Or farewell, my chilly

Gary Dymski, Newsday, November 4, 2004

I was leafing through old case files when she slinked into the office. She perched herself at the edge of my desk, crossing legs longer than a cool glass of water.

"I need help," she said.

"What did you have in mind?"

"It's my fireplace. It should be warm and cozy, but it's a big, cold brute. I'm desperate."

If desperation sends in this kind of dame, I'm definitely in the right business, I thought. But the better part of me knew she'd be trouble. I'd soon be elbow-deep in soot and ashes. I didn't care. It's part of the job. I'm the house detective.

When my wife tells me to fix the fireplace, or else, I like to think she sees me as Philip Marlowe or Sam Spade or Spenser. A sort of investigative handyman. Hey, every little bit helps.

I've solved a few house mysteries in previous columns. There was the case of the missing kitchen cabinet handle, and I worked overtime to solve the mystery of the black smoke that haunted an elderly couple in Merrick. The culprit turned out to be a nasty oil burner.

But my freezing fireplace could be a candidate for "Unsolved Mysteries." Here's the scoop.

In 1997 my wife and I purchased a new home with a prefabricated fireplace, a Heatilator model EC42, that was installed by the builder. For the first few years, because of relatively warm winters, we didn't notice the fireplace was sucking in a steady stream of cold air -- a dastardly deed known as "backdrafting." But during the last two much-colder winters, our family room was like a meat locker. Last winter the chill was so big that I sealed the fireplace opening with shrink-wrap insulation, the plastic film that covers drafty windows from the inside.

My wife did not approve. "This winter," she said, "plastic wrap is not an option."

So, to keep her off my case, I went sleuthing. Using a little of Sherlock Holmes' deductive reasoning, I figured one problem was the fireplace's location -- it was installed on an exterior wall. The opening faces a large air-return vent for a forced-air furnace. Such vents feed furnaces fresh air. And since the vent was just 30 feet away, the fireplace opening was its primary source of outside air, creating the backdraft.

I figured an air-tight damper – a plate that controls the flow of air, smoke and draft – at the top of the chimney might eliminate the backdraft. So I turned to Chim Cap Corp., a Farmingdale manufacturer of chimney supplies. The company does not sell to the public, but Debbie, who handles phone calls, suggested I contact Don Chiapetta, who operates Top to Bottom Chimney Cleaners.

Chiapetta needed just a few minutes to tell me the return vent was the least of my problems. "That might be a small, small part of it," he said, "but you have a couple of things going on here, and I don't think an air-tight damper is going to do much good."

Chiapetta thought the larger problem was in the "chase," the exterior structure that encloses the chimney from the foundation to the roofline. Sometimes called a "doghouse" because it looks like a separate structure on the exterior wall, the chase also contains venting. "My guess is that the chase is poorly insulated or not insulated at all," he said.

What now? Was my only option tearing away interior walls or vinyl siding and sheathing to insulate the chase? Chiapetta believed that was indeed the best approach, but he also suggested another option.

His suggestion led me to a small town called Killaloe, about 100 miles west of Ottawa, in the province of Ontario, Canada. Now the game was afoot – or at least on the phone. John Gulland was on the other end of the line, and after hearing my case, he didn't have good news. "You might be better off using a half-stick of dynamite on the existing fireplace and starting over," he said.

According to Gulland, a wood-burning consultant whose clients include training associations and the Canadian government, more than one thing was wrong. He agreed it was wise to assume the chase was the major source of cold air. "A good chase is almost impossible to build," he said. "They are almost always leaky."

Gulland, who oversees a Web site called woodheat.org, said builders should not be making chases. "Yours is a problem that is affecting thousands and thousands of homeowners," he said. "We should not be putting fireplaces in chases." Instead, he said fireplaces should be installed inside a wall as part of the home's interior.

My other problem is known as the "stack effect," which occurs when a fireplace is not burning wood. The stack effect is created because warm air in buildings, like flue gases in a chimney, is buoyant. The greater the difference between the outdoor and indoor temperature, the more cold air flows into the chimney in lower floor levels. Our chimney is on the ground floor.

So, cold air is leaking in from the chase, and when it is really cold outside, the stack effect sucks cold air into the lower levels of the house and releases warmer air upstairs through any small openings.

Can this drafty fireplace be fixed?

"Even if you tear down interior walls and seal every crack and crevice, it might not be enough," Gulland said.

She was back in my office, hoping for good news.

"How much do you love your fireplace?" I asked her.

"I can't give it up," she said. "I need it."

This would be rough, but she had to know. "The interior wall around the fireplace, it will have to come down. I have to insulate. It's not going to be pretty, and even then, I'm not sure I can save it."

Her blue eyes were like daggers. She didn't say anything. But I knew what she was thinking: "My walls. My family room. Oh, no."

The next installment will appear soon.

Yes, but open fireplaces give all fireplaces a bad name

A technical rant by John Gulland

Talk about a clash of technologies: In a house that is to be tightly-constructed and well-insulated so it will be cozy and easy to heat, the homebuyers want to have a traditional open fireplace, a device whose design was state-of-the-art a couple of centuries ago. Once built, this new house and old fireplace will not coexist without conflict and the owners might regret reaching back in history to select their fireplace.

To perform reliably in a modern house, the unruly traditional fireplace must be tamed by some new technology, but it need not lose the essential qualities that have always compelled us to gather around the hearth.

Declaring my bias, I freely admit my enthusiasm for fireplaces and think that every house needs a hearth to be complete. A fire burns on my hearth all winter and I never tire of watching the flames and being within range of their warmth.

It is not much to ask, really, that a fireplace work properly

But, I also think the traditional open fireplace is headed for extinction and I, for one, won't shed a tear at its passing. The end will come because the open fireplace is an antique technology that is incompatible with modern housing. It is wasteful by temperament, and through its gluttonous appetite for fuel and air, it scoffs at the ideas of energy conservation and environmental correctness.

If you build a standard house using the latest in materials and techniques, its tight skin will not leak enough to supply the air demands of an open fireplace. The problem is not with the house, but with the anachronistic fireplace.

Strong opinions, often colored by myth and misinformation, usually surround discussions of fireplaces. So, to avoid any misunderstanding, allow me to propose this basic principle: A fireplace should work well all the time and never screw up in a big way; should not belch acridly during a party, should not set off the smoke detectors at 2:30 in the morning, and should not stink and gush cold air when no fire burns. And further, given the advanced state of construction and fireplace technology, a builder should be able to confidently guarantee to the homebuyer that the fireplace will perform properly.

An open fireplace with the characteristic smoke stain above the hearth openingIt is not much to ask, really, that a fireplace work properly, no more than we ask of most other building components. Yet, complaints about nuisance fireplaces are among the most common call-backs in the building industry. Despite the voodoo preached by proponents of certain variations on the theme, there is nothing magical about fireplace design. For example, here is a pretty reliable rule of thumb: the more air the fireplace demands for normal operation, the more susceptible it is to smoke spillage and backdrafting.

If you place the fire on the room side of a flow restriction, like a throat damper, you need strong draft and high flow up the chimney to keep smoke from spilling into the room. An open fireplace consumes between 200 and 600 cubic feet per minute (cfm) of room air—more if it is a big fireplace with a big, big fire. Tightly built houses cannot tolerate a 200 cfm exhaust flow without getting meaningfully depressurized, so there's a problem right away.

Another example of a very expensive custom fireplace that fills the room with smokeIf a home buyer rigidly demanded an open fireplace, it could be made to work if you threw enough money and horsepower at the problem. A chimney top fan could be installed at considerable cost, but it could severely depressurize the house in its attempt to flow enough air to prevent smoke spillage from the fireplace, and would likely backdraft a conventional gas furnace or water heater. Alternatively, a high-volume, fan forced, pre-heated outdoor make-up air system could be designed and installed. Just before lighting the fireplace, the user would turn on the make-up air fan, pressurizing the house and forcing the necessary flow through the fireplace and up the chimney. This large-capacity make-up air system would be complicated because the incoming air would need tempering by a thermostatically-controlled electric duct heater of substantial output. Distributing the air effectively could also be a challenge. Both options—the chimney top fan and large make-up air system—are expensive and both have drawbacks.

Custom glass doors on a masonnry fireplace. Doors like this don't improve efficiency very much, but they can help to reduce smoke spillage.There are easier ways to tame the fireplace. When you place the fire behind the main flow restriction, say a glass door assembly, you can get away with lower flow rates and draft levels without smoke spillage. With doors, even a set of leaky bi-fold doors, the flow rate drops by three-quarters to 50 to 150 cfm, depending on flue size, fire size and door leakage. The barrier between the fire and the room formed by the doors makes the fireplace more spillage-resistant by a huge margin. The doors don't make this fire place an efficient heater, just less of a nuisance.

Some people claim that glass doors spoil a fireplace. (Do they mean in the same way electric lights spoiled the pleasure of reading by candle light? Or the way shock absorbers on cars took away the feel of the road?) In reality, at least a spark screen is needed to prevent damage to rugs, floors and furniture when the characteristic crackle of the fire spits glowing bits from the hearth. True, glass doors do block out most of the sound of the fire, which is just fine for those of us who find the crackle only makes them apprehensive about those glowing bits. Given the choice of looking through a wire mesh screen or clear glass, I'll take the glass.

This is an EPA certified, high-efficiency fireplace.Beyond the open fireplace at 400 cfm average air demand and the fireplace with doors at 100 cfm, there is a third category in this descending order of air demand. Call it a controlled-combustion fireplace. It has doors with gaskets and it manages both the amount and location of combustion air it admits. By limiting the flow of air to an amount closer to that needed for combustion of the wood, the demand falls by three-quarters again to 15 to 30 cfm. Within this category, I would include all the factory-built fireplaces that meet the Environmental Protection Agency (EPA) emission limits for wood heaters, as well as massive heat-storage units like masonry heaters, Russian fireplaces and their ilk. There is also some EPA certified single burn rate (SBR) fireplaces, which, because they are fairly modest consumers of room air, can function well in tight houses.

A masonry heater is a high-efficiency fireplace that is compatible with modern houses.Not incidentally, a fireplace's consumption of room air directly affects its efficiency - that is, how much of the energy contained in the logs is transferred as cozy warmth to the room. Because they suck up so much room air, open fireplaces deliver between zero and 20 per cent net efficiency. The low efficiency results from the house furnace working so hard to heat up the outside air that must come in to replace air exhausted by the fireplace. The colder the weather, the lower the delivered efficiency from an open fireplace. A fireplace with doors can deliver between 10 and 30 per cent efficiency, depending on whether it has a heat exchanger that works, but this is still lousy efficiency by modern standards.  A fireplace that uses current technology, one that is EPA certified for low emissions, for example, will deliver between 60 and 70 per cent efficiency.  This means a modern woodburning fireplace is competitive with most other forms of home heating in terms of energy efficiency.

Some housing technologists recommend that builders avoid using any heating or hearth appliance that vents through a chimney and operates on natural draft. This caution would apply to all wood burning fireplaces because, with current technology, they must be vented through a vertical chimney. While I'm sure such advice is well-intentioned, if adopted, it would mean the elimination the natural hearth from every new house. Home buyers could not enjoy the comfort and quality of a well-built modern home while sitting in their favorite chair in front of a real wood burning fireplace. They could not stay cozy and comfortable during an electrical power failure by burning wood in the fireplace. They would be unable to use this renewable energy source as one route to environmental responsibility, but would be forced to heat with fossil fuels and be locked into a one-sided relationship with a large energy utility. If they wanted a hearth, their only option would be a virtual fireplace burning gas or propane with its designer flame and mind-numbing sameness. Of course, gas fireplaces are fine for urban houses and apartments, but one of the great pleasures of living on the urban fringe and beyond is to build a real fire on a beautiful hearth and sit back to enjoy it.

A future of houses without real fireplaces is not particularly appealing. Luckily, it's not necessary either. By matching technologies, it is possible to combine a modern house with a real fireplace. In specifying a spillage-resistant fireplace for a well-built house, the first line of defense is a set of glass doors. These must have panels of ceramic glass, a miracle material that won't shatter, but will allow infrared (heat) radiation into the room.

Better still, select an EPA certified fireplace or a masonry heater from a reputable supplier. These units consume very little room air and can tolerate a modest level of room depressurization without complaint. They can be just as beautiful as a traditional open fireplace, but their manners are so much better.

JG

This article, which appeared in the June 2002 edition of Hearth & Home Magazine, was commissioned by the Technical Committee of the Hearth, Patio and Barbecue Association. It represents a consensus of the major factory-built fireplace manufacturers.

Prevent smoking, drafts and odors from fireplaces installed in new homes

Fig 1. The fireplace in this house would not operate reliably because it has many of the features that lead to problems.

Introduction

The ideal wood-burning fireplace is a pleasure to use. It doesn't smoke when lit or spill cold air and odors when not in use; it doesn't back draft when the kitchen fan is on, and it works well regardless of wind speed or direction. For obvious reasons, everyone involved in putting fireplaces into houses, including manufacturers, architects, builders and installation contractors, want every fireplace to give pleasure and never frustrate the home owner. But sometimes fireplaces don't work well and the results are costly, not only in lost time but in the reputation of everyone concerned.

Over the years the fireplace industry has spent a lot of time and money investigating problems and working to improve fireplace performance. We now know how to prevent problems through effective installation design. This paper provides a concise overview of the characteristics of good design. But before getting to he details of best practices for integrating fireplaces into today's houses, there is one essential fact you need to know. The most common fireplace problems are difficult and expensive to correct after the fireplace is installed, so the installation design stage is critical to success.

Fig. 2 This system will function reliably becuase it has the characteristics that promote successful venting.

Although installations that meet all of these best practices are ideal and are most likely to give trouble-free performance, sometimes house designs or client objectives make compromises necessary. Where one aspect of best practice cannot be met, fireplace performance might not suffer noticeably. However, installations with several characteristics known to cause problems are much more likely to create user dissatisfaction because of smoking and backdrafting. Therefore, while complying with all the best practices is a good target to aim for in all installation, some compromise will not necessarily result in poor performance.

These best practices can be expected to produce good performance in most fireplaces. However, the installation instructions provided by the fireplace manufacturer take precedence, so they should be followed if they differ from the recommendations made here.

Venting failure is usually caused by the location of the fireplace and its chimney in the house and the way other equipment affects fireplace operation. For this reason the best time to prevent smoke spillage from fireplaces is during the planning stage as the fireplace system is integrated with the house design. Following, and in Figures 1 and 2, is a summary of the elements of best practice that are discussed in this paper.

1. Install fireplaces and chimneys inside the building.

2. Penetrate the building envelope at or near its highest level.

3. Avoid large, uncompensated exhausts.

4. Avoid very short chimney systems.

5. Use straight chimney systems.

6. Provide glass doors.

1. Locate Fireplaces and Chimneys Inside Houses

A common installation practice involves locating the fireplace and its chimney in a chase projecting outside the building envelope to conserve interior floor space. Despite is popularity, the practice of locating fireplaces in outside chases is one of the main causes of complaints about fireplaces that spill odors and cold air when not in use and smoke when a fire is lit. A fireplace depends on the buoyancy of its hot exhaust to draw in combustion air and create flow up the chimney. But when the chimney runs up the outside of the house, its ability to resist the negative pressure in the house due to stack effect is weakened (see discussion of stack effect below).

Draft which is the pressure difference needed to vent fireplaces successfully, is influenced by the temperature of the exhaust and the height of the chimney. That is, the hotter the exhaust gases, the stronger the draft. And the taller the chimney (at a given temperature), the stronger the draft. In well-designed systems there tends to be a low level of draft present during the heating season even when the fireplace is not in use. This "standby draft" is produced because the room temperature air in the chimney is warmer than the outdoor air, so it rises. Without standby draft, chimney flow can reverse, spilling foul odors and cold air from an unused fireplace.

Under standby conditions the air in a fireplace and chimney installed in an outside chase tends to cool gradually to below room temperature, even if the chase is sealed and insulated. as the chimney temperature falls, draft declines along with it. The loss of standby draft is worsened by the fact that negative pressure inside the house can work against upward flow in the chimney. The three most common causes of negative pressure in houses are stack effect, exhaust fan effects and air circulation system imbalances. One or more of these sources are found in all houses to varying degrees.

Stack Effect

Just as warm air in a chimney produces draft, the air in the house is warm relative to the outdoor air so it tends to rise, producing a pressure difference called stack effect. Stack effect creates negative pressure in lower levels of the house, where fireplaces are normally installed. the negative pressure due to stack effect is enough to force a cold backdraft in a fireplace chimney that is cooler than room temperature. If one attempts to light a fire in a backdrafting fireplace, smoke will flow into the room instead of up the chimney. The negative pressure due to stack effect experienced by the fireplace is strengthened if the house had excessive leakage at high levels (see below). The cure for this form of venting failure is straightforward: Install chimneys through the warm space enclosed by the building envelope.

A chimney installed inside the house will produce more standby draft than the house produces in stack effect. This is because the air inside the chimney is at room temperature, but the chimney is taller than the warm space of the house. The negative pressure due to the stack effect in the house is never strong enough to overcome standby draft in an interior chimney (subject to the effect discussed below).

2. Penetrate the Top of the Building Envelope

Keeping a chimney at room temperature during standby conditions deals with one of the main influences on chimney draft. The other factor is height and it is just as important. To produce enough standby draft, a chimney must not only be as warm as the house, but it must also be as tall as the highest part of the building envelope in order to overcome the negative pressure due to stack effect.

Fig. 3 The chimney should penetrate a vaulted ceiling at or near its highest pointA chimney installed in a single-story section of a two-story house can suffer cold backdrafting at standby (Fig. 1). This is because the chimney may be shorter than the warm part to of the building and in addition, cooling of the chimney's exposed section reduces its average temperature. A chimney installed low to the caves of a house with a vaulted ceiling can backdraft for the same reasons. (See Fig. 3)

The problems resulting from a chimney being installed in an outside chase or penetrating the building envelope at or below its top are made far worse if the majority of leaks in the building envelope are concentrate at high levels. High level leakage can be created by recessed light fixtures, ceiling fan mounts, poorly fitted attic hatches, fold-up stairs and skylights. High level leakage sites should be minimized if possible and, where unavoidable, they should be carefully sealed to the building air barrier.

To avoid these problems, a chimney should penetrate the highest part of the building envelope. For most common house designs, this means that the fireplace and chimney should be located on an interior wall rather than a perimeter wall.

Wind Effects

Fireplaces and chimneys that are located on perimeter walls (or outside perimeter walls in chases) are more vulnerable to the adverse effects of wind because their chimneys tend to be low relative to roof lines. The general strategy for preventing cold backdrafts under standby conditions is to locate fireplaces and their chimneys centrally in buildings rather than against perimeter walls. The same approach is effective in reducing the potentially adverse effects of wind by placing the top of the chimney above areas of wind turbulence.

Even in cases where venting problems are assumed to be wind-related, the replacement of the standard chimney cap with on of specialized design should only be done with the approval of the fireplace manufacturer. The standard chimney caps supplied by manufactures of factory-built fireplaces and chimneys are usually of good design, so replacing standard caps supplied with these fireplaces is not necessary. In fact, the supplied cap should never be replaced or left off for aesthetic or other reasons because the result could be venting failure due to adverse winds. Decorative shrouds for chimney tops should never be used unless listed by the fireplace manufacturer.

3. Avoid Large, Uncompensated Exhausts

When a large exhaust, such as a down-draft kitchen barbecue fan, is turned on in a modern tightly constructed house the pressure inside can drop below atmospheric pressure outside. This negative pressure competes with upward flow in a chimney produced by draft and can result in spillage of smoke into the house. Once they are aware of it, most homeowners can manage this potential problem, but it can be alarming when first experienced.

4. Avoid Very Short Chimney Systems

At a given temperature difference, a taller chimney will produce more draft than a shorter chimney. While factory-built fireplaces are normally approved for minimum system heights in the 14 to 15-foot range, taller systems than this are preferable for good performance particularly for fireplaces with generous heath openings relative to chimney diameter. The larger the fireplace opening, the more air must pass through it to prevent spillage. For fireplaces with large openings or with more than one open side, such as see-through or corner fireplaces, a system height of at least 20 feet is preferable. Note that the installation instructions for listed factory-built fireplaces provide chimney height limitations and these should be followed precisely.

Fig. 4 Chimney offsets can be implicated in smoke spillage5. Use Straight Chimney Systems

Chimney offsets should be avoided where possible. Each elbow or offset in venting system creates turbulence in the flue gas steam and therefore presents resistance to flow. Offsets in chimneys are not uncommon but their use demands special attention to the other aspects of system design. Manufacturer’s instructions for factory-built fireplaces should be reviewed carefully for criteria associated with the use of offsets.

6. Provide Glass Doors

Open fireplaces are particularly vulnerable to smoke spillage for two reasons. First, the main restriction to flow - the chimney - is downstream of the fire, and there is little resistance to spillage flow into the room. Second, most new homes do not provide enough natural leakage to supply the large amount of air that an open fireplace consumes. Spillage resistance is increased significantly if the main flow restriction is on the room side of the fire in the form of glass doors, which also reduce the amount of air that he fireplace needs for satisfactory operation.

Many homeowners enjoy the crackle of an open fire and some fireplaces in some houses can operate successfully this way. But changing conditions, like adverse winds, the operation of an exhaust fan, unbalanced airflows from one room to another, or even people walking in front of the fireplace, can induce spillage from the open heath. See-through or multi-sided open fireplaces are particularly vulnerable to these pressure differences and airflows. If smoke spillage occurs, the quickest and most effective way to stop the spillage is to close the glass doors. Glass doors can also help to reduce air leakage up the chimney and hearth odors from spilling into the room when the fireplace is not in use. For these reasons all fireplaces should be provided with glass doors, even if the purchaser expects to use the fireplace as an open heath most of the time.

JG

By Jim Gillam, editor of SNEWS - The Chimney Sweep's Newsmagazine. This article originally appeared in the March 2001 issue of SNEWS, which is an independent trade journal for chimney professionals.

The U.S. Environmental Protection Agency says certified woodstoves degrade with use, but they still burn cleaner than uncertified stoves.

Jim Gillam says with conscientious woodburning and regular service by a professional chimney sweep, certified woodstoves in the real world nearly match their laboratory emission numbers.

Particulate emissions measured from woodstoves after extended use don't match the laboratory numbers reported for the same stove models when certified to the U.S. Environmental Protection Agency's (EPA) Phase II emissions standards, and in most cases are higher, according to an EPA-sponsored study released in December. "But, on average, after about 7 years they still have lower emissions than uncertified conventional stoves," the EPA report concluded.

Close analysis of the small sample in this study also suggests that conscientious woodburning and regular service of the stove and chimney system by a professional chimney sweep enables a woodstove in active use to burn so cleanly as to nearly achieve the laboratory emissions values.

Due to concerns about air pollution, a maximum level of particulate emissions is enforced for woodstoves. Before any stove model can be sold, manufacturers must submit a sample for testing under controlled conditions in an emissions laboratory.

Air quality regulators are also concerned about the levels of polycyclic organic matter (POM) produced by woodburning appliances.

Primarily due to the high operating temperatures characteristic of woodstoves, some components of woodstoves may become damaged with long-term use. These components include baffles, catalytic combustors, catalytic combustor bypasses, gaskets and seals.

This study attempted to test the suspicion among air quality regulators that air emissions from woodstoves with damaged or worn out parts would be higher than values accepted during the certification process. EPA hired OMNI Environmental Services, Inc. of Beaverton, Oregon, a leading emissions testing laboratory, to examine sixteen EPA Phase 2 certified woodstoves that had been installed in residences prior to autumn 1992. They were monitored "in order to assess the level of long-term degradation and potential increase in PM (particulate matter) and POM (polycyclic organic matter) air emissions of older Phase 2 certified stoves under actual in-home usage."

The testing took place in November and December of 1998.

The Testing Emissions in the Real World

A total of 43 test runs were performed during three one-week periods. The stoves were located in Klamath Falls and Portland, Oregon.

Though in the same state, the two locations have dissimilar climates. Klamath Falls, situated in an intermountain basin at 4100' elevation, is relatively arid and cold in the winter with an average heating degree-day (HDD) value of 6600. Portland has a mild maritime climate with rainy winters. Portland's HDD value is 4109. The intent was to produce results more widely applicable to the nation as a whole than if homes in a single city were selected.

Participants in the study burned locally available cordwood fuel and were reimbursed for its cost. Fuel moisture was measured with a Delmhorst moisture meter, or determined through drying/gravimetric analysis in the laboratory. Wood was div ided into pre-weighed bundles, and any leftover wood was also weighed.

A variety of species was burned. Softwoods and hardwoods including Douglas fir, maple, alder, oak, cherry, birch, and lodgepole pine were burned in the Portland woodstoves. In the Klamath Falls appliances, conifers including lodgepole pine, ponderosa pine, juniper and Douglas fir were consumed.

Wood moisture in this study ranged from 9% to nearly 53% on a wet basis. Wood moisture averaged considerably less in the Klamath Falls group.

A sampling device known as the AWES (Automated Woodstove Emissions Sampler) was attached to the stovepipe of each stove. The AWES was developed by OMNI Laboratories to measure emissions of residential woodburning appliances during normal in-home use. It has previously been used in studies quantifying emissions from woodstoves, masonry heaters, pellet stoves and fireplaces.

In appearance, the AWES was simply an aluminum box that sat near the stove. A stainless steel inlet probe was inserted into the stovepipe 30 centimeters above the flue collar of the stove.

During this study, the AWES was programmed to sample for two minutes every fifteen minutes whenever the temperature of the flue gases exceeded 100°F, indicating that the appliance was in use.

Samples of the flue gases flowed into the AWES through stainless steel tubing. Particulate samples were captured with a heated filter and the oxygen content of the flue gas was measured with an electrochemical cell. Flue gas temperature and room temperatu re were recorded and the flue gas was returned to the woodburning appliance chimney above the point where the sample was withdrawn.

The Results

The sixteen used certified woodstoves in this study emitted an average of 11 grams per hour (g/hr) of particu late matter. This is more than double the certification value for those stove models, but substantially lower than the emissions measured from uncertified woodstoves in similar tests.

"Out of the 16 stoves inspected, all showed the effects of use," the report concluded. "Routine maintenance or minor repairs could have kept all units in good operating condition if they had been done," the authors (Lawrence H. Fisher, James E. Houck and Paul E. Tiegs of OMNI Environmental Services, Inc., Beaverton, OR and James McGaughey of the Eastern Research Group, Inc., Morrisville, NC) added.

Although this was not specifically tracked in the study, I have personal knowledge of five of these woodstove systems, having serviced them annually as Ash Bros. Chimney Sweep for a number of years.

The maintenance history of the remaining three Klamath Falls stoves, and of the eight Portland stoves, is unknown.

The average emissions rate for the five chimney sweep maintained woodstove systems was 4.8 grams per hour (g/hr). This is very close to the average certification value, 4.2 g/hr, derived in laboratory testing for those stove models. All of these stoves were non-catalytic models. The certification threshold for EPA Phase 2 certified non-catalytic stoves is 7.5 g/hr.

The average emissions rate for the 11 stoves with unknown maintenance histories was 13.8 g/hr, while the average certification value for those stoves was 3.9 g/hr. These stoves included five catalytic models. The certification threshold for Phase 2 catalytic stoves is 4.1 g/hr.

Conscientious Wood Burning

One objective of this study was to document changes in emissions performance of woodstoves over time. An attempt was made to return to woodstoves studied in real-world emissions monitoring conducted in 1989/1990 [see SNEWS July 1990, p. 20] and 1991/1992. This proved to be possible in only two cases. In only one case were the same homeowners (stove operators) involved.

In the only case where emissions from the same stove with the same operators were compared, emissions actually were lower in 1998 testing than they were when the stove was new. In this instance, the same woodstove with the same operators was tracked through three studies over a nine-year period.

The authors of the EPA report said, "The higher emission factor [for this stove] in the 1989/1990 study cannot be readily explained. However, it is probably simply a reflection of the variability often seen in woodstove emissions when different fuels are burned and different burning patterns are used."

"We've learned about the stove," said Karine Neubert, the owner of the Haughs 171E non-catalytic woodstove that emitted fewer particulates than did any other in this study.

"It burns really well," Mrs. Neubert continued, "but we were concerned about how it would measure up in this study, because there is a crack in the baffle."

Fuel Moisture

Mrs. Neubert gave some of the credit for their stove's low emissions in the tests to their firewood. "We always burn good wood," she said. "We keep it dry and covered."

The report documents that the Neuberts burned mostly lodgepole pine during the 1998 study, lodgepole and Douglas fir in the 1991/1992 tests, and juniper during emissions testing in 1989/1990. In each of the three tests, the Neuberts' wood moisture measured between 13-17%.

The EPA report noted that particulate emissions for stoves in Portland were higher on the average than the stoves in Klamath Falls. "This result is consistent with the average higher fuel moisture content and burn rate characteristics of the Portland portion of the study as compared with the Klamath Falls portion of the study," the authors said.

Drawing Conclusions

"The emission rates for phase 2 stove models reported as part of the NSPS (new source performance standards) certification process do not represent emission levels of the same stove models in homes after extended use," the authors concluded. "On the average, they still have lower emissions than uncertified conventional stoves."

The authors were careful to note that "no direct statistical correlation between emissions and wood moisture, burn rate or stove condition could be made due to the number of variables associated with real-world in-home use of woodstoves."

With this in mind, their conclusion that "the particulate emissions factors of the certified phase 2 stoves evaluated in this study appear to have become higher with use" would appear to be questionable. The disappointingly small subset of two stoves that participated in previous emissions tests and thus are available for comparison doesn't lend support to this view. One of the two stoves actually had lower emissions numbers in the later tests.

However, observation and photographic evidence definitely confirm that the stoves 'showed the effects of use."

The Bottom Line

With the authors' hint that "routine maintenance or minor repairs could have kept all units in good operating condition" we are led to the most important conclusion available from this small study, although they did not explicitly state it, or perhaps even realize it:

With proper installation and conscientious operation, including use of covered, seasoned wood and regular service by a competent professional chimney sweep, certified woodstoves after years of use burn nearly as cleanly in the real world as they did under laboratory conditions for certification.