Fairfax County, VA HVAC permit requirements

2021 Virginia Residential Code (2021 IRC as amended by VCC 310.8, 2021 USBC, 13VAC5-63), effective January 18, 2024. Fairfax: applicants could choose the 2018 or 2021 USBC technical provisions until Jan. 17, 2025. 'Beginning Jan. 18, 2025, all applications and plans must meet the 2021 USBC requirements.'

2021 Virginia Energy Conservation Code (2021 IECC as amended by VCC 1301.1.1.1) and VRC Chapter 11 as amended in VCC 310.8. This is the same statewide text as Arlington, with no local amendments.

VRC M1401.3 and N1103.7 are amended by the VCC (Manual S sizing on Manual J loads, with the multi-stage/VRF, next-larger-size and lowest-capacity-unit exceptions to the Manual S cap). Fairfax Residential HVAC Certification Form instructions: 'Per the Virginia Residential Code, equipment sizing shall be in accordance with ACCA Manual S based on building loads calculated in accordance with ACCA Manual J or other approved methodologies. It is the applicant's responsibility to conduct a load caclulation [sic] in accordance with ACCA Manual J for all HVAC installations. While not initially required at permit application, this calculation may be required for permit issuance.'

IRC 2021 M1601.1 is kept without Virginia amendment ('ACCA Manual D, the appliance manufacturer's installation instructions or other approved methods'). On the Fairfax HVAC Certification Form, the system designer certifies that the information is 'in conformance with ACCA's Manual J, Manual S, Manual D, the ASHRAE Handbook of Fundamentals or other approved methods'. The form requires an 'HVAC DUCT LAYOUT DIAGRAM' showing 'trunk, branch, and outlet sizes'.

The Fairfax sources conflict. The LDS 'Does My Project Require a Permit?' page says a permit IS required for 'Direct replacement of household appliances Includes stoves, ovens, water heaters, HVAC, etc.', yet under NOT required lists 'Direct replacement of electrical, plumbing and mechanical work (no change in location and must be a like-for-like replacement)'. The MECHR page requires a permit for 'New, Replacement, Repair or Conversion of HVAC Systems' and 'Duct Installation (new or replacement)'. Statewide VCC 108.2 item 14.4 exempts replacement of mechanical appliances 'not fueled by gas or oil' in R-3/R-4/R-5. The HVAC Certification Form 'is required to be onsite for all mechanical inspections'.

Same statewide 2021 VECC / VRC Chapter 11 structure: prescriptive (R401.2.1 / N1101.2.1), total building performance alternative, and ERI (R406 / N1106, with VA amendment to R406.3.2). No Fairfax-specific compliance path guidance was retrieved.

Apply for the residential mechanical (MECHR) permit in PLUS. 'Residential HVAC Certification may be required for HVAC projects.' The form (one per system) asks for building/mechanical permit numbers, system area in sf, heating equipment type/manufacturer/model/input/output in Btu/h, cooling equipment total capacity at evaporator, sensible capacity and tonnage, and a duct layout diagram. It must be signed by the system designer with license number and must be onsite for all mechanical inspections. Owners may pull permits, 'however, it is strongly recommended a properly licensed contractor pull the permits'.

Same as Virginia statewide: the DHCD 2024 Code Development Cycle is in progress. The USBC update NOIRA stage is complete (comments ended 12/02/2025) and the BHCD met May 11, 2026 on '2024 Code Development Cycle proposed regulations'. No 2024 USBC effective date has been published in official sources found.

plus.fairfaxcounty.gov/CitizenAccess/Default.aspx