You’re a few days into your inspection window, the report just landed, and one line stops you cold: the furnace is original to the house, and nobody can say for sure how many winters it has left. The rest of the home looks solid. So now what?

Heating and cooling equipment is one of the most expensive systems in any home, and it’s also one buyers misjudge most. An old unit isn’t automatically a reason to walk, and a newer one isn’t a guarantee of clear sailing. What matters is what the inspector actually documented, how close the system sits to the end of its service life, and what a replacement would cost you in the first couple of years. Read that finding like a buyer who’s done this before, and it stops being scary.

Does a home inspection even check the furnace and AC?

Yes. A standard home inspection includes the heating and cooling systems. The inspector runs the equipment through its normal controls, looks for visible defects, notes the apparent age, and reports whether the system responded the way it should. What the inspection doesn’t do is predict how many years the unit has left or size a replacement for you.

The scope is set by professional standards, not guesswork. Under the InterNACHI Standards of Practice, an inspector describes the heating and cooling systems, operates them where it’s safe, and reports defects they can see — but is not expected to measure efficiency, test capacity, or forecast remaining life. That line matters. A furnace can run fine on inspection day and still be one cold snap from failing.

Here in Bucks and Montgomery County, that means we photograph the equipment’s data plate so you can read the manufacture date yourself, and we document the system’s condition in writing as part of a standard home inspection. Pennsylvania’s home inspection law requires that written report, which is exactly why a documented evaluation of your heating and cooling beats a quick verbal once-over that leaves you nothing to act on.

One caveat trips up buyers every spring and fall: an inspector may not run the central air if it’s too cold outside, because starting a compressor below roughly 60 degrees can damage it. That isn’t the inspector cutting corners. When the AC can’t be safely tested, a good report says so plainly and recommends a warm-weather follow-up, so you treat the cooling side as an open question rather than a clean pass.

What does the system’s age actually tell you?

Age is the best single clue you have, but it’s a range, not a verdict. Most gas furnaces last 15 to 25 years, heat pumps 10 to 15, and central air condensers somewhere between 8 and 20 depending on maintenance and how hard they’ve run. A system inside its expected window can still have years left. One well past it is living on borrowed time.

Those numbers aren’t ours. They come from the same industry data inspectors lean on. InterNACHI’s home component life-expectancy chart puts a furnace at 15 to 25 years and a heat pump at 10 to 15, with condensers ranging widely based on their workload. So a unit that’s 22 years old isn’t broken. It’s just closer to the replacement conversation than most buyers want to be during a deal.

How do you find the real age of a furnace or AC?

Start with the metal data plate on the unit. It lists the manufacturer, model, and serial number, and the serial usually encodes the build date — often the first four digits as week and year, though the format varies by brand. Cross-check it against any permit or replacement records the seller can produce. When the plate is missing or painted over, treat the equipment as older than it looks until proven otherwise.

A quick example: a serial number that begins 0492 usually points to the fourth week of 1992, which would put a furnace well past its expected life. Brands differ, so treat the decode as a strong hint, not gospel, and confirm with a contractor when the number is ambiguous. What you’re really after isn’t a birthday. It’s whether the equipment is early, middle, or late in its run.

Aging equipment turns up constantly during inspections. It’s one of the issues inspectors flag most often, right alongside worn roofs and tired water heaters. That’s good news for a buyer, honestly. It means the pattern is well understood, the fix is predictable, and you can plan for it instead of being blindsided later.

When is an aging furnace or AC a real dealbreaker?

Rarely on its own. An old-but-working system is usually a budgeting item, not a deal-killer. It tips toward dealbreaker when the inspector finds an actual safety defect — a cracked heat exchanger, unsafe venting, or heat scorching — or when a full replacement stacks on top of other big-ticket problems the house already carries. Then it’s the pile, not the furnace, that ends the deal.

The real distinction is condition versus age. A 20-year-old furnace that heats evenly and vents properly is a very different animal from one with a cracked heat exchanger, which can leak carbon monoxide and is the kind of finding that can be serious enough to walk away from the house. Safety defects change the math. Ordinary age usually just changes your budget. We flag when a system is near the end of its service life precisely so you can tell those two situations apart.

Which HVAC defects should worry a buyer most?

Three findings deserve real attention. A cracked heat exchanger can send carbon monoxide into the air you breathe. Improper venting or backdrafting can do the same, quietly, over a whole heating season. And a compressor that won’t start or keeps tripping its breaker often signals a cooling system at the end of the line. Any of these moves the conversation from “budget for it later” to “address it now,” and each is worth a licensed contractor’s eyes before you remove the inspection contingency.

What should you do after the inspection flags old HVAC?

Get a real number before your contingency ends. Bring in a licensed HVAC contractor for a full evaluation and a written replacement quote, then decide whether to ask the seller for a credit, adjust your offer, or budget for the work yourself. The worst move is guessing at the cost and hoping the unit limps along. Guessing is how buyers end up with a surprise five-figure bill in year one.

Once you’re holding a contractor’s quote, you have leverage. Plenty of buyers ask for a repair credit at closing instead of a lower sale price, because a credit puts cash straight toward the new system without reopening the entire negotiation. We flag systems near the end of their life early in the report for that reason — so you have time to line up the estimate before the inspection window slams shut.

Timing is everything here. In Pennsylvania, your leverage lives inside the inspection contingency window written into the agreement of sale, and once it closes, asking for anything gets much harder. So the moment the report flags an aging system, book the contractor evaluation the same day if you can. A quote in hand three days before the deadline is worth far more than a better price you asked for too late.

Should you replace the system before or after closing?

Almost always after, and on your own terms. Asking a seller to swap a working furnace before settlement usually stalls the deal and gets you a rushed, builder-grade unit. A credit lets you close, then choose the size, efficiency, and contractor that fit the home. The exception is a genuine safety defect a lender or insurer won’t overlook, which sometimes has to be corrected before the sale can fund.

Frequently Asked Questions

How long does a furnace usually last?

A gas furnace typically lasts 15 to 25 years, and a heat pump closer to 10 to 15. Maintenance history, run time, and installation quality all move that range. A unit near the top of its expected lifespan can still work fine, but you should treat it as a near-term replacement you’ll want to budget for.

Is a cracked heat exchanger always a dealbreaker?

Not automatically, but it’s serious. A cracked heat exchanger can allow carbon monoxide into the living space, so the furnace should be shut down until it’s replaced or professionally cleared. Many buyers use that finding to request a full furnace replacement or credit rather than a patch. Treat it as a safety issue first and a negotiation second.

Does a home inspection include the air conditioning?

Yes, when weather allows. Inspectors operate central air using normal controls and report visible defects and apparent age. They generally won’t run the system if outdoor temperatures are too low to test it safely, since that can damage the compressor. When AC can’t be tested, the report should say so and recommend a follow-up once it’s warm enough.

Can you negotiate an old furnace after the inspection?

You can, and a written contractor quote is your strongest tool. Age alone gives you less leverage than a documented defect, but a nearing-end-of-life system plus a replacement estimate is a reasonable basis for a credit. Frame the ask around the number, not the worry, and keep your request tied to what the report actually documented.

How much does it cost to replace a furnace or AC?

Replacing residential heating or cooling equipment generally runs several thousand dollars, and more when ductwork, electrical, or a full system swap is involved. A licensed HVAC contractor’s written quote for your specific home is the only figure worth negotiating on. Rough online averages are fine for early budgeting but too vague to bring to a seller.

Should I get a separate HVAC inspection?

Often yes, when the equipment is aging or the stakes are high. A home inspection tells you condition and apparent age; a dedicated HVAC contractor can measure performance, check refrigerant, and estimate remaining life. If your inspector flags the system as near the end of its service life, a contractor’s evaluation is money well spent before you commit.

Want to know what your HVAC really has left before closing?

An aging furnace or AC isn’t a reason to panic, and it isn’t a reason to skip the details either. An inspection that documents the true condition and age of the heating and cooling systems is the difference between a confident offer and an expensive surprise. It helps to weigh what a full home inspection costs in Bucks County against the price of a furnace you never budgeted for.

Serving Bucks County, Montgomery County, and Philadelphia, our team documents every major system in a written report you can actually act on. Schedule your inspection before your window closes, and buy with your eyes open.