If you are tired of watching your heating bills spike every time the temperature drops, an outdoor furnace might be the solution you’ve been looking for. These units sit outside your home and feed heat into your existing system, letting you burn firewood instead of paying for expensive natural gas or oil. Wood is cheaper, renewable, and widely available. But before you light a match, you need to pick the right size unit and prepare for a serious DIY project.
Installing this system isn’t just about stacking wood. It requires digging, pouring concrete, and running pipes. If you skip steps, you risk frozen pipes or lost heat. Here is how to actually get it done.
Pour a Solid Foundation
You cannot just drop a heavy furnace on grass. You need a concrete pad. Make it big enough to hold the unit comfortably. You also need space to stand while you are loading wood. The pad must be at least 4 inches (10.16 centimeters) thick. To do this, you will need to build a mold for the concrete pour. Once the concrete sets, you have a stable base that won’t sink or shift.
Dig Below the Frost Line
This is where many people go wrong. If you bury pipes too shallow, the water inside will freeze in winter. That stops the heat flow and can burst the pipes. You need to dig a trench from the furnace to your house. Use a backhoe if you can. The trench must go below the frost line. This ensures the ground stays between 45 and 55 degrees Fahrenheit (7 and 13 degrees Celsius). That constant temperature protects the pipes from freezing.
Run the Pipes and Power
Measure the exact distance from your furnace to the house. You will need two main things to run from the unit to your home.
- PEX Pipe: This is the hot water pipe. Cut it to the length you measured.
- Electrical Wire: You need a 12/3 110V wire.
Place the PEX pipe in the trench. For the electrical wire, slide it into a 4×6 PVC pipe first. This protects the wire from moisture and damage. Put the PVC pipe into the trench alongside the PEX line.
Connect the Heat Exchange
Once the pipes are in place, you need to handle the heat transfer. Mount a heat exchanger in the outlet plenum of your furnace. The plenum is basically the ventilator area. You should be able to buy a heat exchanger that fits your specific plenum model. It needs to slide in easily. Secure it with an L-shaped bracket so it doesn’t wiggle loose.
Wire the System
Now connect the plumbing. Attach one end of the PEX pipe to the furnace outlet. Connect the heat exchanger to your home’s hot water heater. You will need another run of pipe and a pump to connect the other end of the PEX line to the hot water heater. This creates a loop.
For the electricity, install a circuit breaker in your breaker box. Attach the 110V wire to the breaker and then to the furnace. Install a thermostat too. This controls when the system runs.
Start the Fire
Everything is connected. The concrete is dry. The pipes are buried. The
