Wednesday, January 11, 2012

High-Performance Masonry Heating

By Stephen Bushway
Deer Hill Masonry Heat

(This information is based on emission test results done with a Finnish contraflow heater design with a grate and air supply from under and in front of the grate)
Whether you're a seasoned masonry heater owner or are reading this as a new owner, there are some newly discovered firing techniques you will want to employ to get the most out of your hearth.
  • Use regular cordwood! Yes, it is not necessary to burn sticks 2" to 3" across to get the rapid, complete combustion that masonry heaters are noted for. Actually, 4" to 6" pieces such that 9 to 12 pieces will fill your firebox when cross hatched will provide better air/fuel ratio for complete, and more usable combustion. The bigger pieces allow more time for the masonry mass to soak up the fire's heat - yielding better heat transfer to your home.
  • Place smaller wood, kindling and paper on top of this load and light from the top! The revolutionary top burn greatly reduces emissions during the dirtiest part of a firing - the first 10 minutes or so. Lighting the load from the top of the pile yields a candle-like burn, allowing the firebox to heat up as the volatile gases are being more evenly released.
  • Take a little extra care in laying up your fire. A good "fuel load configuration" is well balanced and won't topple over prematurely. Allow a 1" airspace between pieces, placing the largest pieces first and the bottom row running "front to back" in the firebox.
  • Don't admit air from below the grate until the fire is down to coals. Use the air slots in the door, if provided. If not, cut scrap dimensional lumber so that a piece will cover the grate and air is admitted from the front. With a top burn fire the piece will block grate air until it is burned through - well into the firing. Alternately, you can adapt your doors so that they will 3/4 inch of air between them but can not be accidentally be opened further. This modification was lab tested for emissions with excellent results. During the coal burning phase, rake the coals so they evenly cover the grate with air coming from below.
  • It is more efficient to have one full firing than 2 fires half as large.
If you've been burning small pieces kindled at the bottom in your contraflow heater, chances are there is soot in the heat exchange channels. This can effectively be cleaned from the cleanout door usin a rod and brush designed for cleaning pellet stove chimneys. This will better allow them to absorb heat from future fires.
Burning cordwood has so many benefits, economy-wise. And as you're probably aware, masonry heaters provide the cleanest burning solid fuel appliances available. Now, following these simple practices you can be assured that you are providing yourself and your loved ones simple, yet state-of-the-art heat more cleanly than ever.

High-Tech Old World Technology Latest Trend in Heating

By Marge Padgitt
HearthMasters, Inc.


Sometimes old things are better than new, like old houses, historic buildings, and castles. The latest trend in home heating fits into that category. Masonry heaters have been around for hundreds of years in Europe, but are just recently catching on in the U.S. And the great thing about heaters is that they are GREEN. People needed to heat their homes in an efficient manner in olden times just as today in order to save their forests. Inefficient open fireplaces took too much of their valuable resources, so another method had to be developed. No one knows who the first mason was who came up with the idea of devising something that would retain heat for long periods of time, then radiate it into the home while using less wood, but whoever he was he was a genius.

Masonry heaters have been redesigned and altered over the years by different masons in Finland, Russia, Germany, Austria, and the United States. But heaters all have the same characteristics with complex channels to slow down and trap heat from flue gasses, and a mass of masonry to retain that heat, then radiate it to the living space over a period of up to 20 hours. By the time the products of combustion get to the exit of the flue, the smoke is white and the particulate emissions are very low. One load of wood can usually provide heating for the average size home for 8-12 hours. Compared to even the best high-efficiency wood–burning stoves on the market today, gas and oil-fired furnaces, and certainly inefficient open fireplaces, masonry heaters can’t be beat.

Custom granite masonry heater
Courtesy of HearthMasters, Inc.
Another benefit masonry heaters offer is that they don’t require electricity, gas, or ductwork to distribute the heat. In a properly designed home with an open floor plan and the heater in the center of the home, the heat will radiate evenly throughout. Ideally, heaters are built in new home construction, but they can be added to existing homes if the layout is right. Heaters require a suitable foundation to support the massive masonry, which weighs three to six tons by the time all of the firebrick, block, cast iron doors, dampers, and exterior masonry facing is installed.

Heaters can be enhanced with heated benches to sit on, mantels, wood storage bins, and even bake ovens. Pizza and bread from a wood-fired bake oven has an incredible and unique taste that is not to be missed, and entire meals can be cooked in the oven if desired. An experienced heater mason can not only design and build the right size and type of heater for a home, but make it beautiful to look at as well. An exterior finish of soapstone, tile, sandstone, or brick can make a dramatic statement. Heater masons will work with the homeowner to come up with a custom design that suits the home, or use one of many masonry heater kits that are available from several manufacturers (usually incorporating soapstone) in a variety of designs.

Use of natural non-toxic materials and the renewable resource of wood make masonry heaters the perfect solution for a green home.
The trade is very specialized, with only a few heater masons scattered across the U.S. Fortunately, most of these masons will travel to do installations. Some have even traveled to Japan, China, and South America to build heaters. Often several heater masons will help each other out since these are big projects. In days of old, the heater masons kept their trade secret, even to the point of not leaving the room until the heater was completely finished so no one else could see how the interior was built. At that time, the livelihood of the masons was dependent on this secrecy. The trade is so skilled that the only way to learn is to do hands-on assistance with an experienced heater mason, and that is part of the reason the Masonry Heater Association was formed. The older masons do not want this to become a lost art, so they help train others. The Certified Heater Mason program was developed by the experienced MHA members in order to assure that the knowledge is not lost.

In the U.S. many people are not yet aware of masonry heaters, so it is a challenge for a heater mason to make a living out of just building heaters. Most heater masons also build other types of projects such as fireplaces, chimneys, outdoor bake ovens. Some are timber frame or log home builders or own brickyards. Most are very aware of the green building trend and are interested in sustainable living. Many heater masons will travel to build a heater because they love doing it, and love the satisfaction they get out of building something that is very specialized.

Pricing for heaters is what most would consider being on the high end, and a long-term investment. The average cost a homeowner may expect to pay is from $15,000 to $30,000, with price depending on the complexity of the heater, material costs, and labor. The expected time to get a return on your money is approximately 10 years. The time to build a completed heater may be up to four weeks or more, depending on how many skilled craftspeople are working. Many homeowners will elect to be an assistant on the job in order to lower their costs. In some cases, if a heater mason is traveling the homeowner will put him up at their house or a local hotel. When traveling the masons usually work long hours in order to get the project done sooner.

Mark Twain discovered masonry heaters while traveling through Europe and wrote about them: "All day long and until past midnight all parts of the room will be delightfully warm and comfortable … Its surface is not hot: you can put your hand on it anywhere and not get burnt. Consider these things. One firing is enough for the day: the cost is next to nothing: the heat produced is the same all day, instead of too hot and too cold by turns… America could adopt this stove, but does America do it? No, she sticks placidly to her own fearful and wonderful inventions in the stove line. The American wood stove, of whatever breed, is a terror. It requires more attention that a baby. It has to be fed every little while, it has to be watched all the time: and for all reward you are roasted half your time and frozen the other half... and when your wood bill comes in you think you have been supporting a volcano. It is certainly strange that useful customs and devices do not spread from country to country with more facility and promptness than they do."

Find out more about masonry heaters, including technical specifications and testing results, photos of heaters, manufacturers, and a list of heater masons, contact the Masonry Heater Association of North America through www.mha-net.org. There is a chat list set up for anyone interested in masonry heaters at http://groups.yahoo.com/group/MasonryHeaters.

Marge Padgitt is a past board member for the MHA and currently the PR Chair.  She is president of HearthMasters, Inc. in Kansas City, Missouri. Her husband, Gene Padgitt, is a Certified Heater Mason.

When the Wind Blows - its Cold: The indoor wind chill factor

By Doug Hargrave
Mid-Atlantic Masonry Heat
Everyone has experienced the cooling effect of a strong wind or breeze while engaging in some outdoor activity. The extent of the cooling effect is determined by the speed of the wind and the temperature of the air. For example, a warm breeze has to be significantly stronger than a cool breeze to produce a cooling effect. The cooling effect of wind can be moderated by the use of insulation and/or a wind breaker. Someone is more comfortable wearing a wind breaker in a strong breeze. In a strong winter breeze one would have to add a sweater (insulation) under the wind breaker in order to achieve the same relative comfort.

When weathermen talk about outdoor temperature condition they often refer to the wind chill factor. The wind chill temperature is always lower than the air temperature. The movement of air indoors is not generally referred to as "wind", however, the effect of air movement indoors is the same as outdoors - it has a cooling effect - it does not make you warmer.

Air movement is often introduced into indoor living areas in a number of different ways; a few of the prime examples are as follows:

  1. Outdoor air infiltration that causes noticeable drafts through leaky doors, windows and other openings.
  2. Forced air systems and fans that mechanically move the air
  3. Natural convection of air from a hot radiator surfaces in the primary living areas.
The most uncomfortable type of indoor air movement (draft) is outdoor air infiltration that causes noticeable drafts. Just as you would wear a wind breaker for comfort in windy outdoor conditions you want the shell of your home to act as a wind breaker for indoor comfort. No amount of insulation will help if you have drafts from the outside blowing in around it. The only way to counteract the effect of this type of indoor wind chill is massive amounts of hot air which will mask the effect of the infiltration. However this is accomplished at a high energy cost and only marginal improvement in personal comfort. The first line of defense in any home heating plan is reducing the air infiltration so that drafts from the outside are not noticeable. Only after this problem is fixed should someone turn their attention to other issues in the home heating plan.

In the United States the use of forced air heating systems is so pervasive that it is difficult for most people to imagine any other way of heating their home. The fact that these systems produce indoor wind chill is accepted as a necessary evil.
These systems typically force heated air into a room at the outside walls (usually under the windows) and then extract return air from locations high on interior walls. This forced air ducting arrangement results in relatively strong drafts at the ceiling level while minimizing drafty conditions at floor level. In a room with standard eight foot ceilings the movement of the heated air at ceiling level mixes fairly well with the cooler air lower in the room but there is always a marked temperature difference between the warm ceiling and the cold floor. In rooms with higher ceilings (especially vaulted ceilings) the mixing results of warm air near the ceiling and cooler air near the floor is compromised by the greater separation and larger volume. In order to compensate for this, more heated air is required and more mixing of air is required. This results in more air movement and more indoor wind chill. It is not unusual for someone seated in a vaulted ceiling room during cold weather to wrap a blanket around them self as a shield from this intensified indoor wind chill.

Hot radiators cause air movement through natural convection which is then felt as indoor wind chill. The best known example of this is the wood stove where surface temperatures often run between 400 - 600 °F. At these temperatures when the air in the room makes direct contact with the stoves surface it expands dramatically and quickly rises to the ceiling. Other air follows behind creating a draft at floor level in the direction of the stove. This draft is quite cool because it comes off the coolest surfaces in the room usually the least insulated window areas. The wind chill effect from the combination of hot stove surfaces combined with cold window surfaces is very noticeable. Less noticeable wind chill is felt from electric resistance or hot water radiators placed on outside walls (usually under windows). These radiator heat systems send heated air up along the cooler surfaces in the room to the ceiling level. Cooler air to replace the heated air is drawn along the floor toward the radiator but it comes from warmer areas of the room resulting in less indoor wind chill than with a wood stove or other centrally located radiators that would tend to draw air from the outside walls and windows.

The question is often asked, "Wouldn't it be a good idea to use a ceiling fan to blow the hot air near the ceiling down to the floor or reverse the fan and draw the cool air up to the ceiling?" On close examination, this solution, could come right out of the pages of Alice in Wonderland. When the ceiling fan is used in the winter time to "blow" the warm air down you almost always can see the slowly turning fan blades, which means it is not really blowing the warm air down but rather just stirring it up at the ceiling level. If the fan were actually run at a high enough speed to blow the air down (or draw the air up), the wind chill factor in the room would increase substantially and your comfort would decrease.
On the other hand, in the summer time, when you have hot air at the ceiling and relatively cooler air at the floor, you can turn on the ceiling fan, force the hot air down on you and the indoor wind chill will make you feel cooler and more comfortable. The fan cools in winter and it cools in summer - period.


Types of Heat Transfer




By Doug Hargrave
Mid Atlantic Masonry Heat
radianthomeheating.org
Radiant heat is transmitted from a warm object to a cooler object through infrared radiation. This is the same type of heat transfer that takes place when the rays of the sun shine on the earth. The distance between objects, their surface area and their temperature difference affect the rate of the radiant heat exchange. A good example of radiant heat transfer is the warmth you feel when you sit close to another person. Another example would be the way a radiant heater warms the surfaces and objects inside a home rather than the air.
When the distance between two solid objects of differing temperatures goes to zero and they come into direct contact, the heat exchange between them is then called conduction. Conduction between solid objects results in a faster rate of heat exchange than that of radiation. A good example of this difference is the amount of heat one would feel holding their hand just above a hot stove (radiation) versus actually touching the stove (conduction).
Heat transfer within solid objects is accomplished through conduction. The heat storage capacity and the transfer rate will vary with different solids. For example, the higher density of soapstone allows it to absorb and then radiate more heat per unit volume than common brick which has a lower density. The heat transfer rate within metals is much faster than the transfer rate within masonry materials.
Heat transfer within gases is quite different from heat transfer within solids. Gases have relatively little mass (weight) and very little density (weight per unit volume) when compared to solids. Unlike solids gases can dramatically expand or contract their density. Their density expands when they are heated and contracts when they are cooled. Warm gases that are expanded are lighter than cool gases that are contracted. The difference in weight causes warmer gases to rise and cool gases to fall creating movement within the body of gas. This movement is called convection. The speed of the convection (movement) is largely determined by the how much and how quickly heat is introduced into the body of gas. For example, a 600 degree wood stove causes much more convection (air movement) than a 200 degree masonry heater in the same living area.