What is the Best Water Heater for Efficiency?

heat pump water heaterHeating water in the average home accounts for up to 15% of a home’s energy use. So what is the best water heater for efficiency?  Should you purchase a conventional water heater with a low up front cost or go to a more efficient unit?

Demand (tankless) water heaters circulate water through a large coil that is heated using gas or electricity. There is no storage tank continuously heating water. There is an endless supply of hot water, but there can be limitations on the number of fixtures that can be used at one time.

Heat Pump Water Heaters transfer energy from the surrounding air to the water in the storage tank. They are most effective in warm climates with long cooling seasons. They will cool a room by 1-2 degrees and dehumidify the space.

Solar Water Heating takes heat from the sun to heat water. Solar systems require a conventional water heater as a backup to ensure heated water at night.

water heaterSo which is the right option for efficiency? The 13 year cost of a minimum efficiency electric storage water heater is $6,800. Most of the costs are in utilities for this option which can be offset with solar PV.

A on-demand gas unit costs more up front, but the 13 year cost is $5,000 with all of the savings being in energy use.

A solar water system with electric backup eliminates most of the electric costs, but the 13 year cost is $7,000 due to high initial costs.

So based on my research the electric heat pump water heater with a 13 year cost of $4,000 is the winner. This is a $2,800 savings over 13 years and the low energy costs can be offset with solar pv.


Green Term Defined: High Efficiency Water Heater

High efficiency water heating can save you a considerable amount of energy each day. There are several systems used to efficiently heat water for usage inside a building. The most common is either an on-demand water heater or a heat pump water heater. Here are several options to consider, with any also insulating supply piping will increase your overall efficiency.

indirect water heater

Water heater that draws heat from a boiler used for space heating; a separate zone from the boiler heats potable water in a separate, insulated tank via a water-to-water heat exchanger.


heat-pump water heater

An fixture that uses an air-source heat pump to heat water. Most heat-pump water heaters include an insulated tank equipped with an electric resistance element to provide backup heat whenever hot water demand exceeds the capacity of the heat pump. Since heat-pump water heaters extract heat from the air, they lower the temperature and humidity of the room in which they are installed.


on-demand water

System used to  deliver hot water either at point of use or in a traditional one fixture supplied whole house system. The advantage is water is only heated on demand instead of through the day as with a traditional tank water heater.


Solar Thermal Water Heating

System comprised of a storage tank and solar collector on the roof. Solar collectors absorb heat and transfer it into the water either directly or through the use of a heat transport fluid. They can be flat plate collectors, evacuated tubes, or dark storage tanks.

A continuing series to help understand green building terms by Harrisonburg Architect. More terms defined here: http://harrisonburgarchitect.wordpress.com/?s=green+term+defined

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