NFPA 54, the National Fuel Gas Code, currently does not explicitly address installation requirements for appliance sidewall vent terminations located in screened-in enclosures. There is some concern that screen-in enclosures may impede the dispersion of combustion gases. There are many parameters that are, or could be, important in determining how flue gas will disperse in the real world and what the limits might be for safe venting in screened enclosures. These include: the appliance input rating, excess air, and efficiency which determine the combustion gas flow rate, temperature, and composition; the design and location of the sidewall vent terminal; the enclosure volume and screen mesh free area; and other factors such as wind speed and direction, outdoor ambient temperature, nearby topology, the presence of barriers such as nearby buildings, trees, and hills, the accumulation of lint from clothes dryers exhausting into the screen space(for dryer appliances). In 2011, the Foundation initiated a project to develop practical guidance on this issue.