Wood and Pellet Boilers
Wood as a renewable fuel source
Sustainably harvested wood offers a net-zero CO2 emission domestic heating fuel at roughly half the cost of foreign oil. Heating Maine homes with oil is one of the largest contributors of greenhouse gas emissions statewide and, as the cost of fuel oil continues upward, people are looking for sustainable, cost-effective heating alternatives. ReVision Energy has been installing wood boilers for years, gaining valuable experience and know-how to help people and businesses transition away from expensive, polluting oil boiler systems. We have had particularly strong results from Tarm wood and pellet boilers. The fact that we have a Tarm wood boiler heating our main headquarters in Liberty is evidence of how highly we esteem this product. We also recommend the Greenwood, particularly for larger homes needing high BTU outputs from the boiler.
Wood Gasification—The Key to Efficiency & Low Emissions
ReVision Energy's wood and pellet boilers burn at 80 to 85% efficiency through a process called ‘wood gasification.' These wood and pellet gasifying boilers emit no visible smoke because the combustion temperatures reach 1800+ degrees Fahrenheit. Smoky outdoor wood boilers, on the other hand, burn at 50-60% efficiency, and are coming under state restrictions due to their polluting emissions. It is also worth noting that typical older model wood stoves burn wood at between 50-60% efficiency, requiring much more wood to produce the equivalent BTUs from a wood boiler.
WOOD CONSISTS OF TWO DISTINCT FUELS:
- The combustible gases: These are given off mostly in the beginning stages of a fire after the new fuel is heated. These gases are visible as smoke and flame.
- The fixed charcoal: These are the glowing coal-like red embers remaining after the gases have been driven from the wood.
Scientists have found that over 50% of the heat value in wood is in the form of these combustible gases. The complete burning of these gases has long been the main concern of engineers and designers seeking clean wood-burning devices.
In designing the Excel and Solo Plus Series, HS-TARM engineers decided that the best way to burn these gases was to use a firebox with two distinct chambers. In the primary chamber (firebox) the wood charge is ignited. The burning occurs at the bottom of the firebox and the heat from the fire bakes the wood above releasing the wood gas from the fuel. The combustion draft fan then blows these gases through the live coals and into the superheated ceramic tunnel where secondary air is injected to complete the burning process.
These boilers burn so clean and hot that virtually no visible smoke comes out of the chimney. How clean is clean? Tests have shown that the HS-TARM boilers can burn wood with a smoke output of less than 1 gram per hour. This is equivalent to the smoke released from one cigarette. A HS-Tarm boiler burns up to 100 times cleaner than an older woodstove. With millions of folks now burning wood it is very important that we burn it wisely.
For over 70 years, Denmark-based Tarm has been the world leader of solid fuel technology. When fed dry wood, these boilers burn at 85% efficiency; they not only burn much less wood than conventional wood boilers and wood stoves, but burn so clean that there is virtually no risk of a chimney fire. During an average winter day in Maine, these boilers generally would be fired only a few times a day, depending on the efficiency of the building and amount of heat storage (see below). If you’d like to see one in action, please come to the ReVision Energy shop in Liberty, or we can arrange to have you visit one of our installations in southern Maine.
Greenwood boilers are American-made and offer similar performance to the Tarm boilers. We often recommend the Greenwood for larger homes because of its high BTU output. Like the Tarm, Greenwood boilers burn their wood fuel completely through gasification, achieving efficiencies that approach 85%. The Greenwood's firebox is made of super-duty ceramic refractory, cast four to six inches thick, and surrounded by outer layers of insulation designed to keep the heat in. The natural draft system pulls air into the furnace which fans the flames and creates a roaring fire with sustained temperatures of 1800º to 2000º F. Heat from the fire is captured by a water tube heat exchanger located above the firebox in the path of the escaping superheated gases. The furnace extracts heat from these escaping gases, not the fire below.
This innovative design enables the Greenwood wood boiler to burn cleanly and operate at a very high level of efficiency. By the time the escaping gases leave the furnace, they have cooled to around 300º F. The 1700º F difference in temperature between firebox and the vent represents the amount of energy captured to heat your home.
Prices
ReVision Energy offers a wide range of solid fuel boiler options for residential systems and businesses. Please read the 
wood and pellet boiler purchase options document for more information.
Pellet Boilers
We sell two brands of pellet boilers, the Tarm Multi-Heat and the Traeger. The Tarm Multi-Heat is a wonderfully efficient boiler, attaining combustion efficiencies upwards of 90%. It’s easy to use, needing cleaning only every few weeks, and it’s incredibly well-built. You can enjoy independence from fossil fuels and reap significant savings on your heating bills with this fully automatic pellet boiler, which can run for days on a single load of domestic fuel. The feeder mechanism automatically adds the correct amount of fuel into the combustion chamber and the built-in blower produces the precise mixture of primary and secondary air. The only maintenance is filling the hopper with fuel (Automatic Feed Head Available) and ash removal when needed.
The Traeger is a more conventional boiler, a bit oversized, a bit less efficient than the Tarm, a bit less expensive, but well built. The Traeger can be vented through a 5” vent pipe and does not need to be vented over the roof, which can be a real advantage over the Tarm in houses where there isn’t a spare flue in the basement. Given the choice, we’d recommend the Tarm every time, if it weren’t for the venting issue.
Check out the Tarm Multi-Heat at http://www.tarmusa.com/mh_home.asp and the Traeger at http://www.pinnaclestove.com/residential.html.
For houses where the Traeger makes sense, we can simply connect to the existing distribution system. The Tarm can pipe into a spare flue, if one exists. If not, a metal flue can be installed, or, another option is to use a backup propane boiler, or a backup electric boiler (if the house has 200 amps), to make the flue available for the Tarm.
Pellets are now available from a company called Biomass commodities from Athens or Strong. Today, pellets are selling for roughly half the cost of oil. The good news is that Biomass commodities will deliver to a silo outside of your house or a bin inside your house, saving you the effort of lugging bags.
Thermal (Hot Water) Storage
The beauty of thermal storage is that it makes heating with wood as easy as one 5-minute trip to the boiler each day to kindle one fire. A large thermal storage tank allows the wood boiler to run at maximum combustion temperature, and highest efficiency, because the large amount of heat energy generated can be discharged into the storage tank. The heat stored in the tank is then siphoned off over time to heat your house and domestic hot water. Another option is to discharge the heat into a concrete slab. Much like water storage, concrete storage allows you to burn at the highest possible efficiency and then gradually use the heat energy as needed, over time. ReVision Energy’s custom-built thermal storage tanks are the result of years of research and development to come up with a design that offers maximum durability and excellent insulation to store the precious BTUs generated by your wood or pellet boiler.
Thermal storage tank with controls, pump & plumbing
Tank Fabrication
We build our own tanks right in our Liberty workshop, starting with a steel frame with mid-length supports that is lined with ¾” plywood, then lined with 4” of polyisocyanurate foam, and finally an E.P.D.M. liner folded inside to create an impermeable membrane. The tank cover is made by gluing a sandwich of foam and luan and using a spray adhesive to attach the liner. The top is constructed in two sections: one smaller section allows pipe penetrations while the larger section allows access should the tank need servicing. After the tank is filled and everything else is in place, the top is simply spray foamed in place to prevent evaporation.
Temperature Limit & pH balance
The tank liner is rated to withstand a temperature of 175 degrees F indefinitely. They make no claims regarding higher temperatures. We have seen such liners last a very long time without any deterioration, so long as the tank is pH balanced and not being overheated.
Physical Dimensions:
650 gallon tank…………… 8’ 2” long, 50” wide and 54” tall
900 gallon tank……………9’ long, 9’wide, 54” tall
1200 gallon tank…………..11’ long, 11’ wide, 54” tall
R-Value for all tanks: 28
Tank Pricing
Our tanks can be purchased as a simple kit, or as a complete kit.
Simple Kit:
Includes the following
- Steel Frame, unpainted
- Two Part Assembled top with penetrations
- Fasteners
- EPDM Liner
- Instruction Sheet
The simple kit does not include the following
- Plywood for side walls (3 sheets of ¾”)
- 2” isocyanurate (6 sheets)
Complete Kit:
Includes the following
- Steel Frame, painted
- Two Part Assembled top with penetrations
- Fasteners
- EPDM Liner
- Instruction Sheet
* Luan for side walls (3 sheets of ¾”) cut to size and urethaned
* 2” isocyanurate (6 sheets) cut to size
| 650 gallon Simple Kit | $1,750 |
| 650 gallon Complete Kit |
$2,570 |
| 900 gallon Simple Kit | $2,130 |
| 900 gallon Complete Kit | $2,975 |
| 1200 gallon Simple Kit | $2,550 |
| 1200 gallon Complete Kit | $3,540 |
| 120’ heat exchange coil | $575 |
| 180’ heat exchange coil | $750 |
More information:
If you would like some more information on what type of boiler would suit your needs, and more accurate information on your loads, we’ll need some information, namely the following:
- A year's worth of fuel deliveries, with dates and gallons
- The square feet of your house
- Is there an extra flue in the basement
- What heats your domestic hot water and your house
To learn more about the advantages of high-efficiency wood boilers, download the 
Woodboiler News Newsletter.
Frequently Asked Questions
There are many considerations to the decision to install a wood boiler. The decision is an expensive one, and one that will be with you for a good long time, so careful consideration of all the options is crucial. What follows are some commonly asked questions to help guide you in the process.
- Why should I consider an HS Tarm gasifying wood boiler?
Tarms are slightly more expensive than their competition, and for good reason. Tarm has been selling wood boilers in the U.S. since the 1970's. They are a well-established business that will be around when you need spare parts 20 years from now. The boilers are built to last, with a 20-year warranty. They are constructed with _" plate steel, which is what gives them their long life. They are beautifully engineered for high efficiency, ease of use, and longevity. - What type of chimney do I need for a wood boiler?
Any solid fuel boiler needs its own dedicated, lined masonry or manufactured chimney. If you have only one flue, you can install a Tarm multi-fuel wood and oil or wood and propane boiler. Or, you could install a wall hung propane boiler, which vents out the sidewall, as a backup, and use the single flue for the Tarm wood-only boiler. If you have a flue that is currently used for a fireplace or a wood stove upstairs, you can use that flue for the Tarm by eliminating the stove/fireplace. Most conveniently, you can install the boiler with a new manufactured chimney. - What type of space is best for a wood boiler?
The best space for a wood boiler is on ground level with easy access to the firewood pile. Garages work very well, though the boiler will need to be separated from where cars park with a partition and separate access door. Most people put the wood boiler into their basement. This works great in walkout basements, or in basements with bulkheads. The key is convenience, moving firewood from storage to the boiler. - What is Gasification?
Most wood boilers are of a very simple design. There is a firebox surrounded by water. The wood burns and heats the water surrounding the firebox. This is simple, but not very efficient. H S Tarm uses a much more sophisticated and efficient design. There are three chambers in a Tarm wood boiler: gasification, combustion, and heat exchange. The first chamber, gasification, allows in just enough air to turn the wood into smoke. The smoke is then forced into the second chamber, the combustion chamber, where more air is added with a fan and combustion occurs, reaching temperatures of 1800 degrees. The super-heated air is then sent up through heat extraction tubes in the back of the boiler, passing through the boiler water volume, giving up its heat to the water. This process allows for efficiencies of up to 85%. There is no visible smoke emitted from a Tarm wood boiler when it is running up to temperature with dry wood. - What is thermal storage?
Conventional wood boilers require that a fire be kept smoldering until there is a demand for heat. The fire is always burning, and the fire tenders need to always be tending. Wood burned this way cannot work well during the spring and fall, it can't provide hot water during the summer months, it causes creosote buildup, and drags down efficiency tremendously. To burn at high efficiency, a wood fire needs to maintain high combustion temperatures throughout the burn. The fire never smolders. Thermal storage is what allows this to happen. Thermal storage consists of a very large water tank, 600-800 gallons. Heat from the wood boiler flows into the tank through two copper coils. Heat is sent out to the house through the same coils. There is an additional coil in the tank that heats the home's hot water. This storage tank allows the wood boiler to run hot for hours at a time, heating the tank to temperatures as high as 180 degrees, always burning at maximum efficiency. It eliminates creosote in any season. Most importantly, it removes the need for us to have to constantly feed the fire, allowing us to go about our lives while burning a free, renewable resource.
We custom-build our own tanks and coils. The tanks are constructed of angle steel-reinforced frame, lined with plywood, 3-4" of foam, and an EPDM liner. These can be custom sized, but are generally 50"x50"x96". They hold the heat very well. A modern house will need the wood boiler fired once on an average winter day, twice when it is very cold. Leaky old farmhouses use more energy and will require more firings. - How much does the Tarm save?
It's quite easy to figure out how much the Tarm saves. A well-dried cord of wood, burned in a Tarm will offset approximately 150 gallons of oil. If you are cutting your own firewood, and oil costs $4.50 a gallon, then each cord of wood you cut will save you roughly $675.
ReVision Energy offers a full range of services for wood boilers, from simply selling the wood boiler, delivering it, and offering technical support, to turnkey systems with full distribution. The further a project is from Liberty, the more cost-effective it is for local contractors to help with parts or all of the installation. Work goes smoothly and costs are minimized when people do what they have done before.