So-called “ecological” logs of densified wood have many virtues, especially if they don’t contain any paraffin or chemical additives.
In practical terms, they have the advantage of being sold both in small and large quantities, in sizes and packaging that allow clean storage. They don’t generate insect or moisture problems and take up less space than traditional cordwood.
In environmental terms, they put wood residues from sawmills and manufacturing plants (hardwood floors, furniture, etc.) back to use. Also, burning them in an EPA-certified stove produces up to 58% fewer harmful particles than natural wood (about 30% fewer in an uncertified device).
Finally, their energy efficiency is 20% to 35% better than that of natural wood. Since they contain up to four times less moisture than ordinary heating wood, burning them produces much more heat. This attribute calls for great caution, however.
Embers that burn hotter than flames
Overheating is a potential risk in any stove or fireplace, especially high-performance units whose leading feature is precisely that they maintain a very high temperature in the combustion chamber. It’s true that any fuel used without restraint can cause overheating, but densified wood may present a higher risk because of its remarkable heating power (BTU/lb.).
Generally speaking, these logs take very little time to produce embers, which account for nearly three-quarters of the heat generated in burning. At Maison DF, a major distributor of supplementary heating units, it has been observed that people often feel the need to add more logs if they don’t see any flames. What happens then is that the bed of embers thickens more quickly than heat transfer can occur, causing the unit to overheat.
This can result in parts becoming twisted, split or discoloured, and firebricks can even come apart under the intensity of the heat, company President Jean-François Fauteux says. He notes that the manufacturer’s guarantee never applies to damage caused by overheating. Some manufacturers, such as Jotul, even advise against using densified wood logs in their products. A piece of advice: check before lighting up!
A thermometer for staying in control
How can you control the heat level and avoid nasty surprises? The simplest and least expensive way is to install a thermometer on the unit or on its flue pipe. Models with magnets are the most common. If a thermometer has to be installed on a double-walled flue, it must be equipped with a sensor (a stem to be put inside). A thermometer will promote safe and efficient use of the unit by indicating the heat generated in its operation on a scale that sets the appropriate temperature zone.
These thermometers provide essential benchmarks for people who have little or no familiarity with wood heating. They are sold in specialty shops and large hardware stores for about $20.
“Eco” wood: caution and judgment
- Remember that densified wood logs must be used in moderation: never more than three at a time in an EPA-certified unit, Mr. Fauteux says. When they are used for heating, it’s more secure to opt for so-called “night” logs, which have the property of releasing heat over a longer period of time.
- Another piece of advice is to steer clear of using ecological logs to start a fire in a cast iron stove so as to avoid thermal shock.
- Printing “eco” on the packaging of a log does not mean the log is free of chemical additives or paraffin, a petroleum industry byproduct. It should be noted that logs with paraffin emit such intense heat that they should be burned solely in open stoves or fireplaces, and this reduces their energy efficiency.
- Some logs display EcoLogo certification, which guarantees that they are made solely of wood residues suitable for burning and that they contain no chemical additives. EcoLogo, the symbol of Environment Canada’s eco-labelling program, is intended to help consumers select products that are less harmful to the environment.