When Diane Williams paid $3160 for insulation to be installed in her ceiling and floor spaces, she expected her home to become toastier than ever before.

But the retiree, who lives in a two-bedroom home in South Auckland, says it's felt colder since the insulation went in last winter.

The Government had chipped in a further $1300 through its Energy Wise subsidy, leaving her concerned the workers had not done the job properly.

"I've lived at this property since 1986 and last winter was the coldest ever inside," Williams says. "I didn't expect it to heat the house, but I expected it to retain the heat."


The Herald on Sunday enlisted Energy Efficiency and Conservation Authority technical adviser Andrew Smith to find out why the house felt unseasonably cold.

While he insisted the insulation was top quality and well-installed, Smith discovered a raft of problems, which meant Williams may as well have left her windows open on cold nights.

"These problems are common. When it comes to heating, New Zealand houses are badly built and badly positioned," Smith said.

In Williams' home, a ranchslider and large, single-glazed windows in the living room meant she was throwing heat out the window. Vertical blinds would do little to prevent heat leaking from the room she spent the most time in, and the blinds did not run to the floor or have pelmets above the railing. Smith said a gap between the window and curtain caught rising warm air, while pushing cold air underneath - a cycle which cooled the temperature inside.

Replacing the blinds with thick, floor-length curtains with pelmets would trap about 30 per cent more heat inside - the same sort of saving provided by ceiling insulation.

"Pelmets aren't the most fashionable, modern thing, but they certainly make a difference," he said.

Smith identified drafts as another issue in Williams' home. "In the average NZ home, all the drafts add up to a one-metre hole in your wall."

In older homes, that would be more like a 5m hole.


He suggested putting draft stoppers - and you can make your own - along gaps in walls and under doors for a cheap, effective fix. Heat would also escape up unused fireplaces.

Although dampness was not an issue in Williams' home, laying damp-proof plastic on the ground under the house was another cheap way to make a big difference.

Many homes were also set on damp ground - making their interiors harder to heat and prone to mould, Smith said.

But all the insulation in the world would not make a home hot and the home heating industry has become full of marketing "trickery", Smith said. For example, it was a myth that some electric heaters were more efficient - one unit of electricity will turn into one unit of heat no matter what style the heater was.

The exceptions are heat pumps, which produce three units of heat from one unit of electricity.

But the initial cost of a heat pump could only be justified in an open-plan home, Smith said. Otherwise, the key to warming a house is to have a small, inexpensive heater in each room.

"You're going to struggle to get heat to move around most NZ houses," he said.

For more information on effective heating and insulation go to energywise.govt.nz