the Mainline ML12HP230NEX-O cost to run per year?: At its rated efficiency it costs about $230-$650 a year in electricity in large U.S. cities, depending on climate and local rates - for example $288 in Phoenix and $547 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 Mainline ML12HP230NEX-O?: ENERGY STAR lists 12 certified combinations for this outdoor unit. The highest-rated ones use MAINLINE ML12HP230CON-I, MAINLINE ML12HP230NEX-I, MAINLINE ML12HP2301WYCAS-I.
What refrigerant does the Mainline ML12HP230NEX-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 $289/yrYou save $330/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 ML12HP230NEX-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: $289
Current system, per year: $619
You save per year: $330
Payback: 13.6 years
Net after 10 years: -$1,198

Cooling $172Heating $117Electricity used: 1,804 kWhSaved vs. a minimum-efficiency heat pump: $186

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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Panasonic CU-YM12CBUC · cold climate24.6 SEER2 · 11.5 HSPF2
Mitsubishi Electric PUZ-AK12NL24.8 SEER2 · 10.9 HSPF2
AproDr ALC24-12H1B · cold climate24.6 SEER2 · 11.0 HSPF2
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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.