What's the cheapest way to heat your home?

RNZ News

3 days ago

The cost of heating your home makes up about a third of what you pay for power each month.
Photo:
123RF
If you're spending your evenings in front of a heater, you might be keeping a wary eye on your power bill.
The cost of heating your home
makes up about a third of what you pay for power each month.
But what's the cheapest way to do it?
Here's an overview of how the various options compare.
They can have a high upfront cost, but Energy Efficiency & Conservation Authority lead adviser on energy efficient appliances Gareth Gretton said heat pumps were "by far and away" the most efficient form of heating.
Depending on how much you're charged for electricity, it might cost you about 25 cents to 35c an hour to run your heat pump, for every kilowatt hour (kWh) of heat produced. A 6kw heat pump would cost $1.50 if you're paying 25c per kWh.
Consumer estimates that a very large heat pump might cost $1000 a year but a small one could be less than $200.
But they will deliver much more heat for that cost than a standard electric heater of the same size.
"I think most people know now they're really magic at transforming electricity into heat. They take heat from outdoors and effectively put it indoors, they sort of upgrade the heat that exists outdoors, even when it's below 0°C, and turn it into useful, comfortable heat indoors," Gretton said.
He said, for every unit of electricity that a heat pump used, it would give three or four units of heat.
"There's literally nothing else that can provide that efficiency other than a heat pump."
He said New Zealand was unusual in that its houses tended to be relatively badly insulated.
"Heat pumps do get a little bit less efficient when you have colder temperatures outside but it's not a huge problem because in New Zealand what we end up doing is quite a lot of heating when it's not cold outside by international standards … say 5°C to 10. Heat pumps are really efficient in that sort of temperature range."
Consumer recommends running a heat pump no higher than 21°C and turning the fan up rather than the temperature if you want to heat a room quickly.
Healthy Homes standards
don't require landlords to install a heat pump
in rental properties, although many have. They are only required to provide a fixed, safe and efficient heating source for the main living room.
Whether it's better to leave your heat pump on all the time or turn it off when it's not needed is a subject of debate. Some people argue it costs more to warm up a room than if it was kept at temperature all day. But James le Page, who has looked into the issue for Consumer, said turning it off made more sense.
"For the few people who have a house that is super airtight - so with no gaps around doors and windows, insulation above building code requirements, double glazing, thermal drapes and a ventilation system - they might be able to leave their heat pump on all day every day," he said.
"But for most of us in New Zealand, if we leave it on, we'll be wasting a lot of energy on heat that will continuously leak out, as our heat pump works hard to maintain the set temperature."
In general, electric heaters all cost the same to run, for the amount of heat they produce.
"Any form of resistance electric heating - what I mean by that is where you pass electricity through a plug-in heater and what it's doing is the device is resisting the flow of electricity - will transform electricity into heat with a ratio of one to one," Gretton said.
"There's ultimately no difference in the electricity to heat conversion efficiency of any type of electric resistance heater, they're all the same."
But he said they could vary in effectiveness. Radiant heat could be good for a large area or a room with high ceilings, for example. "If you're within the range of the heater, you're kind of feeling that heat and you can be a little bit more comfortable at a slightly lower air temperature. It's a bit like the campfire effect. If you're outside and it's pretty cold but you're near a campfire which is tremendously hot then you feel that heat."
Consumer said portable fan heaters were good option in small or occasionally used rooms, such as offices or bedrooms, even though they were relatively expensive to run. "But, with a maximum heat output of 2400W, they don't have the power to tackle anything beyond very small living areas."
A 2kW heater running for five hours a day would typically cost about $2.50 a day while a 1200kW radiant heater with three bars could cost $1.50.
In general, electric heaters all cost the same to run, for the amount of heat they produce.
Photo:
123RF
You might use a dehumidifier to take the moisture out of a room, but it could also increase the temperature by a few degrees, which might be sufficient if it's a room you're only going to sleep in.
"You can sort of regard a dehumidifier as being a plug-in electric heater with the advantage that it will also make your house drier," Gretton said.
"It's a bit of a win-win because all the electricity that goes into your dehumidifier will actually be helping to heat your house. They're a good thing in that sense."
A compressor dehumidifier, which is the most common type in New Zealand, costs about 5c an hour to run.
Gretton said gas heating was not an effective option.
He said people should steer well clear of unflued gas hearers anyway, because they made a house damp and emitted gases such as nitrogen oxide.
"There's an absolute mountain of good reasons why unflued gas heaters are a bad idea. With flued gas heaters, there's no direct health impact but you do have a bit of an efficiency loss so you're not going to be getting one unit of heat for every unit of gas you're burning."
Gretton said wood burners tended to be less efficient than gas heaters.
"It's quite tricky to burn wood both cleanly and efficiently. There's a trade-off between making wood burners efficient and making them clean burning in the sense of lower particulate emissions.
"I think a lot of people assume that wood burners are really cost effective to run, but it really depends on how much you're paying for firewood. Now, for those people that do have free firewood, that's obviously pretty hard to compete with in terms of cost to run because it's basically zero other than the amount of time you'll spend cutting and chopping wood.
"But if you're buying firewood, then it's not particularly cost effective, although it does vary around the country."
He said, at a rough average national rate, it was still usually more expensive than a heat pump.
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