RCM Cad Design Blog

June 2009

By Cyril Courtois (RCM CAD Design Drafting ltd.)
www.loghomedesign.ca

Topic: Wood heating options for log and timber homes.

Wood is a renewable energy resource and contrary to general belief wood burning does not contribute to the climate changes we are starting to witness around the planet.
Fossil fuels like oil, gas and coal which are extracted from deep beneath the earth surface are the main source of greenhouse gases.
Trees recycle CO2 from the air to grow, using the carbon to build its structure to about half the weight of wood.
When the tree dies, it rots on the forest floor and slowly releases the carbon back in the air completing the natural carbon cycle.
When wood is burned, it quickly releases similar amount of carbon in the form of CO2 thus completing the same carbon cycle.
Wood is known as a carbon neutral source of energy.
For example, using wood from responsibly managed forests to build our homes actually stores carbon for many decades which positively offset greenhouse gas emission by delaying the carbon cycle.

Thermodynamics tells us that heat always flows towards colder than itself.
There are three means of heat transfer.
By conduction… direct contact to a heat source
By convection… heat is transferred thru the motion of air or water for example
By radiation… heat is transferred without direct contact by infrared electromagnetic waves just like the sun warms our earth by radiation.
Radiant heat makes us feel warm even though the air around us may be cold.

Conventional open pit fireplaces are still used for visual enjoyment. However they are so inefficient due to lack of tight fitting casketed door, lack of properly designed
heat exchanger and combustion chamber, they are close to or below zero efficiency. They only partially burn wood, creating much pollution outside and inside the home which is nowadays unacceptable to most of us.

Fireplace metal inserts are wood stove fitted in an existing masonry firebox or within a wood framed enclosure. Certified inserts using a properly sized stainless steel liner can be close to as efficient as wood stoves.

Wood stoves are the most popular space heaters in North America. It is best to locate the stove in the center of the main living area (open floor plan design) with flue pipe going straight into chimney close to roof ridge.
Since early 1990 wood stoves have been redesigned to be more efficient and meet mandatory smoke emission limits dictated by EPA in the US and CSA in Canada.

Catalytic stoves are the most efficient on the market but they require more maintenance to run at peak performance. They can burn wood cleanly at a low heat setting. Restriction of the gas flow thru the catalyst can cause some draft issues. They do need regular cleaning and replacing catalyst every few years.

Non catalytic stoves are by far the most common stove on the market. They are about one third more efficient than the old pot belly stoves of the past and produce up to 90% less pollution.
However they can not match the even heat output from catalytic stoves.
Once fired, those stoves will quickly take the chill out of room. But they need to be restocked quite frequently and once the fire dies, the stove and the room cool off rather fast.

Masonry stoves are made of masonry rather than steel.

They were invented in Europe during the first energy crisis in the early 1800 as close wood supplies disappeared from over harvesting.
They are fired once or twice a day for an hour. The heat is stored within the high thermal mass of the heater before being slowly radiated back in the room during the next 12 to 24 hours.
Consequently the first burn of the heating season will take a couple of days to start warming a cold home.
No instant heat but instead constant, even heat with only one daily firing defines this type of stove heating performance.

The efficiency of masonry stoves is comparable to catalytic stoves as they burn wood quickly at high temperatures (over 1500 degrees Fahrenheit). Soot and creosote do not survive those temperatures.
The exhaust from the fire is channeled thru a maze of flue passages thus trapping the hot gases long enough to allow the heat to be soaked in the masonry. The exhaust being finally released from the house is depleted of most of its heat. Therefore almost all the energy contained in the wood is used for heating your home.

Iron stoves will burn at the touch when lit.
Masonry heaters are much safer as the surface temperature is much lower allowing installation of warm seats and beds into or above the stove mass.

Particulate emissions falls well within EPA or CSA limits. They need to be in use only 1 to 2 hours a day compared to 24 hours a day for 24 hours of heat for all other stoves.
Partly because of this limited burning each day, wood consumption is cut by about a third compared to other stoves. This is a large savings in labor from harvesting and hauling the wood fuel, storing it and feeding it to the stove.
Another exiting option is the installation of a baking oven on top of the firebox to bake by radiation pizza, bread, roasts and casseroles…

Disadvantages of masonry stoves are as follow.
They require a large reinforced concrete foundation base to support the mass above.
Installation is easier to plan for new construction.
Cost of a custom masonry stove will be over $20 000.00 with design and installation requiring an experienced mason in that field.

A much cheaper alternative is to buy a masonry stove kit at about a quarter of the cost compared to custom from a reputable and experienced company specializing in the construction of thermal mass heaters.
My wife and I have recently decide to purchase a kit masonry stove from Wildfire Rocky Mountain environmental technologies in Edmonton, to replace our EPA/CSA approved wood stove at our cabin by the lake. The installation is taking place this summer 2009.
We are looking forward to drastically reduce our wood consumption, enjoy even heat day and night and as well use our baking oven to the great enjoyment of our family and visiting friends.
I will be reporting our experience this winter within another newsletter.
Pellet stoves burns compressed wood or biomass pellets.
There are a versatile wood heating option that runs automatically with hopper pellet storage, auger pellet feeder and at least two electric fans.
A hopper load can last more than 24 hours.
You can control the heat with thermostat and remote control.
Special direct vent thru a wall can eliminate costly chimney thru the roof.
Those stoves are high efficiency with low emissions.

Limitations of pellet stoves:
They are dependent on electric power.
The pellet fire does not match the natural look of wood burning flames we are used to.
Stove performance and pollution output are dependent on quality of pellet fuel.
A high grade pellet minimizes maintenance and extend electronic components life cycle.

Outdoor wood burning boilers keep wood handling outside the home. Water heated in the boiler is piped underground to one or more buildings.
Heat distribution can be forced air, in floor heating or wall registers.
Hot water house needs may also be handled by these boilers.
This wood heating option is least desirable as the units are inefficient because they do not burn wood completely. Few municipalities allow them as they produce high level of smoke and creosote.

This entry was posted on Sunday, November 15th, 2009 at 12:21 and is filed under fireplaces, Newsletter. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.