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How Does a GARN Wood Boiler Work?

October 14th, 2024 | 5 min. read

By Louis Greubel

A closeup of a GARN GN2000 wood boiler. Its combustion door is open, and a fire is burning fully inside the unit.

Acquiring a new wood heating appliance for your business is a big decision. There are a lot of options, and it’s important to make the right choice, as the unit you select will likely heat your business for decades to come.

At HY-C, we manufacture one such option: the GARN GN2000 wood boiler. Unlike other commercial wood heating solutions, the GARN boiler’s fire isn’t modulated. Instead, the unit operates by batch burning an entire wood load at once at a very high temperature.

The result is a very clean and highly efficient burn that requires less wood and less work than other comparable units. It also produces less smoke, resulting in a more environmentally friendly solution.

But how can that be? What makes the GARN boiler so efficient? How does it burn so cleanly? And how does it produce less smoke?

That’s exactly what we’re going to explain here.

In this guide, we’ll cover how the GARN GN2000 wood boiler works, all the way from the initial intake of fresh air to the very last ember burnt. After you learn the process, you’ll be ready to decide whether or not a GARN Wood Heating System is the right choice for you and your business.

Discover the GARN GN2000 Wood Boiler

Note: GARN Wood Heating Systems are approved for commercial use only in the United States and all applications in Canada.

GARN GN2000 Wood Boiler Components

At its core, the GARN GN2000 is merely a big tank of water. That water is heated, and the resulting energy is stored and used throughout the day to heat your business.

The water doesn’t just heat itself, though. There are a few design components that work in tandem to produce an adequate amount of heat.

So, before diving into the combustion process, first, it’s a good idea to take a peek at the major parts and components that make up a GARN boiler. We’ll do this by looking at the boiler from three different angles:

  1. The front of the boiler
  2. The back of the boiler
  3. The top of the boiler

GARN GN2000 Wood Boiler: Front

A diagram showing a GARN GN2000 wood boiler from the front. The parts of the unit are color-coded, and arrows and labels point to each part.

Looking at the GARN boiler from the front, there are 8 key components to consider:

  1. The blower motor: This high-powered fan blows air into the air collar.
  2. The air collar: This chamber guides cool outside air into the firebox.
  3. The combustion door: This heavy-duty door seals the firebox from the outside. It’s also the door you open to add a load of wood into the boiler.
  4. The overflow pipe: As the water in the unit heats and expands, this pipe drains out any excess water.
  5. The drain: When it’s time to clean the interior of the unit, the 1,830-gallon tank drains out from this port.
  6. The upper cleanout: This opening provides access to clean the pipes in the top of the unit.
  7. The lower cleanouts: These openings provide access to clean the pipes in the bottom of the unit.
  8. The electric element fittings: These optional add-ons are compatible with the GARN electrical heating kit which allows you to take advantage of off-peak electricity hours.

We’ll see how these vital components work together to create heat in a bit.

GARN GN2000 Wood Boiler: Back

A diagram showing a GARN GN2000 wood boiler from the back. The parts of the unit are color-coded, and arrows and labels point to each part.

The back of the GARN boiler has 4 key components to look at:

  1. The 7” fresh air intake: This port vents in air from the outside to be used in the combustion process.
  2. The hot water supply (HWS) connection: Hot water comes out of the unit at this point. The water that flows from here moves through pipes used to heat the building.
  3. The how water return (HWR) connection: Water that had been used to heat the building returns to the unit through this connection.
  4. The 6” flue connection (horizontal): Combustion byproducts from the firebox exit here and are expelled out of the building. This horizontal flue is to be used when a vertical flue cannot be used.

As you can tell, the ports on the back of the unit are there to accommodate pipes and ducting that allow the unit to work.

GARN GN2000 Wood Boiler: Top

A diagram showing a GARN GN2000 wood boiler from the top down. The parts of the unit are color-coded, and arrows and labels point to each part.

On the top of the GARN boiler, there are 2 key components to know about:

  1. The manway cover: This is the port on the top of the unit into which you add water. It also provides access into the interior of the unit itself for periodic cleaning.
  2. The 6” flue connection (vertical): Combustion byproducts from the firebox exit here and are expelled out of the building. This vertical flue is to be used when a horizontal flue cannot be.

While there aren’t many components on top of the unit, the two that are there are vitally important to the boiler’s operation and maintenance.

How a GARN Wood Boiler Works

Now that you’re familiar with all the important pieces that make a GARN boiler tick, it’s time to see how they work together to produce heat. The process can essentially be broken down into 7 steps:

  1. Air intake
  2. Air movement
  3. Air delivery
  4. Combustion and Gasification
  5. Heat transfer
  6. Exhaust
  7. Draft blower shutoff

Let’s see the process in action step by step.

1. Air Intake

A diagram showing how fresh air enters through a fresh air intake and into the GARN wood boiler unit. Fresh air is represented by a blue arrow.

To start with, air makes its way into the GARN boiler through the 7” fresh air intake on the back of the unit. Pulling in air from the outside of the building not only helps to maintain a constant supply of oxygen, but it also avoids using any already-heated air from inside the building.

2. Air Movement

A diagram showing the interior air pipes inside a GARN GN2000 wood boiler. This diagram shows air moving through the fresh air intake pipes.

As the air works its way toward the air collar, it moves through the intake tubes on the interior of the boiler. These tubes are surrounded by the water that fills the unit through the manway cover on the top (and we’ll see the effects of this in a few steps).

3. Air Delivery

A diagram of the air collar on a GARN GN2000 wood boiler. Blue arrows indicate how fresh air circulates around the collar and into the firebox.

When the air reaches the end of the fresh air intake tube, it arrives at the air collar — an area of open space between the intake tube and the firebox. Air circulates around the air collar, keeping it relatively cool.

Eventually, two openings in the air collar — one at the top and one on the bottom — allow fresh air to flow into the firebox.

4. Combustion and Gasification

A computer-generated closeup of the front of a GARN GN2000 wood boiler. The combustion door is open, and the diagram shows the gasification process.

As the fire burns in the firebox, the smoke and exhaust from the fire then enter into the insulated reaction chamber. Air from the air collar mixes in as well, resulting in a high-temperature secondary combustion called gasification.

Gasification is essentially the process of burning smoke and other gasses produced by the wood fuel. Gasification not only provides more heat for the building, but it also virtually eliminates smoke by burning it away, resulting in a very clean, efficient burn.

5. Heat Transfer

A diagram showing all of the air pipes inside of a GARN GN2000 wood boiler. This diagram shows the route that hot air takes to be vented out of the boiler.

After exiting the insulated reaction chamber, the clean exhaust travels through 30 feet of tubing. While it’s in these tubes, the exhaust transfers its heat into the water inside the boiler. After it’s heated, the water can be used to warm your business in a few different ways:

  1. Baseboard heating
  2. Radiant floor heating
  3. Forced air heating

6. Exhaust

A diagram showing the two exhaust venting methods for a GARN GN2000 wood boiler: a horizontal chimney flue or a vertical chimney flue.

After the exhaust transfers its heat to the water in the boiler, it’s vented out of the building. To vent the exhaust gasses, the GARN boiler offers two options:

  1. A 6” horizontal flue connection
  2. A 6” vertical flue connection

The connection style you use depends on a number of factors, such as the layout of your building and the location of your boiler (among others). Your hydronic heating contractor can help you determine which method is right for your installation.

7. Draft Blower Shutoff

A computer-generated image of the front of a GARN GN2000 wood boiler. A white arrow points toward the unit's draft induction blower.

After the combustion process is complete, the draft blower shuts off until you’re ready to burn again. The GARN boiler stores the heat from the wood fuel until you’re ready to use it.

Depending on how much heat you use and the outside temperature in your area, you may need to burn a new load of wood anywhere from every 12 hours to every 48 hours.

How Can You Get a GARN Wood Boiler for Your Business?

And that’s the magic behind the GARN GN2000 wood boiler! It’s a relatively simple machine that burns cleanly, efficiently, and effectively.

But how do you add one to your business?

It all starts by reaching out to HY-C. Let us know that you’re interested in a GARN unit, and we’ll be happy to talk to you about the steps involved in the purchasing process.

And while you’re at it, be sure to read up on the rest of our commercial wood heat offering. In addition to the GARN boiler, we also offer two wood burning furnaces — one indoor and one outdoor — as part of our commercial wood heating package.

Louis Greubel

Louis earned a bachelor's degree in English with a focus in rhetoric and composition from St. Louis University in 2017. He has worked in marketing as a content writer for over 5 years. Currently, he oversees the HY-C Learning Center, helping HY-C subject matter experts to share their decades of home solution products experience with homeowners and sales partners across the country.