Turn Waste Wood into Home Heat: Buy a Pellet Stove
(Page 5 of 6)
February/March 2009
By Steve Maxwell
In finding a location for a pellet appliance in your home, you’ll need to follow the requirements for safe clearances from combustible surfaces. You’ll want to consider three additional things, too. First, if the vent is to terminate part way up an outside wall of the house, the location must be selected carefully so that exhaust is not drawn back into the house through doors, windows or ventilation openings. Your pellet stove dealer and the pellet stove installation instructions will give the necessary clearances to house openings. Second, you will need a place to store your pellet supply. This area should be under cover, and preferably indoors. And the closer it is to the stove, the more convenient it will be. Third, a standard 110-volt outlet for electrical power to the stove is required.
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Finally, if you decide a pellet stove is a good option for your home, be sure to choose a retailer carefully. Many big box stores try to attract customers by offering low prices, and yet their staff is not trained in pellet technology. To ensure you get the technical support you’ll need, deal with a specialty retailer, preferably one with many years of pellet heating experience.
Non-wood Pellets
Wood isn’t the only source of pellet feedstock. Bark, cherry pits, low-grade grains and farm-raised energy crops (switch grass is one) are also used for pellet heating. Corn was also used for fuel before prices increased significantly. One of the challenges of heating with non-wood biomass involves dealing with the high ash content of these materials. High-quality wood pellets should contain less than 1 percent ash. But it’s not unusual for pellets made of bark or switch grass to contain a whopping 4 percent or 5 percent ash.
This high ash content creates a problem. In most standard pellet stoves, combustion temperatures in the burn pot can exceed 1,250 degrees Fahrenheit. When this happens, minerals within the ash fuse together, forming semi-hard lumps called “clinkers” (like those produced from burning soft coal). These make it impossible to remove the ash automatically from the stove, making high-ash fuels too troublesome to be practical. Who wants a pellet stove that needs to have ash removed manually several times a day? Recently, the challenge of high-ash pellets has been addressed by stoves designed to remove clinkers automatically.
One solution to high-ash fuels is a gasification combustion burner that uses a two-part burning process to sidestep clinker formation, but not all designs use this system. The first stage involves low-temperature, air-starved combustion that converts the fuel’s energy into a volatile gas at temperatures far below the 1,250-degree clinker threshold. This happens in a sealed part of the gasification burner, just before a swirling stream of combustion air is introduced to the process. This secondary air supports complete combustion at high temperatures within the burner, without clinker formation. Augers automatically remove the resulting fluffy ash. Even burning the highest-ash fuels, stoves of this design claim to need cleaning maintenance only every two or three weeks.
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