House saves pile on power

During June - a month when Wanganui had several nasty frosts - the Iliffe family spent $30.25 on heating and had their pellet fire going for a mere hour or two on some nights.

The family of five moved into 5 Webster Pl, in the Lithgow Dr subdivision, in April. It gave Mr Iliffe, a director of the business that built it, an opportunity to monitor its energy use and compare that with the three-year-old house next door.

The Webster Pl house was built to passive house specifications and came within a hair of being the first certified passive house in New Zealand.

After living there for five months Mr Iliffe estimates it will cost its future owner an average of $85.50 a month for both electricity and heating - or $2.85 a day.

When the Chronicle visited on Monday, the outdoor temperature was 15C.

The neighbour's three-year-old house was 15.6C but it was 21C at Number 5. Humidity was 75 per cent outside, and 51 per cent in the house.

"It's typically five degrees warmer than the house next door, even when they're running a heat pump," Mr Iliffe said.

Number 5 stores heat created by cooking, computers, showers and even people's bodies. When there was a birthday party with 21 people, the temperature indoors rose two degrees - while it was 4C outdoors.

A passive house works on three principles: It is well sealed, well insulated and well ventilated.

Number 5 Webster Pl passed the airtightness test and is well sealed. It is ventilated by a 30-watt heat exchange system that completely changes the air in the house every three hours, getting rid of smells and moisture and transferring the heat of indoor air to fresh incoming air from outdoors.

It fell down just a little on the insulation front, because Mr Iliffe and his business partner, Baden Brown, had not yet passed their passive house exams and didn't have the passive house software they now use. All that was lacking at Number 5 was an extra 50mm of insulation under the concrete floor pad and a different aluminium construction for the window and door frames.

"It's leaking energy from the window frames and floor a little bit more than it should. We lose maybe one degree," Mr Brown said.