(first published October 2008, last updated October 2010)
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 can 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. Wood is also a relatively easily renewable resource.
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
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.
Open fireplace
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
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 (and wood) in the long run. Also check
and compare the compliancy label for emissions ratings.
Wood burning tips
- Make sure the wood is dry. Wood that is wet 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.
- 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
- 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.
Sourcing wood
When buying
firewood, ensure it's come 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!
