Can I Buy A New Furnace and Install it Myself?

Yes, you can. However, there are a number of issues to explore before you make the decision to buy and install a new furnace yourself.

With the exception of a few cities and counties with strict installation rules, homeowners around the country are free to purchase and install their own furnace.

Getting the Right Size Furnace

In the past, it was common for some contractors to install a furnace too large for the home’s needs, “just to be sure” it would create enough heat for the coldest winter weather.

Getting the size right is essential to furnace efficiency and comfort control. For example, a furnace that is too large will waste energy and cause temperature fluctuations because it will heat past the thermostat setpoint. The disadvantages of an undersized furnace are inadequate heating and early mechanical failure.

Solution: A Manual J load calculation should be done to determine the right furnace capacity. You have three options:

    • Use a free online load calculator like Cool Calc (free account required)
    • Purchase software, which starts at about $50
    • Hire an HVAC technician to do the test. Pros charge anywhere from $100 to $225 for a Manual J. A professional will give you the most accurate results of the three options.

Voiding Your New Furnace Warranty

Most manufacturers void warranties for furnaces that are purchased online and/or DIY installed. 

Carrier’s wording is similar to most. In the Warranty Conditions Carrier states, “Product must be installed properly and by a licensed HVAC technician.”

Additionally, its Warranty Exclusions include, “any product purchased over the internet.”

The reasons for voiding the warranty are easy to understand. Homeowner-installed furnaces have a higher failure rate and may not reach the furnace life expectancy they’re designed for. And buying a furnace online takes away a sale and installation from a local Carrier dealer (or Trane, Lennox, Heil, etc.).

Solution: Install the furnace and pay a licensed installer to inspect the work and correct any problems. We checked with a handful of installers, and only one would consider such an arrangement.

If there aren’t problems, the inspection will cost $50-$150, possibly more. If there are issues to correct, the bill might be as high as the $1,000-$2,000+ most charge for full installation.

Choosing the Right Furnace for Your Needs

Due to the issues just mentioned, most manufacturers do not sell their products to wholesalers.

Goodman is one exception. Most of its furnace models are sold directly to the public as well as through local Goodman dealers. You’ll find a few entry-level models from Rheem and economy brands like Direct Comfort (a Goodman brand), Blueridge and Revolv (for mobile homes).

Solution: If you’re OK with one of those brands, they’re available from most local and online distributors that sell to the public.

Ductwork Changes for New Furnace Requirements

Today’s gas and oil furnaces are more compact than they used to be, even when the new unit has the same heating capacity as the old.

This means you’ll likely have to change the sheet metal plenums connecting the furnace to the warm air supply and the cold air return.

Solution: Many homeowners buy supply air and return air plenums from a local home improvement store or online seller. An online search will show your options for buying one. Warm air supply plenums start at about $50. Cold air return plenums are usually larger and start at about $125.

We recommend using a local sheet metal shop when possible. Call ahead and tell them what you need. They will walk you through measuring for the plenums. Cost will be a bit higher, but it is the best way to ensure the plenums fit nice and tight.

Furnace Installation Dangers

These “go without saying,” but a reminder never hurts.

    • An improperly wired furnace can cause a short that at minimum burns out the control board. That’s a $225-$750 part. At worst, it can cause a fire that destroys the furnace and possibly your home.
    • An improperly connected gas, propane or oil line can leak and cause an explosion or fire.
    • An improperly vented furnace can leak deadly carbon monoxide, which might be distributed throughout your home via the furnace blower and ducts.

Solution: Read and carefully follow the installation guide that comes with your furnace. Watch installation tutorials and/or find an experienced friend that will double-check all potential safety issues.

Or simply do what most homeowners do and hire a licensed professional for the install.

The Bottom Line

Can you buy and install your own furnace? Yes you can.

Should you buy and install your own furnace? That’s the important question that only you can answer.

Think through the issues and solutions discussed above, and make the DIY determination based on your skill level and whether the possible risks are worth the reward of saving the installation labor cost.