Skip to main content
U.S. flag

An official website of the United States government

Here’s how you know

Dot gov

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

HTTPS

Secure .gov websites use HTTPS
A lock (LockA locked padlock) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

Emergency

This is not the current EPA website. To navigate to the current EPA website, please go to www.epa.gov. This website is historical material reflecting the EPA website as it existed on January 19, 2025. This website is no longer updated and links to external websites and some internal pages may not work. More information »

    • Environmental Topics
    • Air
    • Bed Bugs
    • Cancer
    • Chemicals, Toxics, and Pesticide
    • Climate Change
    • Emergency Response
    • Environmental Information by Location
    • Environmental Justice
    • Greener Living
    • Health
    • Land, Waste, and Cleanup
    • Lead
    • Mold
    • Radon
    • Research
    • Science Topics
    • Water Topics
    • A-Z Topic Index
    • Laws & Regulations
    • By Business Sector
    • By Topic
    • Compliance
    • Enforcement
    • Laws and Executive Orders
    • Regulations
    • Report a Violation
    • Environmental Violations
    • Fraud, Waste or Abuse
    • About EPA
    • Our Mission and What We Do
    • Headquarters Offices
    • Regional Offices
    • Labs and Research Centers
    • Planning, Budget, and Results
    • Organization Chart
    • EPA History
    • Staff Directory

Breadcrumb

  1. Home
  2. Indoor Air Quality (IAQ)

How does outdoor air enter a building?

Most home heating and cooling systems, including forced air heating systems, do not mechanically bring fresh air into the house. Outdoor air enters and leaves a house by:

  • natural ventilation, such as through open windows and doors
  • infiltration, a process by which outdoor air flows into the house through openings, joints and cracks in walls, floors and ceilings, and around windows and doors.
  • mechanical means, such as through outdoor air intakes associated with the heating, ventilation and air conditioning (HVAC) system; outdoor-vented fans that intermittently remove air from a single room, such as bathrooms and kitchens

For more information see Improving Indoor Air Quality .

Related Questions

  • Who can I contact to have the indoor air quality tested at my place of employment?
  • How much ventilation do I need in my home to improve indoor air quality?
  • Has EPA issued specific recommendations on how frequently carpet should be cleaned?
  • What can I do to improve indoor air quality in my home?
  • What can I do to protect indoor air quality if I live in an apartment?
  • How do I protect indoor air quality if I am remodeling my home?

Indoor Air Quality (IAQ)

  • Learn about Indoor Air Quality
    • Introduction to IAQ
    • Improving Indoor Air Quality
    • Climate Change and IAQ
  • IAQ by Building Type
    • Homes
    • Multi-Family Housing
    • Schools
    • Offices & Other Large Buildings
  • Indoor Air Pollutants and Sources
    • Carbon Monoxide
    • Indoor Particulate Matter
    • Secondhand Smoke/Aerosol
    • Volatile Organic Compounds
  • IAQ Science and Technologies
    • IAQ Science
    • IAQ Science Webinar Series
    • Air Cleaners
    • Air Sensor Technology and IAQ
  • Networking and Funding
    • CIAQ
    • Tribal Homes and IAQ
    • Cooperative Agreements
  • Webinars, Meetings and Resources
  • IAQ Trending Topics
  • Frequently Asked Questions
  • Publications
  • Regional and State IAQ Information
Contact Us about Indoor Air Quality
Contact Us about Indoor Air Quality to ask a question, provide feedback, or report a problem.
Last updated on December 20, 2024
  • Assistance
  • Ayuda
  • Arabic
  • Chinese (simplified)
  • Chinese (traditional)
  • Aide
  • Asistans
  • Korean
  • Assistência
  • Russian
  • Tulong
  • Vietnamese
United States Environmental Protection Agency

Discover.

  • Accessibility Statement
  • Budget & Performance
  • Contracting
  • EPA www Web Snapshot
  • Grants
  • No FEAR Act Data
  • Plain Writing
  • Privacy
  • Privacy and Security Notice

Connect.

  • Data
  • Inspector General
  • Jobs
  • Newsroom
  • Regulations.gov
  • Subscribe
  • USA.gov
  • White House

Ask.

  • Contact EPA
  • EPA Disclaimers
  • Hotlines
  • FOIA Requests
  • Frequent Questions

Follow.