Replacing both your AC and furnace in Fairfax runs $9,800 to $21,500 in 2026, with the most common single-family setup landing between $12,400 and $16,800. That range covers a matched 3-ton condenser and 80,000-100,000 BTU furnace, standard line-set reuse, a new pad, permit, and haul-away. The rest of this post breaks that number apart - equipment tiers, labor, Fairfax County permit fees, financing, and the factors that push a quote toward the top or bottom of the band.
We're HVAC Fairfax VA, and we quote these jobs every week in Fairfax, Vienna, Burke, and the surrounding neighborhoods. Here's what actually drives the price.
How much does AC and furnace replacement cost in Fairfax VA?
AC and furnace replacement cost Fairfax VA homeowners pay depends mostly on equipment tier, system size, and whether your ductwork and line set can be reused. A builder-grade swap is not the same job as a two-stage variable-speed upgrade, and the price gap between them is real.
Typical 2026 pricing in this area, installed:
- Builder-grade matched pair (single-stage AC + 80% single-stage furnace, 2-3 ton): $9,800-$13,200
- Mid-tier pair (two-stage AC + 80% two-stage furnace, 3 ton): $13,000-$17,400
- High-efficiency pair (variable-speed AC + 96%+ modulating furnace, 3-4 ton): $17,000-$21,500
- Heat pump + air handler (cold-climate, replaces AC and furnace entirely): $12,500-$19,800
Those numbers assume a standard 1,800-2,600 sq ft Fairfax home, an accessible attic or basement air handler, and an existing 240V circuit at the condenser. Add a new line set, a duct redesign, or a second zone and you're outside the band.
If only one side is dying, a standalone AC replacement Fairfax VA runs $5,400-$11,900 and a standalone furnace installation Fairfax VA runs $4,200-$9,600. Pairing them usually saves $800-$1,600 in labor versus two separate visits.
What factors affect AC and furnace replacement cost in Fairfax VA?
What factors affect AC and furnace replacement cost in Fairfax VA comes down to six things we check on every estimate: system size, efficiency tier, duct condition, electrical and gas capacity, accessibility, and permit requirements. Each one can swing the total by hundreds or thousands.
System size (tonnage and BTU)
An oversized system costs more upfront and short-cycles for years. We run a Manual J load calculation on every replacement - it takes about 45 minutes and it's the difference between a 2.5-ton and a 3.5-ton quote. In Fairfax, most 1970s-1990s colonials land at 3 tons; newer 3,500+ sq ft builds often need 4.
Efficiency tier
SEER2 ratings now start at 14.3 for split ACs sold in Virginia. Jumping from 14.3 to 17 SEER2 adds roughly $1,800-$2,600 to the equipment line. A 96% AFUE furnace versus an 80% adds $900-$1,500. You'll earn some of that back on Dominion Energy bills, but not in year one.
Ductwork condition
Homes in HVAC Annandale VA and older Fairfax City blocks frequently have original 1970s flex duct with crushed runs and disconnected boots. Sealing and rebalancing a 12-run system runs $1,400-$3,200. Full duct replacement runs $4,500-$9,000.
Electrical and gas capacity
If your panel is full or the condenser circuit is 30A where the new unit needs 40A, add $400-$1,200 for an electrician. Gas line resizing for a 96% furnace runs $250-$650.
Accessibility
A basement or garage install is straightforward. A cramped attic with a 24-inch scuttle adds $500-$1,400 in labor. Condensers set on a roof or behind a deck add similar.
Permits and inspection
Fairfax County requires a mechanical permit for HVAC replacement. The fee scales with project value - plan on $150-$320, plus $75-$150 for the final inspection. We pull the permit and handle the inspection; it's built into our quoted price.
AC and furnace replacement cost breakdown Fairfax VA
AC and furnace replacement cost breakdown Fairfax VA homeowners see on our invoices follows a consistent structure. Here's where the money actually goes on a typical $14,200 mid-tier job:
- Equipment - $7,400-$9,100. Matched condenser, coil, furnace, and thermostat. Brand and tier drive most of this.
- Labor - $2,200-$3,400. Two technicians, one to two days, including refrigerant charge and commissioning.
- Materials - $600-$1,100. Line set (if replaced), pad, whip, disconnect, drain pan, filter rack, hardware.
- Permit and inspection - $225-$470. Fairfax County mechanical permit plus final inspection.
- Haul-away and disposal - $150-$300. Old equipment, refrigerant recovery, and recycling.
- Duct work or electrical upgrades - $0-$3,200. Only if needed; we flag this before you sign.
If you want a rough rule of thumb: equipment is about 60% of the invoice, labor and materials about 30%, and permits, disposal, and contingency the rest.
Replacing one system vs. both at once
Replacing both systems at once almost always costs less than two separate projects, and the gap is bigger than most homeowners expect. Here's why.
When we replace only the AC, we still need to open the plenum, recover refrigerant, and recommission the air handler. When we replace only the furnace, we do the same on the heating side. Doing both in one visit means one permit, one crane or lift if needed, one set of materials, and one crew mobilizing to your house. That overlap is worth $800-$1,600.
There's also a compatibility angle. A new high-efficiency condenser paired with a 22-year-old furnace will run, but you won't get the rated SEER2 and you'll shorten the compressor's life. If your furnace is within three years of end-of-life, replacing both is the cheaper long-run decision.
If you're on the fence about whether to repair or replace, our team can walk you through the math on a heating repair Fairfax VA call - sometimes a $600 repair buys you two more winters, and sometimes it doesn't.
Do you offer financing for AC and furnace replacement in Fairfax VA?
Yes - we offer financing for AC and furnace replacement in Fairfax VA, including 0% APR promotional plans for 12-18 months and extended-term plans up to 120 months. Approval takes about five minutes and doesn't require a home equity line.
Here's what that looks like on a $14,000 job:
- 0% for 18 months: $778/month, paid off before interest kicks in.
- 60-month term at 7.99%: roughly $284/month.
- 120-month term at 9.99%: roughly $185/month.
We also handle manufacturer rebates - Carrier, Trane, and Lennox all run seasonal promotions that can knock $500-$1,500 off qualifying high-efficiency systems. Dominion Energy occasionally stacks a rebate on top for qualifying heat pumps.
How long does AC and furnace replacement take in Fairfax VA?
How long does AC and furnace replacement take in Fairfax VA? A standard matched-system swap takes one to two working days - eight to ten hours for the furnace and coil, then four to six hours for the condenser, line set, and commissioning. Most of our Fairfax jobs are done in a single long day.
Add time for the following:
- Duct sealing or rebalancing: +4-8 hours
- New line set through finished walls: +3-5 hours
- Electrical panel upgrade: +4-6 hours (electrician)
- Attic install with tight access: +2-4 hours
You'll have heat or cooling back the same day in almost every case. We schedule the swap so your house is never without conditioned air overnight - if the forecast is below 45°F or above 90°F, we plan the sequence around it.
Common mistakes we see on replacement quotes
Common mistakes we see on replacement quotes usually show up as omissions, not inflated line items. A low bid often means something wasn't included. Watch for these.
- No Manual J. If the quote doesn't include a load calculation, the tonnage is a guess. Oversized systems cost more to run and die younger.
- Permit not listed. Fairfax County requires a mechanical permit. If it's missing, either the contractor isn't pulling one or they're hiding the cost.
- Line set "reused" without inspection. Old line sets with the wrong diameter for R-410A or R-32 refrigerant will kill a new compressor. Ask whether it's being flushed, replaced, or verified.
- No commissioning report. A proper install includes static pressure, refrigerant charge by subcooling, and temperature split. Ask for the numbers.
- Mismatched coil and condenser. A cheaper coil that isn't AHRI-matched voids the manufacturer warranty on the condenser.
- Warranty registration skipped. Most manufacturers cut the parts warranty from 10 years to 5 if the unit isn't registered within 60 days.
If a quote comes in $3,000 below everyone else, one of these is usually the reason.
When to call a professional
Call a professional when your repair estimate crosses 30% of replacement cost, when your system is over 15 years old and needs a second major repair, or when you're seeing refrigerant leaks, cracked heat exchangers, or rust flakes in the burners. Those aren't DIY problems.
We also get calls from homeowners in Vienna HVAC and Fairfax who just want a second opinion on a quote they've already received. That's a fine reason to call. We'll tell you honestly whether the number is fair, and we won't push a replacement if a repair makes sense.
For no-heat or no-cool emergencies, we run emergency HVAC repair Fairfax VA around the clock, including weekends.
Frequently Asked Questions
How much does AC and furnace replacement cost in Fairfax VA?
Most Fairfax homeowners pay $9,800-$21,500 in 2026 for a matched AC and furnace replacement, with the typical mid-tier job landing near $14,000. Builder-grade equipment sits at the low end; variable-speed and 96%+ systems sit at the high end. Duct work, electrical upgrades, and line-set replacement push the total higher.
What factors affect AC and furnace replacement cost in Fairfax VA?
Six factors drive the price: system size (tonnage and BTU), efficiency tier (SEER2 and AFUE), duct condition, electrical and gas capacity, accessibility of the air handler and condenser, and Fairfax County permit fees. Each can swing the total by $400-$3,200. Duct work and electrical are the two biggest wildcards.
Do you offer financing for AC and furnace replacement in Fairfax VA?
Yes. We offer 0% APR for 12-18 months and extended terms up to 120 months. On a $14,000 job that's roughly $778/month on the promo plan or $185-$284/month on longer terms. Approval takes about five minutes and we handle manufacturer rebates on top.
How long does AC and furnace replacement take in Fairfax VA?
One to two working days for a standard matched-system swap - usually a single long day. Duct sealing adds 4-8 hours, a new line set through finished walls adds 3-5 hours, and an attic install with tight access adds 2-4 hours. You'll have conditioned air back the same day.
Is it cheaper to replace AC and furnace at the same time?
Yes - typically $800-$1,600 cheaper than two separate projects, because you pay for one permit, one crew mobilization, and one set of materials. Pairing also lets us match the coil and condenser properly and commission the whole system in one visit.
Get help with HVAC in Fairfax
If you want a real number for your house instead of a national average, we'll come out, run a load calculation, and give you a written quote with equipment model numbers and a full scope. No pressure, no upsell.
Call Fairfax HVAC Experts at +1 (571) 760-4715 to schedule your replacement estimate.