Energy Efficient Hot Water



Hot water is usually one of the biggest energy users in homes, typically about 30%. To save energy, it’s worth targeting hot water systems. Hot water systems must be installed by a licensed plumber, in accordance with relevant plumbing regulations and Australian standards.

The hot water system may be a condition of planning and building approval, so check compliance with the approved plans.

The first priority is to use hot water efficiently.

Shower heads should have a 3 star rating and taps at least 5 star.

To minimise pipe lengths, hot water outlets and the water heater should be grouped as close together as possible. This reduces heat losses and water wastage. If the heater can’t be close to a frequently used outlet, consider installing a demand-controlled water return device. These return the cold water in the pipe back to the water heater until the water at the outlet is hot. They are easy to install and can be fitted to most existing systems.

If the water is at 60 degrees and the air temperature is 15, each meter of copper pipe loses as much energy as it takes to run a 40-watt bulb. So, insulate all hot water pipes, including plastic ones. At least 10 millimeters of closed cell foam insulation is needed.

This can be sold and fitted over pipes before installation or split and installed afterwards. But remember to leave enough clearance between the pipe and the wall for it to fit. Also, insulate tank fittings and the cold inlet pipe within one meter of the tank. If a tempering valve is installed, locate it close to the heater to reduce pipe heat loss.

Hot water storage systems can waste a lot of energy due to heat loss from the tank.

This can be 20-50% of the total energy use. To reduce this, place the tank in a sheltered location, out of the rain and wind. Set the thermostat to 60. They are often set much higher at the factory, which wastes energy. If there are no numbers on the thermostat, use a thermometer to make sure water from the nearest untempered outlet is 60 degrees.

Storage systems can use electricity, gas, the sun or a heat pump as an energy source. Electric storage systems are being phased out due to their high greenhouse gas emissions. Gas storage systems can either use natural gas or LPG. LPG is more expensive and really only suitable for smaller homes with high efficiency heaters.

Heat pumps can be all-in-one or split systems. Split systems allow the tank to be located indoors to reduce heat losses and be closer to the points of use. Leave adequate airflow around the condenser to insure best performance.

The warmer the heat source, the more efficient they are. So, locate the condenser on the warmer side of the house, usually the north or west. Operate them on continuous or extended off peak tariff, that way they can use warmer daytime air as the heat source. Like an air conditioner, they make some noise, so locate them at least 1.5 meters away from bedroom windows, including the neighbors.

Instantaneous systems heat the water when a hot tap is turned on so no heat energy is wasted from a tank.

However, there is a delay of 5 to 10 seconds while the water gets hot, meaning one to two liters of water is typically wasted. A demand-controlled water return device can reduce this. Instantaneous units can use either electricity or gas as the heat source. Gas is the most common and preferred. It has much lower greenhouse emissions and running costs. Choose one with the highest number of stars. Some instantaneous units are not compatible with water efficient shower heads as the flow rate is too low for correct operation. Check with the manufacturer or supplier. Don’t install gas units with wasteful pilot flames. Use electronic ignition models.

So, to get the best out of a hot water system, reduce the water use with efficient fixtures and appliances. Locate the system close to points of use and insulate the pipes. Choose the most efficient system. Choose the most appropriate system for the particular household.