Heating your home with wood – consider efficiency and the environment
(first published October 2008, last updated October 2012)
Sometimes heating your home with wood can be more economical and environmentally friendly than the alternatives; particularly if you have easy access to wood supplies.
While wood fires do generate carbon dioxide and particulate matter, other fossil fuels may generate more greenhouse gases when issues such as extraction and transportation are taken into account.
Fossil fuels are also carbon sources that have been locked away for millions of years, whereas wood is part of the current carbon cycle. Burning wood is considered carbon neutral. Wood is also a relatively easily renewable resource.
However, the key to environmentally friendly wood heating comes down to three things:
- The efficiency of the heater
- The type and quality of the wood
- How the heater is operated
Type of wood heating
There are many factors that will influence efficiency and economy in comparison to fossil fuel counterparts. Wood heaters with high efficiency scores use less wood to generate the same amount of heat, therefore also creating less emissions – if the heater is operated correctly.
Radiant vs convective heating
Radiant wood heaters create the majority of their heat (66%) from the flames and heat people and objects directly rather than heating the air. A convection heater heats and circulates warm air around a room.
While an open fire is a joy to watch, fireplaces are generally very inefficient – only achieving around 5 – 10% efficiency. The fireplace itself is quite expensive to construct and requires a lot of materials. Additionally, an open fireplace only provides heat directly in front of the fire. Much of the heat can be lost not only through the flue, but through the rear wall which is usually outside the home.
An open fire’s efficiency can be greatly improved (up to 35%) by the use of a fireplace insert which is a hollow, metal structure built into fireplace, allowing for a greater degree of convection heating rather than relying purely on radiant heat.
Pot belly stove heater
Pot belly and similar wood heaters have an efficiency generally in the 25–40%; although according to the compliancy tag on mine, which is a relatively new model, it’s 47%.
A pot belly stove generates convective and radiant heat and are a good choice for heating small areas; particularly where space is an issue.
When I firstly installed my potbelly in a smallish area, the first night I was sweating even though the temperatures outside were below freezing. There is a bit of a learning curve in using them to get the right level of heat and particularly having them burn overnight. Pot bellies offer air flow controls which help control the rate the wood burns.
Slow combustion heaters.
Slow combustion heaters are a step up in efficiency – up to 70%. This is due to an airtight firebox, additional airflow controls and air inlets plus secondary combustion chambers to improve efficiency. They are the best option for heating large areas and can be fitted with a fan to help move heat more evenly around the room.
Wood pellet stoves
While not seen much in Australia yet, I understand that wood pellet stoves are very popular in other countries such as the USA. The wood pellets are usually made from sawdust waste from mills that has been compacted. Wood pellet stoves are reported to be incredibly efficient, offering combustion efficiencies of over 90%! Emissions are also said to be very low in comparison to other forms of combustion heating. Wood pellets can also be burned in normal slow combustion heaters and potbelly stoves, but without such high levels of efficiency.
Selecting a wood heater
A good wood heater for a large area can be quite an investment., so when choosing a wood heater, it’s best to consult an expert who can advise you based on issues such as climate, room size etc.
In my case, installing a slow combustion heater in such a small area wouldn’t have been effective as at medium and high burn settings, I would have sweltered. At low burn settings, too many emissions would have been created, so the pot belly was the best choice.
As a general guideline, aim for 1 to 1.5 kilowatts (kW) for each 10 m2 (108 square feet) of area needing to be heated. Always check the compliancy plate for efficiency ratings too. A slightly more efficient heater may cost a few bucks more, but will save you a ton of money (plus wood and emissions) in the long run. Also check and compare the compliancy label for emissions ratings.
Wood burning tips
Whether it’s a wood pellet stove, a pot belly or open fireplace, correct operation is crucial to not only efficiency, but in reducing pollutants. I live in a small farming town where wood appears to be the major fuel source for heating. Over winter, the air in the town is very heavily tinged with the smell of wood smoke – and it’s a particular type of smell that indicates the wood is not being burned properly by some.
- Make sure the wood is dry. Wood that is wet or “green” requires additional energy to evaporate the water; that’s energy that could be used in generating heat. Wet wood also smokes, creating more carbon dioxide and particulate emissions. Burning wet wood can also create a build-up of creosote in your chimney and flue; impacting on its performance and increasing the risk of flue fires.
- If using a potbelly, combustion heater or pellet heater, your fire should only smoke for the first few minutes. If it continues to smoke but the wood is dry, this means it’s not getting enough oxygen, so open up the air controls a little.
- Ensure the wood is burning well before turning down the air flow. This will help reduce emissions.
- Hardwoods are the best type of wood for burning. Softwoods such as pine burn quickly and generate a great deal of particulate matter, including creosote. This creosote will also build up quickly in your chimney/flue, further degrading wood heater performance and could result in a flue fire. If you need to use softwoods, ensure they are very well seasoned – at least 12 months.
- Wood ash isn’t waste. It can be used in many ways.
More wood saving tips
Ensuring your home is properly insulated (roof, walls, and windows – either with double glazing or blackout curtains) will also greatly decrease the amount of wood you’ll need, as will using a ceiling fan which will help push the warm air (which rises) back down.
A wood heater draws cooler air into it, so give some thought as to placement. If you sit a chair directly between the wood heater and the cool air source, such as an open door, you’ll need to burn more wood to achieve a similar level of warmth if it were correctly positioned.
When buying firewood, ensure it has been harvested from a sustainable source. If you’re fortunate enough to have a heavily wooded property, bear in mind also that even dead trees and wood laying around on the ground provides habitat for insects and animals – try not to totally clear areas. If you need to cut live trees as a wood supply, replenish them.
Be careful of using off cuts from mills – ensure that none of it is treated timber which may contain toxic chemicals.
If you’re picking up wood from the roadside or reserves, check first with local authorities. In some cases it may be banned or you may require a permit.
If you live near an industrial estate, there may be a great free source of wood available in the form of old pallets and shipping containers – ask around.
Have any tips relating to wood heaters? Please add them below!
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