"They're actually not doing things quick enough to keep up with him," Mr Hardie said.
Mr Irvine works for Mr Hardie's business, Rivercity Gas, which sells gas appliances as well as installing and servicing them and solving gas reticulation problems. The business has seven full-time and four part-time staff.
Mr Hardie is a member of the Plumbers, Gasfitters and Drainlayers Board NZ and takes an active interest in training for the trade. He would like to set up a facility at Rivercity Gas to train apprentices from other businesses.
As for Mr Irvine, his goal is to finish his apprenticeship and get licensed, then sit another exam, get more experience and become certified as well. He previously worked in plumbing for Wanganui's Wadey Bros, then for Crystal Valley Mineral Water. But he prefers the technical challenge and physical and mental stimulation of gasfitting.
"You have to think your way through the problem as much as you have to use muscle.
"You never really know it all, and that's what keeps it interesting. There's always something new to learn."
He said he would be happy to carry on working in Wanganui when he's fully qualified.
"If you like doing gasfitting work, Wanganui is a very good city to be in. We probably have a higher proportion of gas in homes here than other cities because we have an old and well established gas network."