Of every system in a house, the one homeowners think about last during a renovation is usually the one that matters most in a North Texas summer: the HVAC. It doesn't photograph well, it hides in the attic and the walls, and it's tempting to leave alone if it's "still running." But moving walls, adding square footage, or opening a kitchen to a living room changes how your home gains and holds heat — and a system that was fine for the old floor plan can leave your beautiful new space stuffy, loud, and unevenly cooled. A remodel is the one window when the walls are open and it's dramatically cheaper to get the mechanical side right. Here's how an experienced design-build contractor thinks it through.
Replace or keep? Start with age and refrigerant
The first question is whether your existing equipment is worth building around. Three things decide it.
Age. A central air conditioner typically lasts about 15–20 years and a gas furnace about the same. Per ENERGY STAR, it's worth considering replacement once an AC passes roughly 10 years or a furnace passes 15. Regular maintenance can stretch that, but it won't reset the clock. If your system is original to a 1990s or early-2000s build, plan on replacing it — ideally before you finish the rooms around it.
Refrigerant. This is the quiet budget-killer in older systems. The EPA banned production and import of R-22 refrigerant on January 1, 2020. It's still legal to service an existing R-22 unit, but the refrigerant now comes only from recycled and reclaimed stock and runs roughly $150–$300 per pound in 2026 — so a single significant leak repair can cost more than the aging unit is worth. Newer systems moved to R-410A, and as of January 1, 2025 the industry is transitioning again to lower-impact refrigerants under the EPA's AIM Act. The practical takeaway: an R-22 system is on borrowed time.
Efficiency and symptoms. Efficiency is now rated SEER2, which replaced the old SEER metric on January 1, 2023 using a tougher test method (higher static pressure) that better reflects how a system actually performs behind real ductwork. Beyond the rating, listen to the house: rooms that never match the thermostat, and short-cycling (the system switching on and off in quick bursts), are classic signs of a system that's aging out or was mis-sized from the start.
Why an addition or open-concept forces a fresh load calculation
Here's the mistake that turns a great remodel into a comfort complaint: assuming the old system can just cover the new layout. It usually can't. When you add square footage or open up walls, you change the home's heating and cooling load — the amount of conditioned air the space actually needs. The correct way to size for that isn't a rule of thumb or "add a ton"; it's a Manual J load calculation, the industry standard from the Air Conditioning Contractors of America. It weighs square footage, ceiling height, window area and orientation, insulation values, and local climate to reach the real number. Skip it and you get one of two bad outcomes: an undersized system that can't keep the new room comfortable on a 102-degree August afternoon, or an oversized one that short-cycles, never dehumidifies properly, and wears out early.
An addition is the clearest case. A new primary suite or a home addition or ADU is extra load the original system was never sized for — and often extra distance the existing ductwork can't reach with enough airflow. Sometimes the fix is a modest capacity bump and new duct runs; sometimes a dedicated mini-split for the addition; occasionally a full replacement. A Manual J tells you which, before anyone frames a wall — and many permit departments now expect one (with its companions, Manual S and D) as part of the mechanical review.
The ductwork nobody looks at
If the equipment is the heart, the ducts are the arteries — and in older DFW homes they're frequently the real problem. According to ENERGY STAR, a typical home loses 20–30% of its conditioned air to duct leaks, gaps, and poor connections. You can install a brand-new high-efficiency system and still lose a third of what you paid for to the attic if the ducts are shot.
In homes past the 20-year mark, expect some mix of disconnected joints, crushed flex runs, undersized returns, and insulation that's thinned or fallen away. A remodel is the moment to fix it, because the ducts are accessible and the system is on the table anyway — from sealing existing runs to replacing those undersized for the new layout.
One safety note for older homes: if your house predates the early 1980s, duct wrap, tape, or the insulation around an old furnace can contain asbestos, and a cracked heat exchanger in an aging gas furnace can leak carbon monoxide. Don't disturb or tear out suspect material yourself — have it tested and, if needed, abated by a certified professional, and any gas furnace inspected by a state-licensed HVAC technician. It's exactly the kind of hidden condition a good contractor flags before demo, not after.
Zoning: fixing the room that's always too hot
If your two-story never balances — roasting upstairs, frigid downstairs — a renovation is the time to design in zoning. Motorized dampers and multiple thermostats send conditioned air where it's actually needed instead of blasting the whole house to satisfy one room. It's especially worth it when a remodel reshapes the space or adds a bonus room or ADU with its own comfort profile.
What it realistically costs
Every number below is a national range from Angi's 2026 cost data (or HomeGuide where noted). Your real figure depends on system size, home layout, and how far the ducts have to move — which is why a walk-through beats any online estimate.
| Scope | Typical range | Notes |
|---|---|---|
| Furnace + AC replaced together | $5,000–$12,500 (avg ~$7,500) | The most efficient time to do both is at once |
| AC unit only | $3,900–$8,000 | |
| Furnace only | $2,800–$6,900 | |
| Heat pump system | $6,000–$25,000 | Wide range by size and type |
| New/replacement ductwork | $2,000–$12,000 (avg ~$4,000) | Roughly $10–$25 per linear foot |
| Duct sealing | $500–$4,000 (avg ~$2,250) | Or about $1–$2/sq ft (HomeGuide) |
| Zoning system | $1,500–$8,500 (avg ~$3,000) | ~$2,500–$6,000 for 2–3 zones |
Rolled into a larger project, the mechanical scope is one line among many. For a ballpark on your whole renovation, our cost estimator gets you in the right neighborhood.
A note on rebates and tax credits: these change often, sometimes dramatically. The federal 25C efficiency credit that homeowners leaned on through 2025, for example, expired at the end of that year. Never budget around a guaranteed amount — confirm what's currently available (federal, state, and local utility programs all differ) with a tax professional before you count on it.
Who pulls the permit — and who's accountable
HVAC work requires a mechanical permit and inspection in essentially every DFW city, and in Texas that permit is pulled by a state-licensed HVAC contractor — air-conditioning and refrigeration contractors are licensed through the Texas Department of Licensing and Regulation. That's a genuine license, and it's a fair question to ask of anyone who touches your system.
Where a design-build general contractor earns its keep is bringing that licensed trade in at the design stage — so the load calc, the duct plan, and the equipment selection are in the drawings before framing, and the permit and inspections are coordinated with the rest of the job. (Worth knowing: Texas has no statewide residential general-contractor license, so a reputable GC is insured and bonded rather than "licensed" — while the electricians, plumbers, and HVAC techs on your job carry their own state licenses.)
That's the whole argument for handling HVAC inside the remodel instead of bolting it on later. As an Allen-based design-build contractor serving the DFW metroplex, we build the mechanical system into a whole-home renovation from day one — because the cheapest time to move a duct is while the wall is already open.
Frequently asked
- Do I have to replace my whole HVAC system when I add a room?
- Not always — but you need a Manual J load calculation to know. Adding square footage increases the load; sometimes the existing system covers it with new duct runs, other times the room needs a dedicated unit or the system needs upsizing. The calc, not a guess, answers it before the wall is framed.
- My AC still works but uses R-22. Should I keep it?
- It's legal to keep servicing an R-22 unit, but R-22 now runs roughly $150–$300 per pound (from reclaimed stock only), so any real refrigerant repair gets expensive fast. If it's also 15-plus years old, replacing it during the remodel — when access is easy — usually beats paying premium refrigerant prices to nurse it along.
- Can't my remodeler just reuse the old ductwork?
- Sometimes — but verify rather than assume. Older ducts commonly leak 20–30% of conditioned air (ENERGY STAR), and ducts sized for the old floor plan may not move enough air to a new or opened-up space. Sealing or partially replacing them during the remodel beats opening finished walls later.
- Who is responsible for the HVAC permit?
- A state-licensed HVAC contractor pulls the mechanical permit in Texas. In a design-build project, your general contractor coordinates that licensed trade, the load calculation, and the inspections alongside everything else — one accountable schedule, not five subcontractors you're refereeing.
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