| Looking to purchase a wood stove that is right | | | | the fuel to extract the available heat and heat |
| for your home? Some of the biggest and | | | | transfer efficiency; this testing is performed in |
| best-known hearth manufacturers make some | | | | calorimeter rooms equipped with temperature |
| good wood stoves. There are many factors to | | | | sensors. Similar temperature sensors are installed |
| consider and lots of products to choose from. | | | | in the exhaust flue. The degree changes in the |
| Finding a high quality clean burning wood stove | | | | room and flue are monitored for the duration of |
| that meets your needs may require some digging. | | | | the test fires to determine how much of the heat |
| The specifications and terms used by the | | | | extracted by the fire is delivered into the room, |
| manufacturers and the EPA are technical and | | | | as compared to the heat lost up the flue. |
| generally confusing. Understanding the | | | | Emissions |
| specifications and ratings (and how they are | | | | Measurement of particulate matter emissions in |
| determined) will help you make a better buying | | | | grams per hour. Particulate Matter is a fancy term |
| decision. | | | | for air pollution and means small pieces of matter |
| On top of confusing ratings and specifications | | | | such as dust and soot that are suspended in the |
| there generally are not independent third-party | | | | air. |
| reviews such as Consumer Reports to rely on. | | | | Emissions testing is performed in EPA-approved |
| Underwriters Laboratory (UL) can evaluate gas | | | | test labs using the EPA's prescribed protocol. |
| fired solid-fuel fired hearth appliances, including | | | | When testing for emissions, a nailed-together |
| fireplace stoves and fireplace inserts, to applicable | | | | "charge" of kiln-dried Pine is burned, and the |
| U.S., Canadian and global requirements. The UL | | | | particulate matter in the exhaust is measured |
| mark will appear on hearth products that have | | | | throughout the duration of several fires at various |
| been evaluated. The largest trade group in the | | | | draft control settings. In this way, an average |
| industry, Hearth, Patio & Barbeque | | | | grams/hour particulate emissions rating is derived. |
| Association (HPBA), provides general product | | | | Heating efficiency is not measured during EPA |
| information and guidelines pertaining to buying, | | | | emissions testing. |
| installing and operating hearth products (i.e., | | | | The internal design of wood stoves has changed |
| fireplace inserts, gas fireplaces, gas logs) but does | | | | entirely since 1990, as the result of the EPA |
| not recommend hearth products. | | | | regulation established in the late 1980's. The EPA's |
| Wood stoves are not part of the energy star | | | | mandatory smoke emission limit for wood stoves |
| program, so it's not as easy to know which are | | | | is currently 7.5 grams of smoke per hour. Today, |
| the most efficient stoves (aside from the wood | | | | all wood stoves and fireplace inserts, and some |
| stove efficiency rating which is discussed below). | | | | factory-built fireplaces sold in the U.S. must meet |
| However, as of this year, wood stoves that are | | | | this limit. Stove manufacturers have improved |
| 75% efficient or more will be designated (see | | | | their combustion technologies over the years, and |
| sticker on back of stove) as such in order to | | | | many newer wood stoves have certified |
| show that they are eligible for the 30% Biomass | | | | emissions in the 1 to 4 g/h range. The EPA |
| Federal Tax Credit that is (up to $1,500 federal | | | | certified emission rate is a reliable number that |
| tax credit) available in 2009 and 2010. | | | | can be compared from one model to the next, |
| In order to properly evaluate wood stoves and | | | | but a one or two gram per hour difference in |
| fireplace stove inserts the best place to start is a | | | | smoke emissions does not mean much in |
| basic understanding of the more significant ratings | | | | day-to-day use. |
| and specifications that accompany wood stoves | | | | Heat Output |
| and fireplace stove inserts. | | | | Usually represented as maximum heat output |
| Catalytic versus Non-Catalytic | | | | (you sometimes see a heat output range) of the |
| A catalytic combustor is a device used on some | | | | wood stove expressed in BTU's per hour. The |
| wood stoves to increase combustion efficiency of | | | | British Thermal Unit (BTU) is the primary heat |
| wood stoves by lowering flue gas ignition | | | | measurement unit used by the hearth industry to |
| temperatures of wood stoves. | | | | indicate heat output. It is the amount of energy |
| The two general approaches to meeting EPA | | | | required to raise the temperature of 1 lb. of |
| smoke emission limits are catalytic and | | | | water by 1 degree F. Typically 10,000 BTU can |
| non-catalytic combustion. Both approaches have | | | | heat approximately 500 square feet. All wood |
| proved relatively effective, but there are | | | | stoves and wood burning fireplace inserts are |
| performance differences. In catalytic combustion | | | | rated by BTU output. |
| the smoky exhaust is passed through a coated | | | | The heat output ratings can be misleading. In |
| ceramic honeycomb inside the wood stove where | | | | determining a maximum heat output rating, test |
| the smoke gases and particles ignite and burn. | | | | labs used by manufacturers (usually using |
| Catalytic stoves are capable of producing a long, | | | | hardwood fuel) cram the firebox full of firewood |
| even heat output. All catalytic stoves have a | | | | and crank the draft control wide open. This raging, |
| lever-operated catalyst bypass damper which is | | | | short-duration fire is just the opposite of how |
| opened for starting and reloading. The catalytic | | | | people burn their wood stoves, and can be |
| honeycomb degrades over time and must be | | | | misleading: if the only thing you look at is the |
| replaced, but its durability is largely in the hands of | | | | maximum heat output rating, a small wood stove |
| the stove user. The catalyst can last more than | | | | with a really big air intake can seem just as |
| six seasons if the stove is used properly, but if | | | | powerful as the largest wood stoves. Some |
| the stove is over-fired, garbage is burned and | | | | manufacturers use the heat output rating from |
| regular cleaning and maintenance are not done, | | | | EPA testing, which uses softwood fuel. Another |
| the catalyst may break down in as little as two | | | | way these figures can be misleading is that |
| years. | | | | non-catalytic wood stoves tend to produce a |
| EPA certified wood stoves have a particulate | | | | higher peak heat output, but that alone doesn't |
| emissions limit of 7.5 grams per hour for non | | | | mean they'll produce more heat over an eight |
| catalytic wood stoves and 4.1 grams per hour for | | | | hour burn cycle, which is a more relevant |
| catalytic wood stoves. All wood heating appliances | | | | performance indicator. The result is that you can't |
| subject to the New Source Performance | | | | compare the heat output of stoves because the |
| Standard for Residential Wood Heaters under the | | | | ratings are not standardized. |
| Clean Air Act offered for sale in the United | | | | Heating Capacity |
| States are required to meet these emission limits. | | | | The estimated square feet of space the wood |
| Firebox Size | | | | stove will heat. Many manufacturers display very |
| Size of the chamber where the firewood burns. | | | | wide ranges like 1,000 to 2,000 square feet or |
| Usually referenced in cubic feet and firewood | | | | suggest the maximum area the unit will heat. The |
| capacity of the chamber in weight. Big fireboxes | | | | reason for the big ranges and vague estimates is |
| can be nice. They are easier to load, and can | | | | that a particular wood stove might heat 1,000 sq. |
| often accommodate those extra-long pieces of | | | | ft. in Maryland, but only a 500 sq. ft. house in New |
| firewood that somehow find their way into the | | | | Hampshire due to the climate difference. In |
| woodpile. When choosing your woodstove, | | | | addition, an old house might have twice the heat |
| however, keep in mind that stoves with large | | | | loss of a new house of the same size in the |
| fireboxes tend to produce higher heat output, and | | | | same climate zone. Also, the layout of the house |
| easy fueling is a dear price to pay for being | | | | could materially impact capacity. For example, if |
| cooked out of the house. | | | | your house is divided into many small rooms, you |
| Maximum Log Size | | | | probably won't be able to move the heat around |
| Largest log length that will fit into firebox. The | | | | the rest of the house, so the square footage |
| standard firewood length for wood stoves and | | | | rating is useless to you. And lastly, a stove |
| fireplace stove inserts is 16", mostly because it is | | | | burning softwood will put out much less heat per |
| the most practical length for handling. Knowing | | | | firebox load than it will burning a hardwood. |
| maximum log length is useful because for | | | | Heating capacity ratings based on square footage |
| convenient loading, the firebox should be about | | | | are unreliable. |
| three inches bigger than your average piece of | | | | Burn Time |
| firewood. | | | | Maximum estimated wood stove burn time. Burn |
| Heating Efficiency | | | | time depends on wood species and moisture |
| Measure of how much of the heat value | | | | content, and on how much heat is needed during |
| contained in the firewood is extracted and | | | | the burn. How long will a given stove burn on a |
| delivered into the living space. This is the | | | | single load of wood? The only reasonable answer |
| equivalent of the MPG rating of your car or truck. | | | | is: It depends. One advantage of catalytic wood |
| Remember the quality of the firewood will impact | | | | stoves is that the good ones can deliver a lower |
| actual results. | | | | burn rate over a longer period than non-catalytic |
| The heating efficiency rating is determined by the | | | | wood stoves and yet still burn clean. But the |
| stove manufacturer by testing full loads of | | | | disadvantage of these long burn times is that the |
| seasoned cordwood. When testing for heating | | | | door glass tends to get dirty at very low firing |
| efficiency, two criteria are examined: extraction | | | | rates. In other words, a stove that has a claimed |
| efficiency; the firewood load is weighed going in, | | | | burn time of ten hours may not be better or |
| and the particulate emissions and ashes are | | | | more convenient to use than one that delivers an |
| weighed after the fire to determine how | | | | eight hour burn. |
| effectively a given firebox design breaks down | | | | |