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WILLIS heat pump efficiency: 15 outdoor models compared

WILLIS has 15 heat pump outdoor models certified with this refrigerant group, in 29 AHRI-certified combinations. Each model is compared with models of the same size and duct type, so the scores below do not depend on which sizes WILLIS makes. WILLIS has no QMID (IRS Qualified Manufacturer ID) on file, so it is not ranked against other manufacturers.

New to heat pump ratings? The Simple view explains them in plain words →

ManufacturerData as of updated · sources

Outdoor models
15
AHRI certifications
29
Efficiency index
51%
Typical model vs same-size, same-type peers (20 models)
Meet CEE 2025
86.7%
13 models

How WILLIS compares with comparable models

For each rating: the share of same-size, same-type models that a typical model of this manufacturer beats (50% is typical), its rank, and the raw median for context. Raw medians are not comparable across manufacturers that make different sizes.
WILLIS against every ranked manufacturerPeer scores, 0–100 · grey ticks: each ranked manufacturer · shaded: the middle half of WILLIS’s own modelsWILLIS is strongest on heating capacity at 5°F (its typical model beats 68% of comparable models) and weakest on COP at 5°F (39%).
  • WILLIS
  • Middle half of its models
  • Other ranked manufacturers
WILLIS

Source: AHRI Directory, NEEP · as of

Average peer percentile of WILLIS’s models
RatingBeats comparable modelsRankRaw median
Efficiency index20 models scored51%Not ranked—
COP at 5°F20 models scored39%Not ranked1.84
Capacity retention at 5°F20 models scored64%Not ranked76%
HSPF220 models scored52%Not ranked9.0
SEER220 models scored55%Not ranked21.0
EER220 models scored46%Not ranked12.0
Heating capacity at 5°F20 models scored68%Not ranked13,600 Btu/h

Standards met

Share of WILLIS’s models with at least one qualifying certification
StandardShareModels
CEE 2025 Tier 1 (Split ASHP)86.7%13
CEE 2026 Tier 1 (Split ASHP)80%12
CEE Advanced Tier (Split ASHP)0%0
Xcel Energy Colorado cold-climate ASHP (2025)86.7%13
DOE Cold Climate Heat Pump Challenge0%0
ENERGY STAR Cold Climate73.3%11

Sizes and duct types offered

Models per peer group, and how they score against the other models of that group.
WILLIS’s models inside each size and duct typeShape: every model of the group · blue: the middle half of this manufacturer’s models there, median dot, 10th–90th percentile line
  • WILLIS (median, middle 50%, 10th–90th)
  • All models of the group
Ducted, up to 1.5 tons2.00884 modelsDucted, 2 tons2.00821 modelsDucted, 2.5–3 tons1.901,614 modelsDucted, 3.5–4.5 tons1.911,492 modelsNon-ducted, up to 1.5 tons1.902,417 modelsNon-ducted, 2 tons1.87611 modelsNon-ducted, 2.5–3 tons1.85975 modelsmedian

Source: AHRI Directory · as of

Share of comparable models beaten, per peer group
Size and duct typeModelsIndexCOP@5°FHSPF2SEER2
Ducted, up to 1.5 tons132%25%29%33%
Ducted, 2 tons146%24%45%47%
Ducted, 2.5–3 tons451%32%52%56%
Ducted, 3.5–4.5 tons255%25%67%74%
Non-ducted, up to 1.5 tons844%42%39%47%
Non-ducted, 2 tons172%76%74%69%
Non-ducted, 2.5–3 tons368%49%82%65%

Every WILLIS model in the market

WILLIS’s 20 models with a known size and duct type, over the shape of the whole catalog.
WILLIS models by size and ratingColoured: WILLIS · grey shapes: all 11,475 models · lines: catalog medians by size
  • WILLIS models
  • Ducted median by size
  • Non-ducted median by size
  • Every model at each size (width = count)
  • Standard threshold

Dots: 20 willis models, each through its representative certification, in the colour of the rating shown. The grey shapes count all 11,475 models, half a ton at a time.
Show the data as a table
COP at 5°F by size and duct type (every model, by rated cooling capacity)
Duct type, sizeModels10th pct.25thMedian75th90th
Ducted, 0.5 tons1751.701.851.902.102.26
Ducted, 1 ton3401.851.902.002.402.65
Ducted, 1.5 tons7891.751.852.002.202.55
Ducted, 2 tons7821.731.802.002.102.33
Ducted, 2.5 tons7351.711.801.902.092.48
Ducted, 3 tons6521.681.701.902.062.36
Ducted, 3.5 tons6411.611.801.952.202.50
Ducted, 4 tons3671.701.801.912.022.52
Ducted, 4.5 tons5441.701.801.912.082.34
Ducted, 5 tons251.801.801.901.902.15
Non-ducted, 0.5 tons7171.751.811.972.102.19
Non-ducted, 1 ton1,0641.751.801.902.072.25
Non-ducted, 1.5 tons8861.801.801.872.072.21
Non-ducted, 2 tons5641.801.801.832.042.21
Non-ducted, 2.5 tons2751.801.811.841.862.03
Non-ducted, 3 tons5021.801.801.902.002.09
Non-ducted, 3.5 tons701.821.831.902.002.28
Non-ducted, 4 tons2631.801.801.982.002.10
Non-ducted, 4.5 tons1031.771.771.801.972.02
Non-ducted, 5 tons291.982.002.102.302.47

Source: AHRI Directory · as of

Top WILLIS models

Its top five cold-climate picks and its top five all-around models across sizes (both scores compare each model with models of its own size and duct type, so sizes compare), then, on each single rating, the model that beats the largest share of comparable models.

Cold-climate picks

Top 5 WILLIS cold-climate picks across sizes. 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.
# · Outdoor modelSize · typeCap. 5/47COP@5°FHSPF2Btu/h @5°FSEER2MeetsCombosAHRI ref.Compared withScore
1MZUHW24KCH21S2-OWILLIS · MultiHeat2 tons23,200 Btu/h · Non-ducted90%2.1010.021,60021.0CEE 25CEE 26XcelES CC3214810332Non-ducted, 2 tons76.1
2MZUHW42KCH21S2-OWILLIS · MultiHeat3 tons36,000 Btu/h · Non-ducted81%1.9210.032,40021.0CEE 25CEE 26XcelES CC3214810330Non-ducted, 2.5–3 tons73.7
3MZUHW18KCH21S2-OWILLIS · MultiHeat1.5 tons17,000 Btu/h · Non-ducted76%2.2310.013,60021.0CEE 25CEE 26XcelES CC3214810331Non-ducted, up to 1.5 tons73.5
4MZUHW36KCH21S2-OWILLIS · MultiHeat3 tons34,000 Btu/h · Non-ducted90%1.8210.032,40021.0CEE 25CEE 26XcelES CC3214810329Non-ducted, 2.5–3 tons63.8
5MZUHW30KCH21S2-OWILLIS · MultiHeat2.5 tons28,400 Btu/h · Non-ducted76%1.8410.022,80021.0CEE 25CEE 26XcelES CC3214810333Non-ducted, 2.5–3 tons63.4

All-around best

Top 5 WILLIS models on the all-around score across sizes. 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.
# · Outdoor modelSize · typeCap. 5/47COP@5°FHSPF2SEER2EER2MeetsCombosAHRI ref.Compared withScoreHeating halfCooling halfCold-climate score
1MZUHW24KCH21S2-OWILLIS · MultiHeat2 tons23,200 Btu/h · Non-ducted90%2.1010.021.012.5CEE 25CEE 26XcelES CC3214810332Non-ducted, 2 tons71.576.166.876.1
2MZUHW42KCH21S2-OWILLIS · MultiHeat3 tons36,000 Btu/h · Non-ducted81%1.9210.021.012.0CEE 25CEE 26XcelES CC3214810330Non-ducted, 2.5–3 tons70.273.766.773.7
3MZUHW30KCH21S2-OWILLIS · MultiHeat2.5 tons28,400 Btu/h · Non-ducted76%1.8410.021.012.5CEE 25CEE 26XcelES CC3214810333Non-ducted, 2.5–3 tons69.263.475.063.4
4MZUHW36KCH21S2-OWILLIS · MultiHeat3 tons34,000 Btu/h · Non-ducted90%1.8210.021.012.0CEE 25CEE 26XcelES CC3214810329Non-ducted, 2.5–3 tons65.363.866.763.8
5HW12KUHR410A-OWilliswith ductless indoor unit HW12KUHR410A-I1 ton12,000 Btu/h · Non-ducted70%2.059.523.512.7CEE 25CEE 26Xcel1216772615Non-ducted, up to 1.5 tons63.855.871.755.8

Best model on each rating

WILLIS’s model with the highest peer percentile on each rating, ranked by that one rating only
RatingModelValueCompared withBeatsAHRI ref.
COP at 5°FMZUHW18KCH21S2-O2.23Non-ducted, up to 1.5 tons90%214810331
Capacity retention at 5°FMZUHW30KCH21S2-O89%Ducted, 2.5–3 tons85%214810336
HSPF2MZUHW36KCH21S2-O10.0Non-ducted, 2.5–3 tons82%214810329
SEER2PUHW12KCH24S2-O24.0Non-ducted, up to 1.5 tons83%214609738
EER2MZUHW30KCH21S2-O12.5Non-ducted, 2.5–3 tons84%214810333
Heating capacity at 5°FMZUHW18KCH21S2-O13,800 Btu/hNon-ducted, up to 1.5 tons84%214810339

All 15 WILLIS models in Explore

WILLIS size class by size class: cold-climate and all-around

Its best model on each board in every size and duct type it makes. Both scores are 0–100 against every model of that size class (the line on each bar is 50, the typical model there). Cold-climate picks must keep at least 70% of their heat at 5°F; the all-around score needs all five ratings and has no such bar.
WILLIS: best cold-climate pick and best all-around model per size and duct type, with how many of its models are on each board (top 5 and 5 per class are in the snapshot)
Size and duct typeCold-climate pickCold-climate score, best modelAll-around bestAll-around score, best model
Ducted, up to 1.5 tons36.0(50 is the typical model of its size class)MZUHW18KCH21S2-O1 of 1 models qualify · AHRI 21481033431.5(50 is the typical model of its size class)MZUHW18KCH21S2-O1 of 1 models have all five ratings · AHRI 214810334
Ducted, 2 tons50.1(50 is the typical model of its size class)MZUHW24KCH21S2-O1 of 1 models qualify · AHRI 21481033545.9(50 is the typical model of its size class)MZUHW24KCH21S2-O1 of 1 models have all five ratings · AHRI 214810335
Ducted, 2.5–3 tons55.3(50 is the typical model of its size class)FLEX24/36KUHwith ducted air handler FLEXAH24/36K4 of 4 models qualify · AHRI 21413776553.1(50 is the typical model of its size class)MZUHW30KCH21S2-O4 of 4 models have all five ratings · AHRI 214810336
Ducted, 3.5–4.5 tons56.7(50 is the typical model of its size class)FLEX48/60KUHwith ducted air handler FLEXAH48/60K2 of 2 models qualify · AHRI 21479768657.4(50 is the typical model of its size class)PRT60KUH2 of 2 models have all five ratings · AHRI 214137764
Non-ducted, up to 1.5 tons73.5(50 is the typical model of its size class)MZUHW18KCH21S2-O7 of 8 models qualify · AHRI 21481033163.8(50 is the typical model of its size class)HW12KUHR410A-Owith ductless indoor unit HW12KUHR410A-I8 of 8 models have all five ratings · AHRI 216772615
Non-ducted, 2 tons76.1(50 is the typical model of its size class)MZUHW24KCH21S2-O1 of 1 models qualify · AHRI 21481033271.5(50 is the typical model of its size class)MZUHW24KCH21S2-O1 of 1 models have all five ratings · AHRI 214810332
Non-ducted, 2.5–3 tons73.7(50 is the typical model of its size class)MZUHW42KCH21S2-O3 of 3 models qualify · AHRI 21481033070.2(50 is the typical model of its size class)MZUHW42KCH21S2-O3 of 3 models have all five ratings · AHRI 214810330

All-around board, every manufacturer

Newest WILLIS certifications

By AHRI reference number; AHRI issues references in increasing order.
The 5 most recently certified WILLIS outdoor models
Outdoor modelSize · typeCOP@5°FCap. 5/47HSPF2SEER2MeetsCombosAHRI ref.
HW18KUHR410A-OWilliswith ductless indoor unit HW18KUHR410A-I1.5 tons18,000 Btu/h · Non-ducted1.8074%9.520.5CEE 25CEE 26Xcel1216772616
HW12KUHR410A-OWilliswith ductless indoor unit HW12KUHR410A-I1 ton12,000 Btu/h · Non-ducted2.0570%9.523.5CEE 25CEE 26Xcel1216772615
MZUHW42KCH21S2-OWILLIS3 tons36,000 Btu/h · Ducted and non-ducted and mixed (multi-zone)1.8081%9.018.5CEE 25CEE 26XcelES CC3214810343
MZUHW36KCH21S2-OWILLIS3 tons34,000 Btu/h · Ducted and non-ducted and mixed (multi-zone)1.8083%9.018.5CEE 25CEE 26XcelES CC3214810342
MZUHW30KCH21S2-OWILLIS2.5 tons28,400 Btu/h · Ducted and non-ducted and mixed (multi-zone)1.8083%9.018.5CEE 25CEE 26XcelES CC3214810341

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WILLIS includes these brand names as listed in AHRI: WILLIS. Standards are checked against published thresholds; program rules beyond ratings are not checked.