Wood Boiler FAQ

If you’re looking for a renewable energy source to heat your home, you may find your solution in an indoor wood boiler. An indoor wood boiler heats cleanly and efficiently. These boilers can serve as either a standalone or supplementary heating source in any type of home, old or new. Learn all about wood boilers in our wood boiler FAQs guide below.

Who Is Tarm Biomass? 

Tarm Biomass is a third-generation family-owned company dedicated to bringing efficient, clean-burning heating systems to homes and businesses in North America. For over 25 years, we’ve imported the best-known names in European central heating — our products include Froling wood boilers, HS-Tarm (parts), and LK Armatur boiler installation components. The indoor boilers we offer provide a renewable energy source for home heating that offers an environmentally friendly alternative to other heating options.

How Do Indoor Wood Boilers Work?

These wood boilers are vastly different from outdoor boilers in their operation and design. The use inside means they must be compact, clean-burning, smoke-free while loading, quiet, and water-tight. They have built-in smoke hoods and induction fans to control smoke and to control combustion gasses.

Here’s an outline of the process indoor wood boilers follow to produce heat:

  1. Fill the boiler firebox with firewood. 
  2. The wood is ignited through the unique lighting door, quickly establishing a fire and generating heat. Built-in controls add the right amount of air into the combustion chamber to optimize fuel burning. 
  3. Gasses from combustion travel to a secondary chamber where the remaining fuel in the gasses is burnt out and converted to heat. Many wood boilers, including Fröling wood boilers, have two-stage combustion, otherwise known as wood gasification, to burn off more of the combustion gasses to reduce emissions.
  4. The water traveling through an indoor wood boiler is typically pure, untreated water under pressure. The boiler transfers heat from combustion through heat exchange tubes surrounded by the pressurized system water. Contrary to their name, indoor wood boilers do not boil water, but typically bring the water to about 180 Fahrenheit.
  5. The hot water goes through your home’s central heating system to heat your radiators, radiant flooring systems, or fan coils. As it releases heat, the water cools and returns to the wood boiler to reheat as needed. The thermal storage tanks allow the fuel to burn quickly and hot by absorbing any excess heat the building is not using.

Note that burning wood will produce ash, which you must remove periodically. Additionally, indoor wood boilers operated normally don’t create harmful creosote, making the boilers easier to maintain and safer to operate. Most wood boilers only require adding fuel every 12 to 24 hours during the coldest periods of the year.

Is Installation Complicated? How Long Does It Take?

The complexity and installation time for your indoor wood boiler depends on many factors, such as:

  • The amount of space and height you have for installation.
  • Access to the boiler room for moving the boiler and thermal storage tanks in.
  • The existing heating manifold and controls. Sometimes the installation of a new boiler presents an opportunity to modernize and clean up outdated, worn-out, or inefficient heating systems.
  • Whether you have an existing chimney or need one installed.
  • If you want to set up a domestic water heating system that uses the boiler for its heat source,

Professional installation with experienced technicians will shorten the installation time and ensure your indoor boiler will work as intended.

Is Wood Burning Good for the Environment?

Yes, wood burning is good for the environment. Using wood fuel for heating is a CO2-neutral process for heating. Wood fuel is available in our backyards and is non-toxic. When dead, crooked, or diseased trees are removed to be used as fuel, healthy trees will fill in the space of the removed trees.  The remaining trees grow healthier and larger and absorb more carbon dioxide. Burning wood for heat is the most efficient use of wood fuel and is vastly more efficient than using wood fuel for creating electricity

CO2 Neutral: When alive, trees use CO2 from the air to produce food and give off oxygen. When burned, the CO2 released in combustion gasses equals the amount of gas produced naturally during rotting after a tree falls in the forest. In other words, burning wood produces heat in a method that closely replicates the chemical processes that happen in nature. 

Wood burning is also good for the environment because it replaces non-renewable fossil fuels. When fossil fuels are burned, carbon previously locked away underground from a time when the earth was hotter is released into the atmosphere. Fossil energy sources are controlled by large companies and nation states and are prone to major price fluctuations due to market speculation, war, weather outages, and equipment failure. Further, the equipment needed for accessing and delivering oil and gas disrupts local ecosystems and can destroy native habitats. For example, oil spills present major risks for wildlife and plants in the vicinity, and recovery from such incidents can create lasting damage to the surrounding area. Wood harvests for home heating fuel have been made continuously from the same forests for decades without detriment to the environment. In fact, when we value forests for trees rather than converting them for development and agriculture, we encourage valuable carbon dioxide absorbing natural systems. 


How Long Is the Warranty?

Tarm Biomass warrants Fröling S3 Turbo wood boilers for 20 years. Warranty details can be obtained by calling us at 800-782-9927.

How Long Will Your Wood Boiler Last?

When used properly, Fröling wood boilers will last decades. Some parts are considered wear parts and will need replacement before the boiler wears out. In most cases, Fröling wood boilers need no parts replaced for at least 10 years. Consequently, the health and professionalism of the companies supplying your boiler may be as important as the boiler itself. Tarm Biomass has been in business for 26+ years, and we supply parts for boilers sold as long as 45 years ago!  Following operation and maintenance guidelines are generally easy and ensure long boiler life. Importantly, operation with thermal storage practically eliminates harmful acids known to cause leaks in modern wood boilers. Often wood boilers will outlast their practical life and get replaced because a new technology introduced 20 or 30 years later is superior enough to justify a change. 

How Often Do You Have to Fill a Wood Boiler?

The frequency for filling your wood boiler depends primarily on the outdoor temperature and the size of the heat storage tank. Most operators fill Fröling wood boilers once or twice in a 24-hour period during the coldest weather. On warmer days, a typical January thaw period, or during shoulder seasons, it may be possible to start a fire every two days or longer. 

To find out how a wood boiler and thermal storage system might fit with your lifestyle, please ask our customer service representatives, who can help you choose the best option for your space and domestic water heating needs.

Are Wood Boilers Efficient?

Fröling indoor wood boilers are very efficient in terms of fuel use and heat output. EPA efficiency ratings are seasonal average efficiency ratings, which attempt to account for the true efficiency of boilers during normal operation. Because indoor boilers installed with thermal storage operate exactly the same in real life as in a test laboratory, efficiency ratings are very accurate compared to ratings for outdoor wood boilers.

 The efficiency of all Froling indoor boiler models from Tarm Biomass qualifies them for a 30% Federal tax credit. This tax credit amount depends on the date you installed the indoor biomass boiler. For systems in place before December 31, 2022, the tax credit is 22% and will be capped at $2,000 in total. 


There are currently no state-level incentives for indoor wood boilers.

Tarm Biomass will happily provide you with a certificate indicating your model’s fuel efficiency for tax purposes. Always check with an accountant or tax attorney before filing to see if you qualify for the energy efficiency incentives for federal or state taxes.

Should You Consider a Wood Boiler or Pellet Boiler?

Tarm Biomass is one of the only companies in the United States with expertise in wood, wood pellet, and wood chip boilers. Whether you choose a firewood, wood chip, or pellet wood boiler depends on your access to fuel, the amount of heat needed (are you heating a 2,000-square-foot home or a 20,000-square-foot warehouse?), the space available for fuel and the boiler plant, available incentives and your ability to supply labor for fuel procurement and boiler operation. We find that people with their own trees to harvest or who can obtain inexpensive firewood choose wood boilers. People who prefer automation or who have to purchase expensive firewood by the cord often opt for wood pellets. Tarm Biomass does not supply wood chip boilers for residential applications. We are happy to assist you with making a decision about whether a wood or wood pellet boiler makes more sense. 

How Do You Maintain a Wood Boiler?

Generally, indoor models have minimal maintenance requirements Ash is removed about once a week. This takes about 1 minute. Less frequently, usually every month, a more thorough ash removal is recommended, taking about 30 minutes. An annual inspection and cleaning take about 1 hour. Almost all maintenance is ash removal based. 

For occasional repairs of your indoor wood boiler, contact our technical support team at Tarm Biomass to connect with professionals who can help with your technical issues.

How Much Wood Will It Take to Heat Your Home?

The amount of wood required depends primarily on the size and insulation values of the building being heated. An average home uses about 5 cords of 20% moisture content hardwood per winter for space and domestic water heating. If only conifers are available, approximately 7 cords would be used for the average home. 

Measuring heat generation uses British Thermal Units (BTUs) as the unit of measure. One BTU can raise the temperature by 1 degree Fahrenheit of 1 pound of water.

The heat production from various fuel sources used in indoor boilers is as follows:

  • A cord of mixed northern hardwood produces 24 million BTUs, equivalent to 260 gallons of propane or 170 gallons of heating oil.
  • A cord of softwood (coniferous) yields 18 million BTUs.
  • One ton of wood pellets has the heating equivalent of 170 gallons of liquid petroleum or 115 gallons of #2 heating oil, which is about 16 million BTUs.
  • Regarding moisture content, 1 ton of green wood chips produces 8 million BTUs, but chips with 25% moisture produce 11.5 million BTUs. The former replaces 60 gallons of oil while the latter produces the same energy as 80 gallons of oil.

If you want to become independent of an oil or propane-based heating system, use the current amount of fuel you purchase each winter to estimate your wood fuel needs for heating your home. Tarm Biomass sales staff can also help assess total annual fuel requirements. 

Where Are Froling Boilers Made? 

While our offices at Tarm Biomass are in Orford, New Hampshire, the Fröling boilers we sell come from a family-owned company based in Austria. The company has produced its indoor boilers for the European market since 1961, where they remain highly popular heating options. Tarm Biomass began importing Fröling boilers in 2008. 

Where Can You Get Technical Support for Your Wood Boiler?

If you need technical support for your indoor wood boiler, contact us. Either use our online contact form to tell us about the issue or call us directly. Before calling, please check our technical support page for information on our phone support hours, which may change throughout the year.

What Do You Do When You’re Going Away?

Unlike outdoor boilers that require treating the water to keep them from freezing, indoor boilers are protected inside your home and don’t require that treatment.

If you’ll be out of town and assuming you don’t have a house-sitter to fill the boiler with wood, automatic backup from a conventional oil or gas boiler or another heating system will be required. 

Choose Tarm Biomass for Your Wood Boiler 

At Tarm Biomass, we have several options among our residential indoor Froling wood boilers. Connect online with our customer service representatives to get help choosing the best wood boiler type for your home. Tarm Biomass is here to ensure you receive quality service and products for your home’s energy.




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2 thoughts on “Wood Boiler FAQ

  1. Hi,
    Is it hard to capture the CO2 and reuse it (maybe CHP) do you have that ability or is it something that can be added on? Thanks

    1. Hello Lucas,
      Froling boilers do not capture CO2. Trees and vegetation to capture the CO2. That is the beauty of wood fuel. It is nearly carbon neutral, assuming that forests are not depleted, but sustainably managed.

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