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Wood heating

How to choose your wood stove

It can be difficult to choose a wood stove with the mass of technical information that’s available. The two graphs on the next page summarize the most important information to help you select the Drolet stove that matches your expectations.

Vertical scale (number of BTU's/hr)

One of the most important factors to consider when buying your wood stove is the number of BTU's required to heat your residence. And that number depends to a great extent on the total area of the space to be heated. To find the number of BTU's required for your residence, first determine the total area of the floor on which the stove will be installed and add half the area of the upper floor (if applicable), if you want to heat that floor as well. Example: 25 ft. x 32 ft. residence with basement, main floor and second floor. If the stove is put on the main floor, the total number of square feet to be heated will be: (25’ x 32’) + 1/2 of (25’ x 32’) = 800 + 400 = 1,200 square feet. Then, the number of required BTU's is obtained by multiplying the total area by 17.5 for a house built within the past 25 years or by 35 for a house that is more than 25 years old. In our example, if the house has been built recently, we multiply 1,200 by 17.5, which gives 21,000 BTU. These figures are approximate because each residence has its own specific features. We also assume that the stove is used for auxiliary heating rather than for central heating, which means the temperature is not maintained in uniform fashion throughout the residence.

Horizontal scale (time in hours)

Another factor to consider is the amount of time (in hours) that you want to pass between each load of wood without having to re start the fire completely. This means a bed of embers must always be present. You must therefore add a load when the curve gets almost to its lowest point on the graphs. But you may not want your stove to be lit all the time. If so, you can let the fire go out by itself and start it the next day or even wait until the weekend.

Combustion air

Simply put, the amount of BTU's developed by a wood fire depends on the wood’s combustion rate, which in turn depends above all on the amount of combustion air that is supplied to the unit through the main air vent. A minimal amount of combustion air will generate fewer BTU's. In other words, the smaller the amount of combustion air, the slower the wood will burn. It’s just a matter of finding the right balance between the desired number of BTU's and the desired combustion time.

Firebox size

Combustion time in a wood stove depends, among other things, on the size of the firebox. In general, the larger the firebox, the longer the combustion time.

 

The right choice

The above graphs show that the maximum number of BTU's developed and the combustion time both depend on the amount of air that gets to the fire. The combustion time also depend on the firebox size. When the main air vent is completely open (high, continuous redline), the stove develops maximum BTU output, whereas when it is almost entirely closed (low, dotted green line), the fire will burn the maximum amount of time.

Positioning the vent control at medium-low usually represents the happy medium, that is, the right balance between combustion time and BTU's/hr. Depending on your specific situation, you should choose a stove that will maintain an adequate BTU level in relation to the time you want to pass between loads.



Heating with wood and the environment

When oil, gas, and coal are burned, the carbon they contain is oxidized to carbon dioxide (CO2), the main greenhouse gas. In effect, the combustion of fossil fuels releases ancient carbon (carbon that has been buried within the earth for thousands of years), thereby increasing the atmospheric concentration of carbon dioxide (CO2). In comparison, wood combustion can be considered carbon neutral because trees absorb CO2 as they grow. This process is called carbon sequestration.

 

Approximately one ton of carbon is sequestered for each cubic meter of wood. When trees mature, die, fall in the forest and decompose, the same amount of carbon is emitted as would be released if they were burned for heat. This cycle can be repeated forever without increasing atmospheric carbon. A healthy forest is not a museum, but a living community of plants and animals. When trees are used for energy, a part of the forests carbon "bank" is diverted from the natural decay and forest cycle into our homes to heat them. When we heat with wood, we are simply tapping into the natural carbon cycle in which CO2 flows from the atmosphere to the forest and back. The key to ecologically sound and sustainable wood energy use is to ensure that the forest remains healthy, maintains a stable level of variously aged trees and provides a good habitat for a diversity of other species, both plants and animals. Ensuring there is a healthy fuel wood market is key to a sustainable forestry plan. Landowners have more incentive to remove low value trees and manage their forests sustainability knowing there is a market for this low value material


The combustion of wood produces small particles that are called PM2.5. Those particles are 30 times smaller than a human hair. They can aggravate certain lung and heart diseases and have been
[particulate]








linked with health problems such as asthma. Sources of PM2.5 include combustion under various forms, such as the one used for cars and trucks, wood heating, as well are other industrial processes. While it is true that old technology like open fireplaces and simple heaters could not burn the wood completely, the new generation of wood-burning appliances are designed to burn particles. They produce almost no visible smoke. The wood-heating industry has evolved. The vast majority of appliances sold on the market now meet the particles emissions limits set by the US Environmental Protection Agency as well as the Canadian standard CSA B415.1. For example, the Environmental Protection Agency, better known as EPA, limits emissions of certified wood heating appliances to no more than 7.5 grams per hour. In comparison, older conventional wood stoves average 40 grams per hour. Numerous countries, provinces and municipalities, have adopted laws that regulate the sale of wood-heating appliances that do not meet the latest standards in terms of particles emissions. Among them, we can name the United States, Australia, New Zealand, as well as numerous countries that are part of the European Union. In Canada, British Columbia, Quebec, Nova Scotia, and Newfoundland have also introduced laws regulating the sale of wood-heating appliances.

Wood, when burned in an appliance that has been tested to the EPA or CSAB415.1 standards, emits up to 90% less particles. It is a clean, renewable energy source. Furthermore, the reduction in fuel wood consumption reaches up to 33% when advanced wood combustion systems are used. This is because certified wood stoves and fireplaces are 60% to 80% efficient, compared with 40% to 60% for conventional units. As for appliances burning wood pellets, they have amongst the lowest particulate emissions of all solid-fuel burning appliances. They are manufactured from waste products and other renewable resources right here in North America. They represent a huge source of heating fuel from material that would otherwise be sent to landfills.

All Drolet and Osburn EPA wood appliances have a secondary air source. Heated air flows, which are circulated through perforated channels located under the firebox baffle, allow for a more complete combustion of particulates before they are released into the atmosphere. You burn less wood and help the environment.