A Flaming Good Fire

Some people say hard wood – others swear by soft , while others hedge their bets and use a mixture of both!

The truth is that many people simply don’t know which is the best fuel to burn in their wood burning heater, or open fireplace.

The “type” of fuel wood really doesn’t matter, because weight for weight dry wood has about the same heat content. Preferences vary from pine or manuka in the north to macrocarpa or willow in the south.

The key, though, is that for best performance, irrespective of the type of appliance or fuel, the wood must be as dry as possible. But, you might say, dry wood just lights easier and burns faster. Not so. Dry wood is the key to real winter comfort.

Apart from the user avoiding a huddle around a pile of logs which bubbles moisture from the ends as it struggles to burn, a bright fire is more heat efficient, increasing the heat output and reducing smoke levels.

The result? A warmer home, and happier family – and neighbours!

But how dry is dry? Wood can hold at least its own weight in water, irrespective of species, and to burn efficiently, the moisture must be reduced to about 20%. At this level, combustion efficiencies in excess of 90% have been recorded in modern wood burning appliances.

But it takes time to dry – or season – wood.
Some hard woods, such as manuka, can take up to two years to season properly, while soft woods like pine may well be ready to use in as little as 6 months.

They key is to think ahead. Obtain fuel in summer or as early in the heating season as you can. Stocks at wood yards are generally high, and the fuel well on its way to drying.

And if you collect or cut your own, moisture levels can be reduced quite quickly in the autumn breezes. And split larger logs so that more of the surface is exposed to the air.

When stacking your fuel, leave gaps between the pieces so air can pass through the pile to speed the drying process.

If you have to obtain fuel during the winter, shop around, be selective and make sure it is as dry as possible.

A trip to your local wood merchant will pay off. Not only is fuel cheaper in bulk, the merchant can tell you which is most suitable at that time of the year. Bagged fuel, such as manuka which is offered at retail outlets, is often freshly cut and will not burn efficiently, no matter how hot you manage to get the fire.

And be careful when buying demolition timber. While this has a very low moisture content, it may be chemically treated, which may pose a health hazard or cause damage to your appliance and chimney system.

So what about the fire itself?

A brightly burning fire means good heat so it is important to create the right conditions for good combustion. Most modern wood heaters have been designed to develop these with the minimum of user input once a base fire has been established.

Unfortunately the “art” of creating a good fire has been lost to many people, so here are a few guidelines.

You will need a supply of newspaper or fire starter blocks, some dry kindling or small light pieces of fuel wood, and some slightly heavier pieces of timber.

Crumple the paper into a tight ball, or roll it into a tube and knot it, and place it on the base of the heater or grate. Alternatively, use three or four fire starters instead of the paper.

Criss-cross the paper or fire starters with a good amount of dry kindling, then light the paper or starters. Wait until the kindling begins to burn brightly, then slowly add the heavier pieces of starter fuel.

Wait until the pieces have started to burn before adding the main fuel wood. This takes less time than it may seem, and you can be sure that you have the start of a good hot fire. It is worth the few moments of care in the long run.

Once the fire is established don’t wait for it to burn to embers before adding more fuel – use the heat from your existing fire to dry the remaining moisture from the new fuel. But don’t douse the flames with the fresh wood. Place it along side the existing fire, or sparingly on top, because the hotter you can keep the burn, the cleaner and more efficient it will be, and the more heat you will be able to enjoy.

A few words on air slides are appropriate here, too.

Never start the fire, then close the air control immediately. It’s important to use the initial heat to warm the chimney system, and to bring the combustion process into equilibrium.

A masonry chimney will take longer to reach a good operating temperature, than a metal one, simply because of the tonnes of bricks which have to be heated to generate flue draught.

Once the heater is operating properly, the air control may be adjusted to set the burn rate. Don’t use the air control alone to control the fire, because the lower the air setting, the lower the temperatures in the appliance, which can result in reduced combustion efficiency.

The more air going into the combustion zone, the brighter and more efficient the fire will be. A better way is to control heat output by the amount of wood you put on the fire at any one time. Less on a warmer night – more on a colder one. Experience will tell you how much you’ll need to meet your comfort level.

Most appliances which meet international clean air standards cannot be completely shut off, so that the correct temperatures are maintained to produce a clean burn even when the appliance is dampened down for an overnight burn.

Setting an overnight burn needs a little extra care. You must have a good fire base before attempting this. Add the logs, and leave the air slide open until they have started to char and flame before adjusting the air setting down for the night.

There should still be enough hot embers in the morning to allow you to restart the heater for the coming day. If in doubt, follow the instructions in the user manual.

If you have any queries about getting the best from your fire, call your nearest member of the New Zealand Home Heating Association. (The Fireplace technician) They have been trained in all aspects of wood heating, and will be happy to help you or provide professional advice.