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.


  1. Great explanation, thanks for the posting! Performance Parts

  2. Very informative content. After reading this, dealing with the heating issue becomes quite interesting and easy. Keep on sharing such fruitful concepts in future as well.

  3. This is exactly what I have been doing with my TempCast masonry stove. It did not come with air access below the grate, so I inserted a 2" black iron pipe through the wall about three inches below the grate. I screw a cap onto the pipe until the fire has burned down to a bed of coals, then I remove the cap and partially close the opening that feeds around the door frame. This reduces burn-time by about an hour and saves valuable heat from escaping through the chimney.

    My question is, "Can a fire burn too hot for the stove?" I use very dry black locust and hedge-apple wood, and it burns extremely fast and hot. I must wear gloves and long sleeves when I use a 30 inch poker to level out the burning coals on the grate, and any exposed flesh will burn quickly from the radiant heat. The firebrick has a vertical crack between the door frames and a vertical hairline crack in the back just above the grate. The brick enclosure also has a vertical hairline crack between the two doors. This is the second year firing the stove. Are cracks inevitable, or am I doing something wrong that is causing them? I have not exceeded the recommended 100 pounds of wood per day, and average about 1.5 burns per day.

  4. I would like to see proof that it is better to burn 4-6 inch pieces of wood than 2-3 inch pieces. Longer burning times mean longer times for heat to escape up the chimney. I close the damper as soon as possible, even before all coals are out. But I never do that unless all doors to the stove have been opened to allow sufficient oxygen to get to the remaining live coals. Not opening all doors will starve the live coals from oxygen and cause the formation of deadly carbon monoxide. I have a carbon monoxide detector located a few feet from the masonry stove and will know if any carbon monoxide is generated. The main drawback of closing the damper early and opening the stove doors is the release of a small amount of ash dust into the air.


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