Guide to efficient use - Hot Water

Hot water

Table of Contents

1 Introduction

2 Is it for me?

3 How much does it cost?

4 What are the benefits?

5 Step by step guide

6 Case studies

7 Where can I find out more?

Step by step guide

The advice given for Heating systems can also be applied to hot water. In fact, in many cases both systems are integrated, using a single boiler to heat water and warm your building.

Select a water heating system according to your needs

Storage tank water heaters	Indirect water heaters	Heat pump water heaters
This is the most common technology and have very low equipment costs. They can heat and store large volumes of water. Electric storage heaters need about 10-20% more energy because of the “stand-by” energy losses.	The water coming from the gas or oil fired boiler goes through a coil immersed in the tank containing the domestic water. Indirect water heaters are able to supply large volumes of hot water, but operate less efficiently when space heating needs are lower.	They use the heat from the surrounding to heat the air to the water heater tank. The energy savings can be up to 50% compared to storage tanks. In addition, they cool and dehumidify the air surrounding the unit, which is useful if there are cooling needs. Despite high initial cost and greater maintenance needs, heat pump water heaters can be more cost-effective than conventional electric storage tank heaters, especially in warm to moderate-cold climates.
Instantaneous electric water heaters	Solar water heaters	Heat recovery water pre-heaters
These systems do not have a storage tank. They heat water on demand, by means of electrical energy as water passes through the heater. They can continuously supply hot water but require great amounts of electricity and have high initial costs. They may not have enough capacity to supply large volumes of hot water, therefore they are often used as auxiliary heaters to supplement another water heating system. Generally, hot water storage systems are more efficient.	They use the energy of the sun to heat water. Most common solar water heaters use active solar systems (collectors) to warm up the water. They can significantly reduce hot water costs, since the energy of the sun is free. Nevertheless, they cannot operate alone, because they are not able to supply the whole hot water needs (usually not more than 50%). In addition, their high initial costs may not make the installation cost-effective.	They use waste heat recovered from air or water to pre-heat cold water before it is sent to a conventional storage tank water heater. At present, this system is generally not cost-effective due to the high initial costs and additional space requirements. However, this technology is under continued develpment, with very promising results.

Consider energy efficient water heaters if you are replacing your water unit. They are more expensive but include additional design features allowing significant reduction in energy consumption.
Avoid oversized water heaters as they will heat up more water than you need, wasting energy.
Disconnect water heaters if they won't be used for more than 3 days.
Make sure your hot water tank and water distribution pipes are well insulated and do not have any leaks. You can add an insulating wrap to the tank (especially for electric water heaters) and install tubular fibreglass or foam insulation around the pipelines.
Try to install the hot water tank as near to the point of use as possible. This will reduce energy losses.
Never set hot water temperature to over 60°C. This would waste energy and corrode the pipelines. There are taps with temperature preselection options, regulating the chosen temperature of water. Savings may reach 50%.
Avoid turning the water flow up when adjusting water temperature. Balance water temperature by decreasing the hot water flow in preference to increasing the cold water flow.
Clean your hot water tank to prevent sediment accumulating on the bottom. Sediment decrease the efficiency of the tank, therefore it is advisable to flush or empty the tank every two years.
Consider the possibility of installing solar hot water. This could reduce your energy consumption by over 60%. (See the Solar thermal energy module).

Further advice focused on water savings:

Stop taps dripping. A dripping tap wastes about 80 litres/day or 2.4 m3/month. A 1.6 mm stream of water loses about 180 l/day or 5.4 m3/month. A 3.2 mm stream of water loses 675 l/day etc.
Install low-flow showerheads - they can reduce your hot water use by up to 30%.
Use tap aerators to lower water flow. Aerators mix air into the water flow and reduce water consumption by 25 - 50% per tap.

Use taps with low-flow restrictors. They enable you to limit the maximum water flow. Some of them can be installed without taking the tap apart.
Use labels promoting water conservation near baths, showers, sinks, etc.
30 seconds is enough for hand washing. Infrared sensors allow savings between 70 and 80% but are one of the most expensive tap types we have discussed. Push button taps are less expensive are a good alternative to save water.