Furnace replacement in Fairfax.
A new gas furnace in Fairfax runs $4,285 to $14,040 installed, keeping your AC. In the City’s 1960s basements, the chimney question comes first.
- Installed price in writing
- Sized to the house, not the old nameplate
- Dedicated HVAC team
Get your furnace priced in writing
A Fairfax furnace swap starts with which side of the city line you’re on.
The City of Fairfax and Fairfax County each run their own permit office, and a new gas furnace needs a permit on either side of the line, even the same size in the same spot. Inside the city it’s the City’s inspector who comes out. In Fair Lakes, Mantua or Kings Park West it’s the county’s, and the county also asks for a chimney vent certification any time a fuel-burning appliance is replaced.
That chimney matters most in the City and Mantua, where the typical owner’s house dates from the 1960s and the furnace usually shares a masonry flue with the gas water heater. Swap in a high-efficiency furnace that vents out the side in plastic pipe, and the water heater is left alone in a chimney built for two, often too big for it to draft well by itself. The quote should say what happens to the water heater’s vent before you sign it.
On the county side most houses went up from 1980 on, and in Fair Lakes, Fair Oaks and Navy plenty still run the builder’s 1990s furnace. That’s past the fifteen to twenty years most gas furnaces get, and the air conditioner beside it is usually just as old. A furnace and air conditioner replaced together run $8,898 to $23,000 installed, and since the coil sits right on top of the furnace, doing both means opening that closet once.
Condo owners in Merrifield and Fair Oaks get a tighter job. The furnace lives in a closet, the new one has to fit the same footprint and the same doorway, and anything that changes an outside wall or the roof usually needs the association’s say first.
The furnaces across Fairfax, place by place.
Census figures for the owner-occupied homes in each place, and what that usually means for the furnace that’s there now.
| Place | Median home built | Most homes are | Heated with | The furnace there now |
|---|---|---|---|---|
| Fair Oaks | 1995 | condo and apartment buildings, about 5 in 10 | gas, about 6 in 10 | Condo and apartment buildings: compact furnaces in closets. |
| City of Fairfax | 1966 | single-family houses, about 5 in 10 | gas, about 7 in 10 | Gas furnaces on their second or third round, often on a chimney shared with the water heater. |
| Fairfax Station | 1982 | single-family houses, about 9 in 10 | gas, about 5 in 10 | 1980s and 90s houses, many on their second furnace. |
| Kings Park West | 1976 | single-family houses, about 7 in 10 | gas, about 5 in 10 | Gas furnaces on their second or third round, often on a chimney shared with the water heater. |
| Merrifield | 1990 | condo and apartment buildings, about 6 in 10 | gas, about 6 in 10 | Condo and apartment buildings: compact furnaces in closets. |
| Fair Lakes | 1998 | townhouses, about 3 in 10 | gas, about 7 in 10 | 1980s and 90s houses, many on their second furnace. |
| Long Branch | 1968 | single-family houses, about 9 in 10 | gas, about 7 in 10 | Gas furnaces on their second or third round, often on a chimney shared with the water heater. |
| Mantua | 1968 | single-family houses, about 7 in 10 | gas, about 7 in 10 | Gas furnaces on their second or third round, often on a chimney shared with the water heater. |
Fairfax houses, by the numbers
From the Census Bureau’s 2020 to 2024 survey, owner-occupied homes unless it says otherwise.
The City of Fairfax
- Median home built1966 Census
- Built before 1980about 7 in 10 Census
- Built since 2000about 2 in 10 Census
- Most homes aresingle-family houses, about 5 in 10 Census
- Heated withgas, about 7 in 10 Census
- Rentedabout 3 in 10 Census
- Houses this age are often on their second or third furnace, still blowing through the original ducts, and the new one has to suit them.
- Most heat here is gas, so the usual job is gas furnace for gas furnace, and the real choice is how efficient the new one should be.
The Fairfax County side
Most of the Fairfax Station Census place, in the table, has Fairfax mail, so it counts here.
What a new furnace costs in Fairfax.
The same price book our estimator runs on, for a gas furnace on its own, 2 to 5 tons, keeping the air conditioner you have. A single-stage furnace in a small house sits near the bottom; a modulating one in a big house, near the top.
- A gas furnace alone, keeping your air conditioner, installed$4,285 to $14,040
- A furnace and air conditioner together, installed$8,898 to $23,000
- Repair diagnostic visit, if it may be worth fixing$99
The HVAC replacement cost estimator narrows it to your house. Then a tech measures, and you get the installed price in writing, at no charge, before anything is ordered.
Natural gas or propane, in a house, a townhouse or a condo, we replace them all. Oil furnaces we don’t.
When a new furnace makes sense in Fairfax.
Three repairs in two winters
On a 1990s Fair Lakes or Navy furnace that’s the usual pattern: an inducer motor one year, a control board the next, an igniter after that. Each repair is fair on its own. Added up, they’re a good part of the way to a new furnace.
It shares a chimney with the water heater
A high-efficiency furnace vents out the side in plastic pipe, which can leave the water heater alone in a chimney sized for two. Ask about that before you pick a furnace, not on install day.
The heat exchanger is cracked
It’s the wall that keeps the burner’s exhaust out of the air the furnace blows through the house. Nobody patches one; a crack ends the repair conversation.
Who signs off on a new furnace in Fairfax.
Fairfax County
Fairfax County requires a permit to replace any gas appliance, even like for like: a gas water heater, furnace or boiler. Replacing a fuel-burning appliance also needs a chimney vent certification. Source.
How to pick the best furnace replacement company in Fairfax.
Questions to ask anybody who quotes you, us included.
Did they say what happens to the water heater’s vent?
Ask in so many words. If the old furnace shared a chimney with the water heater and the new one vents through the wall, the water heater’s venting has to work on its own before the inspector signs off.
Did they size it to your house?
Ask how they picked the size. Copying the old nameplate repeats whatever was guessed when the house was built.
Did they check the air conditioner you’re keeping?
A new furnace has to work with the coil and the outdoor unit already there. Ask whether they looked at both before quoting a furnace on its own.
Will they tell you if it’s worth fixing?
A good company puts the repair price next to the replacement range and lets you choose. Already holding somebody’s big number? Take the free second opinion first.
What our customers say.
I would gladly recommend them to anyone in the greater Fairfax/Alexandria area without reservation.
Swiftpro came out the same day I called when my AC was out and had it fixed in less than an hour after arriving.
Ndung and Oscar were great. Everything went smoothly, and after the install they made sure to show me everything I needed to know about the new unit.
5.0 stars across 884 Google reviews. Read them on our reviews page.
Furnace replacement questions from Fairfax.
Who issues the furnace permit in Fairfax, the City or the county?
That depends on which side of the city line the house sits, not on the mailing address. Inside the City of Fairfax it’s the City’s own permit office. Outside it, in Fair Oaks, Fair Lakes, Mantua or Merrifield, it’s Fairfax County.
Should I replace my Fairfax furnace with a heat pump instead?
In Kings Park West close to half the homeowners already heat with electricity, so a heat pump is nothing unusual there. With a gas line in the house, the middle road is a heat pump paired with a gas furnace for the coldest nights. The HVAC replacement cost estimator prices a furnace or a heat pump system for your house.
How much does a new furnace cost in Fairfax?
$4,285 to $14,040 installed for a gas furnace on its own, keeping the air conditioner you have; size and efficiency set where yours lands. A furnace and air conditioner together run $8,898 to $23,000. The HVAC replacement cost estimator gives your house its own number.
Should I repair it or replace it?
Fix the small parts on almost any furnace. Past fifteen years, with a repair over a third of the price of a new one, replacing usually wins. Not sure which you’re looking at? The diagnostic visit is $99, and the tech prices the repair before starting it.
Furnace replacement in the towns next door.
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The range first, then your number.
Call, or book online and pick a window. A tech measures the house and puts the installed price in writing before anything is ordered, and if the old furnace is worth fixing, you’ll hear that first.
SwiftPro Heating, Cooling & Plumbing is a licensed, BBB Accredited (A rating), independently owned heating, cooling and plumbing company in Chantilly, serving Fairfax and the rest of Northern Virginia. Virginia contractor license #2705192276. 5.0 stars across 884 Google reviews. SwiftPro maintains a dedicated HVAC team and a dedicated plumbing team.
SwiftPro Heating, Cooling & Plumbing, 4230 Lafayette Center Dr, Suite N, Chantilly, VA 20151, (703) 997-9757. Book online, read our reviews, or see every town we serve.