Krystal Barna, of Clean-Sweep Chimney Sweeps, says there is an increase in untrained and ill-equipped individuals offering their services as chimney sweeps in Dunedin.
It meant some people were left with chimneys they thought were clean but were not, while others were now reluctant to get their chimneys properly cleaned.
Either way it left them "open to the risk of a chimney fire", Mrs Barna, who co-owns the business with Reuben Parker, said.
Owners of other chimney sweep businesses in Dunedin said there were always some people who did not provide a professional service, but they had not noticed an increase in incidents.
Fire risk management officer Barry Gibson, of the New Zealand Fire Service, said there had been a sharp increase in the number of chimney fires in Dunedin, but he did not know if it was because of poor-quality chimney sweeping.
"I'm concerned about a growing trend of dodgy chimney sweeps operating in the Dunedin and Oamaru area," Mrs Barna said.
"We are hearing more and more instances of door knockers doing dodgy work and putting people off getting their chimney cleaned."
The reports included work being done badly or not being finished, or people using it as a pretext to "case" houses.
"Someone who turns up without a ladder or a vacuum cleaner and just some cheap brushes is like having a mechanic turn up with just a few screwdrivers to fix your car."
People offering to clean chimneys for $20 or $30 were also putting people off using more established businesses, which had a proven track record but charged $60, Mrs Barna said.
Chimney sweeps did not have a national guild or association to set standards.
Perhaps this was needed, she said.
David Brown, of Brown's Chimney Cleaning Service, said all industries had people "doing a bad job".
He had not noticed "more than the usual" in his industry.
Mr Gibson said, while there had been 30 chimney fires in Dunedin in the 12 months to the middle of this year, there had been 38 chimney fires in the past six months.
"If this trend continues, we are going to have a very high count," he said.
"Whether that's related to the quality of chimney sweeping or the lack of it I don't know.
We'll be having a look into that."
The fire service encouraged chimney sweeps to "do a full job ... top to bottom including the hat on top".
It was important people had their chimney properly cleaned yearly because a chimney fire could ignite timber around the chimney "setting their property on fire, with the potential for loss of life", Mr Gibson said.
