Is the efficiency of heat pumps all it is cracked up to be? As Ellie Constantine discovers, there are several variables to consider, and one or two myths to discount.
The energy efficiency of heat pumps is not cut and dry.
Heatpump Systems Ltd owner Tony Bush has been in the business for 18 years and said when it came to the operation of heat pumps "there is no-one rule".
People often believed it was more efficient to keep the machines running day and night.
However, he described it as the "biggest urban myth there is".
He warned people against leaving them running all the time as "otherwise you will be unpleasantly surprised" when the power bill arrived.
When it came to getting the most out of a heat pump, consumers needed to consider the brand, how well the house was insulated and which power tariff the user was on.
"You want one that's going to be as efficient as possible for people's needs and purposes," Mr Bush said.
Buying over the counter was also not recommended as a professional could ensure the right-size heat pump was installed for the space and it was being put in the most appropriate spot.
The Heating Company manager John Bayne agreed, adding that cleaning filters every three months meant a more efficient heat pump.
"They can use a significant amount of power if you let them."If a consumer wanted to run the heat pump through the night, he recommended setting it to 16degC, or setting the timer so it would turn on an hour before occupants got up.
Keeping it on auto-fan, so it would adjust itself accordingly, and setting it to an appropriate temperature was also more economical.
"If you are going to run it at 25degC it's going to cost more than [running at] 20degC," he said.
The Energy Efficiency Conservation Authority said heat pumps were the most efficient way to use electricity to heat a house.
However, it also said some were better than others and running costs and performance could differ significantly.
Older style heat pumps operated on a fixed speed compressor motor.
These were either on or off so they stopped and started repeatedly to keep the temperature at the set level - much like a fan heater set on a thermostat.
Newer, inverter style heat pumps used a variable speed compressor electric motor which slowed down and sped up as required, making it more energy efficient, the EECA website says.
Consumer New Zealand showed, in its July 2009 issue, a medium-sized. oil-filled or convection heater used 2kW and cost 45c an hour to run, a 2.4kW fan heater used 2.4kW and cost 53c an hour to run while a 4.5kW heat pump used a minimum of 1.25kW, a maximum of 1.8kW and cost between 28c and 40c an hour to run.
• Heat pumps
How do they work?
They use the same technology as a refrigerator but in reverse.
They take heat from the air outside and transfer it inside using a vapour compression refrigeration cycle.
Even when it gets down to below 0degC, there is still warmth in the air which can be utilised.
How do you get the most out of your heat pump?
Learn to use the timer. Set it so it comes on an hour or so before you get up in the morning or get home at night.
Do not leave it on 24 hours a day unless people are home all day and you want to keep the house warm at night. Otherwise you are wasting energy.
It uses less energy to warm the house up when you want it than to keep it constantly warm.
Only heat spaces you are using. Turn it off when it is not needed. Shut doors, windows and draw curtains to keep the heat in.
Do not set the temperature higher than you need it.
A comfortable working temperature is 18degC-22degC; if required, 16degC overnight.
Keep the interior and exterior units well maintained as per the manufacturer's instructions, including ensuring the filters are cleaned regularly.
Source: Energy Efficiency and Conservation Authority www.eeca.govt.nz
