Introduction
Ventilation numbers don’t exist in a vacuum — they’re governed by building codes, and the code always wins over any calculator, guide, or rule of thumb. The good news is that residential ventilation codes are among the more straightforward parts of the code: they set minimum exhaust rates for bathrooms and kitchens, whole-house ventilation rates (often via ASHRAE 62.2), and rules for duct termination and make-up air. The complication is that the local authority having jurisdiction (AHJ) — your city or county building department — decides which code edition and amendments apply to your project.
Use the Ventilation Calculator to compute your airflow targets, then use this guide to understand which code provisions typically govern them — and how to confirm the exact requirements with your local AHJ before you buy or install.
How Ventilation Codes Are Structured
In the US, residential ventilation requirements typically come from the International Residential Code (IRC) — mechanical ventilation provisions in chapters covering exhaust systems — often supplemented or replaced by state-specific codes (California’s Title 24, for example, has its own ventilation chapter). Many jurisdictions reference ASHRAE Standard 62.2 (“Ventilation and Acceptable Indoor Air Quality in Residential Buildings”) for whole-house ventilation rates.
Three things to understand about this structure:
- Codes set minimums, not designs. Meeting the code minimum is the floor; good design often exceeds it (quieter fans, humidity controls, better duct practice).
- Editions and amendments vary. Your AHJ may enforce the 2021 IRC, the 2018 IRC with local amendments, or a state code — the ventilation numbers can differ between them.
- The AHJ’s interpretation is final. When in doubt, the building department’s answer overrides anything you read online, including this guide.
Bathroom and Kitchen Exhaust Requirements
The provisions most homeowners encounter, in their typical form:
| Application | Typical code-level requirement | Notes |
|---|---|---|
| Bathroom, intermittent | 50 CFM (≈ 85 m³/h) | Switched or timer-controlled |
| Bathroom, continuous | 20 CFM (≈ 34 m³/h) | Runs 24/7 at low speed |
| Kitchen, intermittent | 100 CFM (≈ 170 m³/h) | Range hood or exhaust fan |
| Kitchen, continuous | 25 CFM (≈ 42 m³/h) | Less common residentially |
These align with the planning values used throughout this guide series — the formula-explained guide shows the sizing logic behind them. Note that some jurisdictions require the bathroom fan to be on a timer or humidity control rather than a plain switch, and nearly all require exhaust to terminate outdoors — venting into attics or crawlspaces is prohibited.
Whole-House Ventilation: ASHRAE 62.2
Where adopted, ASHRAE 62.2 sets the continuous whole-house ventilation rate:
Q = 0.03 × conditioned floor area (ft²) + 7.5 × (bedrooms + 1), in CFM
The standard also addresses local exhaust (the bathroom/kitchen minimums above), system controls, and sound ratings (it limits whole-house ventilation equipment noise — typically 1.0 sone or less at continuous speed). Key compliance nuance: editions differ. ASHRAE 62.2-2016, -2019, and -2022 each refined the formula and added provisions (such as infiltration credits and compartmentalization requirements for multifamily). Confirm which edition your AHJ references — the estimating guide works through the calculation step by step.
Make-Up Air Provisions
High-capacity exhaust triggers make-up air rules in most codes: above a threshold — commonly 400 CFM for range hoods — the code requires a means of supplying replacement air, typically a dampered intake interlocked with the exhaust equipment. This provision exists for combustion safety as much as performance: a powerful hood in a tight house can backdraft a gas water heater or furnace.
If your project includes a hood near or above that threshold, treat make-up air as a design requirement from day one, not an afterthought. It affects equipment selection, duct planning, and cost — see the cost guide for the budget impact — and it’s squarely in licensed-professional territory per the DIY vs pro guide.
Permits and Inspections
The typical pattern across jurisdictions:
- Like-for-like fan replacement: usually no permit required.
- New exhaust fan with new duct and/or circuit: mechanical and/or electrical permit commonly required.
- Range hood installation: permit commonly required, especially with new ductwork or make-up air.
- ERV/HRV or whole-house system: mechanical permit virtually always required; plans may need to show the ASHRAE 62.2 calculation.
Inspections generally verify: correct fan/hood ratings, duct material and termination outdoors, damper operation, make-up air interlock where required, and electrical connections. A failed inspection usually means rework, not fines — but unpermitted work discovered later (during a home sale, for instance) can force retroactive permitting. When a contractor proposes skipping a required permit, find a different contractor.
How to Confirm Requirements with Your AHJ
A practical process that takes one phone call or counter visit:
- Identify your AHJ: the building department of your city or county (some areas use a regional authority).
- Ask three questions: which code edition governs residential ventilation here; whether ASHRAE 62.2 is adopted and in which edition; and whether my project scope needs a permit.
- Get it in writing: note the staff member’s name, date, and the answers — or request the relevant code section numbers.
- Bring your calculation: a one-page sheet with room volumes, target CFM per room, and the ASHRAE 62.2 whole-house figure from the Ventilation Calculator shows the department (and your contractor) that the design is deliberate.
Most building departments answer these questions routinely — it’s among the most common homeowner inquiries they receive.
Documentation to Keep
Keep a project file: equipment specification sheets (CFM, sone, certifications), the ventilation calculation sheet, permit cards and inspection sign-offs, and contractor invoices listing installed model numbers. This file proves code compliance at resale, supports warranty claims, and gives the next homeowner (or your future self) the system’s design basis. The checklist guide includes a documentation section for the project closeout.
Related Guides
- Ventilation Estimating Guide — the ASHRAE 62.2 calculation workflow.
- DIY vs Pro — permits and when each path needs one.
- Pro Tips — installation practices that pass inspection.
- Ventilation Calculator FAQ — quick answers to the most asked questions.
- Ventilation Checklist — closeout and documentation checklist.
Frequently Asked Questions
Do I need a permit to replace a bathroom fan?
Usually not for a like-for-like swap on existing wiring and duct. New circuits, new duct penetrations, and new fan locations commonly do need permits — confirm with your local building department.
Is ASHRAE 62.2 legally required?
Only where your jurisdiction has adopted it into code — many have, some with amendments, some not at all. Your AHJ’s answer is the one that counts, not the standard’s publication status.
What happens if my work doesn’t meet code?
At inspection: rework until it passes. If discovered later (e.g., during a sale): retroactive permitting, rework, or price concessions. The inspection process is designed to catch issues while they’re cheap to fix.
Can my HOA add ventilation requirements?
HOAs can add restrictions (e.g., on exterior vent terminations or roof penetrations) but can’t waive code minimums. Check HOA rules early — exterior appearance approvals can delay a project that the building department would otherwise approve quickly.
Do these codes apply to renovations or only new construction?
Both, with nuances: new construction must meet the full current code; renovations typically must meet code for the altered systems, and some jurisdictions trigger broader upgrades past certain project thresholds. Ask your AHJ how your scope is classified.
Confirm, Then Build
Code compliance for residential ventilation is a short checklist — minimum exhaust rates, whole-house ventilation per the adopted standard, outdoor termination, make-up air where triggered, permits where required — but the details belong to your AHJ. Compute your targets with the Ventilation Calculator, confirm the governing edition and permit requirements with your local building department, and keep the documentation. That’s the entire compliance workflow.
Disclaimer: This guide summarizes typical US code provisions for general planning purposes and is not legal or code-consulting advice. Code editions, amendments, and interpretations vary by jurisdiction. Your local authority having jurisdiction (AHJ) is the final word on requirements — verify with them directly and consult a licensed professional for compliance decisions on your project.
