AC Unit Depreciation Life: 5, 7, 15, 27.5, or 39 Years?

An AC unit’s depreciation life depends on what it is and where it sits: 27.5 years for a central system in a residential rental, 39 years for one in a commercial building, 15 years for interior commercial HVAC that qualifies as Qualified Improvement Property, and 5 or 7 years for standalone or portable equipment. On top of those schedules, several elections let a qualifying business deduct the full cost in the year of purchase, so the “life” on paper can collapse to a single tax year.

Which Recovery Period Applies to Your AC Unit

The classification turns on one question: is the unit a structural part of the building, or is it separate equipment? Function and attachment decide it, not size or cost.

Built-In Systems: 27.5 or 39 Years

A central HVAC system with ductwork running through walls and a condenser on a permanent pad is treated as part of the building. 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 straight-line and the mid-month convention.¹ In a commercial office, retail building, or warehouse, the same logic produces a 39-year life.²

Those timelines are long. A $15,000 AC unit in a rental duplex produces roughly $545 per year in deductions at straight-line rates. The same unit in a commercial warehouse yields about $385 per year.

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 itself can qualify as personal property with a 5-year or 7-year recovery period. Server-room cooling units bolted to a rack, portable spot coolers on a factory floor, and window units in a construction trailer are the usual examples. Shorter lives mean larger annual deductions and access to accelerated methods.³

A mini-split permanently installed in a rental is still a structural component at 27.5 years, even though it’s smaller and cheaper than an 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 the reasoning behind your classification.

Qualified Improvement Property: 15 Years

Interior HVAC upgrades to a commercial building can land in a third category: Qualified Improvement Property. QIP covers improvements to the interior of a nonresidential building placed in service after the building was first put into use, but 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 equipment do not.

QIP has a 15-year recovery period, roughly half the standard 39-year commercial life. The 15-year classification also keeps QIP within the 20-year ceiling for bonus depreciation.

How MACRS Calculates Your Annual Deduction

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 spent getting the unit operational: installation labor, permits, ductwork modifications, and electrical upgrades.

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

5-year and 7-year property uses the 200% declining balance method, which front-loads deductions, with the half-year convention.
15-year property (QIP) uses 150% declining balance with the half-year convention.
27.5-year and 39-year property uses straight-line with the mid-month convention, starting the clock at the midpoint of the month the unit was installed.

The difference is substantial. A $12,000 unit classified as 5-year property generates a first-year deduction of $2,400 under 200% declining balance, before any bonus depreciation. The same $12,000 classified as 39-year property yields about $154 in its first partial year. Both methods eventually recover the full cost. The timing is what shifts.

Ways to Deduct the Full Cost in Year One

Three provisions can compress an AC unit’s depreciation into a single tax year. They work differently, carry different limits, and often combine.

De Minimis Safe Harbor

If the total cost of an AC unit, including installation, falls under a per-item threshold, you can expense it immediately without depreciating it. The de minimis safe harbor election lets you deduct small capital expenditures in the year you pay for them.⁴ The threshold is $5,000 per item or invoice if your business has an applicable financial statement (audited financials), and $2,500 per item or invoice 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 clears the $2,500 limit. The IRS will disallow the election if a single asset is split across multiple invoices to stay under the cap. You make the election annually by attaching a titled statement to your timely filed return.⁴ For most small businesses without audited financials, this covers window units, portable coolers, and minor repairs rather than central installations.

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 equipment above) or “qualified real property,” which the IRS defines to include HVAC systems installed in nonresidential buildings.⁶ A commercial building owner replacing a central AC system can elect to deduct the full cost in year one instead of spreading it over 39 years.

The main limit: Section 179 cannot reduce active business income below zero. If your net business income is $18,000 and you install a $25,000 system, you can deduct $18,000 this year and carry the remaining $7,000 forward. You claim the election on Form 4562, and you generally must do so on the return for the year the unit was placed in service.

One important boundary for landlords: 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 for Section 179 unless you’re a real estate professional who materially participates in the rental activity.

Bonus Depreciation

The One Big Beautiful Bill Act, signed into law on July 4, 2025, permanently restored 100% bonus depreciation for qualified property placed in service after January 19, 2025.⁷ Qualifying property includes any asset with a MACRS recovery period of 20 years or less, which 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. Central systems classified as 27.5-year or 39-year property do not qualify, because those recovery periods exceed the 20-year cutoff.

Two features set bonus depreciation apart 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 system, bonus depreciation lets you deduct the full $50,000 and produces a $20,000 NOL you can carry forward.

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

Replacing an Old Unit

When you tear out an old AC system and install a new one, two assets are in play. 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 written off over 27.5 or 39 years. Left alone, that basis keeps 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 of disposal.⁹ No special form is required; you make the election by reporting the loss on your timely filed return for the replacement year. You’ll need to identify the old component, document its original cost and placed-in-service date, calculate its adjusted basis, and reduce the building’s overall basis accordingly. If you bought a property with an existing HVAC system and don’t have a separate cost figure, allocating a portion of the purchase price usually calls for a tax professional or a cost segregation study.

What Recapture Costs You When You Sell

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

Personal Property (Section 1245)

AC units classified as 5-year or 7-year personal property fall under Section 1245. On sale or disposal, 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 is treated as capital gain. If you sell below adjusted basis, the loss is generally deductible as an ordinary loss.

This recapture includes any Section 179 or bonus depreciation taken in year one. Fully expensing a $12,000 portable cooler and then selling it two years later for $8,000 produces $8,000 of ordinary income, because your adjusted basis after full expensing is zero.¹¹

Real Property (Section 1250)

AC units depreciated as part of a building (27.5 or 39 years) are Section 1250 property. Because these assets use straight-line depreciation, there’s typically no excess depreciation to recapture as ordinary income. Instead, the gain attributable to prior depreciation is taxed at a maximum rate of 25% as unrecaptured Section 1250 gain, lower than most taxpayers’ ordinary rate.¹² Any gain beyond the depreciation amount qualifies for long-term capital gains rates.

Keep thorough records of each 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 the information years later is expensive, and the IRS will assume you claimed all available depreciation whether you actually did or not.

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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