Designing homes to conserve energy and use it efficiently, from sources that cause least environmental harm.

Water heating

Water heating accounts for 27% of energy use in an average New Zealand house, so achieving energy efficiency can make a significant difference to energy use and costs.

A hot water system must be designed to provide sufficient hot water for household needs. It must meet health and safety requirements such as controlling temperature and pressure to ensure there is minimal risk of scalding or of a storage cylinder exploding, and to prevent the growth of Legionella bacteria.

A well-designed system will also support efficient energy and water use, by:

  • using a heating source that is efficient and minimises environmental harm
  • locating the heating source close to points of use, and ensuring that pipe runs are relatively short
  • insulating hot water pipes and – if a storage cylinder is used – a Grade A insulated cylinder located in a warm space
  • heating and storing only as much water as is needed to meet peak demand
  • only heating water to the temperature needed to meet regulatory requirements
  • using low flow fixtures
  • using energy efficient and water efficient appliances, or appliances that heat their own water (unless you use solar or heat pump water heating).

For Building Code requirements, information about controlling temperature and pressure, and information about system layout and capacity, see hot water supply in the Water section of this site.

In general, the most energy efficient system for most household purposes will be an appropriately sized storage system with solar or heat pump water heating. For outlets that are rarely used or remote from the main hot water supply, a continuous flow system may be more convenient and minimise energy use.

The government’s Gen Less website has online information here to help homeowners and their advisors select a water heating system.


Updated: 25 April 2024