Water Heaters

Product Definition/Scope of Product Category – TopTen USA lists two configurations of residential water heaters: storage and tankless. Storage water heaters feature a storage tank and heating mechanism such as a gas-fired burner or heat pump. Water is kept warm and drawn from the top of the tank when there is demand. Tank sizes typically range from 20-80 gallons or more. Tankless water heaters do not have storage tanks; instead they use a large gas burner or electric element to heat water only when there is demand.

Market Segmentation – We include four categories of water heater: electric storage, gas storage, medium capacity gas tankless (maximum input of 160 MMBtu), and large capacity gas tankless (160>200 MMBtu).

Performance Criteria - In developing the list of products that are eligible for Top Ten USA we evaluated products based on the following criteria:

Gas Storage: Estimated annual energy use (therms/year) – Average annual energy use is estimated based on a unit’s thermal efficiency rating, which is calculated through American National Standards Institute (ANSI) test method “Z21.10.3–1998,” which includes draws and a standby period. This test procedure is codified in 10 CFR 431, Subpart G. From a unit’s energy factor we calculate approximate average annual energy use with the following formula: (41,045 BTU/TE x 365)/100,000, where 41,045 is the average Btu of hot water energy drawn per day. This formula is the same as that which EnergyStar uses to estimate annual energy use for residential gas water heaters.

Gas Tankless: Estimated annual energy use (therms/year) – Average annual energy use is estimated based on a unit’s energy factor rating, which is calculated through a twenty-four hour test procedure using six equal draws totaling 64.3 gallons and a standby period. From a unit’s energy factor we calculate approximate average annual energy use with the following formula: (41,045 BTU/EF x 365)/100,000, where 41,045 is the average Btu of hot water energy drawn per day. This formula is the same as that which EnergyStar uses to estimate annual energy use for residential gas water heaters.

Electric Storage: Estimated annual energy use (kWh/yr) – Average annual electricity use is estimated based on a unit’s energy factor rating, which is calculated through a twenty-four hour test procedure using six equal draws totaling 64.3 gallons and a standby period. From a unit’s energy factor we calculate approximate average annual energy use with the following forumula: (12.03/EF) x 365, where 12.03 is the kWh conversion for 41,045 Btu of hot water energy drawn per day. This formula is the same as that which EnergyStar uses to estimate annual energy use for residential electric water heaters.

Test Methods – For gas tankless and electric storage water heaters we use manufacturer reported test data according to the following test method:

10 CFR 430, Subpart B, Appendix E, Uniform Test Method for the Measuring Energy Consumption of Water Heaters, as amended in 63 Federal Register 25996.

For gas storage water heaters we use manufacturer test data according to the following test method:

10 CFR 431, Subpart G, Commercial Water Heaters, Hot Water Supply Boilers and Unfired Hot Water Storage Tanks Test Procedures 

Data Sources and Quality Assurance - We use manufacturer reported data from the EPA ENERGY STAR Web site and certified data from the AHRI Web site.

Market Availability - In order to be qualified the model must be currently available to consumers through plumbers, contractors, retail outlets such as department stores, big box stores, independent appliance retailers, and/or on-line retailers.

Families of Similar Products – For instances in which multiple models produced by the same manufacturer (under one or more brand names) were substantially the same, we listed these products as a “tie” for one place on the list.  These instances could include models with different features or amenities (e.g., color) that do not impact energy consumption or models produced by one manufacturer for sale under multiple brand names through distinct divisions of a parent company or under contract to other firms.

Product Ranking – Presently, there are less than 10 models available in three of our product categories (electric storage, gas storage, and medium capacity gas tankless. For these three product categories we selected a maximum energy usage limit that corresponds with significant savings above the rest of the product field for each product category. Energy usage estimations were based on the previously mentioned calculations. All gas water heaters are condensing units and all electric water heaters use heat pumps. For large capacity gas tankless units, we selected the top ten products with the lowest average annual energy consumption.

Gas Storage:  Units with a storage tank of 34-80 gallons, maximum input of 100 MMBtu, and average annual energy consumption of 166.5 therms or less.

Medium capacity gas tankless: Units with an average annual energy consumption of 165 therms or less.

Large capacity gas tankless: Units with an average annual energy consumption of 163 therms or less.

Electric storage: Units with storage tank of 40-100 gallons and average annual energy consumption of 2,195 kWh or less.

Glossary

  • Average annual energy use - The average amount of energy (expressed in site electricity (kWh) or natural gas therms) that a typical American household uses for a water heater is based on the rated efficiency (energy factor or thermal efficiency). This includes specific assumptions on use patterns by the household, inlet water temperature, and even relative humidity (for heat pump water heaters). It is not expected that real households will match these conditions, but they allow decent relative comparisons among products.
  • Energy factor (EF) - EF designates the amount of hot water a residential-rated water heater can produce for each unit of site energy it consumes, and is intended to predict a water heater’s annual energy use. A higher energy factor indicates greater energy efficiency. This measurement takes into account a water heater’s recovery efficiency, standby losses, and cycling losses.
  • Thermal Efficiency (TE) - TE is a measurement that indicates how efficiently a commercially-rated unit converts input energy into hot water. Federal test procedures stipulate that commercial water heaters must be able to maintain thermal efficiencies “greater than or equal to 98% of the certified rating” during testing. Standby loss is a measurement of how much heat energy is lost from the water while the unit is in standby mode, or while it is not actively heater water. Like thermal efficiency, standby losses during testing must be “less than or equal to 110% of the certified rating.”
  • Gas Storage Water Heater - A tank-type water heater with a nominal input of 75,000 Btu/hr or less and a rated storage volume from 20 to 100 gallons.
  • Electric Storage Water Heater - A tank-type water heater with a Nominal input of 12 kW (40,956 Btu/hr) or less and a rated storage volume from 20 to 120 gallons.
  • Heat Pump Storage Water Heater - An electric storage water heater with a maximum current rating of 24 amperes, voltage no greater than 250 volts, and a transfer of thermal energy from one temperature to a higher temperature level for the purpose of heating water.
  • Gas Tankless Water Heater - A tankelss water heater with a nominal input of over 50,000 Btu/hr up to 200,000 Btu/hr and a rated storage volume of 2 gallons or less
  • Input - The maximum capacity of a gas-fired burner, usually stated in MMBtu.
  • First Hour Rating - The amount of hot water, in gallons, that a water heater can provide in one hour. For a storage water heater, the first hour rating is calculated with the tank starting out fully heated.
  • Standby Loss - The ratio of the amount of heat lost from the stored water per hour to the heat content of the stored water, expressed as a percentage (applicable to water heaters with storage tanks).
  • Condensing Gas Water Heater - Gas-fired water heater that extracts enough heat from the flue gas that the water vapor in the flue gas cools and condenses.
  • Heat Pump Water Heater - Electric water heater that moves heat from ambient air into water rather than producing heat directly through a traditional electric element.

 Further Information -

  • Federal Standards –

http://www1.eere.energy.gov/buildings/appliance_standards/residential/heating_products_fr.html
 http://www1.eere.energy.gov/buildings/appliance_standards/commercial/ashrae_products_docs_meeting.html

http://www.ashrae.org/technology/page/548

  • Energy Star –

http://www.energystar.gov/index.cfm?fuseaction=find_a_product.showProductGroup&pgw_code=WHC
 http://www.energystar.gov/index.cfm?fuseaction=find_a_product.showProductGroup&pgw_code=WH
 http://www.energystar.gov/index.cfm?fuseaction=find_a_product.showProductGroup&pgw_code=WHH