“Green” Fireplaces

Contrary to popular belief, they fit quite nicely into the sustainable movement.

Source: MASONRY CONSTRUCTION MAGAZINE
Publication date: 2008-10-01

By Jim Buckley

There is very little written in “green” literature about fireplaces, and most of that found is negative. There seems to be an underlying assumption that fireplaces are dirty and inefficient. Some would say that the concept of a “green fireplace” is an oxymoron.

The emerging <i>National Green Building Standard</i> pretty much views fireplaces negatively. The standard requires new masonry fireplaces to “have gasketed doors, outside combustion air, and a chimney top damper.” It awards up to seven points for removing fireplaces altogether in renovations.

The “LEED for Homes” program has some comments about fireplaces under “combustion venting.” The statements seem to be mostly concerned about smoking fireplaces and indoor air quality. LEED has also added a preferred “install no fireplace” option.

On a positive note, fireplaces are still permitted according to LEED and <i>National Green Building Standard</i> guidelines, but it may be a struggle to get any points for including them. Green fireplaces have to be clean burning and efficient. They also may have to be provided with combustion/ventilation air and sealed off with tight-fitting doors and dampers.

Fireplace doors, of course, would block most of the radiant heat emitted into the room, but the tight-fitting dampers and combustion/ventilation air sound good, if accomplished in conjunction with the LEED recommended whole house perspective on ventilation. With a passing familiarity with the LEED program and the masonry industry's efforts to emphasize its strengths, I would add durability and thermal mass to the list. Locating the chimney mass inside the exterior walls of the house and exposing the masonry chimney walls to take advantage of all that thermal mass could be worth points.

Fireplaces should qualify for LEED points because of their sustainability characteristics.

By knowing how fire places heat, I would also add the advantages of radiant heat and the use of wood as a renewable fuel.

Almost every fireplace tested in accordance with the Washington State standard, designed to be “equivalent” to the EPA Phase II stove standard, passed. Some fireplaces, like Rumfords and Rosins, tested two or three times cleaner than the stove standard.

So, why do so many people think fireplaces are dirty and inefficient?

It all began nearly 30-years ago when the American Lung Association tried to get the EPA to regulate the airtight European stoves that flooded the U.S. market during the energy crisis of the late 1970s and early 1980s. Americans didn't know how to use the stoves and allowed them to smolder, as they bragged to their friends about how long they could bank a fire. The Lung Association eventually had to sue the EPA, which did not want to get into regulating on a retail basis. It was easier to regulate the industry than to dictate what people could do in their own homes.

Clean burning fireplaces will probably be about 63% efficient.

The suit brought against the EPA resulted in a very narrowly drawn “smoldering stove” standard. Fireplaces, masonry heaters, and other “inherently” clean-burning appliances were exempted. The American stove industry and its Hearth, Patio & Barbecue Association grew up developing equipment that would pass the EPA emissions standards, and while they were at it, keep the European stoves out of the U.S. market.

After 30 years of testing and marketing American stoves, is it any wonder that most of the scientists who do the testing and most of the people who write the articles and research papers work for or are paid by the stove manufacturers? Not that they weren't objective, especially the scientists running certified independent test labs, but they all had an interest in showing how clean the new and improved American stoves were compared with the bad old stoves and fireplaces.

How could that be? Does General Motors hire Ford to do marketing? Why didn't the masonry industry take an interest? Suffice it to say that fireplaces were “exempt” and the masonry industry wasn't focused.

Who should take responsibility for masonry fireplaces? Masons? Brick and block manufacturers? Flue liner or fire brick manufacturers? Independent dealers who sell the materials?

The bottom line was that no one took responsibility. The industry just watched masonry fireplaces denigrated and its markets slip away.

The industry needs clear objective performance standards and rules that allow fireplaces that meet the same performance standards that the stoves are allowed to follow. It is now working on an ASTM national consensus fireplace emissions standard that the EPA will recognize.

Studies from OMNI Environmental Services, Beaverton, Ore., revealed that EPA-certified stoves have an average efficiency of about 63%. Masonry fireplaces tested between 20% and 50% efficient, with either open or closed glass doors. The one “zero-clearance” metal fireplace tested the lowest at 7% efficient, again with or without doors.

Outdoor fireplaces serve as a social gathering spot in many areas of the country.

The scattered test results might indicate that there is a lot of room for improvement in fireplace efficiency. Fireplaces have not been tested for efficiency very often, and I think clean-burning equipment will probably be about 63% efficient, or similar to stoves.

While the study compared the efficiencies of various fireplaces and stoves, it only tells half the story, maybe not even that much. The approach used to test for efficiency is called the “flue gas loss method.” The energy lost up the chimney, which can easily be determined by the volume and temperature of the flue gasses, is deducted from the total energy known to be in the fuel burned. All the rest of the energy is assumed to be useful.

This approach doesn't address the vast differences in the way the heat is transmitted, or even if it's transmitted. How much heat is wasted into the brickwork if the chimney is outside the house? How much heat is wasted when cold air is sucked down the chimney to cool a light weight air-cooled metal chimney? In what situations would the heat be delivered more effectively radiantly or by convection? How does air lost up the chimney relate to the ventilation system?

Realistically speaking, fireplaces, even cheap, poorly designed ones, are not negatively efficient, as some would contend. In fact, there is reason to believe that fireplaces can be as efficient as other wood-burning appliances and can meet level-playing-field efficiency standards.

We applaud the whole house approach promoted by LEED, and advocate including the fireplaces when balancing the ventilation system for the structure. Only by taking a holistic approach can the industry hope to minimize the air necessarily lost up the chimney to carry away smoke and ensure good indoor air quality.

Fireplaces heat radiantly, so it is not sensible to require fireplace doors which block nearly all of this energy. Fireplaces need outside make-up air for combustion and ventilation, just like any other appliance that vents exhaust gasses or stale air to the exterior.

The make-up air a fireplace requires, which is about 1 cu ft/min/sq in. of flue area, should not be provided directly into the firebox. It's inadequate at best, and can bring with it bad smells, blowing ash, and in some situations, be a fire hazard.

Thermal mass is an advantage that masonry has over almost every other material. Mass inside the house complements the way fireplaces heat, which is radiantly. The masonry fireplace and chimney walls get warm. The fireplace also heats up the other surfaces in the room – walls, ceilings, and floors – bringing up the “mean radiant temperature” so people are more comfortable at cooler air temperatures, and with good ventilation.

The average temperature of all the surfaces in a room is roughly inversely proportional to air temperature. If the walls, windows, etc. average 60º F and the air temperature has to be 72º F to feel comfortable, you can reverse that and feel comfortable at 60º F if you can bring up the mean radiant temperature to 72º F.

When a room isn't so warm and there is less differential between indoor and outside air temperature, the insulation works better and good ventilation doesn't cost as much.

Rumford fireplaces are high intensity radiant heaters that work best in large, open rooms with high ceilings, even outdoors. These fireplaces provide an efficient means of delivering thermal comfort directly to people and surfaces, such as floors and walls, without having to condition the entire space. Highly efficient thermal comfort can be delivered because radiant heaters focus thermal energy, and therefore thermal comfort, directly on the occupants, rather than controlling room temperature, as do other heating systems.

Determining the amount of heat required to accomplish a desired comfort level for any space relies upon an estimation of the space heat loss. The desired inside temperature when using a radiant heating system can be about 10 deg F lower than one for a conventional warm-air heating system to achieve the same level of thermal comfort. With lower indoor air temperatures, the home's insulation works more efficiently and there is less heat loss through the building envelope. Adequate ventilation is also less expensive in a radiantly heated space because the fresh outside make-up air doesn't have to be warmed up as much.

<i>Jim Buckley is one of the country's leading experts on historic and efficient fireplaces. He was instrumental in changing the BOCA and ICBO codes, and more recently the new International Residential Code (IRC), to permit the tall and shallow Rumfords. He is a member of the ASTM C4 and E6 committees, ASHRAE, Residential Mason Contractors Association (RMCA), Western States Clay Products Association (WSCPA), Clay Flue Lining Institute (CFLI), and Hearth Products Association (HPA). Buckley is on the Editorial Advisory Board of MASONRY CONSTRUCTION.</i>