The most common residential units are rated for class A, B, and C fires. and weigh 7 lbs. Residential is generally a plastic version, verses the metal version you are accustom to seeing in restaurants or office buildings. The residential ones need to be inspected each year by a licensed professional They also have a life expectancy, and will eventually need to be replaced. Chris Atzenhofer, with International Fire Protection Chattanooga recommends “2-4 fire extinguishers per home.