There has been much debate within the development industry between architects, services engineers, ESD consultants, other design consultants and Planning Authorities as to which hot water system is the most suitable for a multi-unit residential development.

With a vast portfolio within this sector, GIW Environmental Solutions (“GIW”) has conducted research on the application of several hot water systems within medium density multi-unit residential developments in Melbourne’s inner suburbs.

During the investigation, we have considered each major technology under the triple bottom line framework; economic, environmental and social impacts.

Technologies reflected within the research include the following:

  • Centralised gas storage
  • Centralised gas – continuous flow
  • Solar with gas backup
  • Centralised instantaneous condensing boiler
  • Commercial heat pumps
  • Instantaneous electric

Based on inputs from several manufacturers and suppliers on cost, maintenance, efficiencies, warranties, hot water delivery, redundancies and billing accuracy; we have graded each system under the appropriate triple bottom line analysis.

The results demonstrated the following:

Due to reasonable capital cost, high efficiencies, low maintenance and gas fuel input, the condensing boiler met the best economic outcome. Condensing boilers for residential applications are currently available and have energy efficiency ratings of 6 Stars (94%).

Again, due to high efficiencies and gas fuel input, the condensing boiler maintained the lowest greenhouse gas emissions over a 10 year period; ahead of the gas boosted solar thermal system.

A social impact analysis considered hot water quality, warranty; for both minor and major components, billing convenience and accuracy, access and redundancy. As the electric instantaneous systems are provided per unit, they can be easily accessed, maintained and billed. In addition to this, the single units allow hot water to be shut down and maintained per individual apartment, without affecting the remainder of building occupants. This makes them the highest ranked performer under a social analysis.

Of course other items need to be taken into account such as spatial considerations, access to fuel sources, administration and incorporation of renewable energy technologies. These and other site constraints will determine the final system selection. The following charts provide an indication of how currently available technologies for use in multi-unit residential developments can be evaluated:


Any reliance on this information shall be entirely at such party’s own risk. GIW Environmental Solutions Pty Ltd provides no warranty or guarantee to any party, express or implied, as to the information and/or professional advice indicated in this article, and accepts no liability for or in respect of any use or reliance upon this information.

Use or copying of this information in whole or in part without the written permission of GIW Environmental Solutions Pty Ltd constitutes an infringement of copyright. Information shall not be assigned to any other party without prior consent.

For access to calculation parameters or any other relevant information please contact our office.