AC Unit Depreciation Life: 5, 15, 27.5, or 39 Years?

The depreciation life of an AC unit is 27.5 years in a residential rental, 39 years in a commercial building, 15 years when it qualifies as Qualified Improvement Property inside a nonresidential space, and 5 or 7 years when it’s standalone equipment rather than part of the building. Those are the IRS recovery periods on paper. In practice, Section 179, bonus depreciation, and the de minimis safe harbor let many businesses deduct the entire cost in the year of purchase.

What Determines Which Recovery Period Applies

The classification turns on one question: is the AC unit a structural part of the building, or is it separate equipment? Function and attachment matter more than size or cost.

Structural Components: 27.5 or 39 Years

Most central HVAC systems are built into the building. Ductwork runs through walls, condensers sit on permanent pads, and the system can’t function independently of the structure. The IRS treats these units the same as the building they serve. A replacement furnace or AC compressor in a residential rental is “in the same class of property as the residential rental property to which the furnace is attached” and depreciates over 27.5 years using the straight-line method and the mid-month convention.¹ Commercial offices, retail buildings, and warehouses follow the same logic on a 39-year schedule.²

Those timelines are long. A $15,000 unit in a rental duplex produces roughly $545 per year in straight-line deductions. The same unit in a commercial warehouse yields about $385 per year. That math pushes many taxpayers toward the accelerated options below.

Standalone or Portable Equipment: 5 or 7 Years

An AC unit that cools a specific process, piece of machinery, or portable workspace rather than the building as a whole can qualify as personal property with a 5-year or 7-year recovery period. Server-room cooling that bolts to a rack, portable spot coolers on a factory floor, and window units in a construction trailer are typical examples. These shorter lives allow larger annual deductions and qualify for accelerated methods that front-load the tax benefit.³

A mini-split permanently installed in a rental property is still a structural component at 27.5 years, even though it’s smaller and cheaper than a portable industrial cooler that qualifies for 5-year treatment. The IRS looks at how the unit is attached, what it cools, and whether removing it would damage the building. Document why you classified a unit the way you did.

Qualified Improvement Property: 15 Years

Interior HVAC upgrades to a commercial building can fall into a third category: Qualified Improvement Property, or QIP. QIP covers improvements to the interior of a nonresidential building placed in service after the building was originally put into use, and it excludes building enlargements, elevators, escalators, and changes to the internal structural framework.² Replacing interior ductwork or adding a new air handler inside a retail space generally qualifies. Rooftop condensers and other exterior HVAC equipment do not.

QIP has a 15-year recovery period, roughly half the standard 39 years for commercial buildings. The 15-year life also keeps QIP eligible for bonus depreciation, since only property with a recovery period of 20 years or less qualifies for that benefit.

How MACRS Treats Each Class

Nearly all business property placed in service after 1986 uses the Modified Accelerated Cost Recovery System.³ Your cost basis includes the purchase price plus everything you spent getting the unit operational: installation labor, permits, ductwork modifications, and electrical upgrades.

MACRS assigns a depreciation method and a timing convention based on the asset’s class:

5-year and 7-year property uses the 200% declining balance method, producing larger deductions in the early years, with the half-year convention that treats the unit as placed in service at the midpoint of the year regardless of installation date.
15-year property (QIP) uses the 150% declining balance method with the half-year convention.
27.5-year and 39-year property uses straight-line depreciation, spreading the cost evenly, with the mid-month convention that starts the clock at the midpoint of the installation month.

The practical difference is substantial. A $12,000 unit classified as 5-year property generates a first-year deduction of $2,400 under the 200% declining balance method before any bonus depreciation. That same $12,000 classified as 39-year property produces roughly $154 in its first partial year under straight-line and mid-month rules. Both methods eventually recover the full cost. The timing of the tax benefit is drastically different.

Ways to Deduct the Full Cost in Year One

De Minimis Safe Harbor for Smaller Units

If the total cost of an AC unit including installation falls below a certain threshold, you may be able to expense the entire amount immediately without depreciating it. The de minimis safe harbor election under Treasury regulations lets you deduct small capital expenditures in the year you pay for them.⁴ The per-item threshold is $5,000 if your business has audited financial statements (an “applicable financial statement” in IRS terminology) and $2,500 if it doesn’t.

Installation costs count toward the threshold when they appear on the same invoice as the unit. A $1,800 window unit with $400 in installation on one invoice totals $2,200 and fits under the $2,500 limit. A $2,000 unit with $800 in installation on the same invoice totals $2,800, exceeding the threshold and requiring normal depreciation. The IRS will disallow the election if a single asset is artificially split across multiple invoices to stay under the limit.

You make this election annually by attaching a titled statement to your timely filed tax return.⁴ For most small businesses without audited financials, this route helps with window units, portable coolers, or minor repairs rather than central HVAC installations that typically run several thousand dollars.

Section 179 Expensing

Section 179 lets you deduct the full cost of qualifying property in the year it’s placed in service, up to a statutory cap of $2,500,000 indexed for inflation.⁵ An AC unit qualifies if it’s tangible personal property (the 5-year or 7-year standalone equipment above) or “qualified real property,” which the IRS defines to include HVAC systems installed in nonresidential buildings.⁶ A commercial building owner who replaces a central AC system can elect to deduct the full cost in year one rather than spreading it over 39 years.

The biggest limitation: Section 179 cannot reduce your taxable income from active business operations below zero. If your net business income is $18,000 and you install a $25,000 system, you can deduct only $18,000 this year. The remaining $7,000 carries forward. You claim the election on Form 4562 with the return for the year the unit was placed in service. Miss that window and the deduction is forfeited for that year.

One boundary for residential rental owners: Section 179 is available only for property used in an active trade or business. Rental real estate income is typically passive, so a central AC replacement in a rental duplex usually does not qualify unless you’re a real estate professional who materially participates in the rental activity.

Bonus Depreciation

The One Big Beautiful Bill Act, signed on July 4, 2025, permanently restored 100% bonus depreciation for qualified property placed in service after January 19, 2025.⁷ For AC units placed in service in 2026, that means the entire cost can be deducted in the first year if the unit qualifies.

Qualifying property includes any asset with a MACRS recovery period of 20 years or less. That covers 5-year, 7-year, and 15-year AC equipment, including QIP.³ An interior HVAC replacement in a commercial building classified as QIP is fully deductible in year one. A central system classified as 27.5-year or 39-year property does not qualify, because those recovery periods exceed the 20-year cutoff.

Two features distinguish bonus depreciation from Section 179. It applies automatically unless you elect out, while Section 179 requires an affirmative election.⁸ And bonus depreciation can create or increase a net operating loss, so it isn’t limited by current-year taxable income. If your business earns $30,000 and you install a $50,000 qualifying AC system, bonus depreciation lets you deduct all $50,000, producing a $20,000 net operating loss you can carry forward.

Many taxpayers combine both tools, using Section 179 first to offset active business income down to zero and then applying bonus depreciation to any remaining basis. Both provisions apply to property acquired from an unrelated party, whether new or used.

What Happens to the Old Unit You Tore Out

When you replace an old AC system, you’re dealing with two assets. The new unit starts its own depreciation life from its placed-in-service date. The old unit likely still has undepreciated cost on your books, especially if it was being depreciated over 27.5 or 39 years. Without action, that remaining basis stays there, generating small deductions for years on a system that no longer exists.

The partial disposition election under Treasury Regulation 1.168(i)-8(d)(2) solves this. It lets you recognize the retirement of the old component and deduct its remaining adjusted basis as a loss in the year you dispose of it.⁹ No special form is required. You make the election by reporting the loss on your timely filed return for the year of replacement.

To support the election, identify the old component, document its original cost and placed-in-service date, calculate its adjusted basis (original cost minus depreciation already claimed), and reduce the building’s overall basis accordingly. If you bought the property with an existing HVAC system and don’t have a separate cost figure, you’ll need to allocate a reasonable portion of the purchase price to it, which usually requires help from a tax professional.

Recapture When You Sell

Every dollar of depreciation you claim reduces your tax basis. When you sell, the IRS recaptures some of that benefit. How much you owe depends on whether the AC unit was classified as personal property or as part of the building.

Personal Property (Section 1245)

AC units classified as 5-year or 7-year personal property fall under Section 1245. When you sell or dispose of one, any gain up to the total depreciation previously deducted is taxed as ordinary income at your marginal rate.¹⁰ Only gain exceeding total depreciation claimed gets capital gain treatment. A loss below adjusted basis is generally deductible as an ordinary loss.

Recapture applies to all depreciation claimed, including Section 179 and bonus depreciation taken in year one. Fully expensing a $12,000 portable cooling unit and selling it two years later for $8,000 produces $8,000 of ordinary income, since your adjusted basis after full expensing is zero.¹¹

Real Property (Section 1250)

AC units depreciated as part of a building (27.5-year or 39-year property) are Section 1250 property. The rules here are more favorable. Because these assets use straight-line depreciation, there’s typically no “excess” depreciation to recapture as ordinary income. Gain attributable to depreciation previously claimed is taxed at a maximum rate of 25% as “unrecaptured Section 1250 gain,” which is lower than most taxpayers’ ordinary rate.¹² Gain beyond the depreciation amount qualifies for long-term capital gains rates.

Keep thorough records of every AC unit’s original cost, installation date, classification, and annual depreciation claimed. Those records determine your adjusted basis and your tax bill when the property changes hands. Reconstructing this information years later is expensive and error-prone, and the IRS will assume you claimed all available depreciation whether you actually did or not.

1
Internal Revenue Service. Depreciation and Recapture 4
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Office of the Law Revision Counsel. 26 US Code 168 – Accelerated Cost Recovery System
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Internal Revenue Service. Topic No. 704 Depreciation
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eCFR. 26 CFR 1.263(a)-1 – Capital Expenditures; In General
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Office of the Law Revision Counsel. 26 US Code 179 – Election To Expense Certain Depreciable Business Assets
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Internal Revenue Service. Depreciation Expense Helps Business Owners Keep More Money
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Internal Revenue Service. One, Big, Beautiful Bill Provisions
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Internal Revenue Service. Additional First Year Depreciation Deduction – FAQ
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Internal Revenue Service. Examining a Taxpayer Electing a Partial Disposition of a Building
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Office of the Law Revision Counsel. 26 US Code 1245 – Gain From Dispositions of Certain Depreciable Property
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eCFR. 26 CFR 1.1245-3 – Definition of Section 1245 Property
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Internal Revenue Service. TD 8836 – Capital Gains Regulations