What is the difference between a factory-built fireplace and a fireplace insert? Find out. The Wood Heat Organization:
Answers to your questions about burning wood for heat and enjoyment.

Categories of Wood Heating Equipment

Wood heating takes a lot of different forms and each category of equipment has particular features and uses. This short outline should save you time and give you the language you can use to discuss them.

Wood Stoves * Fireplace Inserts * Hearthmount Stoves * Masonry Heaters * Masonry Fireplaces * Factory-Built Fireplaces * Pellet Stoves * Cook Stoves * Furnaces * Boilers, both indoor and outdoor.

 

Woodstoves

Wood stoves are free-standing space heating appliances. Used either as the principal source of heat for a home or to supplement conventional heating systems, wood stoves are the most popular form of wood heating equipment because of their relatively low cost and installation flexibility.

There are two general categories of wood stoves based on differences in combustion technology, emission characteristics and efficiency: conventional wood stoves and advanced technology, EPA certified wood stoves.

Conventional stoves do not have the advanced combustion technologies needed to meet emission standards (see discussion below). This category would include older cast iron box stoves, parlour stoves, Franklin fireplaces, and the so-called ‘airtights’ of the 1970s and 1980s.

Advanced combustion wood stoves are defined as those that meet the emission limits set by the U.S. Environmental Protection Agency (EPA) and are tested by EPA accredited agencies. The EPA emission test measures and reports on particulate (smoke) emissions as a surrogate for all other pollutants. Manufacturers use one of two general approaches to achieving lower stack emissions. 

The non-catalytic advanced combustion design includes an insulated firebox, an internal baffle that acts as a reflective surface and separates the firebox from the secondary combustion chamber, and a system to pre-heat and distribute a secondary air supply above the fuel bed.

A catalytic stove is equipped with a ceramic combustor coated with palladium located in the appliance downstream of the firebox. The catalyst reduces the ignition temperature of the smoke so it burns more completely, cutting smoke emissions at normal stove operating temperatures.

Both catalytic and non-catalytic designs have proved successful in achieving lower emissions, but in recent years the non-catalytic category has come to dominate the market.

Pellet Stoves

Sawdust or other waste biomass material is compressed into small cylinders about 8 mm in diameter and from 10 to 30 mm long to produce pellets. The raw feedstock for pellet production does not include binders or other additives, except in some cases to assist in the extrusion process. In the pellet stove, the fuel is moved from the integral hopper to the small combustion chamber by a motorized auger. The exhaust is forced into the vent with a fan. Because steady state combustion can be approximated by adjusting the fuel and air mixture, pellet stoves can burn with lower emissions, on average, than wood stoves. In contrast, the combustion of a batch of wood in a wood stove never stabilizes, so combustion air requirements are constantly fluctuating and good combustion conditions are transitory. Pellet stoves deliver about the same efficiency as EPA certified natural firewood-burning stoves.

Fireplaces

The term fireplace was traditionally used to describe a wood burning device built into the structure of a living area and in which the fire can be viewed while it burns. However, the distinction between wood stoves and fireplaces is no longer as clear as it once was. For example, virtually all advanced wood stoves have glass panels in their doors and incorporate a technology that sweeps combustion air behind the glass to keep it clear for effective fire viewing. Also, some fireplaces now have advanced combustion technologies that permit them to meet EPA emission limits and can have heat ducts connected for use as central heating systems. As well, some masonry heaters look like fireplaces but have the efficiency and low emissions of advanced wood stoves. Therefore, the term fireplace must be used with some caution.  It is used here to mean a device that is not free-standing but is built into the wall of a living space. The term does not refer to strictly decorative appliances.

Fireplaces can be divided into two broad categories:

·       masonry fireplaces constructed of brick, stone or other masonry materials, are assembled on site and usually connected to a masonry chimney, and

·       factory-built (also called prefabricated and informally as zero-clearance) fireplaces in which the main structural material is usually metal and which are installed on site as a package with the specified metal chimney.

Conventional fireplaces, whether masonry or factory-built, do not incorporate emission reduction technologies, and may or may not have glass doors. Generally, conventional fireplaces are not effective for home heating purposes because of high dilution air demands and inadequate heat transfer characteristics. Some masonry and virtually all factory-built conventional fireplaces incorporate an air circulation jacket around the firebox connected to grilles that take air from floor level, heat it and return it to the room. However, these air circulation systems are rarely effective enough to overcome the other limitations inherent in conventional designs and are used mainly to permit reduced clearances to combustible material by cooling the outer skin of the fireplace rather than for space heating.  

Advanced technology fireplaces are factory-built units that use the same technologies used in advanced stoves and are also EPA certified for low smoke emissions. Unlike conventional fireplaces, these fireplaces can be used for home heating. Some of these fireplaces have a central heating capability through the attachment of ducts to distribute heat to other parts of a house.

Fireplace inserts  

Fireplace inserts are wood stoves that have been adapted by their manufacturers to fit within the firebox of masonry fireplaces. A few inserts are certified for installation in factory-built fireplaces.  An insert converts a conventional fireplace into an effective heating system. Both conventional and advanced technology fireplace inserts have been on the market and their emissions performance can be assumed to be about the same as conventional and advanced wood stoves. A hearthmount stove is a wood stove that is vented through the throat of an existing masonry fireplace in the same way as an insert is. In Canada, fireplace inserts and hearthmount stoves are required to have a stainless steel liner installed between the appliance flue collar and the top of the chimney.

Wood Cook Stoves

Wood cooking stoves have a cook-top surface, a bake oven and sometimes a reservoir for domestic hot water. Cook stoves are not common in Canada, although a few models are still available for sale in specialty stores. Cook stoves are exempt under the EPA wood burning regulations because the numbers were considered small and their manufacturers testified that practical cooking features and low emission combustion technology are incompatible. Smoke emissions performance for cooking ranges is not available, but particulate emissions are probably similar to conventional wood stoves.

Masonry Heaters

The masonry heater is a traditional space heating system of Northern European origin that has been adapted for North American conditions. It has an enclosed firebox in which a charge of wood is burned rapidly. The hot exhaust gases are routed through heat transfer channels embedded in the massive masonry structure before being expelled to the chimney. The heat stored in the masonry is released slowly to the room for up to 24 hours after the fire goes out.  Relatively complete combustion is achieved through the rapid, turbulent combustion that is characteristic of masonry heaters. In North America masonry heaters are a niche product, partly because of their unique operating cycle and partly because they cost in the range of $10-$20,000.

Central Heating Furnaces and Boilers

Wood-fired central heating systems are available in several forms: add-on warm air furnaces for connection to existing oil or electric furnaces; combination furnaces that use electricity or burn oil in addition to wood; and boilers that heat water and use a system of pipes to distribute heat. Most furnaces and boilers tend to produce relatively high smoke emissions, although there is one Canadian wood furnace that is EPA certified for low emissions.

Outdoor boilers have been gaining popularity over the past decade, particularly in rural areas and small towns. An outdoor boiler is enclosed in a small shed and uses insulated underground piping to deliver heat to the house. These units have been notorious for producing large plumes of smoke. Many municipalities have passed by-laws restricting their us in populated centres due to smoke pollution.