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.

IWAE and ZEPHYR 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, ZEPHYR scores higher on 6 of the 6 ratings.

IWAE
ZEPHYR
Other ranked manufacturers

Source: AHRI Directory, NEEP · as of Oct 9, 2026

Average peer percentile, raw median and rank among ranked manufacturers
Rating	IWAE	ZEPHYR
Efficiency index	52%median —	63%median —
COP at 5°F	26%median 1.80	57%median 2.00
Capacity retention at 5°F	61%median 80%	64%median 80%
HSPF2	35%median 8.0	59%median 10.0
SEER2	40%median 17.0	67%median 22.0
EER2	36%median 11.2	65%median 12.3
Heating capacity at 5°F	50%median 16,250 Btu/h	57%median 13,400 Btu/h
Outdoor models	23	23
AHRI certifications	27	49

Share of models meeting each standard

Percent of each manufacturer’s models with a qualifying certification
Standard	IWAE	ZEPHYR
CEE 2025 Tier 1 (Split ASHP)	34.8%8 models	100%23 models
CEE 2026 Tier 1 (Split ASHP)	34.8%8 models	95.7%22 models
CEE Advanced Tier (Split ASHP)	0%0 models	8.7%2 models
Xcel Energy Colorado cold-climate ASHP (2025)	34.8%8 models	82.6%19 models
DOE Cold Climate Heat Pump Challenge	0%0 models	8.7%2 models
ENERGY STAR Cold Climate	26.1%6 models	73.9%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 · 7 groups where both have models

IWAE
ZEPHYR
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 9, 2026

Models per peer group · efficiency index within the group
Size and duct type	IWAE	ZEPHYR
Ducted, up to 1.5 tons	1 · index —	1 · index 65%
Ducted, 2 tons	2 · index 37%	1 · index 80%
Ducted, 2.5–3 tons	3 · index 52%	3 · index 71%
Ducted, 3.5–4.5 tons	5 · index 41%	2 · index 71%
Ducted, 5 tons and up	None	1 · index 81%
Non-ducted, up to 1.5 tons	8 · index 58%	14 · index 62%
Non-ducted, 2 tons	2 · index 65%	2 · index 48%
Non-ducted, 2.5–3 tons	2 · index —	2 · index 63%
Non-ducted, 3.5–4.5 tons	None	1 · index 44%

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	IWAECold-climate score, best model	ZEPHYRCold-climate score, best model
Ducted, up to 1.5 tons	None on this board (0 of 1 models qualify)	66.2(50 is the typical model of its size class)ZE-518M2251 of 1 models qualify · AHRI 216684162
Ducted, 2 tons	42.5(50 is the typical model of its size class)AESHV8T2421BAwith ducted air handler AEAMPVT24D21BA1 of 2 models qualify · AHRI 217732895	82.1(50 is the typical model of its size class) (higher)ZE-624HPAwith ducted air handler AH-624A1 of 1 models qualify · AHRI 215381145
Ducted, 2.5–3 tons	55.4(50 is the typical model of its size class)AESHV9T3621BAwith ducted air handler AEAMPVT36D21BA1 of 3 models qualify · AHRI 217732896	87.9(50 is the typical model of its size class) (higher)ZE-636HPAwith ducted air handler AH-636A3 of 3 models qualify · AHRI 215381146
Ducted, 3.5–4.5 tons	43.2(50 is the typical model of its size class)AESHV8T4821BAwith ducted air handler AEAMPVT48F21BA2 of 5 models qualify · AHRI 217732897	77.3(50 is the typical model of its size class) (higher)ZE-648HPAwith ducted air handler AH-648A2 of 2 models qualify · AHRI 215381147
Ducted, 5 tons and up	No models in this size class	88.7(50 is the typical model of its size class)ZE-660HPAwith ducted air handler AH-660A1 of 1 models qualify · AHRI 215381148
Non-ducted, up to 1.5 tons	51.8(50 is the typical model of its size class)AEPLMHV23S0932B1Awith ductless indoor unit AEPLAWM23E0932B1A5 of 8 models qualify · AHRI 218451556	89.7(50 is the typical model of its size class) (higher)ZE-09UB32Owith ductless indoor unit ZE-09UB32I10 of 14 models qualify · AHRI 217596868
Non-ducted, 2 tons	61.6(50 is the typical model of its size class) (higher)AEPLMHV22S2431B1Awith ductless indoor unit AEPLAWM22E2431B1A1 of 2 models qualify · AHRI 218451561	54.1(50 is the typical model of its size class)ZE-24CB25Owith ductless indoor unit ZE-24CB25AI2 of 2 models qualify · AHRI 218046582
Non-ducted, 2.5–3 tons	None on this board (0 of 2 models qualify)	53.7(50 is the typical model of its size class)ZE-536M4252 of 2 models qualify · AHRI 216684171
Non-ducted, 3.5–4.5 tons	No models in this size class	16.4(50 is the typical model of its size class)ZE-542M5251 of 1 models qualify · AHRI 216684168

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	IWAEAll-around score, best model	ZEPHYRAll-around score, best model
Ducted, up to 1.5 tons	None on this board (0 of 1 models have all five ratings)	64.6(50 is the typical model of its size class)ZE-518M2251 of 1 models have all five ratings · AHRI 216684162
Ducted, 2 tons	37.2(50 is the typical model of its size class)AESHV8T2421BAwith ducted air handler AEAMPVT24D21BA1 of 2 models have all five ratings · AHRI 217732895	79.5(50 is the typical model of its size class) (higher)ZE-624HPAwith ducted air handler AH-624A1 of 1 models have all five ratings · AHRI 215381145
Ducted, 2.5–3 tons	51.6(50 is the typical model of its size class)AESHV9T3621BAwith ducted air handler AEAMPVT36D21BA1 of 3 models have all five ratings · AHRI 217732896	82.3(50 is the typical model of its size class) (higher)ZE-636HPAwith ducted air handler AH-636A3 of 3 models have all five ratings · AHRI 215381146
Ducted, 3.5–4.5 tons	43.2(50 is the typical model of its size class)AESHV8T4821BAwith ducted air handler AEAMPVT48F21BA2 of 5 models have all five ratings · AHRI 217732897	82.3(50 is the typical model of its size class) (higher)ZE-648HPAwith ducted air handler AH-648A2 of 2 models have all five ratings · AHRI 215381147
Ducted, 5 tons and up	No models in this size class	81.1(50 is the typical model of its size class)ZE-660HPAwith ducted air handler AH-660A1 of 1 models have all five ratings · AHRI 215381148
Non-ducted, up to 1.5 tons	63.4(50 is the typical model of its size class)AEPLMHV23S1232B1Awith ductless indoor unit AEPLAWM23E1232B1AAlso listed as AEPL**MHV23S1231B1A5 of 8 models have all five ratings · AHRI 218451557	94.5(50 is the typical model of its size class) (higher)ZE-09UB32Owith ductless indoor unit ZE-09UB32I14 of 14 models have all five ratings · AHRI 217596868
Non-ducted, 2 tons	64.8(50 is the typical model of its size class) (higher)AEPLMHV22S2431B1Awith ductless indoor unit AEPLAWM22E2431B1A1 of 2 models have all five ratings · AHRI 218451561	61.3(50 is the typical model of its size class)ZE-24CB25Owith ductless indoor unit ZE-24CB25AI2 of 2 models have all five ratings · AHRI 218046582
Non-ducted, 2.5–3 tons	None on this board (0 of 2 models have all five ratings)	64.2(50 is the typical model of its size class)ZE-527M3252 of 2 models have all five ratings · AHRI 216684164
Non-ducted, 3.5–4.5 tons	No models in this size class	43.7(50 is the typical model of its size class)ZE-542M5251 of 1 models have all five ratings · AHRI 216684168

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	IWAE	ZEPHYR
COP at 5°F	beats 71% · 2.10AEPL**MHV22S2431B1ANon-ducted, 2 tons	beats 100% · 2.53ZE-18CB22ONon-ducted, up to 1.5 tons
Capacity retention at 5°F	beats 70% · 89%AEPL**MHV23S0932B1ANon-ducted, up to 1.5 tons	beats 94% · 75%ZE-660HPADucted, 5 tons and up
HSPF2	beats 69% · 10.0AEPL**MHV22S2431B1ANon-ducted, 2 tons	beats 96% · 10.5ZE-636HPADucted, 2.5–3 tons
SEER2	beats 82% · 19.0**AESHV9T3621BADucted, 2.5–3 tons	beats 99% · 32.0ZE-09UB32ONon-ducted, up to 1.5 tons
EER2	beats 70% · 13.0AEPLMHV23S1232B1AAlso listed as AEPLMHV23S1231B1ANon-ducted, up to 1.5 tons	beats 100% · 18.4ZE-09UB32ONon-ducted, up to 1.5 tons
Heating capacity at 5°F	beats 86% · 15,000 Btu/hAEPL**MHV22S1831B1ANon-ducted, up to 1.5 tons	beats 93% · 18,000 Btu/hZE-18CB25ONon-ducted, up to 1.5 tons

More comparisons

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IWAE vs ZEPHYR heat pumps