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Technology

Updated: April 2021

Wood Stoves

  1. Non catalytic Stoves
  2. Catalytic Stoves
  3. Hybrid Stoves
  4. Automated Stoves
  5. Inserts vs. freestanding stoves
  6. Uncertified (vs. certified) wood stoves
  7. Modern Single Burn Rate Stoves
  8. Exempt Wood Stoves
The modern wood stove emerged in the early 1990s after the EPA required that almost all new stoves meet minimum emission requirements. These new stoves can use up to 30 to 40 percent less wood than older models, saving homeowners a lot of work and money, and they can emit far less smoke when they are used properly. One of the key ways to identify a more modern, EPA certified stove is whether it has glass to view the fire. Tempered glass became popular in stoves right when stoves were being first being certified.

Traditionally people think of two types of wood stoves: catalytic and non-catalytic. But today, there are also hybrid stoves and automated stoves. These two new categories offer great economic and environmental benefits to consumers – and their neighbors. All four types are discussed below in detail in addition to a description of wood stove insert. Another class of stoves, usually called masonry heaters is discussed here.

The EPA issued new wood heater (including wood stoves) regulations in the spring of 2015. As of May 15, 2020, all wood and pellet stoves had to meet stricter emissions standards of 2 grams an hour (or 2.5 grams an hour if tested with cordwood). Previous exemptions that allowed some pellet and wood stoves to be manufactured and sold without EPA certification are gone. Key provisions that will impact consumers can be found here.

The EPA requires stoves tested after May 15, 2015 to report verified efficiency numbers that can be found on the list of EPA certified stoves. As of May 15, 2020, all certified stoves have verified efficiencies on the EPA database. Make sure to check for efficiencies on the EPA site as efficiencies on manufacture websites and literature are often exaggerated.

Non-catalytic stoves
Non-catalytic stoves are the most popular and common type of stove. Almost all of them are controlled by a single air lever and shoot pre-heated air through pipes in the top of the stove to reburn smoke before it goes up the chimney. They typically cost between $1,000 and $3,000 and tend to burn through fuel more quickly than catalytic or hybrid stoves. Only the larger fireboxes, usually 2.0 cubic feet and larger, can consistently hold a fire overnight or through the day without reloading. They are more idiot-proof than catalytic stoves. Efficiencies tend to range between 65% and 75% using the higher heating values (HHV).
Catalytic stoves
Catalytic stoves tend to be more expensive ($2,000 to $3,500), can hold a fire longer and are more efficient, using less wood for the same heat compared to non-catalytic stoves. They tend to be 75%- 83% efficient (HHV) and are often favored by people who live in colder climates or want to use their stove as their primary or sole heat source. Catalysts last longer than the ones in stoves in the 1980s. If seasoned wood is consistently used, they can last 3 to 4 years. They also produce less smoke but require more care and attention by the consumer. There is a longstanding and vigorous debate about the pros and cons of cat vs. non-cat stoves.
Hybrid Stoves
Hybrid stoves use both non-catalytic and catalytic technology to achieve maximum efficiency and cleanliness. Many manufacturers make them now and they can offer the best of both technologies. They typically run in the $2,500-$4,000 range and achieve 78-85% efficiency. Hybrid stoves are now one of the technology subtypes listed in the search function of the new EPA stove database. The Alliance for Green Heat recommends this new breed of stove for those who want a cleaner, higher efficiency appliance. Another version of “hybrid” stoves can use either wood or pellets, but they are not yet on the US market.
Automated Stoves
The newest type of stove on the market is the automated or ‘smart’ stove that use sensors and computer chips to adjust airflow. Automated stoves enable the consumer to "load and leave," allowing the stove to maximize efficiency and emissions reductions on its own. Automated stoves are an emerging class that is more well-known in Europe and just starting to enter the US market. MF Fire, a Maryland based company launched an automated stove model in 2016. Charnwood, a British manufacturer is entering the US market in 2020 with their Skye E2700. Napoleon is coming out with an affordable automated smart stove in late 2020. The Canadian manufacturer SBI won an award at the 4th Wood Stove Design Challenge for their progress toward an automated stove. In the single burn rate category, the RSF Delta Fusion is an excellent example of a fast burning stove that cannot be adjusted or made to smolder.
Inserts vs. freestanding stoves
Wood stove or fireplace inserts usually refer to stoves that are designed to fit into a masonry fireplace, but they operate just like any other stove and are certified by the EPA. Fireplace inserts that are not EPA certified cannot advertise as heater appliances by including BTU output and square footage of space heated. They are typically a bit more efficient than an open fireplace, but if you really want to heat with your stove, make sure it is EPA certified and has an EPA approved efficiency rating.

The main difference between an insert and a freestanding stove is that an insert has a vertical skirt around the stove so that you cannot see into the fireplace, and thus if it’s a flush insert, it requires electricity to power a fan to get the heat out of the cavity behind the skirt. Some inserts stick out 6 to 8 inches in front of the fireplace, allowing more radiant surface to be exposed and heat better without the blower. Freestanding stoves can also be placed in masonry fireplaces and allow air to naturally flow around the stove and more easily heat the room. The electric wire from inserts to the closest wall socket can be noticeable and annoying to some people.
Uncertified (vs. certified) wood stoves
The EPA began certifying stoves in 1988 so any stove made before that is uncertified and likely to burn dirtier and less efficiently than stoves made since then. (Oregon briefly ran its own certification program in the mid-1980s). Of the 10 – 12 million installed stoves in the United States, a majority of them are still estimated to be uncertified ones made before 1988. Certified stoves are designed with secondary combustion technology that reburns some of the smoke, making them cleaner and more efficient. Uncertified stoves are often easy to spot because they rarely had glass on their doors, but the definitive sign is that they do not have a metal EPA certification label on the back. Characteristics of certified stoves that indicate cleaner burn technology is usually,

1. Introduction of pre-heated air into the firebox at the front base of the stove for primary combustion,
2. Tubes at the top of the stove with air holes for secondary combustion,
3. Firebrick surrounding 3 sides of the combustion chamber and
4. A lever to adjust air supply, allowing the user to maximize air when the fire is getting going and limit air when the fire is well-established.

The challenge of reducing the number of more polluting uncertified wood stoves has been met with scores of local and statewide wood stove change out programs that provide incentives for households to replace an old wood stove with a new wood, pellet or gas stoves or a mini-split heat pump. Uncertified stoves can still be purchased on the second hand market and installed, except in Washington and Oregon and a smattering of cities and counties. However, very affordable new certified stoves are now available that often sell for well under $1,000 and will use far less fuel, create less creosote and be safer, and better for your family's health, and your neighbor's health.
Modern Single Burn Rate Stoves
Single burn rate stoves are stoves that do not have any mechanism for the operator to adjust the amount of air going into the firebox. Up until 2015, this category of stove was exempt from EPA emissions regulations (see more below) and virtually all of them were cheaply made, cheap to buy, often made in China and widely regarded as more dangerous than EPA certified stoves. However, beginning in 2015, mainstream stove producers began making EPA certified single burn rate stoves of the same quality as adjustable burn rate stoves and today they offer consumers another option.

Single burn rate stoves can have nice big fireboxes, produce low emissions, make a good looking fires and the glass can stay cleaner. These can be a good option for people who don’t want to have adjust an air control at all and want to be sure their stove doesn’t go into smolder mode. Hearth & Home Magazine ran an article about them from RSF, one manufacturer of these units. Other examples of single burn rate stoves are the MF Fire Nova and a line of stoves by Stuv, the Montpelier II and Aspen C3 made by Vermont Casting. One potentially problematic aspect of single burn rate stoves is that some manufacturers do not advertise them as single burn rate and the EPA list of certified stoves does not designate them either. In 2011, HPBA urged the EPA to establish a new category of stoves called “Utility heater” which included single burn rate stoves and would be subject to different testing protocols. However, the term doesn’t do justice to these modern, stove and HPBA’s effort was not adopted. It is outlined in this memo.
Exempt wood stoves
The 1988 wood heater regulations left a loophole, allowing for stoves with an air-to-fuel ratio of 35 to 1 or greater to be exempt from regulation. This was meant to apply to fireplaces, but led to a huge trade in uncertified, exempt wood stoves blossomed in the United States. In 2014 the EPA disclosed that 40,000 of these uncertified wood stoves were being sold each year, which could be up to a third of all annual wood stove sales. Sometimes this class of exempt wood stoves was called “single burn rate stoves” because they had to be designed to With both exempt wood stoves and outdoor boilers, deceptive and misleading advertising bolstered sales, and the EPA does not address this. The exempt stove sector was shut down in 2015 when new EPA regulations removed this loophole and required that all residential heating stoves be subject to certification testing. Pellet stoves, contrary to what many people think, were not exempted from the 1988 EPA regulations, unless they also allowed more than 35 units of air per unit of fuel, but the EPA did not enforce this, and many pellet stoves did not establish that they were exempt or get certified. New EPA regulations also made it clear that all pellet stoves must be certified as of 2015.
 
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