Does a new HVAC system increase home value?

By less than it costs. Like-for-like replacement is not tracked in the national cost-versus-value data, and the nearest entry, a gas-to-heat-pump conversion, has seen its recouped share swing by roughly a third from one year to the next. A working assumption is that a new system returns half to three-quarters of its cost in the sale price, so a $10,000 replacement moves the price $5,000–$7,500 and the other $2,500–$5,000 comes out of your proceeds.

When should I replace the HVAC before selling?

When it would block the sale rather than discount it: the furnace does not run, so a financed buyer cannot close (FHA's HUD Handbook 4000.1 requires an operable, adequate heating system and VA's minimum property requirements ask for the same; neither sets an age limit); the furnace has been red-tagged for a cracked heat exchanger; or the air conditioner is leaking R-22, which is a replacement, not a repair. Age alone is not a reason.

Is it better to replace the HVAC or offer a credit?

Compare the credit to what replacing would actually cost you, the unrecouped share, not to the quote. On a $10,000 system that is $2,500–$5,000. A credit below it beats replacing and lets the buyer pick their own equipment. A credit at the full $10,000 leaves you $5,000–$7,500 worse off than doing the work. Hold the number with two written quotes.

What should I do to an old HVAC system before listing?

A tune-up on each unit with a written report ($100–$250 each), the service records in a folder, two written replacement quotes so the credit conversation starts at your number, and a one-year home warranty ($450–$700) transferred at closing. If only one half is failing, replace that half: an AC alone is $3,500–$8,000, a gas furnace alone $3,000–$7,500.

What will the buyer's inspector say about a 15-year-old furnace?

Some version of "at or near the end of its expected service life; budget for replacement," which is a statement about age, not condition, and the buyer will bring it to the table as a credit request. It is not a defect and it does not block financing. A tune-up report dated last month, service records, and a home warranty answer it for a few hundred dollars; a new system answers it for thousands you mostly do not get back.

Should you replace the HVAC before selling?

Usually no. A working furnace and air conditioner are what a buyer assumes they are getting; a brand-new pair is a nice line in the listing and a modest bump in the offer, and the difference between the two is a lot less than the $8,000–$18,000 a full system costs. The exceptions are the systems that would stop the sale rather than dent the price: a furnace that does not run, a red-tagged heat exchanger, or an air conditioner leaking a refrigerant nobody wants to refill. Replace those. For everything else, the cheaper move is to service it, document it, and let the buyer choose their own equipment with a credit sized to what replacing would actually cost you.

What a new system is worth at closing

Like-for-like HVAC replacement does not appear in the national cost-versus-value tables at all. The closest entry, converting a gas furnace and air conditioner to an electric heat pump, has had its recouped share swing by roughly a third between consecutive years, which tells you buyers are not paying a steady premium for mechanicals. A reasonable working assumption, and it is an assumption rather than a measurement, is that a new system returns half to three-quarters of its cost in the sale price, and only when the old one was visibly at the end of its life.

Run that on a $10,000 full-system replacement. The sale price moves $5,000–$7,500; the other $2,500–$5,000 comes out of your proceeds. That $2,500–$5,000 is the real cost of replacing before you list, and it is the number every alternative has to beat.

When to replace before listing

Replace when the system would block the sale, not just discount it:

It does not heat. A financed buyer cannot close on a house without working heat. FHA's appraisal standards in HUD Handbook 4000.1 require a heating system that is operable and adequate for the home, and VA's minimum property requirements ask for the same in different words. Neither sets an age limit, so a 25-year-old furnace that runs passes and a five-year-old one that does not run fails.
The furnace has been red-tagged for a cracked heat exchanger or a carbon monoxide reading. The technician or the utility has already made the decision. A known safety defect is a disclosure item, and a buyer's inspector will find the tag if the form does not mention it.
The air conditioner runs on R-22 and is leaking. Units installed before about 2010 may use it, production ended in 2020, and a recharge can cost more than the unit is worth and will leak out again. The R-22 test applies to a seller exactly as it applies to an owner: a leaking R-22 unit is a replacement, not a repair, and the buyer's inspector knows it.
You are listing in the season it matters and it is failing. A furnace that limps through showings in January, or an AC that cannot hold 75 degrees in August, costs you buyers before it costs you a credit. That is a replacement dressed as a marketing expense, and it is the one case where the marketing expense is worth it.

What to do instead of replacing

A tune-up with a written report on each unit, $100–$250 apiece. Ask for the combustion and refrigerant readings in the paperwork and leave it on the kitchen counter for showings and for the inspector.
Every service record you have, in a folder with the filter size written on the front. Age is only a defect when it looks like neglect.
A one-year home warranty that covers the HVAC, $450–$700, transferred to the buyer at closing. It answers the question a buyer asks about a 15-year-old system for a fraction of the $2,500–$5,000 that replacing would cost you.
Replace only the half that is failing. An AC alone is $3,500–$8,000 and a gas furnace alone $3,000–$7,500. If the furnace is 22 and the AC is 8, the furnace is the conversation and the AC is not.
Two written quotes in the file, so that when the inspection report says "at or near the end of its expected service life, budget for replacement," which on a system past 15 it will, the number on the table is yours.

Replace it or offer a credit? Run the comparison

The mistake sellers make is comparing the credit to the quote. The quote is not what replacing costs you; the unrecouped part is. On a $10,000 system that is $2,500–$5,000. A credit under that beats replacing, and most buyers prefer it, because they get to choose the equipment and the contractor. A credit at the full $10,000 does not: it leaves you $5,000–$7,500 worse off than if you had just done the work. So set the ceiling at the unrecouped share, hold it with the two quotes, and remember that a buyer opening with the whole replacement cost is opening, not closing. The same arithmetic governs every pre-sale project: measure the credit against what you would not get back, never against the invoice.

If you are staying a few more years

Then this is not a resale question and the answer flips. A furnace past 15 with a repair over $1,000 on the table is a replacement on its own merits — the age and repair-cost test in our HVAC replacement cost guide — and an AC past 14 is the same call under the age test in our repair-or-replace guide for air conditioners. You get the efficiency and the warranty for the years you are there, with whatever resale bump is left at the end as a rounding error. Replacing in the shoulder season, when contractors are slow, is how you land at the low end of the bands.

The bottom line

Do not replace a working HVAC system to sell the house. Service it, document it, offer a warranty, and size any credit to the $2,500–$5,000 you would not recoup on a $10,000 system, not to the quote. Replace before listing only when the system would stop the sale: no heat, a red tag, or a leaking R-22 unit. If you are deciding between this and the rest of the pre-sale list, our guide to upgrades that actually add resale value puts mechanicals in their place: near the bottom, unless they are broken.