Unless you have fire sprinklers installed, a fire extinguisher is a necessity for any home. They’re a crucial tool in your defense against home fires. But most people don’t realize there are several different sizes and types of fire extinguishers. The ratings system can seem complicated at first glance, but once you understand it, it can help you choose the right fire extinguisher for your home to help you prevent fires.

Check the class. There are three different classes of extinguishers: A, B and C. Class A fire extinguishers are formulated to take care of fires fueled by wood, paper, cloth, rubber and most types of plastics. Class B extinguishers are for flammable liquid fires such as gasoline, oil and grease—they’re usually best for kitchens and garages. Class C extinguishers are made to address electrical fires, most often caused by faulty wiring or appliances. There are also multi-class extinguishers available combining several different classes, including all three.

Check the number rating. Fire extinguishers also come with number ratings signifying the size of the fire they can handle. The larger the number, the larger the fire. For example, a 2A 40B-C fire extinguisher has the capacity of about two gallons of water and can cover approximately 40 square feet of B-class fire.

Think about the right extinguisher for each room. For most people, a class A-B-C fire extinguisher is the most practical—you never know what type of fire will erupt, and you don’t want to have to think about the type of fire and whether you have the right fire extinguisher during a crisis. But even if you have an all-purpose model, it’s better to own several and keep them in key locations where fires are more likely. As for size, smaller and more portable is considered better for the kitchen, where stovetop and oven fires may occur. A larger all-purpose canister should be kept in an accessible place in the house. Garages, laundry and utility rooms may need a larger model as well.

Disposable or rechargeable? There are two different types of fire extinguishers: disposable and rechargeable. Disposable fire extinguishers tend to be less expensive, and they typically lose pressure after about ten or twelve years. When you use them once, you have to throw them away. Rechargeable fire extinguishers are more expensive, but they can be refilled after use or if they lose their pressure, and should be brought to a manufacturer for regular yearly service.

Check the pressure gauge. When buying a fire extinguisher, look for one with a pressure gauge. This will tell you whether there is enough pressure in the unit for it to work when needed. It will also tell you if the pressure is dropping. If it is, you may need to replace the canister or get it recharged, depending on the type of fire extinguisher you have

Look for the UL rating. Underwriters Laboratories, Inc., is an independent underwriting company that certifies product safety in 99 countries. They also certify fire extinguishers. When buying, look for a UL rating to ensure that the fire extinguisher is safe and functional.

Buying a fire extinguisher isn’t as complicated as it sounds. Look for at least two multi-class ABC fire extinguishers—one in a larger size to cover large fires, and another small, portable unit that can take care of fires in small and hard-to-reach areas. Follow these tips, and you should be able to pick the perfect type of fire extinguisher for your home.