I agree with Grumpy_Mike here. Go buy a devise design to turn on / off 120 VAC @ 15 A. So you simply connected the low voltage section - like a 5 V on / off and the High Voltage section. Just screw the connectors and you are done. Connected the High Voltage in serie with the Power heater. Like : Live ---> Device ----> live heater --- > Neutral ( Canada / US is the same system ) But I recomment an electrician to do the High Voltage section. As for me, I did work on AC, so I know I am doing, but safety is a must - ALWAYS !!!
If you really have an idea how and work on AC line at home - Not talking about screwing a light bulb here - ie - you have experience working with AC - like wired a line from the breaker box , a plug and a switch and a light fixture - Than a high current rated SPST relay will work. The coil voltage may be high 12 V or higher, that you will need a voltage to control the relay - Automotive store may sell those high current type - 12 V coil, And use a transistor, base resistor and a diode and connect it right, than you are in the game.
In conclusion, No experience... let a pro do the job ! - I know, it cost money !!! 