The National Electrical Code (r) added AFCI standards for kitchens and laundry rooms in 2014. Previously, the code required only GFCI protection in these places, but for extra security, they must now have both AFCI and GFCI protection. This means that if you are replacing or adding circuits in these locations, all removable outlets should be replaced with AFCI-protected versions.
AFCI stands for arc fault circuit interrupter. It's a small device that detects high voltage from an arc welder or other source of electricity with voltage between 15 volts and 20 volts DC used for welding or power tools. If it senses this voltage, it will interrupt the power before it reaches the house wiring, preventing any damage to your belongings or home. Modern AFCIs can also detect low voltage generated when someone trips over a cable or walks into an open switch and will also interrupt its flow. These lower currents may not appear dangerous, but they can cause expensive damage to your appliances if they're not corrected.
Kitchen outlets are the most likely to experience an overload condition because many people use them every day for cooking while others who may not know better use them as light switches. Replacing these outlets with new AFCI ones will ensure that anyone who encounters one of these outlets while it's activated is being protected against an arc flash.
Because AFCIs have proven to be so efficient at avoiding electrical fires, the National Electrical Code (NEC) mandates them to be put in practically every room in newly built homes. When an extension, an additional circuit, or even an extra outlet is installed to an existing home, the NEC also requires the installation of AFCIs. So, yes, AFCIs are worth it.
Having said that, there are cases where people claim that they are not needed because a normal receptacle can't cause any fire. But this is wrong! Even if nothing else is used with the outlet, still using a receptacle is dangerous because you are allowing current to flow through anything that gets plugged into it. If something spills onto a floor or desk, for example, it can start a fire.
So, while AFCIs prevent electrical fires, they cannot detect all types of fires. They only inhibit those fires that are caused by heat. If you use any other type of power tool or appliance with an extension cord, then you should definitely get an AFCI outlet too. This way, if the cable inside the extension cord is damaged, it will not allow current to flow and will not cause a fire.
The rule was modified in 2017 to mandate AFCI protection in nearly every room of a home. They will not interfere with the operation of ground fault circuit interrupter (GFCI) outlets, therefore installing AFCIs on circuits with GFCI outlets is safe. However, if you are replacing a GFCI with a new GFCI, it can be done but it cannot be assumed by law that the replacement will work because there may not be enough power available to operate it properly.
For example, an old GFCI used in a bathroom may not have been wired up correctly for maximum effectiveness. Or it may have failed due to corrosion from water getting into the unit. An AFCI will protect against this kind of issue by shutting off the power before it causes damage.
If you are only replacing one GFCI with another of the same type, then yes, you can simply replace it without first testing it. But if the new GFCI is different from the old one (such as a larger wattage unit), then it's best to test it first to make sure it works properly before using it.
In conclusion, you can use an AFCI to replace a GFCI but you should test it first to make sure it works properly. If it doesn't, you may need to also replace the breaker serving that circuit.