Otago homeowners adding wetbacks illegally to their woodburners and multiburners are putting their house insurance in jeopardy and risking a substantial fine.
Dunedin city council chief building control officer Neil McLeod said anyone adding a wetback to a woodburner needed a building consent.
"If you don't, you contravene section 40 of the Building Act."
The maximum penalty is a fine of $100,000.
Mr McLeod was responding to Otago Daily Times inquiries about people "getting around" wood burner and wetback regulations by installing a new fire, having it inspected and consented by a council building inspector and later adding a wetback, without a consent.
This would contravene both the Building Act, administered by the city council, and the Clean Air Act, administered by the Otago Regional Council.
Yunca Heating and Gas manager Harvey Bell confirmed it was not uncommon for wetbacks to be added after new fires were installed.
"A lot of times, people put their fire in and then just run the wetback in after.
"People are so frustrated throughout the whole country, and it's the same in Christchurch, Timaru everywhere ... a lot of people get the fire installed and put the wetback in after.
"It is illegal."
Yunca does not have a Ministry for the Environment-approved woodburner with a wetback, but was developing one, Mr Bell said.
The ministry's website lists the "authorised" wood burners that meet emission standards.
Only a small number have a wetback.
Mr McLeod said he knew of no instances of wetbacks being added illegally, but "if we had evidence of that we would have acted on it".
The council would be unlikely to hear about burners being altered until people tried to sell a house, he said.
"When you come to sell the house, if work has been done without consent, it can be quite difficult to sell the house."
Mr McLeod said a qualified plumber would know the rules about wetback installations and the council would take "a dim view" of a plumber who installed one illegally.
"The reason for this is one of safety.
What you are effectively doing is adding what we call an uncontrolled heat source to your hot water cylinder, so it's got the potential to boil your hot water cylinder."
Insurance Council of New Zealand chief executive Chris Ryan said woodburners were not a major cause of fires.
"But they need to be permitted when they are put in and any changes, including wetbacks, need to be permitted as well."
Mr Ryan said an unconsented wetback "might not be covered for insurance" in a house fire, depending on the cause of the fire.
"General rule of thumb: don't do it.
Get it permitted and then you can just relax."
A regional council spokesman described regulations to do with woodburners and wetbacks as "incredibly complicated".
"I'm not surprised people ... have trouble with it.
If it were me, I would make the safest default response: "No, you can't, in practical terms, retrofit a wetback."
