What You Need to Know About a Gasifying Wood Boiler
Mainers are looking for home heating alternatives that are cheaper and more environmentally friendly than burning fossil fuels. The good news is that today's wood boiler technology gives us the option to heat with locally grown and sustainable wood. We love the fact that the gasification burn process produces little or no creosote, virtually eliminating the risk of a chimney fire, as well as greenhouse gas emissions. ReVision Energy has installed many wood boilers; our goal here is to share that wisdom and experience to help you can make an informed decision about whether a wood boiler is right for you.
Quick Summary of Key Points:
- Wood boilers provide 'carbon neutral' home heating if the wood fuel is sustainably harvested.
- 1 acre of forest produces between ½ and 1 cord of firewood per year.
- 1 cord of wood holds the energy equivalent of 150 gallons of oil.
- Minimum home size is 1,500 sq. ft. to be able to install a wood boiler.
- Wood boilers with thermal storage need tending 1 to 2 times per day in the dead of winter.
- Wood boilers without thermal storage need tending every 8 hours or so.
- The wood boiler needs its own chimney flue to meet code requirements.
Environmental Impact
Gasifying wood boilers are 'carbon neutral' if the fuel supply is sustainably harvested from Maine woodlots. Carbon neutral means that the small amount of CO2 emitted by the wood boiler is actually absorbed by the remaining live trees on the woodlot, resulting in net zero atmospheric emissions. In Maine, the sustainable harvesting rule of thumb is that an acre of land can produce between one-half cord to one full cord of firewood per year.
When burning properly cured firewood, Tarm gasifying boilers emit less than 1 gram of smoke per hour-equivalent to the amount of smoke produced by one cigarette. This is possible because the wood 'gasification' process results in combustion temperatures of 1,800 degrees Fahrenheit, thereby incinerating virtually every molecule of wood such that there is no visible smoke, little ash and virtually zero particulate emissions.
Saving Money
When burned in an efficient gasifying wood boiler, one cord of well seasoned hardwood has roughly the same amount of energy as 150 gallons of oil. If you buy firewood at $200 a cord and you buy oil at $4 a gallon, then each cord of firewood you burn in lieu of oil will save you $400. Of course, the price of wood and oil will change over time, and that will affect savings. It's important to note that oil is a finite resource that can never be replaced when burned. Wood, on the other hand, grows on trees.
Moving Wood
People who burn wood to heat their home generally don't mind moving wood, whether it's from the woodlot to the yard, or from the delivered pile to the storage area. If you see lugging cords of wood around as an excessive chore, then a wood boiler might not be for you. If you see it as good exercise, then read on!
What Size Home is Appropriate for a Wood Boiler?
Typically, houses smaller than 1,500 square feet, or using less than 500 gallons of oil per year, are too small for a wood boiler (unless there is a thermal storage tank; Click Here to learn about thermal storage). Smaller houses are often better served by wood or pellet stoves. Wood stoves are less expensive than wood boilers to install and provide ambiance. On the minus side, wood stoves dry the air, bring the wood into the house, are not as safe as boilers and can't heat domestic water nor the outer reaches of a home.
Tending & Maintenance
Wood boilers need attention on a regular basis; less if you install a thermal storage system that requires fewer fires. Otherwise, you need to "keep the home fires burning" to heat the home. During the coldest part of the heating season, that means going down to the basement roughly 2 to 4 times a day (depending on the boiler and the house). There are two schools of thought for how clients run wood boilers. One way is to just run them during the middle of the heating season, typically mid-November until early March. After that, the backup fossil fuel system kicks in to handle the light load. The issue is that any wood boiler needs enough heating demand to prevent the creation of creosote. During the shoulder seasons, when it is too warm to keep the boiler running all of the time, there are a few options. One is to shut it down and let the oil boiler take the light load. Another option is to "batch fire". When batch firing, the house gets cold during the day, and a fire is run just at night to boost the temperature.
Trips to the Basement
Wood boilers without thermal storage require 3 trips to the basement a day, every 8 hours or so. With thermal storage, you can make fewer trips to the basement, and it is less important when you make them. With thermal storage, as the weather warms, you make fewer and fewer trips to the boiler each day, until, during the summer months, you're firing the boiler just once a week for domestic hot water.
Schematic Diagram of a Wood Boiler with Thermal Storage
Many of ReVision Energy's wood boiler clients install systems with thermal storage (hot water storage tank). Thermal storage systems are a wonderful way to heat with wood, allowing the energy from the wood boiler to be stored in a custom manufactured 650 to 1100 gallon tank. These super-insulated tanks are designed to absorb all of the heat from one firing of the wood boiler, then gradually release that heat over time.
Thermal storage allows people to fire their boiler when it meets their schedule, not the house's schedule. It also allows the boiler to run clean and hot, getting the maximum efficiency possible from wood, which is 85%. With a thermal storage tank, you are able to burn wood whenever space heating is necessary, completely eliminating your dependence on fossil fuels, and eliminating the challenge of running a wood boiler during the shoulder seasons. Domestic hot water comes from the super-insulated storage tank. Even in the summer months, you can fire the wood boiler once every 5 to 10 days to supply all of your domestic hot water needs.
The thermal storage tank, internal copper coils and additional controls and piping typically add between $6,000 to $9,000 to the cost of a wood boiler installation.
Requirements of Thermal Storage
All you need to install thermal storage are the following:
- Space for the tank; most houses need the 650 gallon tank which is 4'x4'x8' (4'x8' footprint)
- Modest distribution temperature requirements. Most houses work fine with 150 degree water in their baseboards. Some houses are 'under-distributed,' in that they require much higher temperatures in the baseboard on the coldest nights. In houses that require very high baseboard temperatures, thermal storage is not a great option unless more baseboard distribution is added.
- The desire to eliminate your fossil fuel consumption. If you burn 600 gallons of oil per year, you'll need at least 4 cords of firewood to idle your oil boiler. If you burn 1200 gallons of oil, you'll need 8 cords of firewood. If you can not see yourself burning 100% of your needs, you might be better off without storage and burn only during the coldest months.
The Flue
Your wood boiler needs its own chimney flue. The flue for the wood boiler needs to be dedicated (no other appliances can occupy the same flue). There are many issues related to proper flues; this is not meant to be a definitive design guide, simply a preliminary list to qualify a chimney's suitability for a solid fuel boiler and to help you sort out where the boiler should go.
Masonry Chimneys
If there is a masonry chimney, that chimney needs to be lined with ceramic liner at a minimum, and with a stainless steel insulated liner at best. If the masonry chimney is run outside, or if there are places where wood is within 2" of the chimney, the masonry chimney needs to be lined with a "supa flue" product, which is a stainless steel, insulated lined chimney. http://www.supaflu.com/products.htm It is never wrong to line a chimney with insulated pipe, as this keeps the flue gasses warm and keeps creosote from condensing.
Metal Chimney
If you have an easy venting situation, such as a one story house, or a boiler in the garage or a shed, installing a metal chimney can be a good solution. Check out http://www.selkirkcorp.com/Selkirk/Product.aspx?id=208. Metal chimneys are easy to install, and are usually installed by carpenters. Chimneys need to terminate 2 feet higher than any roof 10 feet away.
Flue Requirements
| Model | Masonry Flues | Insulated Metal |
|---|---|---|
| Tarm SP 30 | 8" round or 8x8 | 6" |
| Tarm SP 40 | 8" round or 8x8 | 6" |
| Tarm SP 60 | 8" round or 8x12 | 8" |
| Tarm Excell 2000 | 8" round or 8x8 | 6" |
| Tarm Excell 2200 | 8" round or 8x12 | 6" |
| Tarm MH 1.5 | 5" diameter minimum | 5" diameter minimum |
| Tarm MH 2.5 | 5" diameter minimum | 5" diameter minimum |
| Tarm MH 4.0 | 6" diameter minimum | 6" diameter minimum |
Backup Options
Every wood boiler system needs backup to keep the insurance company happy, to keep your house from freezing if you're not around, and, if you don't have thermal storage, to keep domestic hot water hot in the non heating season.
Keep the Existing Boiler
If you've got a spare flue, that's great luck, and you can simply add on the wood boiler to the existing system, either with storage or not. If there is not an existing spare flue available, there are four options:
- Power-vent the oil boiler
- Install an Excell boiler (wood/oil combination boiler)
- Install a direct vent gas boiler or an electric backup boiler.
- Install a new Insulated metal type HT flue
Power Vent Your Existing Oil Boiler
If you want to keep your existing oil boiler, but only have one flue for the wood boiler, one option is to power vent the oil boiler. Power vents can be installed on most modern oil boilers. Termination requires 4' from windows and doors. Power-venting typically adds roughly $1000 to $1500 to the cost of the wood boiler installation.
The Excel
The Tarm Excel is a dual fuel, wood oil boiler that is UL approved for venting into one flue. Because the Excel is such a high mass boiler, ReVision Energy does not recommend it be installed without either thermal storage or an alternate means of heating domestic hot water during the non-heating season. If you are committed to a thermal storage system, the Excel can be an excellent choice.
Gas Boilers
If the oil boiler is on its way out, or you want to switch back up fuels, consider switching to a low mass gas boiler. Oil makes a poor backup fuel, due to the fact that oil boilers are high mass and, as such, they run very inefficiently in periods of low demand. Oil boilers maintain efficiencies of roughly 20% thermal efficiency during the non heating months when used for domestic hot water.
The Prestige gas boiler is a beautiful boiler that we've installed with lots of success. It's a simple boiler, easy to install, and very high efficiency, even during periods of low demand. http://www.triangletube.com/CondensingBoilers/PrestigeOverview.htm
A variation on that theme would be a gas boiler with built in on demand hot water, such as the Baxi Comfort 3 system or the Prestige Excellence, where there is no domestic hot water tank, but a coil in both the back wood boiler and gas boiler.
Electric Backup
It sounds crazy, but electric back up makes more sense every day. When you heat primarily with wood, a back up system is just that. It provides domestic hot water during the non heating season, heats the house while you're away, and provides heat during the shoulder season. Ideally, a back up system is inexpensive to install, reliable, and burns fuel efficiently during low demand. Electric back up boilers do all that. At current prices, look at how various fuel options pan out in terms of $ per Million BTU's.
For current fuel prices see http://tonto.eia.doe.gov/dnav/pet/pet_pri_wfr_dcus_sme_w.htm
- Wood @$200 per cord…………$10 per M BTU
- Pellets@$280 per ton…………$17 per M BTU
- Oil @ $5 per gallon…………$36 per M BTU
- Propane @$3 per gallon…………$32 per M BTU
- Electricity @ $.15 per KWHR………$44 per M BTU
These numbers represent fuel content, so they don't take into account efficiency. Electricity at 100% efficiency costs less than oil at 40% efficiency, which is what you'll see oil run in a backup situation. We use the thermolec electric boiler at http://www.thermolec.com/boilers.htm
Boiler Location Options
The Basement
There are several issues that need to be addressed when figuring out the best place to install your wood boiler, including flue availability, access for wood storage and delivery and arrangement of heat distribution. If you have good access to the basement, either through a walkout basement or a nice bilco door, and you have a spare flue, then the basement is a no-brainer. If you don't have a spare flue, and power venting or adding new boilers is not attractive, or you don't have good access for bringing pellets into a basement, then you might consider the garage or a shed.
The Garage
Maine law makes garage installations tough. You can not open a door from the room that stores the wood boiler directly into a room that can store a car. You can build a hallway, make a room that you can only access from the outside of the garage, or you can wall off one half of a two bay garage and make it so a car can't park in the half with the wood boiler. The state is concerned that if an automobile gas tank develops a leak, the flame in the wood boiler could ignite the gas. The garage is a great site because it can make pellet loading easy, and venting is also straightforward, but you have to be prepared to lose the ability to park a car. Also, you'll have to consider make up air AND freeze protection if it's in the garage.
Build a Shed
Sheds are a great place for indoor wood boilers, either attached to the house or not. Boilers installed in sheds are easy to vent, and easy to bring wood to. The nice thing about building a shed for the wood boiler is that the same shed can store the wood.
The Boilers
Tarm Solo Plus
The Tarm Solo Plus boilers are the most popular boilers among ReVision Energy clients. These are tried and true boilers that offer high efficiency with no headaches. They can be installed with or without thermal storage. They come in 3 sizes; the Solo Plus 30, 40 and 60 which produce 100,000, 140,000 and 200,000 BTUs respectively. If you burn less than 600 gallons oil per heating season, then the 30 is definitely for you. If you burn more than 1100 gallons of oil, then the Solo Plus 40 is for you. If you burn 2,000+ gallons of oil per year, then the Solo Plus 60 is your boiler.
Tarm Excel Wood/Oil Boiler
If you only have one flue, the Tarm Excel combination wood/oil boiler is a great solution. The combo approach allows you to have your wood boiler & your backup oil boiler in one package, hooked up to one flue. With thermal storage, the Excel can fire just once on wood or oil and provide enough heat for the whole day.
Rough Prices
How much is all of this going to cost? That's a bit of a tricky question because every house is different and therefore, every installation is different. The prices below are meant to provide a rough cost range. Once you have a clear idea of what system seems right for you, we're happy to schedule a site visit to determine actual costs for your location, and to really assess feasibility.
If there is an existing flue, and relatively easy access to the basement, the installation cost is roughly $3,000 to $5,000-this is the amount you would add to our "built boiler" prices. Built boilers include pumps, controls and safety equipment, already built in our shop and ready to go. Please refer to our "Boiler Pricing Options" sheet for built boiler prices of various boilers. Difficult delivery, additional overheat protection, re-piping, or additional controls work adds cost to installation.
Since there are very few houses that happen to have a spare flue waiting for the installation of a wood boiler, you want to keep in mind the 'hidden' costs of prepping your home for a wood boiler:
- Installation of a power vent for an existing wood boiler usually adds between $1000 and $1500.
- Installation of a Gas Direct Vent back up boiler adds between $5,000 to $9,000.
- Installation of an Electric Back up boiler adds roughly $4,000 and requires a 200 amp electrical service.
- Installation of Thermal Storage adds between $5,000 and $9,000 depending on the size and complexity of the situation, and how much of the installation you take on.
Ballpark Installed Boiler Prices:
- Tarm Solo Plus Boiler…………$11,000 to $15,000
- Tarm Solo With Thermal Storage…………$17,000 to $19,000
- Excel With Thermal Storage…………$19,000 to $23,000
Note: prices do not include venting issues for indoor boilers, or costs for building a pad or trenching. Prices are ROUGH ranges for fully installed boilers, assuming full installation within a reasonable distance from Portland or Liberty. Lower cost installations can be had by hiring a local installer to install, or by taking on some part of the installation yourself.
Who Should Install My Wood Boiler?
ReVision Energy can provide you with any level of service; from full installation to A La Carte Pricing for the services you receive. Our technicians are fully licensed and have installed many boilers. Distance from Liberty and Portland adds to installation costs, and puts us out of the reach of many installations. If you are interested in dealing only with ReVision Energy, and you are interested in our premium service, we are happy to be a full service installer for your project. If you have a fixed budget in mind, and you want to get the lowest priced installation, then working with our A La Carte Menu may be the way to go.
With our A La Carte Menu, you purchase only the level of services that you need to get the job done right. We can sell you a "naked" boiler in our shop, and avail ourselves to you or your installer for stock drawings for piping and wiring, and we can answer any questions over the phone. Or we can offer custom design services, delivery, boiler firing or troubleshooting as needed.
Want to Learn More?
Contact ReVision Heat for a free pellet heating consultation!
Or call us, (207) 989-8500.
