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Mechanical / HVAC Permit in Unincorporated Twin Falls County, Idaho

Required for heating, ventilation, air conditioning, and fuel gas installations in unincorporated Twin Falls County. Unlike electrical and plumbing (which are administered statewide by the Idaho Division of Building Safety), Mechanical/HVAC permits in Twin Falls County are issued and inspected directly by the county's own Building Department under a locally-run program, using the county's own application and per-square-foot/per-item fee schedule.

Verified 2026-07-08 · Source

When you need this permit

  • Required for new HVAC installations, replacement/retrofit of mechanical equipment, gas lines, solid fuel/gas heating appliances, and hydronic heating systems
  • Residential/Commercial HVAC Permit Application listing parcel number, structure type, and description of work
  • Idaho contractor registration number and expiration date required for contractor-performed work Contractor
  • Property address must be posted at the public road entrance prior to first inspection

Required documents

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Fee schedule

Residential HVAC — New, single-family/duplex/townhome, based on living spaceTwin Falls County 2025 Fee Schedule (TFCO-BLD-FEES-2025-base-FINAL.pdf), 'Mechanical Permits' section, current from 2025
Up to 1,500 sq ft: $120.00; 1,501–2,500 sq ft: $170.00; 2,501–3,500 sq ft: $230.00; 3,501–4,500 sq ft: $280.00; over 4,500 sq ft: $280.00 plus $50.00 per additional 1,000 sq ft or portion thereof
Replacement or Retrofit Systems (existing structures)Twin Falls County 2025 Fee Schedule
$60.00 plus $10.00 per additional piece of mechanical equipment
Miscellaneous ItemsTwin Falls County 2025 Fee Schedule
$60.00 plus $10.00 per additional piece
Commercial HVACTwin Falls County 2025 Fee Schedule
Based on construction valuation chart

Review timeline

Plan review
Not published — contact the department

How long did your Mechanical / HVAC Permit permit actually take in Unincorporated Twin Falls County?

Anonymous — one question, no email. Answers are combined and only shown once at least 5 people have reported.

Inspection process

  1. 1

    Rough-In / Gas Piping Pressure Test

    Call the Mechanical Inspection Request Line at 208-735-4432. Have permit number, property address, contact info, and inspection type ready. Requests called in after 7:00 AM scheduled for next working day.

  2. 2

    Final

    Equipment operational, venting and combustion air verified. Must be signed off before the associated building permit's final inspection can proceed.

See the full Unincorporated Twin Falls County inspection guide — scheduling & re-inspection fees →

Tips

  • Mechanical/HVAC is one of the few trades Twin Falls County issues directly — electrical and plumbing are handled by the Idaho Division of Building Safety (state), not the county.
  • Mechanical inspection requests go to a dedicated line: 208-735-4432 (separate from the general Building Inspection line, 208-735-4429).
  • 'Living Space' for fee purposes includes any space intended for human habitation (sleeping, eating, cooking, bathing, recreation, sanitation) — an unfinished basement counts as living space under this fee schedule.
  • The mechanical permit's final inspection must be signed off before the associated building permit's final inspection can be requested.

Frequently asked questions

Unincorporated Twin Falls County requires a mechanical / hvac permit for: Required for new HVAC installations, replacement/retrofit of mechanical equipment, gas lines, solid fuel/gas heating appliances, and hydronic heating systems; Residential/Commercial HVAC Permit Application listing parcel number, structure type, and description of work; Idaho contractor registration number and expiration date required for contractor-performed work; Property address must be posted at the public road entrance prior to first inspection. If your project isn't listed, confirm with Twin Falls County Community Development Services — Building Department at 208-734-9490 before starting work.

For a new single-family dwelling HVAC system, the fee is based on living space: $120 for up to 1,500 sq ft, $170 for 1,501–2,500 sq ft, $230 for 2,501–3,500 sq ft, $280 for 3,501–4,500 sq ft, and $280 plus $50 per additional 1,000 sq ft above that. Source: Twin Falls County 2025 Fee Schedule.

Unincorporated Twin Falls County does not publish a plan-review timeline for this permit. Contact Twin Falls County Community Development Services — Building Department at 208-734-9490 for current turnaround.

You'll need: Mechanical Permit Application (Updated 10/2021, includes HVAC Fee Schedule). See the required-documents checklist on this page for details on each.

Unincorporated Twin Falls County requires 2 inspection(s) for a mechanical / hvac permit, in order: Rough-In / Gas Piping Pressure Test, Final. Schedule each through Twin Falls County Community Development Services — Building Department (208-734-9490).

Apply through Twin Falls County Community Development Services — Building Department at 630 Addison Avenue West, Suite 1100, Twin Falls, ID 83301. Phone: 208-734-9490. Office hours: Mon–Fri 8:00 AM – 5:00 PM (Building Department closed for lunch 12:30 PM – 1:30 PM). Official information: https://twinfallscounty.org/community-development-services/.

Unincorporated Twin Falls County, Idaho has adopted: 2018 International Building Code (IBC) with Idaho Amendments; 2018 International Residential Code (IRC) with Idaho Amendments; 2018 International Energy Conservation Code (IECC) with Idaho Amendments; 2018 International Mechanical Code (IMC) with Idaho Amendments; 2018 International Fuel Gas Code (IFGC) with Idaho Amendments; 2018 International Existing Building Code (IEBC) with Idaho Amendments; 2018 International Fire Code (IFC) with Idaho Amendments; 2018 Idaho Manufactured Home Installation Standards. Local amendments apply — see the Unincorporated Twin Falls County overview page for the full list.

Twin Falls County issues Mechanical/HVAC permits directly through its own Building Department, using its own application and fee schedule (last updated 10/2021, fees refreshed in the county's September 2025 fee schedule). This differs from electrical and plumbing, which are issued statewide by the Idaho Division of Building Safety, not the county. Source: Twin Falls County Mechanical Permit Application (Updated 10/2021); Twin Falls County 2025 Fee Schedule.

Sources & verification

Verified against official sources. Last reviewed 2026-07-08.

Fees, timelines, and adopted codes are researched from each jurisdiction's published records — see how we verify. Requirements change and vary by project, so always confirm the current details with the Unincorporated Twin Falls County building department before you submit. PermitBase is an independent reference and is not affiliated with any government agency.

Other permits in Unincorporated Twin Falls County

Residential Building Permit (New Construction / Addition)Commercial Building Permit (New Construction / Tenant Improvement)Personal Use Energy Project Permit (Rooftop/Ground-Mount Solar)Electric Vehicle (EV) Charging Station / EVSE Permit

Mechanical / HVAC Permit in other cities

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