Wood Furnaces
Before we begin singing the virtues of wood furnaces for heating, it might pay to read Why your wood heater is a bad idea by Fay Johnson. Her summary is this: “I still love wood heaters, but owning one means owning pollution”. Even if we achieved flawless operation, I knew other heating choices would improve the environment and the community. We replaced our heater with a less polluting alternative. It’s a bit less evocative but does come on at the flick of a switch.”
Having acknowledged that poorly designed wood furnaces are a source of pollution in towns and cities, the New York Dept of Health provides this information about gasifier-type wood furnaces:
Dual Stage Boilers
Dual-stage wood gasification boilers are the most efficient firewood-burning units available today. Installation is indoors or in a structure close to the home. They are called dual-stage, as smoke and gasses burn in a high-temperature secondary chamber. This high-efficiency design results in much less smoke; however, they also have more exacting fuel wood requirements. They work best with dry wood and only operate with moderately seasoned wood. They also work best when used with an auxiliary heat storage water tank. This allows the entire charge of wood to be burned continuously, and with improved efficiency. The stored heat is then used over time, depending on demand. In the non-heating months with an auxiliary heat storage water tank, gasification units only require a fire about every four to seven days, depending on how much hot water you use.
Heat storage water tanks
An insulated water tank stores the heat. They allow a boiler to operate most efficiently by burning the firewood hot and fast. The stored heat becomes available for heating as needed. Heat storage water tanks work with gasification furnaces. Solar heat hot water uses the same principle.
Austria
ETA SH Wood Gasification Boilers are made by ETA Heiztechnik in Hofkirchen an der Trattnach, Austria. The company makes both wood and pellet models. The decomposition into 20% charcoal and 80% wood gas begins at 200°C, which results in the long gas-flame of this wood fire. The fuel chamber accommodates enough half-metre logs to ensure that replenishment is only necessary once a day or twice on cold winter days. The emission levels of the ETA SH are already below the strict dust emsission thresholds that will come into force in Germany on 1 January 2015. ETA produces 10,000 boilers a year and exports to Germany, Italy, France, Luxembourg, the Netherlands, Belgium, Switzerland, Ireland, the UK, Slovenia, the Czech Republic, Spain and Japan.
Canada
Northern Stoker outdoor wood furnaces are designed and built for the Canadian climate to perform through the harshest weather. The new Biomass Stoker allows using grains, corn, pellets, and other wood products. The stoker design works with all furnaces. Additionally, it is fully automated to feed a variety of fuels into the combustion chamber. This addition allows users the versatility of many different fuels from renewable energy sources, cost savings and the understanding that they are environmentally friendly.
Czech Republic
ATMOS Gasification Boilers are made at Bělá pod Bezdězem, in the Czech Republic. The family company ATMOS was founded in Bohemia in 1936 and has developed over 70 types of boilers under 13 patents. It is currently one of the largest European manufacturers of boilers. The reverse and ceramic combustion chambers optimise combustion with minimum polluting emissions. Heating is not lost when the electric power fails, and it operates up to 70 percent of its rated output without the fan. The boilers comply with environmental requirements according to Guideline No. 13/2002 of the Czech Ministry of Environment. They also comply with European Standard EN 303-5 and all the boiler rate in class 3.
The VERNER G25D is a pyrolitic wood gasification boiler. Manufactured by VERNER Inc., Červený Kostelec, Czech Republic. The Verner has a 25kW and 45kW version. The wood furnaces’ inner walls are steel plates with a 5 – 6 mm thickness. A lambda probe controls the combustion process, evaluating the oxygen content of flue gas. According to measured data, it controls the optimum primary and secondary air supply. The boiler has a heavy ceramic lining with micro reinforcement for long-term permanent heat assurance. The boiler design ensures economical and comfortable heating, including hot water in houses, cottages, shops, workshops, etc.
Germany
The German-made KÜNZEL Wood Gasifier Boiler BT isis offered in different power levels ranging from 23 to 31 kW. Suitable for single or two-family homes and small to medium-sized commercial and office buildings. A stand alone unit or in combination with other heat generators. It will take logs and scrap wood with a length of approx 1/3 to 1/2 meter. Control is through lambda processor control panel 621 with buffer accumulator regulation. Two separately controlled air blowers operate in primary and secondary combustion. With almost 100 years of experience, KÜNZEL holds a leading market position in wood heating technology. The company has produced 40,000 wood gasifier boilers since 1986, and many of the systems from the first years are still running.
United Kingdom
Eco Angus gasifier boilers Angus Super Gasification Log Boiler (England, Ireland and Scotland outlets) is available in 7 models, 18, 25, 40, 60, 80, 100 and 130kW. With minimal ash out, it claims 92% heat efficiency. The boilers have an alleged payback period of around three years over LPG, Gas or Oil. Units can take logs from 500mm to 1000mm long and 6″ to 10″ in diameter. Additionally, the boiler uses downdraft gasifier technology, burning the gasses produced during the normal burning process. Therefore, the release of CO2 into the atmosphere is minimal. The secondary burning chamber burns gasses at up to 1200 degrees centigrade. Regulated by a digital display panel that controls the ventilator fan, the boiler is 92% efficient. The log chamber holds enough wood for up to 12 hours of burning.
United States
Lamppa Manufacturing Inc. in Minnesota makes the Kuuma Vapor-Fire 100. The furnace takes about 20″ in length and requires seasoned wood with an 18-28% moisture content. It has a sizeable 2-speed blower that delivers 500 to 1500 CFM (cubic feet per minute) on demand, controlled by a thermostat—a stand-alone central furnace or add-on to an existing oil, gas, or electric furnace. The bonnet opening is 2’x2′, and the heat duct outlet should be 180-200 square inches to prevent excessive back pressure on the blower system. It gives a clean, safe, and automatic front-to-back burn that delivers even heat for 10-12 hours per load, followed by many hours of coals. It heats approximately 3500 square feet. A review is here.
West Virginia
New Horizon Corporation makes the Attack DP Profi wood gasifying boiler in Sutton, West Virginia. It economically heats houses, small plants, and workshops. The Attack range of wood furnaces requires dry wood, and the feeding chamber burns somewhere between 8 to 12 hours when full. An electronic regulator controls the furnace checking the boiler’s water temperature and displaying the value. Also, it controls the waste gas ventilator and central heating pump. Gasification reduces smoke and other emissions to a low level.
Pennsylvania
Alternate Heating Systems in Pennsylvania make the Wood Gun wood gasification boiler . The AHS Wood Gun is available in six sizes: residential units ranging from 100,000 to 250,000 BTUs. The commercial sizes up to 1,000,000. The Wood Gun cycles on and off like an oil or gas-fired boiler. During the off cycle, fuel is not consumed because oxygen is not in the combustion chamber. Due to the large superheated refractory mass, re-ignition of the fuel occurs automatically when a drop in water temperature signals the need for heat. (Automatic re-ignition will take up to 5-6 hours, depending on boiler size.) Wood Gun boilers use 1/4″ thick 304 stainless steel to construct the firebox and door frames. Consequently, some of AHS’s stainless steel boilers have been in service for over 27 years, showing no signs of deterioration.
New York
The EBW-150EBW-150EBW-150 from Econoburn Boilers – Brocton, New York. Econoburn’s wood-fueled boiler is a closed-loop system with a gasification process that delivers an 87% thermal efficiency rating. Constructed of double-welded 1/4″ ASME grade 36 carbon steel, boiler rating is150,000 BTUs. Other sizes range from 100,000 to 500,000 BTU. Burn time varies with wood type and moisture content. A properly-sized system to go from six to eight hours on a cold day. An industrial-grade touchpad control unit optimises combustion efficiency. In conclusion, by installing thermal storage the boiler operates once daily to charge the tank.