HVAC Depreciation Life: 27.5 vs 39 Years and Bonus Rules

The depreciation life of an HVAC system is 27.5 years when the system serves a residential rental property and 39 years when it serves a commercial building. Those recovery periods have nothing to do with how long the equipment physically lasts. They are the schedules the IRS assigns under the Modified Accelerated Cost Recovery System (MACRS), and they follow the building the system is attached to. Commercial owners have several ways to compress that 39-year timeline down to a single year, including 100% bonus depreciation, permanently reinstated by the One, Big, Beautiful Bill Act signed in 2025.¹ Residential landlords have almost none.

Why an HVAC System Follows the Building

The IRS treats a central HVAC system as a structural component of the building it serves. All components of a central air conditioning or heating system count as structural components, even the ones mounted on the roof or next to the exterior wall.² Because it’s a structural component, its recovery period matches the building.

The exception is portable equipment. Window air conditioners and portable space heaters placed in service after 2015 are tangible personal property in the five-year MACRS class.³ If you can unplug it and carry it out, it depreciates over five years. If it’s ducted, piped, or wired into the building, it follows the 27.5- or 39-year schedule.

27.5 Years for Residential Rental Property

A building is residential rental property when 80% or more of its gross rental income comes from dwelling units. The HVAC system in that building depreciates over 27.5 years using the straight-line method.⁴ Straight-line spreads the cost evenly. A $10,000 furnace produces roughly $364 a year in depreciation.⁵

The first and last years use the mid-month convention, which treats the system as placed in service on the 15th of the installation month. A March installation gets 9.5 months of depreciation in year one. A November installation gets 1.5 months.⁶

Residential rental HVAC does not qualify for bonus depreciation or Section 179. The 27.5-year schedule is essentially the only path.

39 Years for Commercial Buildings

Office buildings, retail spaces, warehouses, and any other buildings that fail the 80% dwelling-unit test are nonresidential real property. HVAC in these buildings depreciates over 39 years, straight-line, mid-month convention.² A $50,000 system produces about $1,282 a year at that pace.

That is the default. Most commercial owners never actually use it, because the provisions below usually collapse the deduction into year one.

How Commercial Owners Deduct HVAC in One Year

Qualified Improvement Property

Qualified Improvement Property (QIP) is an improvement to the interior of a nonresidential building made after the building was first placed in service. HVAC work that qualifies as QIP drops from a 39-year recovery period to 15 years, and 15-year QIP is eligible for both bonus depreciation and Section 179.²

The word “interior” matters. Rooftop condensing units, compressors on exterior pads, and other outdoor equipment are not improvements to the interior portion of the building and do not qualify as QIP. Indoor air handlers, ductwork, and furnaces installed inside the walls usually do. The work also cannot enlarge the building or alter its internal structural framework.

100% Bonus Depreciation

The One, Big, Beautiful Bill Act permanently reinstated 100% bonus depreciation for qualified property acquired after January 19, 2025.¹ There is no scheduled phasedown. A commercial HVAC installation that qualifies as QIP can be deducted in full in the year it’s placed in service.

One transitional option: for the first tax year ending after January 19, 2025, a taxpayer may elect 40% (or 60% for property with longer production periods) instead of 100% if a smaller current-year deduction is preferable.¹ For most owners the default 100% is the right answer.

Section 179 Expensing

Section 179 lets a business expense the full cost of eligible property in the year it’s placed in service, subject to annual dollar limits. For 2026, the maximum deduction is $2,560,000, phasing out once total qualifying property placed in service in the year exceeds $4,090,000.

HVAC systems in nonresidential buildings are specifically named as Section 179 property, and this eligibility applies even if the work doesn’t meet the full QIP definition.⁷ So an exterior rooftop unit that fails the QIP interior test can still be expensed in full under Section 179 within the dollar limits. Section 179 is not available for residential rental HVAC.

Repair or Improvement? Not Everything Gets Depreciated

Some HVAC spending doesn’t get depreciated at all. Under the tangible property regulations, repairs are deducted in full in the year paid; improvements are capitalized and depreciated. The classification is worth getting right before you touch a depreciation schedule.

For this analysis, the HVAC system is its own unit of property, separate from the building structure and from other building systems. Work is an improvement if it meets any one of three tests applied to the HVAC unit of property:⁸

Betterment: fixes a pre-existing defect, adds materially to the system, or is reasonably expected to materially increase efficiency, capacity, or output.
Restoration: replaces a major component or substantial structural part of the HVAC system, or replaces a component for which you already claimed a loss deduction.
Adaptation: adapts the HVAC system to a new or different use.

Replacing an entire furnace or air conditioning system almost always trips the restoration test. Replacing a thermostat, cleaning ducts, recharging refrigerant, or fixing a blower motor is usually a deductible repair. In between sits gray territory, like a compressor swap in a multi-unit commercial system, that depends on whether that component is “major” relative to the whole system.

A separate de minimis safe harbor lets you deduct items costing up to $2,500 each (or $5,000 with audited financial statements) without running the improvement analysis at all. The election is made annually on your return.

Replacing an Old System: Claim the Partial Disposition

When you replace an HVAC system, the old system still has undepreciated basis on your books. The partial disposition election lets you recognize that basis as a loss in the year of replacement.⁹ If you installed a $20,000 system, depreciated $8,000, and then replaced it, you can claim the remaining $12,000 as a loss on Form 4797 while beginning depreciation on the new system.

The election is available for both residential rental and commercial property and must be made on a timely filed return (including extensions) for the year of disposition. It’s routinely overlooked, and the deduction disappears if the election isn’t made in time.

What Happens When You Sell

Every dollar of depreciation you claim reduces your basis in the property. When you sell, that depreciation comes back through recapture. For real property and its structural components, the recaptured amount is unrecaptured Section 1250 gain, taxed at a maximum federal rate of 25%, higher than the long-term capital gains rate most sellers pay on the rest of their profit.

Recapture applies whether you depreciated slowly over 39 years or expensed everything in year one under bonus depreciation or Section 179. Accelerated expensing doesn’t erase the tax; it shifts the timing. Owners holding long-term or planning a 1031 exchange to defer gain will almost always come out ahead by taking the deduction now. Owners planning a near-term sale should run the numbers.

How to Report It

All depreciation is reported on Form 4562 and must be claimed in the year the system is placed in service. If you skip a year, you don’t preserve the deduction for later. The IRS treats depreciation as “allowed or allowable,” so a skipped year is lost, and your basis is still reduced as if you had claimed it when you sell.

Straight-line is required for real property depreciated over 27.5 or 39 years. QIP with a 15-year recovery uses the 150% declining balance method and the half-year convention, which treats the asset as placed in service at the midpoint of the year regardless of the actual date.¹⁰ With 100% bonus depreciation available, most commercial owners never compute annual declining-balance amounts on QIP at all.

Quick Reference by Scenario

New HVAC in a residential rental: 27.5 years, straight-line, mid-month convention. No bonus depreciation or Section 179.
Replacement HVAC in a residential rental: 27.5 years on the new system, and elect partial disposition to claim a loss on the old system’s remaining basis.
Interior HVAC replacement in a commercial building meeting the QIP tests: 15-year recovery, eligible for 100% bonus depreciation or Section 179. Typically written off in full in year one.
Exterior rooftop unit on a commercial building: not QIP, but eligible for Section 179 within dollar limits. Otherwise 39 years.
Portable window units or space heaters: five-year MACRS personal property, eligible for bonus depreciation and Section 179.²
HVAC repair that isn’t an improvement: fully deducted in the year paid or incurred. No depreciation schedule needed.

1
Internal Revenue Service. Treasury, IRS Issue Guidance on the Additional First Year Depreciation Deduction Amended as Part of the One, Big, Beautiful Bill
2
Internal Revenue Service. Publication 946 (2024), How To Depreciate Property
3
Internal Revenue Service. Publication 946 (2024), How To Depreciate Property – Section: Which Property Class Applies Under GDS?
4
Internal Revenue Service. Publication 527 (2025), Residential Rental Property – Section: Table 2-1. MACRS Recovery Periods for Property Used in Rental Activities
5
Internal Revenue Service. Depreciation and Recapture 4
6
Internal Revenue Service. Publication 527 (2025), Residential Rental Property
7
Internal Revenue Service. Publication 946 (2024), How To Depreciate Property – Section: Qualified Section 179 Real Property
8
Internal Revenue Service. Tangible Property Final Regulations – Frequently Asked Questions
9
Internal Revenue Service. Examining a Taxpayer Electing a Partial Disposition of a Building
10
Internal Revenue Service. Publication 527 (2025), Residential Rental Property – Section: 5-, 7-, or 15-Year Property