Residential landlords should be aware of two assumptions in the heating tool that greatly increase the required heating capacity of heaters.

A paper by economist Ian Harrison titled “The required heating capacity of qualifying heaters in the main living room: A review of the methodology” shows “serious deficiencies in the formula and the supporting analysis”.

Deficiencies with the model are:

· A requirement for a “qualifying heater” to be able to raise the temperature from the lowest annual external temperature for the region in which the heater is to be installed has been used.

· A “floor space” measure in the formula, which has nothing to do with heating capacity needs, has the effect of pushing capacity requirements about 30 percent above the industry standard.

The external temperature measure starts with a claim that the World Health Organisation recommended 18C as the healthy indoor temperature when they made no such recommendation, Mr Harrison wrote.

“There was actually no evidence for the general population that warming houses to 18 degrees, as opposed to a lower number such as 16 or 17 degrees, would have any health impact. The best evidence on children was that there was no effect, Mr Harrison wrote.

A consequence of the “floor space” measure in the formula is that heat pumps will be required in some small living rooms where they are not economic or technically efficient, and many existing heat pumps, installed on professional advice, will be deemed to be no longer adequate, he wrote.

There is no supporting documentation for this “floor space” requirement. The response by Associate Minister Poto Williams to a request under the Official Information Act was to refuse it because “the policy documents that explain the theoretical basis for the model and the calibration of the inputs do not exist”.

“We found it quite extraordinary that there was no policy document explaining the formula that is at the heart of the heating requirement,” Mr Harrison wrote.

"A heating assessment tool should be a useful aid, not only for tenants and landlords, but for homeowners and others with an interest in home heating," he said.

However, the existing heating tool is flawed. The Associate Minister should go back to the drawing board and instruct the Ministry of Business Innovation and Employment to create an accurate and credible heating assessment framework, Mr Harrison said.

To read the paper, go to http://www.tailrisk.co.nz/ and click on “documents”

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