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.

    • Environmental Topics
    • Air
    • Bed Bugs
    • Cancer
    • Chemicals, Toxics, and Pesticide
    • Emergency Response
    • Environmental Information by Location
    • 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

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
  • IAQ Frequently Asked Questions
  • Publications about IAQ
  • Regional and State IAQ Information
Contact Us about Indoor Air Quality
Contact Us to ask a question, provide feedback, or report a problem.
Last updated on December 20, 2024
  • Assistance
  • Spanish
  • Arabic
  • Chinese (simplified)
  • Chinese (traditional)
  • French
  • Haitian Creole
  • Korean
  • Portuguese
  • Russian
  • Tagalog
  • 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
  • Site Feedback

Follow.