Frequently Asked Questions

Does Greenwood offer indoor wood boilers or outdoor wood furnaces?

The Greenwood Frontier Series and Denali Series are designed to be installed so that they are sheltered from the weather in your basement, garage, shed or other protected location. Both models meet strict UL and CSA standards for indoor heating appliances, so they are safe to install in a building. (Important Note: Installation must comply with local building codes and state/local regulations. Residents of the State of Vermont should insure compliance with state regulations referenced here.)

What are some of the ways I can use a Greenwood wood furnaces?

The Greenwood wood furnaces do one thing extremely well -- they produce hot water. You can use that hot water in almost any way you and your heating contractor can imagine:

  • hydronic radiant heating (in-floor or baseboard) for your home, garage and outbuildings
  • forced air heating (using a water-to-air heat exchanger that fits into existing ductwork)
  • domestic hot water (in conjunction with your existing water heater)
  • heating a hot tub, swimming pool or greenhouse
  • melting the snow on your walk and driveways

What is the combustion efficiency?

While a perfect 100% combustion efficiency is not possible to achieve, Greenwood wood boilers come close to it. Temperatures in the firebox approach 2000 F, assuring maximum gasification of the wood fuel. Little particulate matter remains to create smoke, creosote or ash.

What is the thermal efficiency?

Greenwood systems are some of the most energy-efficient hydronic wood furnaces on the market. It achieves up to 85% thermal efficiency depending on the stage of the burning cycle.

To Top

Does Greenwood's wood boiler meet UL (Underwriter's Laboratory) and Canadian (CSA) standards for safety?

Yes. Greenwood appliances have been designed and tested to UL-391 (U.S.) standards for solid-fuel and combination-fuel central and supplementary furnaces and CSA B366.1-M91 (Canada) standards for solid fuel-fired central heating appliances.

Do Greenwood wood boilers meet EPA emission standards?

In February 2007, the U.S. Environmental Protection Agency announced the voluntary EPA Outdoor Wood-fired Hydronic Heaters Program. The HH program encourages wood boiler manufacturers to improve air quality through developing and distributing cleaner, more efficient outdoor wood-fired hydronic heaters, like the Greenwood Frontier Series wood boiler and Greenwood Denali Series pellet boilers. This program is a recommendation by the EPA and each State will evaluate if and how it will apply it. We are in complete support of tighter air quality standards and the programs that lead to them. Program qualified units are easily identified by an White Tag.

Can I heat more than one building with a single wood boiler?

Yes. A single hydronic wood furnace can provide heat and hot water for your home, as well as your garage, greenhouse, barn or other outbuildings. It can also heat your swimming pool and even provide snow-melt for your walks and driveway. A simple network of insulated pipes or PEX tubing can connect the wood boiler to each location. Keep in mind that each application adds to the demand on the furnace, so it is important to plan ahead and install a unit with sufficient capacity to handle the full load.

What size wood furnace do I need?

Correct sizing of the hydronic furnace is very important for safe and efficient operation. The installation contractor will perform a heat load analyses of your home to determine the wood furnace output required and assess your desired operating behaviors to determine which unit is appropriate for your situation. Many factors must be considered in determining the size of the wood furnace you need, including local winter temperatures, size and insulation rating of your home, additional applications or requirements for heat, and so on.

Will Greenwood Clean Energy design my hydronic heating system?

No, we are not able to help individual consumers but rather refer this work to a local resource -- the Authorized Greenwood dealer, architect, or HVAC contractor, in your area. Local building codes and regulations vary from location to location. An on-site visit will determine the proper location and installation details.

To Top

What fuel do you recommend for the Greenwood Frontier wood boiler?

The Greenwood Frontier Series work best when burning seasoned cord wood. Burning wet or unseasoned log wood will lower the efficiency of the system and potentially create smoke and other byproducts that will degrade the long-term performance of your unit. As far as the type of wood to use as fuel, some species produce more heat than others, however we recommend burning whatever wood species is most readily and economically available in your area.

Can I burn other kinds of fuel in my Greenwood Frontier?

No. The Greenwood Frontier wood furnace is designed, built and certified to burn solid wood fuel only. Other fuels such as dimension lumber, pellets, corn, oil, railroad ties, trash, etc., are likely to cause over-firing of the furnace or other unsafe conditions. Use of any fuel other than solid wood will void the furnace warranty.

How long will a full load of wood last?

The burn duration of each wood load depends on the amount of wood loaded and the demand for heat. You should tailor the amount of wood placed in the firebox to the current weather conditions. If the weather is severe and there is high demand for heat, the firebox should be fully loaded and refilled every 8-12 hours, and sometimes more often. If conditions are milder, less wood is required and the firebox should be checked every 12 hours. Pleases see the load - output chart to better understand your reload frequency.

What is the combustion chamber of the Greenwood Frontier Series made of?

The firebox is made of super-duty, cast ceramic refractory. The firebox walls are 2 to 4 inches thick and will withstand years of use.

To Top

How hot does the wood furnaces get?

There are several answers to this question. Inside the firebox the temperature reaches 2000 F, but thanks to our unique design, the outside surface is only warm to the touch. The temperature of the heat transfer solution reaches 180 F as it flows out of the wood boiler. The temperature of exhaust gases range from 250 - 450 F depending on firing rate.

Can I vent the Greenwood Frontier through a side-wall or do I need a chimney stack?

No. We recommend a vertical flue that is at least 12 feet tall. Proper chimney sizing and venting are extremely important to the efficient and safe operation of the furnace. Your installation contractor should check for local code requirements and carefully follow the instructions in the Greenwood Owner's Manual.

How big a chimney flue is required?

The size of the flue pipe varies with the size of the furnace. The Model CX requires a 5 inch flue.

Do I need a hot water or accumulation storage tank?

Greenwood's wood boiler provides heat-on-demand and does not require a hot water storage tank after an initial offload. If your home or heating situation can not accomodate the initial off-load, your installer will recommend a small buffer tank.

Do I need a back-up source of heat?

We recommend keeping the existing heating source (e.g. furnace, boiler, etc.) as your backup. Greenwood systems are the most efficient way to heat your home during the heating season. But at other times of the year, when heating demands are drastically less, there are more economical ways to heat your home. If this is a new construction, we recommend installing a high efficiency gas or oil water heater (Bock or Polaris are excellent choices) in parallel with your Greenwood wood boiler. The water heater serves as the back-up heat source in winter and the primary in summer.

How do I get technical support for my Greenwood Furnace Series or Greenwood Aspen Series wood boilers?

Unfortunately, Greenwood Clean Energy can not sell or support the Greenwood Furnace or Aspen Series. As a public service, Greenwood Clean Energy is providing information and a support forum for products sold by former Greenwood Technologies here:

If I have a problem, how do I get technical support?

Your first point of contact for support your dealer or contractor. In most situations, Greenwood will refer you to your local dealer, but if necessary you may also contact Greenwood at Our dealer support team will reply as soon as possible.

To Top