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What a furnace replacement really involves
A furnace replacement starts with a load calculation, then covers sizing, venting, ductwork, the permit question and a startup check. A good quote names each one.
A photo essay from the people at Warm in January, Cool in July. Updated .
What does a furnace replacement involve?
It involves a visit, a calculation and several decisions before any equipment arrives. ENERGY STAR's hiring tips say a contractor should spend significant time inspecting the system and the home, size by the house, its insulation and its windows, inspect the ducts for leaks and measure airflow. A glance at the old nameplate and a price on the spot skips most of that. Tell the contractor which rooms run cold. Fort Wayne's normal year brings 5,967.7 heating degree days, so this machine will work for a living.
How big should the new furnace be?
The size should come from a load calculation. ENERGY STAR names the tool: "Your contractor should verify the proper size system for your home using a tool called 'Manual J.'" Its hiring tips add that "a bigger system isn't always better." RESNET's tables for Allen County disagree between one version and another, so read them as a range: around 0°F to low single digits in winter and upper 80s to about 91°F in summer. Your contractor's Manual J sets the real figure. If you've insulated or changed windows since the old furnace went in, its size proves little.
| What | The figure | Where it comes from |
|---|---|---|
| Federal minimum, gas furnaces made before Dec 18, 2028 | 80% AFUE | 10 CFR 430.32, Cornell LII copy |
| Federal minimum, gas furnaces made from that date | 95% AFUE | 10 CFR 430.32, Cornell LII copy |
| ENERGY STAR gas furnace, US North including Indiana | 97% AFUE or greater | ENERGY STAR |
| What ENERGY STAR says certified North furnaces can do | Up to 18% more efficient, can save $160 a year | ENERGY STAR |
| NIPSCO rebate, furnace 95% AFUE or more, from a distributor's copy of the January 2026 flyer | $250, ending Dec 31, 2026 | Munch's Supply flyer |
| Median year built, Allen County | 1976 | Census Reporter, ACS 2020-2024 |
Which efficiency number should you look for?
Look for AFUE, and know which line you're reading. In Indiana, ENERGY STAR means 97% or better. The 95% you may see on a rebate form is NIPSCO's threshold, taken here from a distributor's flyer, so confirm the amount and the rule on NIPSCO's site. The federal credit is over: the IRS says it "will not be allowed for any property placed in service after December 31, 2025."
What happens to the venting and the old furnace?
Ask, and get the answer in writing. The quote should say where the new intake and exhaust leave the house and what happens to any old chimney or flue connection. Choose a spot you can reach after a snowfall if there's a choice. If the old furnace or its ducts wear a wrap you can't identify, point it out before the removal is priced. EPA's words: "If in doubt, treat the material as if it contains asbestos and leave it alone." Repair or removal belongs to trained and accredited professionals.
Does a furnace replacement need a permit?
Call the Allen County Building Department before work starts and ask whether your job needs a permit and how to check a contractor's license or registration. This site couldn't read the county's own pages when last checked, so it states no fee or same-for-same rule here. If a permit is needed, the quote should say who pulls it.
What should the startup check cover?
It should cover the items a pro checks on any gas furnace. ENERGY STAR's maintenance checklist lists gas or oil connections, gas pressure, burner combustion and the heat exchanger, along with the thermostat, electrical connections, condensate drain and controls. CPSC adds that an inspector checks chimneys and flues for blockages, corrosion and disconnections. All of that is the installer's work. Yours is asking that it was done and keeping the paper.
What to do
Right now
- Write down the old furnace's model and which rooms run cold.
- Ask each contractor for a Manual J result on paper.
- Call the Allen County Building Department about permits.
Before next winter
- Compare quotes line by line: AFUE, sizing, venting, ducts, permit, startup check.
- Check NIPSCO's site for rebates before the flyer's Dec 31, 2026 date.
- Put a CO alarm on every level with living or sleeping space and outside sleeping areas.
Call a pro when
- The old furnace stops or a pro finds a problem you can't judge yourself.
- A CO alarm sounds: everyone out first, then call 911 from outside. Don't look for the source. Don't go back until responders say so.
- You smell gas: leave first, no switches, phones or flames inside, then call 911 and NIPSCO from outside. NIPSCO's December 2025 safety release gives its emergency line as 1-800-634-3524.
What neighbors ask
Can a furnace installed in 2026 get the federal tax credit?
No. The IRS says the credit is not allowed for property placed in service after December 31, 2025. Be wary of any quote that still counts it.
Can I still buy an 80% furnace?
For now, yes. The federal minimum is 80% AFUE for non-weatherized gas furnaces made before December 18, 2028, and 95% from that date. Ask for prices at both levels so you can compare them.
Why would a contractor measure airflow on a furnace job?
ENERGY STAR's hiring tips say to measure it and to inspect ducts for leaks. Its checklist says airflow problems can cut efficiency by up to 15%. A new furnace still pushes its air through the old ducts.
Should the old furnace size just be repeated?
Treat it as a clue. ENERGY STAR says the contractor should verify size with Manual J, using the house, its insulation and its windows.
Does ENERGY STAR mean 95% here?
No. The ENERGY STAR line for the US North, which includes Indiana, is 97% AFUE or greater. A 95% figure may appear as a rebate threshold or as the coming federal minimum.
Where this came from
This essay rests on ENERGY STAR, the federal efficiency rule, the IRS and EPA, checked November 3, 2026. The NIPSCO amount comes from a distributor's January 2026 flyer, and this site couldn't read NIPSCO's or Allen County's own pages, so confirm both with them.