How to Install an Outdoor Wood Burning Furnace? A Definitive Guide

Installing an outdoor wood burning furnace (OWBF) allows you to efficiently heat your home and domestic hot water using wood, often reducing your reliance on traditional fossil fuels. However, the process requires careful planning, adherence to local regulations, and a solid understanding of the system’s components to ensure safety and optimal performance.

Planning & Preparation: The Foundation of a Successful Installation

Proper planning is paramount for a safe and effective OWBF installation. This involves understanding your heating needs, assessing your property, and navigating local codes and regulations.

Assessing Your Heating Needs

Before even considering a specific furnace model, calculate your home’s heating load. This measurement, typically expressed in BTU/hour, determines the required furnace output. Consider factors like your home’s square footage, insulation levels, climate zone, and the efficiency of your existing heating system (if any). A heating professional can provide a precise calculation, or you can use online BTU calculators for a rough estimate. Oversizing can lead to inefficient operation, while undersizing will result in insufficient heating.

Property Evaluation and Site Selection

Carefully evaluate your property to determine the ideal location for your OWBF. Key considerations include:

• Distance from structures: Most jurisdictions mandate minimum clearances from homes, sheds, and other buildings to prevent fire hazards. Check local codes for specific requirements.
• Prevailing wind direction: Position the furnace so that smoke is carried away from your home and neighboring properties.
• Accessibility: Ensure easy access for loading wood and performing maintenance, even during winter months. Consider the ease of access for delivery trucks carrying firewood.
• Ground conditions: Choose a level, stable surface. A concrete pad is highly recommended to provide a solid and fire-resistant base.
• Proximity to water lines: Be mindful of underground water lines to avoid accidental damage during excavation.
• Vegetation: Clear away flammable vegetation around the furnace to minimize fire risk.

Navigating Local Codes and Regulations

This is arguably the most crucial step. Contact your local building department and fire marshal to understand all applicable codes and regulations regarding OWBF installations. These regulations often cover:

• Permitting requirements: A building permit is typically required before installation.
• Setback distances: Minimum distances from property lines, structures, and water sources.
• Stack height restrictions: Regulations regarding chimney or stack height to minimize smoke nuisance.
• Fuel requirements: Limitations on the types of wood that can be burned.
• Emission standards: Some jurisdictions have strict emission standards that OWBFs must meet.
• Inspection requirements: Inspections during and after installation to ensure compliance.

Ignoring local codes can result in fines, forced removal of the furnace, and potential legal issues.

Installation: A Step-by-Step Guide

Once you’ve thoroughly planned the installation, you can proceed with the physical installation process. Always consult the manufacturer’s installation manual for specific instructions related to your chosen furnace model.

Preparing the Furnace Pad

A level and stable furnace pad is essential. A concrete pad is the best option, providing a fire-resistant and durable base. The pad should extend beyond the furnace’s footprint by at least 12 inches on all sides. Pouring a concrete pad requires:

1. Excavation: Dig a shallow excavation, typically 4-6 inches deep.
2. Compaction: Compact the soil at the bottom of the excavation.
3. Gravel base: Add a layer of compacted gravel for drainage.
4. Formwork: Build wooden forms to contain the concrete.
5. Reinforcement: Add wire mesh or rebar for added strength.
6. Pouring and leveling: Pour the concrete and level it using a screed board.
7. Curing: Allow the concrete to cure for several days before placing the furnace.

Connecting the Underground Insulated Lines

OWBFs typically connect to your home’s existing heating system via underground insulated lines. These lines carry hot water from the furnace to a heat exchanger inside your home.

1. Trenching: Dig a trench from the furnace location to your home’s foundation. The trench depth should be below the frost line in your area to prevent freezing.
2. Installing the insulated lines: Carefully lay the insulated lines in the trench. Avoid sharp bends or kinks.
3. Protecting the lines: Consider encasing the lines in PVC pipe for added protection from physical damage.
4. Backfilling the trench: Backfill the trench carefully, compacting the soil around the lines.

Installing the Heat Exchanger and Plumbing Connections

Inside your home, you’ll need to install a heat exchanger that transfers heat from the furnace water to your existing heating system (e.g., forced-air furnace, radiant floor heating).

1. Locating the heat exchanger: Choose a location near your existing heating system components.
2. Plumbing connections: Connect the insulated lines to the heat exchanger according to the manufacturer’s instructions. Ensure proper connections and sealing to prevent leaks. Use appropriate fittings and pipe sealant.
3. Integrating with existing system: Connect the heat exchanger to your existing heating system’s water lines or air ducts. This typically requires a qualified HVAC technician to ensure proper integration and prevent damage to your existing system.
4. Wiring: Connect the heat exchanger to your electrical system for controls and circulation pumps, as needed. Ensure proper wiring and grounding for safety.

Setting Up the Furnace

Carefully position the furnace on the prepared pad.

1. Leveling: Ensure the furnace is perfectly level to prevent uneven heating and potential damage.
2. Connecting the chimney/stack: Install the chimney or stack according to the manufacturer’s instructions. Ensure proper flue gas venting.
3. Filling the water jacket: Fill the furnace’s water jacket with water according to the manufacturer’s specifications. Add appropriate corrosion inhibitors to protect the metal components.
4. Testing: Thoroughly test the system for leaks and proper operation.

Frequently Asked Questions (FAQs)

1. How much does it cost to install an outdoor wood furnace?

The cost varies widely depending on the furnace size, complexity of the installation, local labor rates, and required permits. Expect to spend between $10,000 and $20,000 for the furnace, materials, and professional installation. DIY installation can save on labor costs but requires significant expertise.

2. What are the benefits of an outdoor wood furnace compared to an indoor wood stove?

OWBFs offer several advantages: safer operation (reducing indoor fire hazards), cleaner indoor air (smoke and ash remain outside), and greater heating capacity (can heat larger homes and domestic hot water).

3. What size outdoor wood furnace do I need?

The required size depends on your home’s heating load (BTU/hour). Consult a heating professional or use online calculators to determine your specific needs. Oversizing can lead to inefficient burning and creosote buildup.

4. Can I install an outdoor wood furnace myself?

While DIY installation is possible, it’s highly recommended to hire a qualified professional. Improper installation can lead to safety hazards, inefficient operation, and voiding of warranties. Moreover, the complexity of plumbing and electrical connections often requires specialized skills.

5. How often do I need to load wood into an outdoor wood furnace?

The frequency depends on the furnace size, wood type, outdoor temperature, and your heating needs. Typically, you’ll need to load wood once or twice a day during the coldest months.

6. What type of wood is best for an outdoor wood furnace?

Seasoned hardwoods like oak, maple, and ash provide the most heat and burn the longest. Avoid burning green wood, which produces excessive smoke and creosote. Creosote buildup is a significant fire hazard.

7. How do I prevent creosote buildup in my outdoor wood furnace?

Burn seasoned hardwoods, maintain proper airflow, and regularly inspect and clean the chimney or stack. A qualified chimney sweep can perform professional cleanings.

8. What maintenance is required for an outdoor wood furnace?

Regular maintenance includes cleaning the firebox, inspecting the chimney or stack, checking the water level and adding corrosion inhibitors, and inspecting the plumbing connections for leaks.

9. Are outdoor wood furnaces environmentally friendly?

OWBFs can be more environmentally friendly than burning fossil fuels if used properly and if they meet current EPA emission standards. Burning seasoned wood efficiently produces less smoke and greenhouse gases.

10. What are the potential drawbacks of an outdoor wood furnace?

Potential drawbacks include the initial cost, the labor involved in cutting and loading wood, the potential for smoke nuisance to neighbors, and the need for regular maintenance.

11. What is the lifespan of an outdoor wood furnace?

With proper maintenance, an OWBF can last for 15-20 years or more.

12. How do I find a qualified installer for an outdoor wood furnace?

Look for HVAC professionals with experience in installing OWBFs. Check their credentials, read online reviews, and ask for references. Ensure they are licensed and insured.