This document summarizes a study of the field performance of hybrid gas water heaters. The study analyzed data from 61 different water heaters in 34 homes, including various storage, tankless, and hybrid models. The results showed that hybrid water heaters can provide consistent hot water temperatures, meet the largest residential loads, and provide energy efficiency close to tankless water heaters. Hybrids also had lower installation costs than other high efficiency options. Overall, the study concluded that hybrid water heaters perform well in delivering hot water and savings, while reducing costs compared to other condensing water heating technologies.

1. Field Performance of Hybrid Gas Water Heaters
2015 ACEEE Hot Water Forum
Ben Schoenbauer
Senior Research Engineer
October 15, 2014

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Sponsors and Partners
 NorthernSTAR - A DOE Building America Research Team
 Sustainable Energy Resources for Consumers Grants
 Center for Energy and Environment
 Minnesota Division of Energy Resources

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Outline
• Water heater description
• Field study introduction
• System performance
• Efficiency
• Cost
• Savings

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Water Heater Types
• Storage
- High stand by loses
- Can “run out” of hot water
- Dead-band of water temperatures
+ Water starts hot
+ Consistent water temperature
for an event

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Water Heater Types
• Tankless
+ Energy efficient
+ No stand by loses
+ small footprint
- Delay at start up
- Cold water sandwich
- High install cost

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Water Heater Types
• Hybrid
• Energy efficiency of tankless
• Water delivery of storage
• Smaller burner to reduce cost

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Hybrid Gas Water Heaters
Brand Model Thermal Efficiency EF Input Rate Volume
Btu/hr gal
Navien NPE-240A n/a 0.97 19,000 - 199,900 0.5
Eternal GU120 96% 0.94 18,000 - 120,000 2
n/a 0.96 100,000 12
Rinnai RH180 80% n/a 59,500 - 91300 40
Pre-commercial

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Natural Gas Water Heater Field Studies
• Four projects that included detailed water heating field
data in last 5 years
• 28 natural draft storage water heaters
• 8 non-condensing tankless water heaters
• 9 condensing tankless water heaters
• 9 condensing storage water heaters
• 6 condensing hybrid water heaters
• 1 non-condensing hybrid water heaters
• 61 different water heaters in 34 different homes!

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Installation
Gas Use
Water Flow Rate
Cold Water TempHot Water Temp
Electricity

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Appliance Characterization
• Can hybrids provide consistent water temperatures?
• Can hybrids meet biggest residential loads?
• Can hybrids provide the energy efficiency desired?
• Can they do all this with lower install costs than other
high efficiency water heaters?

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Water Temperature
• Natural draft storage water heater

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Water Temperature
• Condensing storage water heater

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Water Temperature
• Condensing tankless water heater

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Water Temperature
• Condensing hybrid water heater
• ½ gallon & up to 199,000 Btu/hr

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Water Temperature
• Condensing hybrid water heater
• 2 gallon & up to 120,000 Btu/hr

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Water Temperature
• Condensing hybrid water heater
• 12 gallon & 100,000 Btu/hr

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Water Temperature
• Hybrid water heater
• 40 gallon & up to 95,000 Btu/hr

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• Winter Shower:
• 67,000 Btu/hr
• Summer Shower:
• 40,000 Btu/hr
• Units had not issues meeting load
• None of the hybrid WHs fired at over 100,000 Btu for
more than 10% of the time
Seasonality Impacts

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Efficiency
~100
gallons

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Compared to other gas products

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Annual Performance Summary
Input Rate Volume Them Eff EF
Btu/hr gal
19,000 - 199,900 0.5 0.97 0.84 0.91
18,000 - 120,000 2 96% 0.94 0.74 0.83
100,000 20 0.96 0.73 0.83
59,500 - 91300 40 80% 0.64 0.71
ND Storage 40,000 40 0.59 0.4 0.51
Tankless 19,000 - 199,000 0 0.95 0.84 0.87
Cond Stor 120,000 50 96% 0.65 0.78
Eff at 30
GPD
Eff at 60
GPD
Hybrids
$82$76$71$71$64
$52
Annual Energy Savings

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Costs
• Equipment cost similar or less than other condensing
products.
• Eliminated all gas line upgrade costs
• ~$500-$800 average reduction in incremental cost compared
to tankless
• Still had incremental costs of venting
• 80% efficient had no incremental cost for installation
• ~$1000 reduction over other models

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Conclusions
• Hybrid units are able to meet loads
• Hybrid WHs provide consistent and quicker hot water
• Hybrid WHs are more energy efficient than standard,
with some units showing the highest gas WH
efficiencies
• Retrofit designs reduce install costs
• Economics are improving, but paybacks still long

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