Do I Need a New Furnace?

Our experts will give you advice to help you decide when you need to replace your furnace

Don't get burned by a bad furnace

New furnaces are more complex than ever with lots of new features, higher efficiencies and higher costs. Knowing what to ask an HVAC contractor is key to buying the right furnace for your home and getting a quality installation.

We asked experienced TFH Field Editors—HVAC pros who do this for a living as well as fellow DIYers who have recently bought a furnace—for their top tips, warnings, lessons learned and best advice about buying a new forced-air furnace.

Top tips from an HVAC pro

  • Don't go with the lowest bidder
    “Service calls are twice as likely to be related to poor installation as to defective equipment. The guy with the lowest bid often makes the biggest mistakes.”
  • Contractor markup makes a difference
    “The heating contractor actually pays about $300 to $500 more for a 95 percent furnace than he does for a 90 percent furnace. So, if that added cost is passed through with little markup, you might be able to cost-justify it. If the contractor marks up the price a whole bunch, then you have no chance of making a payback in your lifetime.”
  • Have a pro install a new thermostat
    “Furnaces and thermostats, just like cars, have gotten increasingly computerized, and they can require some pretty serious know-how to get them to work right.”
  • High vs. very high efficiencies
    “Higher efficiency means higher complexity, and I like to keep the machinery as simple as possible. The more complex it is, the more expensive it is, and the more it will cost to fix when it breaks. Generally, your very best value is to get a 92 percent efficiency furnace with one of the new ECM fan motors.”
  • Get a proposal, not a bid
    “Go with someone who provides a detailed written proposal that outlines exactly what he will and won't do. He should list the manufacturer and model number of the proposed equipment as well as the cost of any plumbing, venting changes or electrical work required.”
  • Buy a reputable brand
    “Stick with the major brands or one of their subsidiaries. If you don't recognize the brand, don't trust what the contractor says about it. Do your own checking online before you buy.”
  • You may need a smaller furnace
    “Older furnaces were usually oversized so that the house was always warm enough. But new higher efficiency furnaces can have a lower Btu rating and still put out the same amount of heat. For example, a new 94 percent efficient furnace that is rated at 80,000 Btu puts out as much heat as an old 75 percent efficient 100,000 Btu furnace.”

New Law May Affect Your Choice

Beginning in May 2013, a new U.S. Department of Energy rule requires newly installed residential gas furnaces in 30 northern states to be rated at least 90 percent AFUE (annual fuel utilization efficiency). That means your new furnace will vent directly through the wall instead of up your chimney or stack. Check with a local HVAC professional for more information or visit

Assess Your Entire HVAC System

When you're shopping for a furnace, get your ducts checked at the same time. There's no sense in getting a new furnace if you’ll let the hot/cold out through leaks or poor insulation in your ductwork.
Thomas Czerwinski

Mid- or high-efficiency furnace?

Cost: $1,500 to $2,500 installed (no A/C) AFUE: 80 to 89 percent.
Savings: 15 to 20 percent of current heating costs (when replacing a 65 percent efficient unit).
Venting: Into a masonry or metal chimney (existing chimney might require upgrading).

Cost: $3,000 to $5,000 installed (no A/C) AFUE: 90 to 97 percent.
Savings: 25 to 30 percent of current heating costs (when replacing a 65 percent efficient unit).
Venting: Directly through a wall to the outside through plastic PVC pipe. Known as “condensing units” because they recover extra heat from combustion gases by extracting water from them.

Highest efficiencies make sense when...

  • You live in a cold climate (may be required by law—see above).
  • You will be staying in your house for 10 years or more.
  • Local energy costs are high.
  • You're replacing an inefficient heating system.
  • The contractor markup is low (see “Top Tips from an HVAC Pro” above).
  • You can take advantage of local, state and utility rebates and incentives. Federal tax credits on high-efficiency furnaces were not renewed for 2012. But state, local and utility rebates may still be available in many areas. Visit for more information.
  • The payback calculation is reasonable. Visit energy/furnace1.php to run a payback calculation.

Highest efficiencies have higher repair bills

Single-stage or two-stage blower?

A traditional single-stage furnace runs the burner at full blast and shuts off until heat is called for. It costs $500 less than a two-stage furnace, but the trade-off is lower energy efficiency, hot and cold spots, and inconsistent temperatures.

A two-stage furnace has a high and a low burner setting. It normally runs on low unless full blast is needed. It costs $500 more than a single-stage unit, but it delivers consistent heat, which means fewer drafts and temperature swings, and is quiet and energy efficient.

Two-speed or a variable-speed blower?

Standard two-speed
A standard two-speed blower (aka “multi” speed) with a PSC motor has one blower speed for heating and one for cooling. It's $600 cheaper than a variable-speed blower and is less complex, which means lower future repair costs. But it's noisier than a variable-speed blower and uses more electricity.

A variable-speed blower uses an ECM motor, which runs on DC power and continually adjusts its speed to your home's needs. It uses a fraction of the electricity of most standard motors and is quiet and comfortable. It costs $600 more than a standard blower and is a more complex system, which potentially means more expensive repairs.

Consider buying through a home center

We got quotes from a few local contractors but went with a home center instead. The home center hired a reputable local company but backed the work, and even gave us a small discount for opening a credit card and charging the work on it.
Steve Markman

Use an experienced pro

Stick with reputable furnace contractors who have been in business for a long time. Chances are they're still in business because they do quality work, and they'll still be around if you have problems down the line. “Our HVAC company went out of business two years after they installed our unit. If we have a problem with it, there could be a big headache down the line.”
Bruce Fox

Incentives can slash the price

My gas company gave me a $100 rebate, the manufacturer gave me a $500 rebate and the city gave me a five-year interest-free loan to make the upgrade. I ended up saving a bundle.
Thomas Czerwinski

Don't assume the contractor knows everything

Most contractors I've talked to don't recommend variable-speed blowers because they don't really understand them. I dug into manufacturers' documentation and a few contractors' message boards on the Internet and read until I understood them. I guess that's what DIY is all about.
Tom Berg

Put details in writing

Confirm that your contractor will remove your old furnace without additional charges.
Jeff Montgomery

Know the true cost of the furnace

I got quotes from $2,800 (furnace and ductwork) to $12,000. Do your own research on the Internet and find out how much you can purchase the unit for online so you can separate the unit from the labor.
David Youngblood

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