Gas Furnace Replacement in Fort Wayne, IN

A gas furnace burns fuel, transfers that heat to the air moving through a heat exchanger, and sends the combustion byproducts outside. Every part of that sentence has a safety dimension, which is why replacing one is more involved than swapping an appliance.

Natural gas vs propane

In Fort Wayne proper, most homes are on natural gas. Farther out — Grabill, Woodburn, Decatur, Churubusco and the rural areas between them — propane is common. Propane has different energy content and pressure requirements, so equipment must either ship configured for LP or be converted using the manufacturer's kit and orifices.

Because propane usually costs more per unit of delivered heat than natural gas, the efficiency conversation carries more financial weight on propane. That doesn't automatically make a condensing furnace the right answer, but it does deserve a careful look.

Sizing a gas furnace correctly

Gas furnaces are sold by BTU input, but what heats your house is BTU output — input multiplied by efficiency. Sizing should come from a heating load calculation that accounts for insulation, windows, air leakage, orientation, ceiling height, ductwork and additions. Manual J is the established residential method.

Oversizing is the most common mistake in gas furnace replacement. An oversized furnace satisfies the thermostat quickly, shuts off, and repeats — producing temperature swings, more wear on ignition components, and noticeable noise cycles. Our sizing guide goes deeper.

Venting: the part that decides a lot

An 80% AFUE gas furnace is non-condensing. Its exhaust is hot enough to vent through a metal flue, frequently into an existing masonry chimney with a liner. A 90%+ condensing furnace extracts so much heat that the exhaust is cool and wet, so it vents through PVC to an approved sidewall or roof termination and drains condensate.

Two consequences matter for Fort Wayne homes:

• If you move from chimney venting to condensing equipment, new PVC intake and exhaust plus a condensate path are required work — a legitimate line item, and a common omission on suspiciously cheap quotes.
• If a water heater shares that chimney with the old furnace, removing the furnace changes how the flue behaves. That needs evaluation rather than assumption.

Gas piping and combustion air

The gas connection should include a properly sized supply, a shutoff valve and a drip leg, and the pipe sizing needs to suit the new furnace's input along with everything else on the line. Combustion air matters too: a furnace drawing air from a small, tight mechanical room can struggle, and depending on the installation, dedicated combustion air may be required. Sealed combustion condensing furnaces pull outside air directly through a PVC intake, which is one of their practical advantages in tight spaces.

Safety checks that should always happen

• Gas leak check on all joints disturbed during installation
• Manifold gas pressure verified against the manufacturer's specification
• Temperature rise measured and confirmed within the rated range
• Vent performance verified, including draft on natural-draft or induced-draft equipment
• Safety controls — limit switch, pressure switch, flame sensing — confirmed functional
• Carbon monoxide awareness discussed, including where alarms should be located

Permits

Residential furnace replacement generally requires the applicable HVAC/mechanical permit through the Allen County Building Department (200 E Berry St, Suite 180, Fort Wayne, IN 46802) for Allen County addresses. Requirements may vary with the scope of work, so confirm what applies to your project. Gas and venting work is exactly the category permitting exists to cover.

What gas furnace replacement costs

Many 2026 Fort Wayne planning estimates fall roughly in the $4,000–$7,500 range for a straightforward furnace-only replacement, with high-efficiency or complex installations falling outside that range. Planning estimate only — your quote depends on the home. See the full cost breakdown or run the cost calculator.

Gas furnace replacement FAQs

Related pages

• High-efficiency furnace replacement
• How installation works
• 80% vs 96% AFUE compared