When is it time to replace a furnace?

It is time to start planning a new furnace when it is past about 15 years old and showing its age: repairs every winter, fuel bills creeping up, uneven heat, new noises, or a yellow burner flame. A safety finding, such as a cracked heat exchanger, needs a licensed technician's diagnosis at any age and can bring the decision forward. The best time to decide is before the furnace quits in January, with a licensed technician's diagnosis and written prices for both repair and replacement in hand.

Age is the first thing to check

ENERGY STAR says it may be time to call a professional contractor about replacing a furnace or boiler that is more than 15 years old.^[1] Manufacturers give similar numbers. Lennox puts it simply: "The average lifespan of furnaces is 15-20 years."^[2] By type, it says gas furnaces can last 15 to 20 years and electric furnaces 20 to 30 years.^[2]

Age is a prompt, not a verdict. Bryant puts it directly: age alone does not determine when replacement is necessary.^[3] A 17-year-old furnace serviced every fall may have years left; a 10-year-old one that was badly installed may not.

If you do not know how old yours is, Lennox suggests you find the owner's manual or look up the serial number on the furnace itself.^[2] The data plate is usually inside the front panel door. For more on what shortens or stretches that lifespan, see how long a furnace lasts.

The signs that a furnace is wearing out

ENERGY STAR lists equipment that needs frequent repairs while energy bills go up^[1] among the signs to call a contractor. Bryant lists rising energy bills, frequent repair calls, uneven heating, strange mechanical noises, and declining performance^[3] as signs a furnace may be nearing replacement age. Lennox adds that a furnace that takes a long time to turn on may be starting to fail,^[2] and that multiple furnace repairs within a few years are a sign the furnace is failing.^[2]

Not every comfort problem is the furnace's fault. ENERGY STAR says rooms that are too hot or too cold can come from improper equipment operation, duct problems or inadequate insulation.^[1] A new furnace on leaky ducts can leave the same bedroom cold, so ask the contractor to look at the ducts as part of the assessment.

Safety problems come first

Some findings need attention before any talk of age or efficiency. ENERGY STAR's maintenance checklist warns: "A dirty burner or cracked heat exchanger causes improper burner operation."^[5] Carrier explains that a severely clogged filter can result in an overheated and possibly cracked heat exchanger, which can lead to a carbon monoxide leak.^[6] Bryant notes that a yellow or abnormal burner flame can indicate a combustion or ventilation problem^[3] that needs a professional inspection, and Lennox warns of health issues from carbon monoxide if components in your furnace are damaged.^[2]

If a technician tells you the heat exchanger is cracked, ask to see the evidence, get the finding in writing, and get a second licensed opinion before you decide between a repair and a new furnace. If you smell gas or have carbon monoxide symptoms, Columbia Gas of Virginia tells its customers to "go outside and call 911" and then call the gas company.^[12]

Weighing the repair bill

The common rule of thumb is Lennox's: "It's best to replace your furnace if a repair costs more than half the cost of a new furnace."^[2] Bryant is more cautious, saying there is no universal rule that a repair must exceed 50% of replacement cost before replacement makes sense.^[4] It suggests looking at the furnace's age and condition, repair history, efficiency, expected remaining service life, and the cost of the proposed repair compared with replacement.^[4]

Efficiency is part of that sum. ENERGY STAR says an ENERGY STAR qualified furnace is 15% more efficient than a conventional furnace,^[1] so an old, inefficient furnace costs you every winter it stays. For the full comparison, read should I repair or replace my furnace; for prices, how much a new furnace costs in Virginia.

Replace on your schedule, not the furnace's

A furnace that dies on the coldest night of the year leaves you choosing from whatever a busy contractor has in stock. Virginia's building code makes room for that: the work can start first, but applications for emergency equipment replacement must be submitted by the end of the first working day after the day the work starts.^[8] But planning ahead gives you time to collect quotes, ask about sizing and compare efficiency.

Whether it is planned or an emergency, the code only exempts the replacement of mechanical appliances that are not fueled by gas or oil,^[8] so a gas, propane or oil furnace replacement needs a permit. See do you need a permit to replace an HVAC system in Virginia.

Getting the assessment

Before you call, ENERGY STAR suggests you know the model of your current system and its maintenance history, and make a note of any uncomfortable rooms.^[7] It also says the contractor should spend significant time inspecting your current system and home,^[7] not just read the old furnace's label. Ask each business for:

• a written description of what is wrong, with photos if it is a safety finding;
• a written repair price and a written replacement price from the same visit;
• how they would size a new furnace, and whether that includes a heating-load calculation;
• what the permit, removal of the old furnace and any venting or duct changes add.

What replacing a furnace involves explains each part of the job, so you can see when a quote leaves something out.

When to call a licensed pro

Deciding when to replace is a judgment you make, but the inspection behind it, and the replacement itself, are licensed work. Under Virginia law, no individual may work as a tradesman without a licence, and the Code's definition of a tradesman includes anyone doing heating, ventilation and air conditioning work for the public for pay.^[9][10] Check a business on DPOR's License Lookup^[11] or read does an HVAC technician need a licence in Virginia.

Book an inspection and both prices when:

• the furnace is past 15 years old and has needed a repair this season;
• a single repair quote is large, or it is the second or third repair in two winters;
• a technician reports a cracked heat exchanger, a yellow flame or another combustion problem;
• fuel bills keep rising with no change in how you use the house.

Getting quotes in Virginia

Loclis lists DPOR-licensed HVAC businesses with their licence number and class. Look up HVAC businesses in Blacksburg, browse furnace replacement, or read more heating and cooling answers.

Describe your furnace and what it is doing and licensed local HVAC businesses quote the repair, the replacement, or both.