Against comparable models

Each cell is the share of same-size, same-type models that the manufacturer’s typical model beats (50% is typical); the higher score is in bold. Raw medians are underneath for context: they depend on which sizes each one makes, so they are not compared.

RUSSELL and ZERO on every ratingPeer scores, 0–100 · grey ticks: every ranked manufacturer · shaded: the middle half of each one’s modelsMeasured against models of the same size and duct type, ZERO scores higher on 4 of the 6 ratings.

RUSSELL
ZERO
Other ranked manufacturers

Source: AHRI Directory, NEEP · as of Oct 11, 2026

Average peer percentile, raw median and rank among ranked manufacturers
Rating	RUSSELL	ZERO
Efficiency index	49%median —	49%median —
COP at 5°F	80% (higher)median 2.20	48% (higher)median 1.89
Capacity retention at 5°F	43%median 57%	43%median 70%
HSPF2	25%median 7.2	46%median 8.6
SEER2	32%median 14.3	53%median 19.0
EER2	42%median 10.6	46%median 11.0
Heating capacity at 5°F	42%median 24,200 Btu/h	44%median 11,700 Btu/h
Outdoor models	60	69
AHRI certifications	1,231	89

Share of models meeting each standard

Percent of each manufacturer’s models with a qualifying certification
Standard	RUSSELL	ZERO
CEE 2025 Tier 1 (Split ASHP)	16.7%10 models	59.4%41 models
CEE 2026 Tier 1 (Split ASHP)	16.7%10 models	55.1%38 models
CEE Advanced Tier (Split ASHP)	3.3%2 models	0%0 models
Xcel Energy Colorado cold-climate ASHP (2025)	13.3%8 models	47.8%33 models
DOE Cold Climate Heat Pump Challenge	3.3%2 models	0%0 models
ENERGY STAR Cold Climate	21.7%13 models	24.6%17 models

Sizes and duct types offered

Models in each peer group, with the efficiency index of those models against the rest of the group.

Side by side, inside each size and duct typeShape: every model of the group · bars: each manufacturer’s middle half, median dot, 10th–90th line · 5 groups where both have models

RUSSELL
ZERO
All models of the group

Raw ratings are only placed side by side within one size and duct type, where they are comparable.

Source: AHRI Directory · as of Oct 11, 2026

Models per peer group · efficiency index within the group
Size and duct type	RUSSELL	ZERO
Ducted, up to 1.5 tons	2 · index 27%	2 · index 59%
Ducted, 2 tons	7 · index 52%	5 · index 69%
Ducted, 2.5–3 tons	17 · index 52%	7 · index 57%
Ducted, 3.5–4.5 tons	26 · index 50%	9 · index 63%
Ducted, 5 tons and up	8 · index 70%	1 · index 57%
Non-ducted, up to 1.5 tons	None	33 · index 48%
Non-ducted, 2 tons	None	9 · index 49%
Non-ducted, 2.5–3 tons	None	8 · index 39%
Non-ducted, 3.5–4.5 tons	None	3 · index 50%

Cold-climate and all-around picks, size class by size class

Each manufacturer’s best model on each board in every size and duct type, side by side; the higher score is in bold. Both scores are 0–100 against every model of that size class (the line on each bar is 50, the typical model there), so the two compare fairly even when they make different sizes.

Cold-climate picks

Best cold-climate pick per size and duct type (keeps at least 70% of its heat at 5°F). Qualifies when its capacity retention at 5°F (capacity at 5°F as a share of capacity at 47°F) is at least 70% and Capacity retention at 5°F, COP at 5°F, HSPF2 are all rated. Score = the equal-weight mean of its peer percentiles on Capacity retention at 5°F, COP at 5°F, HSPF2 (share of the other models in its peer group it beats, 0–100), all from one certified pairing: in each duct type a model is sold in, its qualifying pairing of that type with the best score; equal scores (one decimal) go to the higher heating capacity at 5°F.
Size and duct type	RUSSELLCold-climate score, best model	ZEROCold-climate score, best model
Ducted, up to 1.5 tons	None on this board (0 of 2 models qualify)	52.0(50 is the typical model of its size class)Z3SOV-18HDM-US1 of 2 models qualify · AHRI 214723150
Ducted, 2 tons	74.7(50 is the typical model of its size class)SP18AZ24AJVCwith indoor coil TCFZ2421HEAAM and furnace S951V0403A17UHU2 of 7 models qualify · AHRI 213372369	80.3(50 is the typical model of its size class) (higher)ZSOV-24HDM-USwith ducted air handler ZDV-24HDM-US2 of 5 models qualify · AHRI 212928560
Ducted, 2.5–3 tons	80.6(50 is the typical model of its size class) (higher)SP18AZ36AJVCwith ducted air handler SHMVZ6021SEACA2 of 17 models qualify · AHRI 210106900	57.4(50 is the typical model of its size class)Z3SOV-27HDM-US1 of 7 models qualify · AHRI 213732663
Ducted, 3.5–4.5 tons	76.3(50 is the typical model of its size class) (higher)SP18AZ48AJVCwith indoor coil TCFZ6021SEAAM and furnace S962V1005A21M4S4 of 26 models qualify · AHRI 210106968	74.9(50 is the typical model of its size class)Z5SOV-48HDM-US1 of 9 models qualify · AHRI 213732669
Ducted, 5 tons and up	None on this board (0 of 8 models qualify)	None on this board (0 of 1 models qualify)
Non-ducted, up to 1.5 tons	No models in this size class	86.0(50 is the typical model of its size class)ZMSB-09HV-USHHwith ductless indoor unit ZMSB-09HV-USHH24 of 33 models qualify · AHRI 213917748
Non-ducted, 2 tons	No models in this size class	74.2(50 is the typical model of its size class)ZSOV-24HDM-USwith ductless indoor unit ZEV-24HDM-US4 of 9 models qualify · AHRI 212928564
Non-ducted, 2.5–3 tons	No models in this size class	49.3(50 is the typical model of its size class)Z3SOV-27HDM-US1 of 8 models qualify · AHRI 213732662
Non-ducted, 3.5–4.5 tons	No models in this size class	80.5(50 is the typical model of its size class)Z5SOV-48HDM-US2 of 3 models qualify · AHRI 213732668

All-around best

Best all-around model per size and duct type. Score = 50% heating, the mean of its peer percentiles on COP at 5°F, Capacity retention at 5°F, HSPF2, plus 50% cooling, the mean of its peer percentiles on SEER2 and EER2 (share of the other models in its peer group it beats, 0–100). All five ratings are required; there is no minimum heat kept at 5°F. In each duct type a model is sold in, it is scored on its pairing of that type with the best score; equal scores (one decimal) go to the higher cold-climate score, then the higher heating capacity at 5°F.
Size and duct type	RUSSELLAll-around score, best model	ZEROAll-around score, best model
Ducted, up to 1.5 tons	34.5(50 is the typical model of its size class)SP15AZ18AJ2Nwith ducted air handler SH2CZ2417STANN2 of 2 models have all five ratings · AHRI 211627516	59.4(50 is the typical model of its size class) (higher)Z3SOV-18HDM-US1 of 2 models have all five ratings · AHRI 214723150
Ducted, 2 tons	83.6(50 is the typical model of its size class)SP18AZ24AJVCwith indoor coil TCFZ2421HEAAM and furnace S951V0403A17UHU4 of 7 models have all five ratings · AHRI 213372369	83.8(50 is the typical model of its size class) (higher)ZSOV-24HDM-USwith ducted air handler ZDV-24HDM-US2 of 5 models have all five ratings · AHRI 212928560
Ducted, 2.5–3 tons	87.2(50 is the typical model of its size class) (higher)SP18AZ36AJVCwith indoor coil TCFZ6021SEAAM and furnace S802VA100521Z6 of 17 models have all five ratings · AHRI 210589394	71.5(50 is the typical model of its size class)Z3SOV-27HDM-US3 of 7 models have all five ratings · AHRI 213732663
Ducted, 3.5–4.5 tons	80.3(50 is the typical model of its size class)SP18AZ48AJVCwith indoor coil TCFZ6021SEAAM and furnace S802VA100521Z9 of 26 models have all five ratings · AHRI 210589350	82.0(50 is the typical model of its size class) (higher)Z5SOV-48HDM-US2 of 9 models have all five ratings · AHRI 213732669
Ducted, 5 tons and up	70.2(50 is the typical model of its size class) (higher)SP15AZ60AJ2Nwith indoor coil TCFZ6024STANM and furnace S97MV1005A21DHS1 of 8 models have all five ratings · AHRI 212387320	57.1(50 is the typical model of its size class)ZSOV-60HDM-USwith ducted air handler ZDV-60HDM-US1 of 1 models have all five ratings · AHRI 212928563
Non-ducted, up to 1.5 tons	No models in this size class	86.7(50 is the typical model of its size class)ZMSB-09HV-USHHwith ductless indoor unit ZMSB-09HV-USHH33 of 33 models have all five ratings · AHRI 213917748
Non-ducted, 2 tons	No models in this size class	72.0(50 is the typical model of its size class)ZSOV-24HDM-USwith ductless indoor unit ZEV-24HDM-US9 of 9 models have all five ratings · AHRI 212928564
Non-ducted, 2.5–3 tons	No models in this size class	66.7(50 is the typical model of its size class)Z3SOV-27HDM-US8 of 8 models have all five ratings · AHRI 213732662
Non-ducted, 3.5–4.5 tons	No models in this size class	73.8(50 is the typical model of its size class)Z5SOV-48HDM-US3 of 3 models have all five ratings · AHRI 213732668

All-around board, every manufacturer

Standout model on each rating

Each manufacturer’s model that beats the largest share of comparable models on the rating; the higher share is in bold.

Top model per rating by peer percentile, with its AHRI-certified value and peer group
Rating	RUSSELL	ZERO
COP at 5°F	beats 98% · 2.60SP15AZ60AJ2NDucted, 5 tons and up	beats 96% · 2.22ZMSB-24HV-USHHNon-ducted, 2 tons
Capacity retention at 5°F	beats 100% · 105%SP18AZ48AJVCDucted, 3.5–4.5 tons	beats 84% · 87%Z5SOV-48HDM-USDucted, 3.5–4.5 tons
HSPF2	beats 75% · 9.5RD17AZ24AJ3NDucted, 2 tons	beats 98% · 11.2ZSOV-24HDM-USDucted, 2 tons
SEER2	beats 94% · 20.0SP18AZ24AJVCDucted, 2 tons	beats 99% · 20.9Z5SOV-48HDM-USDucted, 3.5–4.5 tons
EER2	beats 91% · 12.5SP18AZ36AJVCDucted, 2.5–3 tons	beats 95% · 15.8ZMSB-09HV-USHHCAlso listed as ZMSB-09HV-USHHC-ONon-ducted, up to 1.5 tons
Heating capacity at 5°F	beats 100% · 43,500 Btu/hSP18AZ36AJVCDucted, 2.5–3 tons	beats 90% · 17,200 Btu/hZMSB-18HV-USHHCAlso listed as ZMSB-18HV-USHHC-ONon-ducted, up to 1.5 tons

More comparisons

Pick any two manufacturers

RUSSELL vs ZERO heat pumps