Lowering emissions with hybrid hot water heating
1 August 2025
Carbon dioxide emissions from commercial gas-fired water boilers can be reduced significantly with the addition of modestly-sized electric heating elements in an in-situ research project undertaken by Rinnai’s Kez Shruthi.
In the two-year project for her masters’ thesis, Shruthi, a design engineer, trialled a hybrid gas/electric boiler at Foodstuff’s award-winning 8,500 square meter, six green-star-rated North Island head office building in Mangere, Auckland.
The project has demonstrated efficiency savings and annual gas heating cost reductions of several thousands of dollars, together with the parallel savings in emissions.
In a trial partly supported by GasNZ’s Kennedy Educational Scholarship Trust (KEST), the 1.5 kW and 3.3 kW electric heating elements were used to reduce the need to continually cycle the gas fuel on and off to maintain a steady temperature, especially in off-peak hours.
“With reduced need for on/off cycling of the gas heating, there will also be less stress on the system’s components which will lengthen their life,” Shruthi says.
The four-year-old Foodstuff’s building was chosen for the study partly due to the available history of high-quality comparative energy consumption data – a requirement for achieving its green star rating.
Gas hot water heating is usually the only practical, economic option for large buildings, with all-electric systems not being able to match gas in terms of capacity or cost. But the gas/electric hybrid offers the best of both worlds with electricity being used to maintain the water temperature.
Shruthi says Foodstuffs has been pleased with the results achieved, and a hybrid system has now also been installed in its neighbouring massive 77,000 square metre distribution building.