I bought a 77 CHB about a year ago. I'm installing a forced air heating system. It presently has installed, a water heater, and a Red Dot heater that doesn't work. If my understanding is correct the only difference between a marine water heater and one in your home is that engine heat can be circulated through the water heater instead of 120v when the boat is sailing. In other words a hose comes off the outlet port on the engine to the heater, and returns through a hose to the inlet side. On my boat the coolant coming off the engine goes first to a cylinder attached to a bulkhead just off the engine (photo). It then goes through at least two other cylinders, one at least 24" long...and one comes off that to one that is vertical. It then goes through the Red Dot heater and on to the hot water heater. I'm baffled by what these inline cylinders do?? What I would like to do is route the engine coolant directly in and out of the water heater and eliminate the Red Dot heater and all these inline obstacles. I am reluctant to do so until I know what I'm removing. Does anyone know what these are? Certainly they are there for some reason, but what. Its hard to see what I'm talking about in the pictures, but you can see in the pictures there are some pretty substantial galvanized fittings on these things.