Warming To The Concept

While ultimately CCHRC would like to develop templates for refractory core heaters that can be taken into the smallest Alaskan villages, and even offer the possibility of cogeneration of heat and electricity, the challenge with the RTF unit was mainly one of size.

“The amount of BTUs (British thermal units) the unit is capable of putting out had to be sized with the amount of energy use that’s modeled for the structure,” Hebert explains. “We also put a water jacket in the heater to provide warm water to supplement the hot water for our radiant-heat system.”

Click photo to enlargeTo translate the organization’s goals into reality, Hebert – as project superintendent – chose two local subs, Solutions to Healthy Breathing, owned by Bill Reynolds, and Stonecastle Masonry Ltd., owned by Dan Givens.

“Both are members of the (Randolph, Vt.-based) Masonry Heater Association of North America,” he says. “Dan is a master stone mason who did the finish work and Bill is an innovative guy. He was also involved in our ventilation strategy for the building in terms of circulating and filtering the air.”

Reynolds explains that he first became interested in masonry heaters when his wife’s asthma required him to find an alternative to the common wood stove. He installed his first design in his own home three years ago.

“I go to Austria every year and I designed mine with the help of a mason over there,” he says. “We then sampled it for a year and found it was very efficient and very clean.”

Reynolds adds that no requirements were specified going into the RTF project, other than that the interior be capable of being copied. For that reason, that part of the heater is based on a design created by Tom Stroud, now senior manager of codes and standards for  the Hearth, Patio and Barbecue Association (HPBA), in 1988.

The interior design was built from 135 pieces of cast refractory cement and the same fire clay that’s used in fireplaces, which is rated to 2,600°F. The firebox generally reaches temperatures of 1,800°F -2,100°F, literally gasifying the wood.

“It never really hardens because the internal works of a heater are constantly in motion so when it’s very, very hot it won’t crack,” Reynolds says. “Inside the veneer there’s a space of probably a quarter-of-an-inch because the inside expands that much.”

To enhance the efficiency of the masonry heater, Reynolds also incorporated a German design that features nine different chambers. As the air passes from one chamber to the next around the heater, more heat is given up to the veneer and more gases are burned, rather than going up the chimney. Testing by the federal Environmental Protection Agency (EPA) in the mid-1990s showed it to be the best available technology.

“The real objective is to burn all the gases completely,” he says. “We knew this design worked, but we changed the air differently, so it can come from either outside the building or inside the building. And, we can direct the air within the fire chamber itself using a valve system I designed.”

ROCK ON

Although Reynolds makes the design process sound fairly simple, Givens says the end result was what he describes as extra-heavy, from several standpoints. Not only does the masonry heater weigh 12,000 lbs., but it can burn 90-100 lbs. of wood at one time, and it’s supported by 3” X 12” beams in the building’s basement.

Givens adds that the masonry heaters are really the latest trend he’s seen in supplemental home heating as his customers have gone from fireplaces to wood stoves to the heaters.

“The pendulum is swinging back toward centering a masonry heater in the house,” he says. “The hearth is now called the heart, and it’s the focal point. You come in and get warm and people like that ambiance.”

The technology has also been helped by the fact that some countries, such as Finland and Canada, are giving tax credits to people who put them in their homes.

Because masonry heaters work by radiating heat, an exterior that can hold the heat generated on the interior is very important, Givens and Reynolds agreed that the exterior should be an Alaskan river rock.

“We wanted a high-density rock that would hold the heat as much as possible,” says Reynolds. “It required some research, because you don’t want to get the wrong rocks and heat them too quickly or they’ll explode. We brought the finished heater up to temperature over about two weeks to slowly drive the water out of the mass.”