How to Install a Furnace

A man works on a furnace.
What You'll Need
Utility knife
Foil tape
PVC glue
Drip leg fixture
Pipe wrench
Extra ducting materials
Gas detector

The furnace is one of the most important elements in an HVAC system. But between buying a new unit and having it professionally installed, it doesn’t take long before the costs add up. Luckily, you can save some money by setting the furnace up yourself. Here is a quick guide on how to install a furnace on your own.

Step 1 - Prep New Unit

The first thing to do when installing a new furnace is to unbox the unit and take inventory of all of the parts. The unit should come with a setup guide that will tell you everything you need to know about the installation process. Make sure you have all of the required components and necessary tools before moving forward. Make sure that the furnace was not damaged during delivery and everything appears to be in working order.

Step 2 - Determine Air Duct Location

A metal air duct.

Before installing the furnace, locate where the return air duct is placed. This will either be on the side of the unit or on the bottom. The dimensions of the ductwork should be marked on the side of the furnace. Depending on where the furnace is situated, you may need to purchase an elbow or additional piping to connect the furnace to the ductwork.

Step 3 - Decide on Furnace Placement

Once you have the ductwork figured out, you can place the furnace in its desired location. The furnace should be installed on rubber pads to help reduce noise. If you are installing the unit in a basement, it should be raised four inches from the ground. If the furnace is in the attic, it should be equipped with a drain pan to catch condensation during normal use.

Step 4 - Use a Condensation Drain

Every furnace is equipped with a condensation drain. The unit should be slightly sloped towards the drain to avoid water buildup. You want the furnace as level as possible, so do not slope it too much in the direction of the drain.

Step 5 - Connect Pipes

A man works on an HVAC system.

Once the furnace is in place, connect the unit to your home’s ductwork. All of the connections should be tightly sealed with foil tape or sealant. The furnace should also come with PVC exhaust and inlet pipes. When installing these pipes, make sure they are properly glued in place and are sloped towards the furnace. The slope should be around ¼ inch for every 4 feet.

Step 6 - Connect Gas Line

Before connecting the gas line, it is recommended to install a drip leg in the form of a tee. The tee features a capped nipple on the bottom, which helps trap sediment. The gas line is connected in the top of the tee and runs straight into the furnace. Once the gas line is connected, double check for leaks by using a gas detector. For safety reasons, do not proceed with the installation until all leaks have been diagnosed and addressed. It is also a good idea to install a carbon monoxide detector in the furnace room in case of future leaks.

Step 7 - Turn Power On

With all of the pipes connected, it is time to hook up the electrical components. Most furnaces come with two types of electrical connections: regular and low voltage. The low voltage one connects to a shutoff switch while the regular voltage connects to the mains. Follow the instructions in the manual when setting up the low voltage switch. Double check that everything is properly hooked up before turning on the furnace.

Step 8 - Run the Furnace

If the furnace turns on and everything is properly installed, it is time to run the unit through one cycle. While the furnace is running, check the drainage pipes for leaks. You should also compare temperature readings from the outlet air and the temperature rise and make sure they are in line with the specs. Lastly, check again for any gas leaks.