Installing Outdoor Furnace Ducts

What You'll Need
Small tractor with backhoe attachment
Galvanized ducting
Duct section fasteners, screws and duct tape
1/4-inch thick Mylar insulation sheeting
Fine gravel fill, 20 lb bag
Gravel rake
PVC coated plywood panel
Plywood stripping, cut to size
A helper

Installing the furnace ducts into your home from an outdoor wood furnace is less challenging to do than you might expect. Outdoor wood or gas furnaces are safer, cleaner and just as effective as an indoor furnace. Follow these guidelines to install outdoor furnace ducts from your natural outdoor heat source into your home.

Step 1: Disconnect Your Old Furnace from the Ductwork

Disconnect the electrical supply to the old furnace and redirect the existing ductwork toward where you will link it to the new outdoor furnace. Direct the ductwork toward a small basement window where possible to avoid cutting a hole in the foundation or side wall of the house. Measure the window so you can seal it off later with coated plywood and stripping.

Step 2: Site the New Outdoor Furnace in the Best Location

Choose a site for the furnace that is at least 10 feet from your home. The site must not be in the path of prevailing winds, to prevent chimney drafts and extinguishing of the wood or gas fire.

Step 3: Measure and Purchase Sufficient Galvanized Ducting

Determine the exact size of ducting your new outdoor furnace uses and purchase enough galvanized ducting to run the ductwork from the furnace into your house.

Step 4: Dig a Trench for the Ductwork

Use the tractor with backhoe to dig a trench for the ductwork. It should be 1 inch deeper and wider on all sides than the ducting to allow room for insulation materials and an ample amount of soil and gravel fill.

Step 5: Connect and Insulate the Ducting

Fasten the lengths of ducting together with the band fasteners and screws. Cover all band fasteners with a uniform layer of duct tape. Wrap the ducting in a single layer of Solarguard (TM) 1/4-inch Mylar insulation.

Step 6: Prepare the Trench for the Ductwork

Pour the fine gravel into the trench bottom along its entire outdoor length. Level and smooth it with a heavy, broad-spaced gravel rake.

Step 7: Lay the Ductwork into the Trench

With your helper, lay the ductwork carefully into the trench, ensuring all the sections remain fastened securely.

Step 8: Connect the Outdoor and Interior Ductwork

Connect the length of outdoor ductwork to your existing interior ducts. Once you have done this, seal off the window where the ductwork enters. Fit the PVC-coated plywood into the window opening, and nail the plywood stripping around all 4 sides to make a weatherproof seal.

Step 9: Fill in the Ductwork Trench

Replace the soil you dug out of the trench, packing it firmly around the ductwork, and level with the ground surface.

Step 10: Test the Ductwork

Turn on the switch outside for the outdoor furnace, open the register vents, turn on the fan and check whether warm air is coming out. If warm air is not reaching the registers, check the connections to the new furnace and the existing ductwork.