Furnace replacement in Plainfield, IL
The short answer
A furnace replacement in Plainfield, IL runs $5,000–$9,000 installed: about $5,000–$7,000 for a standard 80% AFUE furnace, and $6,300–$9,000 for a 95%+ high-efficiency unit with new PVC venting. Most swaps take one day. FortHouse is family-owned and based in Plainfield, and the price covers Manual J sizing, a ductwork check, removal of the old furnace, and a combustion analysis at startup. Inside the Village of Plainfield, a like-for-like swap needs no permit; in unincorporated Will County, we file the county permit.
Written by Jenna Fortman, Owner of FortHouse Heating & Cooling. Installed by EPA 608 and NATE-certified technicians.
What does furnace replacement cost in Plainfield?
| Option | AFUE | Installed price | Venting and scope |
|---|---|---|---|
| Standard efficiency | 80% | $5,000–$7,000 | Uses the existing metal flue |
| High efficiency | 95%+ | $6,300–$9,000 | New PVC venting and a condensate drain, included |
| Ductwork changes | — | +$800–$2,500 | Only if the existing ducts can't carry the new furnace's airflow |
Two quotes that differ by thousands are usually pricing different tiers, not the same job at different markups. Ask each one what AFUE and venting its number assumes. Which tier pays back in your house depends on your gas bills and how long you'll stay, so we run that math at the sizing visit.
Repair or replace: how do you decide?
Multiply the furnace's age by the repair cost. Over $5,000, replacement usually wins. Separately, if one repair costs more than half of a new furnace, replace. A cracked heat exchanger or a second repair in the same season pushes toward replacement even when the math is close.
| Furnace age | Repair quote | Age × cost | Verdict |
|---|---|---|---|
| 8 years | $400 | $3,200 | Repair |
| 14 years | $350 | $4,900 | Close — check the 50% rule too |
| 18 years | $500 | $9,000 | Replace |
What happens on installation day?
Before install day
Sizing visit
A Manual J load calculation on the house and a check of the existing ductwork, so the new furnace fits the house instead of copying the old unit's size.
Written quote
Furnace tier, venting, and any duct work, priced in writing before any work starts.
Permit check
Inside the Village, a like-for-like swap needs no permit. In unincorporated Will County, we file the county permit before install day.
Install day
Old furnace out
Disconnected, removed, and hauled away. Removal is in the price.
New furnace in
Set, with the venting, gas line, and combustion air done to code.
Startup and combustion analysis
Measured combustion readings at startup, written down and left with you.
After
Inspection, if permitted
For unincorporated Will County addresses, we schedule the county inspection. You don't have to call anyone.
What does a finished FortHouse furnace install look like?
Why is furnace replacement different in Plainfield?
Will County's oldest town
Plainfield is the oldest community in Will County, settled in the 1820s. Much of the older housing stock has been through at least one furnace swap already, sometimes without the ductwork ever being resized to match. We check the duct system's actual capacity before sizing a new furnace, not just the nameplate on the old one.
Two eras of housing
The historic downtown's older homes and the newer subdivisions further out were built to heating standards decades apart, with different duct sizing and venting. That's why we run a Manual J load calculation and check the ductwork on every replacement instead of matching whatever the last furnace happened to be.
Village vs. Will County
Inside Village of Plainfield limits, a like-for-like furnace change-out doesn't need a permit, per the Village's Building Department. Some homes with a Plainfield mailing address sit in unincorporated Will County instead, and there the county does require one. We check which side of that line your address is on before quoting, and file the Will County permit when it applies.
Questions Plainfield homeowners ask
How much does furnace replacement cost in Plainfield, IL?
$5,000–$9,000 installed. A standard 80% AFUE furnace runs about $5,000–$7,000 and vents through the existing metal flue. A 95%+ high-efficiency furnace runs about $6,300–$9,000, including the new PVC venting it needs. If the ductwork has to change, that adds $800–$2,500, quoted separately in writing.
Is FortHouse a family-owned furnace company in Plainfield?
Yes. FortHouse is family-owned and based in Plainfield, not backed by private equity, and the furnace is installed by the crew that answers the phone. More about who we are.
Do I need a permit to replace a furnace in Plainfield?
It depends on which side of the Village line you're on. Inside the Village of Plainfield, a like-for-like furnace change-out needs no permit, per the Village's Building Department. Some homes with a Plainfield mailing address are in unincorporated Will County, and there the county requires a permit; we file it and schedule the inspection. Work beyond a straight swap, like new venting or duct changes, we confirm with the right office before quoting.
How long does furnace replacement take in Plainfield?
Most standard swaps finish in one day: removal, the new furnace, and a combustion analysis at startup. Switching to a high-efficiency furnace that needs new PVC venting, or changing the ductwork, can add a half to a full day.
Is furnace replacement the same as furnace installation?
Yes. A furnace replacement is a furnace installation where the old unit comes out first. The Manual J load calculation runs the same either way, sized to the house you have now rather than whatever the furnace being replaced happened to be.
When should I replace my furnace instead of repairing it?
Replace when a repair costs more than half of a new furnace, or when the furnace's age times the repair cost tops $5,000. ENERGY STAR recommends a professional evaluation once a furnace passes 15 years. If the math still favors a fix, Plainfield furnace repair is the better call.
Do you install heat pumps in Plainfield, or just furnaces?
Both, including dual-fuel systems that pair a heat pump with a furnace for backup. If you're comparing the two, see heat pump installation for the operating-cost math.
Do you install ductless mini-splits too, not just furnaces?
Yes — for additions, converted spaces, and any room the ductwork can't reach. See our Plainfield ductless installation page for per-zone pricing and how sizing works.
What other areas near Plainfield do you serve?
Naperville, Yorkville, Bolingbrook, Oswego, Wheaton, Lisle, Minooka, Shorewood, and Aurora, alongside Plainfield. If you're just outside that list, call anyway — we make exceptions for a reasonable drive.
Sources
Prices are FortHouse's own published installed ranges, last updated September 26, 2026. Your written quote follows a home visit, not a phone call.