Types of Water Heater Hook-ups described

Types of

Water Heater Connections

on sailboat diesels

1. WH in Thermostat by pass

(water heater starts heating before thermostat opens)

same as on my automobile and the recommended method per Westerbeke

Westerbeke, refers to this type as the

"positive flow, hot water heater connection in the thermostat bypass circuit"

2. WH in series with the HE

(WH restricts flow through HE)

3. WH in parallel with the HE

(WH robs some water from HE)

4. WH is heated by sea water that has

passed through the heat exchanger

Type 1 modes

1.A. Thermostat closed

(All flow goes through WH and nothing goes through HE)

WH hoses are warm & HE hoses are cold

1.B. Thermostat starting to open

(lots of flow still goes to WH and some flow goes to HE)

1.C. Thermostat fully open

(Lots of flow goes to HE and some still flows in WH)

Click here for implementation details on 1980 Universal 5432

Type 2 Modes (Series)

2.A. Thermostat closed

( No flow in either WH or HE)

(Great flow in 5" long the by pass hose)

2.B. Thermostat starts to open

(some flow in both WH and HE)

2.B. Thermostat fully open

(max and equal flow in both limited

by the WH hoses and orifice sizes)

Some boats have a water heater by-pass valve with the

type 2 series connection. When open the coolant can

flow directly from the engine to the heat exchanger

without having to go through the water heater. A small

amount of coolant still flows in the water heater. Therefore,

when the valve is open the WH can still get warm just not

as fast. These by pass valves were popular on the M25

powered Catalinas in the 80's and early 90's. Click here

for a picture of a by pass valve.

One of the Catalina 36 owners experimented and found

that with the valve open the max temp was 165, but

closed the max temperature increased substantially

indicating that the thermostat was no longer in control.

This bypass valve with the heater in series is still

recommended by Raritan, but they also caution to use

the engine manufacturers recommendation.

Westerbeke and Yanmar now prefer Type 1.

Type 3 Modes (simple parallel)

3.A. Thermostat closed

( no flow in either WH or HE)

(High flow in 5" long by-pass hose)

3.B. Thermostat starts to open

( more flow in HE than in WH)

3.C. Thermostat fully open

(max flow, HE has much more flow than WH)

Type 4 Modes (WH in Sea Water)

4.A. Thermostat closed

( No flow to HE and sea water does not warm up)

(High flow in 5" long by-pass hose)

4.B. Thermostat starts to open

( increasing flow of anti freeze in HE )

4.C. Thermostat fully open

(max flow in HE and sea water starts to get

warm as it passes through the HE)

I have not figured out any merit to this system,

I am sure sea water will corrode the Water Heater

much faster. The guy who had this on his boat had

an angry wife as the water never warmed up.

High Water Heater