wood stoves

Wood stoves have long been a common way of providing both home heating and cooking.  Now, in the early years of a new millennium, this form of home heating is experiencing a major resurgence thanks to a new generation of more attractive and efficient stove designs.  Moreover, since 1992 wood stoves have been required by the Environmental Protection Agency (EPA) to emit less than 7.5 grams of smoke particulates per hour so they are not only more efficient they are cleaner.  Modern wood burning stoves emit almost no visible smoke.

The economics of heating your home with a wood stove have changed dramatically in the last few years.  In 2007 the cost of home heating oil went up over 97% and propane went up over 52%.  As a result, for many homeowners using a wood stove as either a primary or secondary approach for home heating may make a lot of sense (for more on this see the section on comparing fuel costs).  Moreover, wood stoves are good for the environment.  Not only are they carbon neutral, assuming the wood  was sustainably harvested, but in many cases they can be carbon negative.  This is because in many communities the wood comes from local salvage wood (tree work, dead trees, storm damage).  This wood would have been allowed to decompose (releasing carbon) or burned in an oil or natural gas  waste plant where even more energy resources would be wasted. If you harvested the wood from your own property even more energy is saved because fuel transportation costs are avoided. 

Types of Wood Stoves

There are a wide range of stoves for home heating.  Most stoves are designed to burn wood but more recently stoves have been designed to also burn other types of biomass, everything from olive pits to corn.  Stoves also differ in the approach they take to distributing heat.  Let's review these:

Radiant Wood Stoves

Radiant wood stoves are usually made of a single layer of iron, welded steel or sheet metal.  The metal layers tend to be fairly thick so they can absorb as much of the stove's heat as possible. The heat from the stove's furnace is designed to radiate off the hot metal surface of the stove and circulated via convection currents. Many radiant stoves have a heat resistant glass or Plexiglas window in the front so that the stove provides light as well as heat.  This makes it easier to monitor the fire and it creates a more romantic atmosphere. 

Circulating Wood Stoves

Circulating stoves look pretty much like a radiant stove on the outside but are actually double-walled with an inner chamber constructed of cast iron or welded steel. Fire bricks are often placed in the area between the inner and outer chamber.  By doing this the external part of the stove does not become overly heated which reduces the risk of someone burning themselves on the stove.  This is something you might want to consider if you have small children.

Many circulating stoves make use of small electric fans which can improve air circulation.  This ensures that more of the heat in the inner chamber is fully leveraged.  Depending upon the design a circulating stove can achieve heating efficiencies in the range of 70 to 80 percent.

Combustion Stoves

A combustion stove is a stove in which the doors can be opened when the fire is burning. The old Ben Franklin stoves were an example of this type of stove. Opening the doors provides a direct view of the fire and allows the wood to be loaded from the front if necessary.  In essence it behaves very much like a fireplace.  By opening the doors much more air is allowed to enter the combustion chamber and so the fire tends to burn hotter.  Unfortunately much of this heat is lost up the flue pipe.  Because of this the circulating wood stoves tend to actually provide less heat than a radiant wood stove.  Most are only 50-60 percent efficient. 

Catalytic Converters

One of the major changes to wood stoves in recent years has been the use of catalytic converters. Some of you may remember from high school chemistry that a catalyst is something that speeds up or facilitates a chemical reaction.  In this case what the catalyst does is support the chemical reaction between oxygen and organic materials when heated.  The temperatures inside of a wood stove are generally around 400 degrees to 900 degrees Fahrenheit.  While this temperature is sufficient to heat much of the wood it is too low to ignite all of the hydrocarbons given off during the burning process.  These hydrocarbons contain much of the energy contained in the firewood. 

The catalytic converter has a ceramic honey-comb which has been coated with a special metal such as palladium or platinum.  These metals serve as the catalyst and allow the hydrocarbons to burn at the lower temperature.  This offers two major advantages.  First, it increases stove efficiency by 10% to 25% by burning the hydrocarbons which otherwise would have escaped up the flue.  Secondly, by burning the wood more completely you get less emissions which means cleaner air and less creosote build up in your chimney. 

Catalytic converters overall are a great value.  They significantly add to the efficiency of the wood burning stove and they protect the environment.  Most modern wood stoves will support them and the cost of getting one will more than be paid for by increased efficiency.  The one disadvantage is that they do have to be replaced after 3 to 6 years. 

Non-Catalytic Approaches

If you don't want to bother replacing your catalytic converter ever few years there are other alternatives to getting a high efficiency stove.  One approach is to use a baffle that pushes the unburned hydrocarbon gases back over the flames causing them to ignite.  This process is called secondary burning. 

In most stoves of this type you must first get your stove up to a decent temperature (400-500 degrees) and then flip a lever which causes the gases to be rerouted into the main chamber so they can re-combust. Once this is done the greater air turbulence and additional combustion drives the temperatures even higher.  Overall a stove of this type is as efficient as a stove which uses a catalytic converter. 

Pros of Woodstoves

Availability - Probably the greatest advantage of a modern wood stove is that the fuel is readily available in most locations.  Most communities have vendors who can provide cords of firewood.  In rural locations wood can often be harvested locally. 

Renewability - Wood is a renewable fuel.  The growth of new forests for lumber and fuel is a huge industry and well established.  Therefore, it should be available as an energy resource long into the future.

Simplicity - Most wood stoves are uncomplicated and easy to use. They tend to have very few moving parts.  While some use electric blowers to increase air flow in a room, most have no electronic components.

Reliability -Because of their simplicity wood stoves are extremely reliable heating sources.  They do not require electricity to operate and can be used off-the-grid or whenever the grid goes down.  Many a home owner has saved their pipes during a winter storm even when the electricity went out because they could heat their home with wood.

Cons of Woodstoves

Maintenance - A wood fire has to be tended to some degree even in the best wood stove. New wood must be added and ashes periodically removed.  For some people this is just too time consuming.  If feeding a stove isn't your thing then something like a pellet stove that has an auto-feed mechanism may be a better choice.

Fuel Cost - Firewood is expensive in some parts of the country because there are no nearby sources, particularly in urban areas.  In these situations the cost of heating with wood may be higher than traditional heating methods.

Heat Distribution - A standalone woodstove may not be the most effective or efficient way to heat multiple rooms in a large home depending on its layout.  Older homes were often designed with large rooms which could fully benefit from the heat of a single wood stove, but most modern homes were designed with gas or fuel oil heat and have many small rooms which do not lend themselves to woodstove heating.  To some extent you can compensate for this by using a fan in combination with your wood stove but there are limits to the distance this can be effective.