Signs Your Furnace Needs Replacing (and When Repair Still Wins)

Age matters when a furnace develops a problem, but it does not decide the answer by itself. Condition, maintenance history, heat-exchanger safety, repair history, parts availability, operating cost, comfort, and the homeowner's plans all belong in the repair-versus-replacement decision. A.J. LeBlanc Heating inspects the equipment and explains both options when both are reasonable.

1. Age

These are broad planning ranges, not expiration dates. Some equipment lasts longer and some fails sooner.

• Gas furnaces: 15 to 20 years
• Oil furnaces: 20 to 25 years (often longer with diligent service)
• Cast-iron boilers: 25 to 30+ years
• Condensing boilers: 15 to 20 years
• Heat pumps: 12 to 15 years

Age provides context, but condition, safety, parts availability, repair history, and the homeowner's plans determine whether repair or replacement makes sense.

2. Frequent repairs

The general rule we use: if the cost of an upcoming repair is more than half the cost of a new system, replacement is usually the better value. Some specific patterns that signal end-of-life:

• Multiple service calls within a 12 to 18 month period
• Repeated control board, ignitor, or capacitor replacements
• A repair that requires parts that are increasingly hard to source
• Diagnosed heat exchanger cracks or leaks

A confirmed heat-exchanger crack or breach is a safety issue. Do not operate the furnace until a qualified fuel gas fitter evaluates it. The damaged heat exchanger must not be patched. Depending on the model, age, warranty, parts availability, and repair cost, the safe options may include replacing the heat-exchanger assembly or replacing the furnace.

3. Rising energy bills with no change in behavior

If your gas, propane, or oil bills have crept up year over year (after adjusting for fuel price changes) while your thermostat habits and household occupancy stayed the same, the furnace is likely losing efficiency. Symptoms that confirm this:

• Combustion analysis showing higher flue gas temperatures than spec
• Visible scorching, soot, or rust at the burner
• A combustion CO reading higher than the manufacturer's range
• Longer cycle times to reach the same setpoint

4. Uneven heating throughout the home

If certain rooms are noticeably colder than others, the furnace itself may be the cause:

• A weak blower motor that cannot push air to the far rooms
• A failing variable-speed control that no longer modulates correctly
• A degraded heat exchanger that is not transferring heat fully to the air

Uneven heating can also be caused by leaky or undersized ducts. A good inspection identifies which.

5. Unusual noises

A furnace should run quietly with consistent burner ignition and steady blower operation. Sounds that signal trouble:

• Banging or booming at startup: delayed ignition, dirty burner, or gas pressure issue
• Rattling or vibration: loose panels, failing blower motor or bearings, or fan blade damage
• Squealing: blower belt or motor bearings
• Clicking that does not lead to ignition: failing ignitor or flame sensor
• Whistling: often a return duct or filter restriction

6. Yellow burner flame or visible soot

A properly running gas or propane burner has a steady blue flame. A yellow, flickering, or sooty flame indicates incomplete combustion, which can mean:

• Blocked combustion air intake
• Cracked heat exchanger drawing return air into the combustion side
• Dirty burner
• Improper gas pressure

Yellow flame on a fuel-burning furnace is a safety issue. Stop using the system and call for service.

Repair vs. replace decision framework

On newer equipment, a covered or straightforward repair often makes sense. On older equipment, compare the specific repair with the furnace's condition, safety, warranty, parts availability, recent repair history, efficiency, and the cost of a correctly selected replacement. A percentage rule can start the conversation, but it should not make the decision for the homeowner.

What replacement actually involves

For a typical NH gas furnace replacement:

• A.J. LeBlanc Heating performs a Manual J load calculation for every new-construction heating and air-conditioning system. For existing-home replacements and other projects, we evaluate the home and use the sizing and load analysis appropriate to the scope, followed by equipment selection using the applicable design information.
• Removal of the old furnace
• Inspection and any modifications to the existing ductwork
• Installation of the new furnace, gas line, condensate drain (for condensing models), and venting
• Permits and inspections
• Commissioning, including combustion analysis
• Owner orientation on the new system

For homeowners thinking about a replacement, this is also the right time to consider:

• Whether to switch to a heat pump or dual-fuel system
• Whether to add a high-MERV media filter cabinet
• Whether to address any duct sealing or insulation issues
• What NHSaves rebates and financing options apply to your replacement (the federal 25C tax credit ended December 31, 2025)

Schedule a furnace assessment

If your furnace is showing any of the warning signs above, or is past 15 years old, contact A.J. LeBlanc Heating or call 603-623-0412 for an honest assessment of repair vs. replacement options. Serving New Hampshire families since 1928.

Frequently Asked Questions

How long does a furnace last in New Hampshire?

Gas furnaces typically last 15 to 20 years; oil furnaces often longer (20 to 25 years) with diligent service. Cast-iron boilers last 25 to 30+ years.

What is the most common reason a furnace needs replacing?

Age and accumulated wear. Specific failure modes that trigger replacement: cracked heat exchanger (most common safety-driven replacement), failed blower assembly on an old system, and accumulating repair frequency on aging electronics.

Is a yellow flame on my furnace a safety issue?

Yes. A yellow, flickering, or sooty flame on a gas or propane burner indicates incomplete combustion and possible CO production. Stop using the system and call for service.

When does it make sense to repair vs. replace?

On newer equipment, a covered or straightforward repair often makes sense. On older equipment, compare the repair with the furnace's condition, safety, warranty, parts availability, repair history, efficiency, and replacement cost. A percentage rule can start the conversation, but it should not make the decision by itself.

Should I replace my furnace with a heat pump?

A heat pump is worth comparing when the home also needs cooling or the homeowner wants to reduce fuel use. It can provide both heating and cooling, while a dual-fuel design can retain a compatible furnace for backup. Operating cost and rebate eligibility depend on the home, equipment, current rates, and current program rules.