How To Heat Your House Efficiently

Winter is coming, and all across the southern states eyes turn to energy bills and minds towards how to make them smaller. What is the most efficient way to heat your house? As with anything to do with thermodynamics the answer is complicated, but there are some solid rules to help shape your thinking.

Cat heating picture from Shutterstock

Insulate, insulate, insulate; then add more insulation

Both heating and cooling come down to one fundamental problem; how to put heat where you want it and keep it there. That means outside in summer and inside in winter.

The rate that heat enters or leaves a building is governed by the materials that make up your "building envelope": the surface which surrounds your living spaces. You have to stop heat crossing the boundary of your walls, ceiling, floor, windows and doors without your permission.

We say "without your permission" because in winter your first priority must be getting sunlight into the house and stopping it leaving again.

Direct sunlight is almost entirely ultraviolet (UV) radiation, which passes easily through glass and into your living room. Once it strikes an object it heats up and the sunlight becomes infrared (IR) radiation, which is best thought of as radiant heat. IR radiation doesn't pass through glass as readily as UV radiation, so the room heats up. Ever left your car in the sun for a day where it is a lovely 25 degrees outside but 60 degrees inside your car? It is exactly this mechanism at work.

Insulation will stop heat crossing boundaries. If you own your house, the path is well trodden and fairly simple. Start with the ceiling, adding the thickest insulation you can find.

Next consider how the wall insulation can be improved. There are some new materials and processes available for this task now and you can pay someone to come and pump insulation into your wall cavity for $2000 and upwards. Doing this can make your house about 2 degrees warmer.

Window treatments are just about on-par with walls for making a difference; even more so if you include doors.

If you're on a budget, or renting, there's a lot you can do with windows and doors. First, seal all the gaps around doors in the house, even the internal ones, to control the size of your heated space; there are rubber seals that can do the job for doors and windows.

Then seal all the ancillaries that let heat escape, like bathroom vents and the rangehood, which vents outside. This is where renters can get creative and reap rewards; rolled towels under doors are a good start, but why not go further? Tape a garbage bag over the window that opens onto the neighbour's bathroom. Block the old chimney with anything you can find. Do anything you can to stop heat going where you don't want it to go.

Curtains and pelmets are virtually mandatory in cold climates. Curtains must be as heavy as possible, touch the ground and the walls next to the window. Windows are the last great frontier in home insulation; and honestly, there's no cost-effective way to retrofit them. Energy payback on double-glazing your windows could be close to 70 years. But as with all energy efficiency upgrades there is more to it than the energy savings. What is niceness worth to you? How much nicer is it being in a house which is 14 degrees instead of 10? What is that worth to you?

Once your windows are done think about what you can do to the floor. Slabs are hard to change, but there are products for suspended boards which will make a big difference.

Which fuel?

You have three choices for heating: electricity, gas and wood.

The cost of wood is variable and will likely increase in coming years. The environmental impacts are strongly dependent on your fuel source. Fallen timber is not fair game: it is vital habitat for some animals, so should not be burnt. Particulate emissions are a concern as well.

Gas is great in that it can deliver astonishing amounts of heat quickly, with lower greenhouse gas emissions than grid electricity, but not as low as renewable energy, and the future costs are quite uncertain. Gas heating is traditionally considered to be pretty cheap, but gas prices are tipped by many analysts to climb steeply in the next few years , much as electricity has in the last few years.

That leaves electricity. Unintuitively, it's the only option which can have zero emissions. Switching your electricity supply to GreenPower, an accredited and audited scheme which supplies 100 per cent renewable power, means zero emissions electricity any time you want it. But how you use it is very important, as all electric heaters are not created equal.

There are two distinct classes of electric heater; plug-in heaters, and heat-pumps (or reverse cycle air conditioners).

All of the plug-in heaters end up at the same efficiency; they convert electricity into heat, the most basic form of energy, and will only ever produce a maximum of 2.4kW. It doesn't matter how it does it – radiant bars, a hot wire and a fan or a clicking oil-heater – 2.4kW of electricity becomes 2.4kW of heat and not a drop more. Buy the cheapest one you can.

Heat-pumps have been common in Australia for years — reverse-cycle air-conditioners are a form of heat-pump — but the technology has advanced markedly recently. Heat-pumps have an advantage over the plug in units as they use electricity to move heat around, not create it.

Heat-pumps have access to the ambient heat outside your house, even in small amounts, and can concentrate it and put it in your house. Even well below freezing there is enough heat available for this to be worth doing.

Heat-pumps' performance is reported as a "co-efficient of performance" or COP. This describes the amount of heat transported per unit of energy used to move it. A good heat pump will approach a COP of 5 – five units of heat produced for every unit expended – dependent on the ambient temperature. Newer designs are achieving COPs greater than 3 even when the ambient temperature is as low as -10 degrees.

If you're thinking of getting a heat-pump, look for one with an EC (electronically commutated) motor; it will be described as "Inverter driven". A good heat-pump will have a high energy efficiency rating (that is, lots of stars on its label).

To summarise then: insulate your house, as much as you can, in every way available. Then think about how you want to heat it. If emissions are important to you, go for GreenPower and a heat pump. If you just want heat, then gas is probably your best bet, but be warned the price is on the way up and likely to outstrip electricity price rises in coming years.

This article was substantially based on research by Evan Beaver. Evan is a mechanical engineer and a senior consultant at Energetics, where he advises government on energy policy and industry on energy efficiency.

Will J Grant is Researcher / Lecturer, Australian National Centre for the Public Awareness of Science at Australian National University. He does not work for, consult to, own shares in or receive funding from any company or organisation that would benefit from this article, and has no relevant affiliations. The ConversationThis article was originally published at The Conversation. Read the original article.


Comments

    After 3 winters with a Heat Pump we have switched to a wood heater, the Heat pump was rated for 7kw, but struggled in the dead of winter to give us any really decent heat, we had it serviced and checked, but only a small improvement in output, we now have a Wood heater that is also rated for a 7kw output (it has a built in fan to circulate the air) and we are very warm.
    We spent nearly $2000 last year on heating over the 2 quarters (Launceston Tasmania) and the only real winner was the electricity provider, we lost as we were cold! So far this season we are warm, we have already spent less (I have purchased $1000 of firewood for the season, more than we need) the house is dryer (no condensation like we have with a Heat pump) no noise from the heat pump constantly running, and far less money going to a useless utility provider.
    The Wood heater is the most efficient we could afford, we had it professionally installed and we use a Smartburn with dry timber to ensure as little smoke output as possible (in fact it is a very rare event to see smoke from our fireplace)
    No one will convince me to go back to a heat pump again.

      I have some friends in hobart who had their heat pump replaced three times in one year before the manufacturers worked out what was going on: if it was turned off on a cold night, it'd start to freeze up...and if it was turned on again afterwards, it'd refuse to work or do actual damage to the pump.

      Their solution: Either run the heat pump non-stop or not at all. if it stops running for any reason at night, do not turn it on again until morning. no matter how cold it gets.

      Most systems sold in Australia are designed to work great in a Queensland summer, but they don't do much testing in a Tasmanian winter.

        Panasonic and another brand we used to have detected when it was frozen over and would defrost itself before starting up.

    Hydronic heating, we have underfloor and panel heaters installed.
    Toasty in winter, doesn't take long to heat up and cheap to run although it is prohibitively expensive and difficult to install.

    Don't like heatpumps, makes a bit of a draft like feeling which we dislike. Plus we had hydronic in Russia and it made our home there feel like we lived in Jamaica while it was minus 30 odd outside with about 3 meters of snow...

    Draught-proofing will give you the fastest and cheapest improvement. However, you do it at the expense of fresh air and higher indoor air pollution. Any heating system that uses combustion indoors (gas heaters & wood burners) will dramatically increase the potentially carcinogenic gases and particulates inside the house - so you have to make sure that you ventilate well too.

    I can't believe you advocated buying "the cheapest one you can" for plug-in heaters. It's not just about creating heat, it's about the quality of the heater. Better quality heaters will have things like thermostats, safety tip-over switches, quieter running, etc. I have a Delonghi oil heater which has lasted nearly 10 years, versus a cheap Kmart one I had once which lasted less than 2 years before leaking oil everywhere.

    EDIT - Also, why does this Will J Grant have Angus Kidman's photo up?

    Last edited 21/05/13 2:19 pm

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