Save Energy — Water Heater

Being comfortable in your home includes access to hot and cold water. There are many cleaning and washing functions in your home which require hot water. Energy is needed to heat the water and store it in the water heater (the term hot water heater is redundant). Traditionally it was too energy intensive to generate the water as needed, so a storage tank was needed. Since peak hot water use occurs for short periods of time, a storage tank with a heating element can do the job. Now other reasonable cost options are being offered. On-demand (instantaneous) heaters heat the water as it is used; there is no storage of water. With all these new options you must be aware of energy use.

Your Home Energy Living Plan

  • Set temperature at lowest level, 120 degrees or less.
  • Drain water regularly.
  • Add insulation to tank and insulate hot water piping.
  • Install low flow heads on shower.
  • Take showers instead of baths.
  • Wash and rinse clothes in coldest possible temperature.
  • Use an automatic dishwasher.
  • Consider replacing old heater with more efficient water heater. Install heat traps when replacing heater.
Impact of Your Energy Saving Actions

13% of the average US home’s annual utility bill goes to heating water. This is an average; if you have an old heater that has not been maintained and you do not monitor usage, then your energy costs can be much higher. No cost energy saving actions can lower the energy for hot water and can accumulate to significant savings.

The incremental cost for a Energy Star qualified water heater may be justified.

Be careful of operating on-demand heaters for long period of time.

How Energy is Lost

It takes energy to heat water. If heated by electricity, then all of the heat from the heating element goes into the water. For natural gas (or propane) water heaters a flue must remove combustion gasses. Some of the heat is lost through the flue. The water is maintained at the hot water setting all day. Heat is lost through the tank. When the fixture using hot water is turned off, there is hot water in the piping between the heater and the fixture. All of this heat will be lost.

On-demand water heaters eliminate the heat loss from storing heat and heat loss from piping.

Water Heater Characteristics

On-demand water heaters have different operating characteristics. The short wait for hot water is enjoyed by all users. Usually you mix the hot and cold water to your desired temperature; for warm water less hot water is used. With on-demand heaters the temperature of the water varies with flow rate. Less water becomes hotter. Adjusting to the desired temperature can be difficult and confusing. A desire for a cooler temperature may result in more hot water.

There are other options for hot water. If you have a boiler for heating, then a heat exchanger can be used to generate hot water. The boiler would need to be more efficient than a water heater to save energy. Heat pumps can be used to heat water. You can have a heat pump dedicated to hot water or from a heat pump used to heat the house. This becomes a viable option as part of a geothermal system.

Energy Solutions Explained

The largest factors in energy use at the water heater are the temperature of the water and amount used. Biggest savings come from using as little as possible hot water at lowest possible temperature. Beyond this is the effectiveness of heating and maintaining hot water.

As water is heated the impurities settle out in the bottom of the heater. The burner of a gas water is under the tank. The heat must pass through the sediments to heat the water. This acts as an insulator and reduces the efficiency. For electric water heaters, the coils are higher up to be less affected by sediment. However in severe cases, the level of sediments can rise to the lower coil. For both types of heaters, build up of sediment reduces the amount of hot water and can corrode the bottom of the tank or around the drain connection. Leaking hot water will waste energy. (Since water heaters are out of sight and a drain is usually near the heater, a small leak may be ignored. Just visualize dollar bills going down the drain.)

Heat will be lost from the tank of the water heater. Tanks are insulated, but adding more insulation can be cost effective especially for older heaters. Make sure you do not cover up any controls, drain, and valves. Heat is also lost through the hot water piping; this piping is generally not insulated. Insulating the pipes may help especially if there is a long run from heater to fixture. Heat is also lost through natural convection. The hot water, being less dense, rises up into the pipes; both hot and cold sides. Cold water drops into the heater causing it to cool. The hot water in the pipes lose heat and cool; and is replaced by hot water. This cycle, while not a high flowrate, runs all the time the heater is not being used. Anything to stop this natural flow can be used. Some manufactures include a “heat trap” in the tank. You can install devices called heat traps. These are just check valves that prevent backward flows. Or you can just route the pipe down a few feet then back up to the tank connections. The more buoyant hot water cannot naturally flow downward. Since these actions involve cutting into your existing piping, it may be more practical to include these actions when a new water heater is installed. Special note: follow manufacturer’s instructions carefully or hire a plumbing contractor who will guarantee the work. Check valves can create closed systems that when heated may over pressure your piping causing leaks.

Reducing the amount of hot water used relies on the appliances and fixtures reducing their use of hot water. At plumbing fixtures like faucets and showers, low flow heads reduce the water usage including hot water. See the sections on dishwashers and laundry for ways to reduce the hot water use of these appliances.

Before 2008 water heaters where not rated by Energy Star. In 2008, water heater manufacturers were able to obtain an Energy Star qualification for some types of high efficiency models.

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