What is the SEER2 rating of the Westinghouse WHP42M5A21S?

The Westinghouse WHP42M5A21S is rated at up to 20.0 SEER2 and 10.5 EER2 for cooling and up to 9.0 HSPF2 for heating. The exact figure depends on the indoor unit it is paired with; across its 2 certified matchups SEER2 ranges from 18.0-20.0.

Is the Westinghouse WHP42M5A21S good for cold climates?

Yes. At least one certified matchup meets the ENERGY STAR cold-climate criteria, delivering up to 36,000 BTU/h at 5°F with a COP of 1.84, so it is still 1.8 times as efficient as electric resistance heat at that temperature.

How much does the Westinghouse WHP42M5A21S cost to run per year?

At its rated efficiency it costs about $991-$2,902 a year in electricity in large U.S. cities, depending on climate and local rates - for example $1,256 in Phoenix and $2,451 in Minneapolis. The calculator on this page works it out for your city and compares it with your current system.

What refrigerant does the Westinghouse WHP42M5A21S 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.

42,000 BTU mini-split heat pump · Hi MULTI Xtreme

Westinghouse WHP42M5A21S

Below average cooling and heating efficiency for a 42,000 BTU mini-split heat pump, and certified for cold climates.

Ranks #51 of 61 42,000 BTU mini-splits for cooling efficiency, and costs about $1,189 a year to run in a mixed climate like Atlanta.

SEER2: 20.0 Cooling efficiency over a season
Below average · beats 18%
HSPF2: 9.0 Heating efficiency over a season
Below average · beats 7%
EER2: 10.5 Cooling efficiency on a 95°F day
Below average · beats 6%
Heat at 5°F: 36,000 BTU/h86% of its 47°F output
Below average · beats 18%

A good fit if…

Your winters get properly cold - it is ENERGY STAR cold-climate certified, with 36,000 BTU/h at 5°F.
You want steady temperatures and quiet running - the compressor varies its speed.

Think twice if…

Cooling cost matters most - its SEER2 is below average for mini-splits.
You mainly need heat - its HSPF2 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

Specifications42,000 BTU, R-410A

General
Brand	Westinghouse
Outdoor unit model	WHP42M5A21S
Series	Hi MULTI Xtreme
Type	Mini-split heat pump
Nominal size	42,000 BTU
CompressorVariable-speed units run longer at low power	Continuously variable
Refrigerant	R-410A
Connected (smart) capable	No
On the market since	April 1, 2024
Last certified	June 13, 2026
Cooling
SEER2Seasonal efficiency, higher is better	20.0 (range 18.0-20.0)
EER2Efficiency at 95°F outdoors	10.0-10.5
Cooling capacity	41,000-42,000 BTU/h
Heating
HSPF2Seasonal efficiency, higher is better	8.8-9.0
Capacity at 47°F	41,000-42,000 BTU/h
Capacity at 17°F	27,000-28,400 BTU/h
Capacity at 5°F	36,000 BTU/h
COP at 5°F2.0 = twice as efficient as a space heater	1.84
ENERGY STAR cold climate	Yes

Heating output as it gets colder86% kept at 5°F

Every heat pump delivers less heat as the outdoor temperature drops. Certified output of its best matchup 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.
- WESTINGHOUSE · cold climate	20.0	10.5	9.0	36,000	206517597
- WESTINGHOUSE · cold climate	18.0	10.0	8.8	36,000	208404160

Yearly running cost in 10 large cities$991-$2,902

Phoenix, AZ$1,256/yr
Miami, FL$991/yr
Houston, TX$1,127/yr
Atlanta, GA$1,189/yr
Los Angeles, CA$1,168/yr
New York, NY$2,902/yr
Chicago, IL$2,367/yr
Denver, CO$1,977/yr
Seattle, WA$1,222/yr
Minneapolis, MN$2,451/yr

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

Questions4

What is the SEER2 rating of the Westinghouse WHP42M5A21S?: The Westinghouse WHP42M5A21S is rated at up to 20.0 SEER2 and 10.5 EER2 for cooling and up to 9.0 HSPF2 for heating. The exact figure depends on the indoor unit it is paired with; across its 2 certified matchups SEER2 ranges from 18.0-20.0.
Is the Westinghouse WHP42M5A21S good for cold climates?: Yes. At least one certified matchup meets the ENERGY STAR cold-climate criteria, delivering up to 36,000 BTU/h at 5°F with a COP of 1.84, so it is still 1.8 times as efficient as electric resistance heat at that temperature.
How much does the Westinghouse WHP42M5A21S cost to run per year?: At its rated efficiency it costs about $991-$2,902 a year in electricity in large U.S. cities, depending on climate and local rates - for example $1,256 in Phoenix and $2,451 in Minneapolis. The calculator on this page works it out for your city and compares it with your current system.
What refrigerant does the Westinghouse WHP42M5A21S 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 $1,265/yrYou save $901/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 Westinghouse WHP42M5A21S

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: $1,265
Current system, per year: $2,166
You save per year: $901
Payback: 17.8 years
Net after 10 years: -$6,992

Cooling $739Heating $526Electricity used: 7,905 kWhSaved vs. a minimum-efficiency heat pump: $396

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 42,000 BTU models

OLMO OS-MSR42-230VO · cold climate20.0 SEER2 · 9.0 HSPF2
DELLA 048-TLP-MODU-1D5 · cold climate19.5 SEER2 · 9.0 HSPF2
Friedrich FPHMR42A3A · cold climate20.0 SEER2 · 9.0 HSPF2
Fujitsu AOUH42KUAS1 · cold climate19.0 SEER2 · 10.4 HSPF2
Mitsubishi Electric PUZ-AK42NLHZ · cold climate20.0 SEER2 · 9.2 HSPF2
LG KUSUB421A · cold climate18.5 SEER2 · 9.5 HSPF2
Hisense AUW-48U3TH1(JCH) · cold climate20.0 SEER2 · 9.5 HSPF2
GE Appliances ASH4248UCDD · cold climate18.0 SEER2 · 8.8 HSPF2

See all 61 42,000 BTU mini-splits, ranked

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