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However, with a growing plague of waste-oil stockpiles around the country, more and more businesses are using waste-oil heaters to heat water, and there are applications for households, as well.
Sales at two-year-old Cromwell-based burner supplier Omniheat New Zealand had more than doubled in the past year, distribution manager Dion Prentice said when contacted.
"Basically, it's turning a cost to business [oil disposal] into free energy for them,'' he said.
Mr Prentice said the niche waste-oil sector was gaining momentum in New Zealand, mainly in industries but with increasing interest from schools and other groups, many of them looking to swap coal for a cleaner heat.
In Dunedin, Escudo Coatings' managing director, Scott Taylor, was last week replacing an obsolete diesel/oil burner with a new Omniheat model, costing about $6000 all-up, given he had an existing tank and the burner sat next to the electroplating baths.
He said the burner heated both the degreaser and rinse baths to about 50degC.
Crucially, the new burner could automatically sense the type and viscosity of filtered oil and adjust the burner accordingly, without having to be manually reset.
"It's the new generation ... it flies on autopilot. Way more efficient and less down time,'' Mr Taylor said.
While Fulton Hogan supplies the waste oil, Mr Taylor said the new burner and its efficiencies now gave him several oil options.
Mr Prentice understood the former Holcim cement plant in Westport used to take more than 50% of the country's waste oil to burn, but its closure now meant a glut of waste oil was becoming stockpiled.
"Getting rid of the oil waste product is becoming a major environmental issue for New Zealand,'' he said, of storing, transporting and disposing of the hazardous waste.
He said one business had recently contacted Omniheat, looking to get 36,000 litres of waste oil off its hands.
Fulton Hogan is now collecting waste oil and acting as a distribution centre, with prices per litre around 51c.
The waste oil comes from several sources, including fish and chip shops, transport companies, hydraulics and transformers.
It is burnt under pressure as a fine mist at around 700degC, which Mr Prentice said eliminated much of the emissions; they were about 25% of those emitted by a car.
The super-heated oil, in turn, heats a thermostatically controlled water cylinder and the water is then reticulated into wall radiators, underfloor or wherever required.
Mr Prentice estimated a house conversion cost about $20,000 and, depending on oil source, could be run with no further costs after the installation spend.
Mr Prentice said an Otago swimming pool that had had to raise $8500 a year to buy coal, had recently installed the system and cut costs to an estimated $2500-$3000.
"Of course, that depends on whether you're getting your oil free,'' he said
An Otago hydroponic horticulturist had also installed the system, heating the water used to grow hundreds of thousands of plants, Mr Prentice said.