Does anyone know how to install cabin heater using FW cooling system on a Mercruiser 470?
Thank you.

I'm stupid and drunk now so I don't know what a FW is but all you have to do is run a loop from your circ water to an automotive "heater coil" (like the small radiator under your dash in a car) and mount a small elec. fan behind it. I think Overton's and others sell a kit.

Or buy an "equipment grade" heaterbox like they use in trackhoes. Comes with box, hose, switch, etc.