ReVision Energy's solid fuels division has become its own company, ReVision Heat, to help Maine and New Hampshire homes transition away from fossil fuel based heating. Visit www.revisionheat.com for more information about 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's experience installing wood boilers has to the creation of our sister company, ReVision Heat, to help you transition your home's heating from fossil fuels to renewable energy.
Wood Gasification—The Key to Efficiency & Low Emissions
Gasifying 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 wood stove. 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.
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.
- 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 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.
Our sister business, ReVision Heat 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.
Want to Learn More?
Contact ReVision Heat for a free wood heating consultation, or call: (207) 989-8500.