If you're not sure whether your hot water heater is 110 or 220, there are a few things you can do to find out. First, check the voltage rating on the heater. This should be clearly marked somewhere on the unit. If it says 110 then you have a 110 volt heater. If it says 220 then you have a 220 volt heater. Another way to tell is by looking at the wiring. 110 volt heaters will have two wires coming into the unit, while 220 volt heaters will have four wires. Finally, you can check with your local utility company to find out what voltage your home is wired for. Most homes in the US are wired for 220 volts, but it's always best to check to be sure.