Energy efficiency ratings for hot water

The energy efficiency star rating on any new gas or electric appliance is becoming increasingly more important. The higher the rating, the less fuel the hot water system will consume to do the job it says it can do. Gas and electrical systems have separate ratings for their respective fuels. Solar hot water systems draw the majority of their power from the sun so do not need rating for this part, but any booster component will be scored by the relevant rating method.

The energy rating of a system is an indication not only of how good it is for the environment, but also of how much money you can expect to save in long term running costs.

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Energy star ratings allow you to see how efficient a particular hot water system is compared to other systems using the same type of fuel.


Energy ratings for gas hot water systems

Gas energy ratings are based on a set standard of gas use to perform a certain task over the course of a year. For gas hot water, it is 37.7 megajoules (MJ) per day of hot water delivered, which equates to 13761 MJ per year. The difference between this standard and the total energy used by the water heater (covering things from burner efficiency to heat lost through the tank insulation) gives the heater its comparative energy consumption rating. This rating is an indication of how well the hot water heater performs against the national standard.

It is quickly becoming mandatory for 5 star and above hot water systems to be installed in new homes, so if you are seeking to build, make sure the system you choose complies with your state’s requirements.



Energy ratings for electric hot water systems

Electric energy ratings are more familiar, as they appear on many other common appliances such as refrigerators and air conditioners. These ratings are called Minimum Energy Performance Standards, or MEPS. The equation used to determine the energy efficiency ratings of electric hot water systems is similar to the one for gas in that there is a set standard that all electric water heaters are measured and rated against. However, electrical systems are broken down into ranges of allowable heat loss for a given amount of hot water delivery.

Heat exchange systems (like heat pumps and geothermal systems) conform to a slightly different standard than standard electric storage systems.


Further information

For more insight and specific details into energy ratings and what they mean, visit