soft plug heater

It is getting cold up here, and I need to install a soft plug heater in my kids ZX2. Does any one know which plug ( front or back side) needs to be removed and what size I need to order? Should have done this in summer time, but it fell off the radar as other work piled up.

I believe the soft plug is on the front of the engine just below the exhaust manifold. I've no idea what size it is.