Check the breaker on that circuit and if it's 15A use 14 gauge, if it's a 20A breaker use 12 gauge. Also, make sure the Ranco can handle what the heater demands. Definitely do not use 14 gauge wire on a circuit with a 20A breaker.Thank you! Would you recommend the 16 gauge wire (as opposed to the 14 gauge)?
I've been using the standard Ranco to control a tankless gas water heater for five or six years. My Ranco controller is rock solid.