Furnace Repair

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

Dave Jones

Dave Jones is a 35-year licensed professional engineer and a TFH Field Editor. He is the Engineering & Design Manager at Temperature Systems Inc. in Madison, WI, and has been involved in the design and construction of hundreds of HVAC projects across the United States, ranging from lake cabins to large research facilities.

• 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.”

Mid- or high-efficiency furnace?

Which efficiency furnace is best?

Factor in local energy costs, rebates and tax credits and contractor markups when you compare furnaces.

MID-EFFICIENCY
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).

HIGH-EFFICIENCY
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 dsireusa.org for more information.
• The payback calculation is reasonable. Visit yourmoneypage.com/ energy/furnace1.php to run a payback calculation.

Highest efficiencies have higher repair bills

Diminishing returns?

I’m an HVAC repairman. Most furnace installers prefer that you buy the most efficient furnace and claim it will save you money. What they don’t tell you is that the parts to repair it are about three times as expensive and in the long run you’re not saving anything. You can buy a furnace rated at 95 percent and still stay away from the high repair bills of a 97 or 98 percent.
Lee Schmidt

Single-stage or two-stage blower?

Single-stage
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.

Two-stage
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.

Variable-speed
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

Steve Markman

Steve’s next project is a display case for the large wood sailing ship models he builds.

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

Bruce Fox

Bruce just finished remodeling his den from the studs up.

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

Thomas Czerwinski

Tom just wrapped up a half-bath remodel (taking the room down to the studs and the subfloor and adding new windows, doors, vanity, sink, toilet, etc.).

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

Tom Berg

Tom has taken on HVAC as a hobby and has reduced his utility costs by 25 to 30 percent by sealing ductwork and replacing his own furnace, thermostat and other HVAC equipment.

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

Jeff Montgomery

Jeff’s recent projects include installing flooring and cabinets in his children’s home schooling classroom.

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

Know the true cost of the furnace

Dave Youngblood

David is currently building a dock for his pond.

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

Video: 6 Tips for Furnace Troubleshooting

Remove the combustion chamber door

Make sure the power is off

Flip the electrical power switch to “Off.” Remove the combustion chamber door by lifting up and pulling it out, and remove the burner cover (if you have one). It’s usually held in place by two screws.

Inspect the burner flames

Flames should be even and blue

Turn the power switch on and activate the burners by turning up your thermostat. Inspect the burner flames. The flames should be fairly even and blue. Yellow flames indicate dirty burners. (Don’t breathe on the flames because the extra oxygen will also make them turn yellow.) Don’t adjust the burners yourself. Call in a pro.

Vacuum out the burner and blower cavities

Vacuum the burners

Turn off the power switch again and shut off the gas by giving the valve one-quarter turn. Vacuum the burners and the furnace base. To get at the back of the burners, tape a 20-in. length of 1/2-in. drain line to your vacuum hose. Vacuum everywhere you see dust. While everything is open, use a flashlight to look for signs of soot (fine black powder), which often indicates poor combustion. Lift off the lower door (blower door) and vacuum the blower compartment.

Remove the blower to clean it

Remove the bolts that secure the blower

Remove the blower (also called a squirrel cage) in order to clean it. If you have a control panel in front of the blower, two screws will loosen it and you can let it hang. Next, using a 7/16-in. socket and ratchet, remove the two bolts that hold the blower in place, then gently lift it out.

Vacuum and brush the blower blades

Clean the blower blades carefully

Clean the blower blades thoroughly with a vacuum and small brush. Take care not to stress the wiring or disturb the counterweights that will be on the fan blades. If you can’t clean the blower thoroughly, don’t clean it at all; you could throw it off balance.

Change the furnace filter

Use cheap fiberglass filters

Change the furnace filter every one to three months. A $1 fiberglass filter will adequately protect the blower and blower motor. If you want to install a more expensive, high-efficiency filter, check the owner’s manual for the manufacturer recommendations. High-efficiency filters can restrict the airflow, strain the blower motor and make your furnace less efficient. If you want cleaner air, the best option is a separate air-cleaning system.

Blow dust off the pilot

Use a drinking straw to dust the pilot

Blow dust off the pilot. Direct air to the exact spot by blowing through a drinking straw. A dirty pilot can cause the flame sensor (or thermocouple) to get a false reading that the pilot isn’t lit. Some newer furnaces have hot surface igniters instead of pilots and electronic igniters.

Clean the flame sensor

Use fine emery cloth to clean the sensor

The flame sensor occasionally becomes coated with residue and will prevent your furnace from lighting. Remove it by pulling it down out of its bracket. Lightly clean the surface with fine emery cloth and slip the sensor back into its bracket.

Dust the hot surface igniter without touching it

Don’t touch it—blow off any dust

Hot surface igniters are the most common ignition system on furnaces being manufactured today. They take the place of standing pilot lights and electronic igniters. Clean the dust off the hot surface igniter by leaving the igniter in place and blowing air through a straw. This part breaks very easily; don’t even touch it. In fact, when you replace the furnace doors, do so gently to avoid breaking the igniter.

Inspect the drive belt

Inspect for cracks or frayed areas

The belts on belt-driven blowers need occasional adjustment or replacement. Inspect the drive belt for cracks or frayed areas. A new belt costs about $5. When you install the new belt, tension it so it deflects 1/2 to 3/4 in.

Lubricate bearings if necessary

Don’t over-lubricate

Some older furnaces have two motor bearings and two blower shaft bearings that require annual oiling. Clean around the oil caps and remove the caps. Apply two to three drops of lightweight machine oil and replace the caps. Don’t over-lubricate!

Adjust dampers if necessary

Adjust the seasonal settings

If your furnace heating ducts also serve as air conditioning ducts, they may have dampers that require adjusting for seasonal changes. The seasonal settings should be marked. Two-story homes often have separate supply trunks to serve the upstairs and downstairs. To send more warm air downstairs (winter setting) or more cold air upstairs (summer setting), adjust the damper handle on each supply trunk.

Seal leaky air ducts

Use special metal tape to seal leaks

Seal leaky ducts, especially return air ducts, with special metal tape or high temperature silicone. Then conduct a backdrafting test to make sure the combustion gases go up the flue: Adjust the thermostat so the burners come on. Hold a smoking stick of incense beside the draft hood. The smoke should be drawn into the hood. Also inspect the exhaust vent pipes on your furnace and water heater (while they’re cool). White powdery residue can indicate corrosion. Call in a pro to fix these problems.

Choosing the right filter for your furnace

The choice of which filter to buy for your furnace depends on how much you want to spend, what you're trying to filter, and how diligent you are about changing the filter.

The minimum efficiency reporting value (MERV) scale goes from 1 to 16. Most residential filters range from 4 to 12. Furnace manufacturers prefer the traditional spun fiberglass filters (MERV 2) because they filter out enough of the large particles to protect the furnace while providing maximum airflow. Maintaining the furnace manufacturer's specified airflow is critical to achieving energy efficiency and maximum life from the blower motor and heat exchanger. An inexpensive MERV 4 filter captures 80 percent of the particles 50 microns and larger, but only 25 percent of the particles in the 3 to 10 micron range.

For most homeowners, a more expensive MERV 7 or 8 pleated filter provides a good balance between cost and filtration efficiency. These filters trap 80 to 95 percent of the particles 5 microns and larger—more than enough filtration for most households.

Furnace efficiency is one thing. But if you're a clean freak or have family members with allergies or low-immunity issues, spend more on a high-efficiency (MERV 11 and higher) filter. Then just make sure you stay on top of filter changes to protect your furnace.

High-efficiency filters capture 99 percent of airborne particles as small as 0.3 microns (bacteria and viruses, fumes and pollen). But you'll have to run your furnace fan full time to get the maximum benefit from a high-efficiency filter, and that will cost more. Figure the extra cost into your decision.

Finally, never switch from a fiberglass filter to a high-efficiency filter without first talking to your HVAC technician. The technician can boost fan speed to compensate for the reduced airflow. Even then, you still have to be diligent about replacing the filter regularly. A clogged filter can burn out the blower motor, damage the heat exchanger and cost you hundreds of dollars in wasted energy.