Fifteen years in, the heat exchanger is the question

The problem a furnace tune-up is solving

A furnace in Lake City might run from the first freeze in December through the last cold snap in early March, on and off, a few hundred hours total. By hours it barely ages. By years it does: gaskets dry out, the flame sensor oxidizes, the igniter grows brittle, the inducer bearings dry, and on a gas or propane unit the heat exchanger goes through a heating-and-cooling cycle every time the burners light. At fifteen years, the exchanger is the part that decides whether the furnace is a maintenance customer or a replacement customer, because a crack in it puts combustion gases into the air you breathe.

That is the problem a fall inspection solves: not “is the furnace efficient” first, but “is the furnace safe to run this winter,” and then efficiency. Lake City’s housing makes the question sharper than it is in newer towns. The in-city stock is largely 1950s-80s block ranches and older frame houses, and the furnaces in them were often replaced once, in the 1990s or 2000s, which puts a lot of them right at the fifteen-to-twenty-five-year mark now.

What the fall inspection checks

In the order the technician works, grouped by what each group protects.

Safety 1. Gas or propane pressure at the manifold, and a leak test at the valve, unions and flex connector. 2. Heat exchanger inspected visually and with a scope where the design allows; a CO reading taken in the supply air with the burners running. 3. Flame roll-out switches, high-limit switch and the door switch tested, not just looked at. 4. Flue pipe and termination checked for corrosion, slope and blockage. Wasps and squirrels like a flue that sat quiet all summer. 5. Carbon monoxide detectors in the house noted: present, absent, expired.

Combustion and ignition 6. Burners removed and cleaned; flame pattern observed and photographed. 7. Hot-surface igniter resistance measured; flame sensor cleaned and its signal checked. 8. Combustion analysis at the flue: oxygen, CO, flue temperature, efficiency. 9. Inducer motor amp draw and bearing noise.

Airflow and water 10. Filter checked for size and rating; a too-restrictive filter in a one-inch slot is a common cause of limit trips. 11. Blower wheel inspected and cleaned if dusty; motor amps logged. 12. Static pressure measured across the furnace. 13. On condensing furnaces, the condensate trap, tubing and drain cleared and treated; on well-water homes, scale is the usual finding.

Controls 14. Thermostat cycle rate and staging settings reviewed; a full heating cycle observed start to finish. 15. Control board and wiring inspected for heat discoloration or storm damage.

What we find in Lake City furnaces

Finding	Where it shows up	What it means
Flame sensor film	Nearly every furnace past five years	Cleaned on the spot; prevents the three-seconds-and-off failure
Scaled condensate trap	High-efficiency furnaces on private wells	Cleared; a cleanout recommended so you can flush it
Dust-packed burners	Furnaces in dusty closets and garages	Cleaned; restores a clean flame
Lazy or yellow flame	Propane units with a drifting regulator; gas units with blocked burners	Adjusted or referred to the propane supplier
Elevated CO at the flue	Older units with a dirty exchanger surface	Cleaned and retested; if CO reaches the supply air, the furnace is shut down
Cracked or rusted-through exchanger	Furnaces past fifteen, especially with a history of limit trips	Replacement conversation; the furnace does not run until then
Heat-scorched control board	Homes that took a lightning surge over the summer	Replaced; surge protection recommended
Return duct too small	1950s-80s ranches with one hallway return	Noted, quoted separately; the furnace will keep tripping its limit until fixed

Book a fall furnace inspection

What the visit costs

The inspection is quoted as one flat price before it’s scheduled. Anything found during it is priced separately and done only with your approval; the technician does not replace a part because it’s convenient. A Cook’s maintenance agreement includes the fall furnace visit alongside the spring cooling visit, with priority scheduling when the freeze warning posts; ask for the full list of member benefits. [[CONFIRM WITH JERRY]]

What it saves is mostly the emergency: a furnace that fails its first start on a 28-degree night, with the whole county calling at once and Cook’s a long drive away in Palm Coast. The efficiency side matters too. A furnace with clean burners, a correct gas pressure and a clean blower wheel burns less fuel per hour of heat, which shows up on the Lake City Utilities gas bill or the propane invoice over the season.

When a tune-up becomes a replacement estimate

A twenty-year-old furnace can still pass every test, and as long as yours does we’ll keep maintaining it. The inspection turns into a replacement conversation when:

• The heat exchanger is cracked, rusted through or leaking CO into the supply air. That’s not a judgment call. The furnace is shut down and you get a written estimate at no charge, usually the same day.
• Repairs in the last two winters add up to a third of a new furnace and the unit is past fifteen.
• The inducer or blower motor fails on a unit where parts are discontinued, which is common on early-2000s models.
• The furnace was never right for the house. Oversized furnaces that short-cycle and undersized ones that run constantly both wear out early and heat badly, and a load calculation shows it.

In that case the estimate covers gas, propane or electric options, and a heat pump or dual-fuel alternative, since a heat pump handles most Lake City winter days on its own and the furnace only needs to carry the freezes. Financing is available on new equipment, and we’ll point you to any current utility or manufacturer incentives; the federal credit for high-efficiency furnaces ended with 2025 and isn’t part of the math.

October is the month to book; call 866-266-5709.