Called te po wairakau (the pile of manure), the project is about using the school's compost, along with additions from the local livestock saleyards, to create a water heater.
Project organiser and parent Bernard Mullane is using a 40-year-old design pioneered by Frenchman Jean Payne.
They will construct a compost heap about one storey high, with a water drum in the centre and a coil of pipe winding around it to pass the water through.
Mr Mullane said others who had tried the design had been able to heat their water to 58degC using the same method and that seemed to be as hot as it got.
A plumber has volunteered to help build the pipes, including a heat regulator that mixes cold water in when the temperature gets too hot.
The key to a successful compost was to have the right ratio of green matter (nitrogen) to brown matter (carbon). A healthy heap would generate heat and quality compost and was not smelly, he said.
The eventual aim of the project was to have a warm shower available to wash sandy hands and feet at the back of the school near the beach.
Getting the required quantity of compost material was not likely to be a problem and they already had several compost bins and worm farms plus access to other sources like a local lawn-mowing business, he said.
