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Should I repair or replace my furnace?

Repair it if the furnace is under about 15 years old, safe to run and the fix is a fraction of a new furnace's price. Consider replacing it once it is past 15 years, needs repairs often, a repair would cost more than half the price of a new one, or there is a safety problem such as a cracked heat exchanger.

Free to ask. Local shops send quotes, and you pay only when you book one.

By Kasra Taheri, Founder, LoclisUpdated

Researched and drafted with AI, then checked claim by claim against the sources listed below before it was published. Prices and rules change; the dates beside each source say when it was last checked.

This is a job for a licensed pro in Virginia

This page explains what the work involves, the permits, what a licensed pro does and what drives the cost. It does not give step-by-step instructions, because this work needs a licence, a permit or both, and doing it wrong can injure someone. Before you hire, check the licence on Virginia's DPOR record.

Repair the furnace when it is younger than about 15 years, safe to run, and the fix costs a modest share of a new furnace. Start planning a replacement when it is past 15 years, needs repairs every season, a single repair would cost more than half the price of a new furnace, or the technician finds a safety problem such as a cracked heat exchanger. In every case, get the diagnosis and both prices in writing from a licensed business before you decide.

A condensing gas furnace in a utility room, with white plastic vent pipes on top, metal ductwork behind and a small condensate pump at its base
Photo: Wtshymanski, CC BY-SA 4.0, via Wikimedia Commons

Age: the first number to check

Find the furnace's age on its data plate or in the paperwork. 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] Lennox gives a similar range: "The average lifespan of furnaces is 15-20 years."[4] By type, it says gas furnaces can last 15 to 20 years, boilers 15 to 30 years and electric furnaces 20 to 30 years.[4]

Age alone does not settle it. A 17-year-old furnace that has been serviced every fall and needs a small part may still be worth repairing, while a 12-year-old one with a serious fault may not be.

Repair cost against replacement cost

Lennox's rule of thumb is blunt: "It's best to replace your furnace if a repair costs more than half the cost of a new furnace."[4] To use it, you need two written numbers, the repair and a replacement, from the same visit or from two businesses.

Count the pattern as well as the single bill. ENERGY STAR lists equipment that needs frequent repairs while energy bills go up as a sign to consider replacement,[1] and Lennox says multiple furnace repairs within a few years are a sign the furnace is failing.[4] A second or third repair in two winters is money that could go toward a new furnace.

For what drives the repair side, see how much furnace repair costs in Virginia; for the other side, how much a new HVAC system costs in Virginia.

Efficiency and fuel bills

A gas or oil furnace's efficiency is its AFUE rating. Virginia Cooperative Extension explains that a furnace with an AFUE rating of 80 converts 80% of the fuel it burns into usable heat, and that older furnaces will be in the 50s or 60s.[5] ENERGY STAR says an ENERGY STAR qualified furnace is 15% more efficient than a conventional furnace.[1] On an old, low-AFUE furnace, part of the cost of a new one can come back through lower fuel bills.

Extension's advice before replacing is to check with your local utility before replacing an existing system,[5] since the fuel available to you, and any rebates, affect which replacement makes sense.

Comfort problems may not be the furnace

ENERGY STAR's list of replacement signs includes rooms that are too hot or too cold, humidity problems, excessive dust and a noisy system,[1] but it also points out that the cause can be duct problems or inadequate insulation.[1] Ask the contractor to look at the ducts before you pay for a new furnace to fix a cold bedroom.

Safety settles the question faster

ENERGY STAR's heating check-up explains: "A dirty burner or cracked heat exchanger causes improper burner operation."[3] Lennox warns of potential health issues from carbon monoxide if components in your furnace are damaged.[4] If a technician says the heat exchanger is cracked, ask to see what they found, get the finding in writing, and get a second licensed opinion before spending on either option.

The wait for that second opinion is not time to run the furnace as normal. Bryant warns that when a furnace blows cold air, if the cause is a cracked heat exchanger or gas valve issue, it can be hazardous.[10] Ask the first technician to state in writing whether the furnace is safe to run until it is repaired or replaced, and if the answer is no, leave it off and use other safe heat in the meantime. Columbia Gas of Virginia advises a carbon monoxide detector on every level of your property and in every room where someone sleeps.[12] If one sounds, or anyone has symptoms of carbon monoxide poisoning, its instruction is to "leave the area to get to fresh air and immediately call 911."[12]

What replacing a furnace involves in Virginia

Permit. Virginia's building code only exempts the replacement of mechanical appliances that are not fueled by gas or oil,[6] so a new gas or oil furnace needs a permit. Localities say so in their own guidance. For example, Fairfax County lists new, replacement, repair or conversion of HVAC systems among the projects that need a residential mechanical permit.[7] When a furnace fails in winter, applications for emergency equipment replacement must be submitted by the end of the first working day after the day the work starts.[6] More in do you need a permit to replace an HVAC system in Virginia.

Sizing. ENERGY STAR says a contractor should size the heating and cooling system based on the size of your house, level of insulation, and windows,[2] not on the size of the old furnace.

Contract. ENERGY STAR advises signing a written proposal before work starts, specifying project costs, model numbers, job schedule and warranty information.[2]

For the full job, read what installing a new HVAC system involves.

When to call a licensed pro

The repair-or-replace call is made with a technician's diagnosis, not before it. 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.[8][9] Check the business on DPOR's License Lookup.[11]

Ask for an inspection and both written prices when:

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

If you smell gas, Columbia Gas of Virginia's instruction is to "go outside and call 911 and then call us at 1-800-544-5606 (24/7)."[12] If another company supplies your gas, use its emergency number. If a carbon monoxide alarm sounds, leave the area to get to fresh air and immediately call 911.[12]

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 the furnace problem once and licensed local HVAC businesses quote the repair, and the replacement if it comes to that.

Common questions

How old is too old for a furnace?
There is no fixed cut-off. ENERGY STAR suggests talking to a contractor about replacement once a furnace or boiler is more than 15 years old, and Lennox puts the average furnace lifespan at 15 to 20 years. A well-kept furnace can run longer; one that needs frequent repairs is a candidate sooner.
What is the half-cost rule for furnace repair?
It is Lennox's rule of thumb: it is best to replace a furnace if a repair costs more than half the cost of a new furnace. It works best with a written quote for both the repair and a replacement in front of you.
Is a cracked heat exchanger a reason to replace the furnace?
It is a safety problem. ENERGY STAR says a dirty burner or cracked heat exchanger causes improper burner operation and can make equipment operate less safely, and Lennox warns damaged furnace components can lead to carbon monoxide health issues. Ask the technician to show you what they found, to say in writing whether the furnace is safe to run in the meantime, and to price both a repair and a replacement.
Do I need a permit to replace a gas furnace in Virginia?
Yes. The Uniform Statewide Building Code only exempts replacing mechanical appliances that are not fueled by gas or oil, so a gas or oil furnace replacement needs a permit from the local building department. Ask each contractor whether their quote includes the permit.
Should I get a second opinion before replacing my furnace?
For a large decision, yes. Ask a second licensed business to inspect the furnace and give a written repair price and a written replacement price. Comparing the two diagnoses tells you more than comparing two replacement quotes.

Sources

  1. [1] When is it time to replace?, ENERGY STAR, U.S. Environmental Protection Agency. Checked October 26, 2026.
  2. [2] 10 Tips for Hiring a Heating and Cooling Contractor, ENERGY STAR, U.S. Environmental Protection Agency. Checked October 26, 2026.
  3. [3] Maintenance Checklist, ENERGY STAR, U.S. Environmental Protection Agency. Checked October 26, 2026.
  4. [4] How Long Does a Furnace Last?, Lennox. Checked October 26, 2026.
  5. [5] ENERGY SERIES: What about the Heating System?, Virginia Cooperative Extension, Virginia Tech. Checked October 26, 2026.
  6. [6] 13VAC5-63-80, Section 108 Application for permit, Virginia Uniform Statewide Building Code, Virginia Administrative Code. Checked October 26, 2026.
  7. [7] Mechanical (MECHR) - Residential, Fairfax County, Virginia. Checked October 26, 2026.
  8. [8] Va. Code § 54.1-1129, Necessity for licensure, Code of Virginia, Virginia General Assembly. Checked October 26, 2026.
  9. [9] Va. Code § 54.1-1128, Definitions, Code of Virginia, Virginia General Assembly. Checked October 26, 2026.
  10. [10] Why Is My Furnace Blowing Cold Air? Troubleshooting and Solutions, Bryant. Checked October 26, 2026.
  11. [11] License Lookup, Virginia Department of Professional and Occupational Regulation. Checked October 26, 2026.
  12. [12] Carbon Monoxide, Columbia Gas of Virginia. Checked October 27, 2026.

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Describe the job once. Licensed local businesses send quotes, and you pay only when you book one.