Low emission wood heaters and what the Australian standards mean
If you are shopping for a clean-burning wood heater, you will meet two standards and a handful of numbers. They are easy to misread. This guide explains what each one measures, how to compare heaters fairly and what else decides how cleanly a heater burns in your home.
The two standards
Australia tests wood heaters under two separate standards. They answer different questions.
AS/NZS 4013 measures emissions. Specifically, it measures how much particulate matter a heater releases for each kilogram of wood it burns. The result is quoted in grams per kilogram, written g/kg. A lower number means less particulate matter released.
AS/NZS 4012 measures efficiency. It tells you how much of the energy in the wood ends up as useful heat in your room rather than leaving up the flue. The result is a percentage. A higher number means more of the wood’s energy is delivered as heat.
A heater needs both. A heater can be efficient and still emit more than you would like, or emit little and deliver less heat than you expected. Look at both figures together.
What g/kg tells you
Emissions in g/kg are a laboratory result. A test lab burns a standard fuel load in a controlled way and measures what comes out. The number is a fair way to compare heaters because every model faces the same method.
It is not a measure of what will happen in your lounge room. Wet wood, a smouldering fire or a choked air supply will all raise real-world emissions above the laboratory figure. We return to that below.
What efficiency tells you
Efficiency matters because it affects your wood bill and your workload. A more efficient heater gives you more warmth from each load.
Efficiency has two figures worth understanding. Peak efficiency is the best result in the test. Average efficiency is the result across the whole burn. Compare peak with peak and average with average. Do not mix them.
The Parkray Aspect Eco figures
All three Aspect Eco models are tested to AS/NZS 4013 and AS/NZS 4012. Here are the results, stated as tested.
| Model | Emissions (AS/NZS 4013) | Peak efficiency | Average efficiency |
|---|---|---|---|
| Aspect 5 Eco | 0.7g/kg | 72% | 67% |
| Aspect 8 Eco | 0.8g/kg | 77% | 67% |
| Aspect 14 Eco | 0.9g/kg | 68% | 63% |
We are not claiming these figures beat any other heater. Compare them with the published figures for any model you are considering, using the same two measures. The numbers are there to be checked.
For the full specification of each model, see our side-by-side comparison.
How a heater keeps emissions down
Most of the smoke from a wood fire is unburnt gas. A good design burns more of it before it reaches the flue.
The Aspect Eco range uses TripleBurn, which feeds air to the fire in three stages. Primary air enters through the base and drives the fire. Pre-heated secondary air runs down the glass as an airwash, which keeps the glass clearer and feeds the flames above the logs. Tertiary air enters through a rear bar and burns the gases that remain.
Hot air burns gas more completely than cold air, which is why the pre-heating matters. The design helps. It does not replace good operation.
Dry wood matters as much as the heater
You can buy the cleanest-testing heater on the market and still produce a lot of smoke if you feed it wet wood.
Wet wood has to boil off its water before it burns. That cools the fire, which makes combustion incomplete and sends more smoke up the chimney. It also deposits creosote in the flue and blackens the glass.
Firewood should be below 20% moisture. A moisture meter gives you a reading in seconds. Season hardwood for at least 12 months. Read our guide to seasoning firewood for the full method.
Operation matters too
A few habits make the biggest difference.
- Light it hot. Use dry kindling and small splits to get a strong fire going fast.
- Keep the air open after loading. Give a fresh load enough air to catch properly before you turn the controls down. Our guide to lighting your wood stove walks through the steps.
- Burn small, hot loads. A bright, active fire burns cleaner than a slow, smouldering one.
- Never burn rubbish or treated timber. Painted, treated or glued wood releases substances you do not want in your air.
- Watch the flue. Thick smoke from the chimney means something is wrong. Open the air, check the wood and check the heater.
Installation and maintenance
A heater only performs as tested if it is installed correctly. Installation must be by a qualified installer to AS/NZS 2918. Seals, baffles and the flue connection also need attention over time. See what an annual service covers.
Choosing with the numbers
When you compare heaters, use this checklist.
- Check the heater is tested to AS/NZS 4013 and AS/NZS 4012.
- Compare emissions in g/kg. Lower is better.
- Compare efficiency, peak with peak and average with average. Higher is better.
- Match the output to your space. See our sizing guide.
- Plan to burn dry wood and operate the heater properly.
Hunter Stoves Australia sells only through authorised dealers. Find one with our dealer locator, browse the wood heater overview or phone 1800 064 234. Questions about cover are covered on the warranty page.
Ready to find your heater?
Browse the full Parkray Aspect Eco range.