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.

DIRECT AIR 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, DIRECT AIR scores higher on 6 of the 6 ratings.

DIRECT AIR
ZERO
Other ranked manufacturers

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

Average peer percentile, raw median and rank among ranked manufacturers
Rating	DIRECT AIR	ZERO
Efficiency index	67% (higher)median —	53% (higher)median —
COP at 5°F	62% (higher)median 2.00	45% (higher)median 1.94
Capacity retention at 5°F	64% (higher)median 83%	52% (higher)median 74%
HSPF2	76% (higher)median 10.3	57% (higher)median 9.5
SEER2	71% (higher)median 20.5	58% (higher)median 19.0
EER2	62% (higher)median 12.0	48% (higher)median 11.7
Heating capacity at 5°F	66% (higher)median 26,000 Btu/h	55% (higher)median 18,750 Btu/h
Outdoor models	47	119
AHRI certifications	198	164

Share of models meeting each standard

Percent of each manufacturer’s models with a qualifying certification
Standard	DIRECT AIR	ZERO
CEE 2025 Tier 1 (Split ASHP)	93.6%44 models	70.6%84 models
CEE 2026 Tier 1 (Split ASHP)	93.6%44 models	69.7%83 models
CEE Advanced Tier (Split ASHP)	2.1%1 models	0%0 models
Xcel Energy Colorado cold-climate ASHP (2025)	85.1%40 models	64.7%77 models
DOE Cold Climate Heat Pump Challenge	2.1%1 models	0%0 models
ENERGY STAR Cold Climate	87.2%41 models	52.9%63 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 · 10 groups where both have models

DIRECT AIR
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	DIRECT AIR	ZERO
Ducted, up to 1.5 tons	12 · index 73%	7 · index 68%
Ducted, 2 tons	6 · index 63%	13 · index 51%
Ducted, 2.5–3 tons	13 · index 69%	20 · index 54%
Ducted, 3.5–4.5 tons	11 · index 65%	26 · index 54%
Ducted, 5 tons and up	1 · index 63%	2 · index 64%
Non-ducted, up to 1.5 tons	11 · index 75%	39 · index 53%
Non-ducted, 2 tons	2 · index 82%	9 · index 50%
Non-ducted, 2.5–3 tons	13 · index 61%	13 · index 45%
Non-ducted, 3.5–4.5 tons	8 · index 55%	6 · index 52%
Non-ducted, 5 tons and up	1 · index 59%	2 · index 27%

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	DIRECT AIRCold-climate score, best model	ZEROCold-climate score, best model
Ducted, up to 1.5 tons	82.3(50 is the typical model of its size class) (higher)DIRM4-18HXPRO28-1Zwith ducted air handler DIRM4-18HP-DU11 of 12 models qualify · AHRI 217447834	72.6(50 is the typical model of its size class)Z4SOV-18HDMB-USAlso listed as Z3SOV-18HDMB-US5 of 7 models qualify · AHRI 217138401
Ducted, 2 tons	85.7(50 is the typical model of its size class) (higher)DIRM4-24HXPRO28-1Zwith ducted air handler DIRM4-24HP-DU6 of 6 models qualify · AHRI 216788527	70.4(50 is the typical model of its size class)ZRRV07HPBYFC-18SAlso listed as ZPRVO7HPBYFC-18S, ZPRV07HPBYFC-18S11 of 13 models qualify · AHRI 217904930
Ducted, 2.5–3 tons	83.2(50 is the typical model of its size class) (higher)DIRM4-36LCHX-1Zwith ducted air handler DIRM4-36HP-DU11 of 13 models qualify · AHRI 216788531	82.5(50 is the typical model of its size class)Z4SOV-36HDMB-USHH13 of 20 models qualify · AHRI 217752806
Ducted, 3.5–4.5 tons	82.7(50 is the typical model of its size class)DIRM4-48HXPRO28-5ZAlso listed as DIRM4-48HXPRO28-6Z11 of 11 models qualify · AHRI 215213809	82.7(50 is the typical model of its size class)Z4SOV-48HDMB-USHH19 of 26 models qualify · AHRI 217752809
Ducted, 5 tons and up	None on this board (0 of 1 models qualify)	None on this board (0 of 2 models qualify)
Non-ducted, up to 1.5 tons	96.7(50 is the typical model of its size class) (higher)DIRM4-06HXPRO28-1Zwith ductless indoor unit DIRM4-06HP-WM11 of 11 models qualify · AHRI 216571371	85.9(50 is the typical model of its size class)ZMSB-09HV-USHHR2-Owith ductless indoor unit ZMSB-09HV-USHHR2-I31 of 39 models qualify · AHRI 216097679
Non-ducted, 2 tons	89.4(50 is the typical model of its size class) (higher)DIRM4-24HXPRO28-1Zwith ductless indoor unit DIRM4-24HP-CA2 of 2 models qualify · AHRI 216788526	77.2(50 is the typical model of its size class)ZMSB-24HV-USHHCR2-Owith ductless indoor unit ZMSB-24HV-USHHCR2-I7 of 9 models qualify · AHRI 216097676
Non-ducted, 2.5–3 tons	89.4(50 is the typical model of its size class) (higher)DIRM4-36LCHX-1Zwith ductless indoor unit DIRM4-36HP-CF11 of 13 models qualify · AHRI 216571385	72.6(50 is the typical model of its size class)Z4SOV-36HDMB-USHH9 of 13 models qualify · AHRI 217752807
Non-ducted, 3.5–4.5 tons	73.4(50 is the typical model of its size class) (higher)DIRM4-48HXPRO28-5ZAlso listed as DIRM4-48HXPRO28-6Z7 of 8 models qualify · AHRI 215213810	69.9(50 is the typical model of its size class)Z4SOV-53HDMB-USHH6 of 6 models qualify · AHRI 217752813
Non-ducted, 5 tons and up	None on this board (0 of 1 models qualify)	None on this board (0 of 2 models qualify)

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	DIRECT AIRAll-around score, best model	ZEROAll-around score, best model
Ducted, up to 1.5 tons	86.5(50 is the typical model of its size class) (higher)DIRM4-09HXPRO28-1Zwith ducted air handler DIRM4-09HP-DU12 of 12 models have all five ratings · AHRI 217447830	77.4(50 is the typical model of its size class)Z4SOV-18HDMB-USHH6 of 7 models have all five ratings · AHRI 217752800
Ducted, 2 tons	78.8(50 is the typical model of its size class)DIRM4-24DA25-1Zwith ducted air handler DIRM4-24HP-DU6 of 6 models have all five ratings · AHRI 216788529	79.6(50 is the typical model of its size class) (higher)ZOV-24HDGBwith ducted air handler ZAV-24HDGB12 of 13 models have all five ratings · AHRI 217619841
Ducted, 2.5–3 tons	83.6(50 is the typical model of its size class)DIRM4-36HXPRO28-4ZAlso listed as DIRM4-36HXPRO28-5Z13 of 13 models have all five ratings · AHRI 215213806	83.6(50 is the typical model of its size class)Z4SOV-36HDMB-USHH18 of 20 models have all five ratings · AHRI 217752806
Ducted, 3.5–4.5 tons	85.1(50 is the typical model of its size class)DIRM4-48DA25-5ZAlso listed as DIRM4-48DA25-6Z11 of 11 models have all five ratings · AHRI 215213797	85.1(50 is the typical model of its size class)Z4SOV-48HDMB-USAlso listed as Z6SOV-48HDMB-US23 of 26 models have all five ratings · AHRI 217138410
Ducted, 5 tons and up	62.5(50 is the typical model of its size class)DIRM4-60DA25-6Z1 of 1 models have all five ratings · AHRI 218331780	64.7(50 is the typical model of its size class) (higher)Z4SOV-60HDMB-US2 of 2 models have all five ratings · AHRI 217138413
Non-ducted, up to 1.5 tons	96.2(50 is the typical model of its size class) (higher)DIRM4-06HXPRO28-1Zwith ductless indoor unit DIRM4-06HP-WM11 of 11 models have all five ratings · AHRI 216571371	86.7(50 is the typical model of its size class)ZMSB-09HV-USHHR2-Owith ductless indoor unit ZMSB-09HV-USHHR2-I39 of 39 models have all five ratings · AHRI 216097679
Non-ducted, 2 tons	86.8(50 is the typical model of its size class) (higher)DIRM4-24DA25-1Zwith ductless indoor unit DIRM4-24HP-WM2 of 2 models have all five ratings · AHRI 216571370	74.3(50 is the typical model of its size class)ZMSB-24HV-USHHR2-Owith ductless indoor unit ZMSB-24HV-USHHR2-I9 of 9 models have all five ratings · AHRI 216097682
Non-ducted, 2.5–3 tons	78.3(50 is the typical model of its size class) (higher)DIRM4-36HXPRO28-4ZAlso listed as DIRM4-36HXPRO28-5Z13 of 13 models have all five ratings · AHRI 215213805	66.3(50 is the typical model of its size class)Z4SOV-36HDMB-USHH13 of 13 models have all five ratings · AHRI 217752805
Non-ducted, 3.5–4.5 tons	75.6(50 is the typical model of its size class) (higher)DIRM4-48HXPRO28-5ZAlso listed as DIRM4-48HXPRO28-6Z8 of 8 models have all five ratings · AHRI 215213808	62.6(50 is the typical model of its size class)Z4SOV-53HDMB-USHH6 of 6 models have all five ratings · AHRI 217752811
Non-ducted, 5 tons and up	58.6(50 is the typical model of its size class) (higher)DIRM4-60DA25-6Z1 of 1 models have all five ratings · AHRI 218331779	32.5(50 is the typical model of its size class)Z4SOV-60HDMB-USAlso listed as Z6SOV-60HDMB-US2 of 2 models have all five ratings · AHRI 217138412

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	DIRECT AIR	ZERO
COP at 5°F	beats 99% · 2.51DIRM4-12DA25-1ZNon-ducted, up to 1.5 tons	beats 98% · 2.80ZOU-42HDCA-S14Ducted, 3.5–4.5 tons
Capacity retention at 5°F	beats 98% · 126%DIRM4-09HXPRO28-1ZNon-ducted, up to 1.5 tons	beats 97% · 103%ZRRV07HPBYFC-18SAlso listed as ZPRVO7HPBYFC-18S, ZPRV07HPBYFC-18SDucted, 2 tons
HSPF2	beats 99% · 14.8DIRM4-06HXPRO28-1ZNon-ducted, up to 1.5 tons	beats 99% · 11.0Z4SOV-48HDMB-USHHDucted, 3.5–4.5 tons
SEER2	beats 97% · 25.0DIRM4-27DA25-3Z*Also listed as DIRM4-27DA25-4ZNon-ducted, 2.5–3 tons	beats 99% · 22.0Z3SOV-27HDTB-USDucted, 2.5–3 tons
EER2	beats 99% · 18.0DIRM4-06HXPRO28-1ZNon-ducted, up to 1.5 tons	beats 93% · 13.3ZOV-24HDGBDucted, 2 tons
Heating capacity at 5°F	beats 98% · 39,500 Btu/hDIRM4-36LCHX-1ZNon-ducted, 2.5–3 tons	beats 97% · 39,000 Btu/hZSOVA-36HDMB-USHHDucted, 2.5–3 tons

More comparisons

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DIRECT AIR vs ZERO heat pumps