What is the SEER2 rating of the Mainline ML09HP230NEX-O?

The Mainline ML09HP230NEX-O is rated at up to 26.0 SEER2 and 16.2 EER2 for cooling and up to 13.9 HSPF2 for heating. The exact figure depends on the indoor unit it is paired with; across its 12 certified matchups SEER2 ranges from 19.5-26.0.

Is the Mainline ML09HP230NEX-O good for cold climates?

Yes. At least one certified matchup meets the ENERGY STAR cold-climate criteria, delivering up to 8,600 BTU/h at 5°F with a COP of 2.33, so it is still 2.3 times as efficient as electric resistance heat at that temperature.

How much does the Mainline ML09HP230NEX-O cost to run per year?

At its rated efficiency it costs about $163-$451 a year in electricity in large U.S. cities, depending on climate and local rates - for example $203 in Phoenix and $378 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 ML09HP230NEX-O?

ENERGY STAR lists 12 certified combinations for this outdoor unit. The highest-rated ones use MAINLINE ML09HP230CON-I, MAINLINE ML09HP230NEX-I, MAINLINE ML09HP2301WYCAS-I.

9,000 BTU mini-split heat pump · ML Series

Mainline ML09HP230NEX-O

Excellent cooling and heating efficiency for a 9,000 BTU mini-split heat pump, and certified for cold climates.

Ranks #119 of 395 9,000 BTU mini-splits for cooling efficiency, and costs about $187 a year to run in a mixed climate like Atlanta.

SEER2: 26.0 Cooling efficiency over a season
Excellent · beats 91%
HSPF2: 13.9 Heating efficiency over a season
Excellent · beats 98%
EER2: 16.2 Cooling efficiency on a 95°F day
Excellent · beats 97%
Heat at 5°F: 8,600 BTU/h96% of its 47°F output
Very good · beats 88%

A good fit if…

You want low cooling bills - its SEER2 beats 91% of mini-splits.
Your winters get properly cold - it is ENERGY STAR cold-climate certified, with 8,600 BTU/h at 5°F.
It will heat most of the year - its HSPF2 beats 98% 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

Specifications9,000 BTU, R-454B

General
Brand	Mainline
Outdoor unit model	ML09HP230NEX-O
Series	ML Series
Type	Mini-split heat pump
Nominal size	9,000 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	26.0 (range 19.5-26.0)
EER2Efficiency at 95°F outdoors	12.8-16.2
Cooling capacity	9,000 BTU/h
Heating
HSPF2Seasonal efficiency, higher is better	11.0-13.9
Capacity at 47°F	9,000-11,000 BTU/h
Capacity at 17°F	7,900-9,300 BTU/h
Capacity at 5°F	8,000-8,600 BTU/h
COP at 5°F2.0 = twice as efficient as a space heater	2.17-2.33
ENERGY STAR cold climate	Yes

Heating output as it gets colder96% kept at 5°F

Every heat pump delivers less heat as the outdoor temperature drops. Certified output of its matchup with ML09HP230CON-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.
ML09HP230CON-I MAINLINE · cold climate	26.0	16.2	13.9	8,600	217607274
ML09HP230CON-I MAINLINE · cold climate	26.0	16.2	13.9	8,600	215864361
ML09HP230NEX-I MAINLINE · cold climate	24.6	14.7	13.0	8,200	217607247
ML09HP230NEX-I MAINLINE · cold climate	24.6	14.7	13.0	8,200	215864334
ML09HP2301WYCAS-I MAINLINE · cold climate	22.1	14.4	11.8	8,000	217607279
ML09HP2301WYCAS-I MAINLINE · cold climate	22.1	14.4	11.8	8,000	215864366
ML09HP230STDCAS-I MAINLINE · cold climate	21.6	14.3	11.3	8,300	217607263
ML09HP230STDCAS-I MAINLINE · cold climate	21.6	14.3	11.3	8,300	215864350
ML09HP230HSDUC-I MAINLINE · cold climate	19.7	13.0	11.5	8,300	217607270
ML09HP230HSDUC-I MAINLINE · cold climate	19.7	13.0	11.5	8,300	215864357
ML09HP230LSDUC-I MAINLINE · cold climate	19.5	12.8	11.0	8,600	217607267
ML09HP230LSDUC-I MAINLINE · cold climate	19.5	12.8	11.0	8,600	215864354

Yearly running cost in 10 large cities$163-$451

Phoenix, AZ$203/yr
Miami, FL$163/yr
Houston, TX$182/yr
Atlanta, GA$187/yr
Los Angeles, CA$183/yr
New York, NY$451/yr
Chicago, IL$367/yr
Denver, CO$305/yr
Seattle, WA$188/yr
Minneapolis, MN$378/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 ML09HP230NEX-O?: The Mainline ML09HP230NEX-O is rated at up to 26.0 SEER2 and 16.2 EER2 for cooling and up to 13.9 HSPF2 for heating. The exact figure depends on the indoor unit it is paired with; across its 12 certified matchups SEER2 ranges from 19.5-26.0.
Is the Mainline ML09HP230NEX-O good for cold climates?: Yes. At least one certified matchup meets the ENERGY STAR cold-climate criteria, delivering up to 8,600 BTU/h at 5°F with a COP of 2.33, so it is still 2.3 times as efficient as electric resistance heat at that temperature.
How much does the Mainline ML09HP230NEX-O cost to run per year?: At its rated efficiency it costs about $163-$451 a year in electricity in large U.S. cities, depending on climate and local rates - for example $203 in Phoenix and $378 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 ML09HP230NEX-O?: ENERGY STAR lists 12 certified combinations for this outdoor unit. The highest-rated ones use MAINLINE ML09HP230CON-I, MAINLINE ML09HP230NEX-I, MAINLINE ML09HP2301WYCAS-I.
What refrigerant does the Mainline ML09HP230NEX-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 $202/yrYou save $278/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 ML09HP230NEX-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: $202
Current system, per year: $480
You save per year: $278
Payback: 12.6 years
Net after 10 years: -$720

Cooling $122Heating $81Electricity used: 1,265 kWhSaved vs. a minimum-efficiency heat pump: $168

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 9,000 BTU models

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DIRECT AIR DIRM4-09DA25-1Z · cold climate26.0 SEER2 · 13.9 HSPF2
Midea MO1ES-H09B-2A · cold climate26.0 SEER2 · 13.9 HSPF2
Cooper&Hunter CH-RES09-230VO · cold climate26.0 SEER2 · 13.9 HSPF2
NOVAIR LEA09SZ26-O · cold climate26.0 SEER2 · 13.9 HSPF2
Carrier 37MARAQ09AA3 · cold climate26.0 SEER2 · 13.9 HSPF2
ComfortStar CHF3-09CD(O) · cold climate26.0 SEER2 · 13.8 HSPF2

See all 395 9,000 BTU mini-splits, ranked

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