You're absolutely correct. However, all he'll need is one ball valve on the hose that feeds the heater. I might add to occasionally open the valve to keep the heater core from rotting (drying) out.olsarge said:Many vehicles do not have a valve to shut off flow of the hot water through the heater core. If yours is one of them you'll have to put one in yourself. Go to the hardware store and get two ball valves from the plumbing department with inlets to match your hose size. I found it waorks best to put them in both the supply and return. It's a pain because you have to manually change them back and forth depending on the weather but it deffinately cools off the incoming air. Un less you can find an electric valve of some kind that you can rig up.