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Old 10-25-2015, 09:16 PM   #1
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Engine heat

I am interested in running both a bus heater and domestic hot water off my single propulsion engine. I know others have done this, but I am wondering how they have plumbed their systems. Series or parallel, heater by-pass loop, booster pump or no?
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Old 10-25-2015, 09:53 PM   #2
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I did what you are describing with 3 Heatercraft units. Ended up with 70' of loop so I incorporated a pump. My system has valves on the engine to isolate the loop in the event of a leak. The discharge from the motor goes to the water heater. There is a return line from the water heater back to the engine. At the water heater there is a Y valve for the return line. In one position it returns to the engine. In the other position it feeds the pump which circulates fluid to the 3 heaters which are plumbed in series. The return line from the heaters and the water heater tee together before going into the engine. There is enough flow from the engine water pump to run the water heater, but the heater loop would offer to much frictional line loss, so I have a pump. When you don't need heat, the valve isolates the heater loop so that only the water heater gets flow. When you want heat, flip the valve the other way and turn on the pump. Added a temperature switch to the engine coolant loop so that if I'm drawing to much heat out of the engine, it will turn off the heater fans until the engine temperature is back to normal.

This is how I designed and set mine up. It hasn't been run yet as I'm just finishing up my refit. Should have results in a few weeks.


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Ted
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Old 10-26-2015, 09:13 PM   #3
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That sounds like a well thought out system! I'll be very interested to hear how it works out. With that much hose, I'm sure you are right about needing a circulation pump. I am only planning to use one heater, so I have some hope that I won't need one. I'll also be interested to hear if your thermostat ever shuts the blowers down.

Many thanks for your reply.
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Old 10-26-2015, 09:45 PM   #4
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I have a bus heater off my main engine. One thing I found was at hull speed, the heater could suck down the engine temp well below normal temps. Not great for the engine, and not great for keeping warm!! Engine just does not make a huge amount of heat while making 35hp. If temp starts dropping, I add a little power.

Doug, I would go series, and probably put the bus heater first, then water heater. 180F in the heater is good stuff, if it cools it to 140F that is still plenty for domestic water.
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Old 10-27-2015, 06:15 PM   #5
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Ski, point well taken regarding the heater first -- that was one of my main questions. I gather you don't have a water heater in your setup?

I'm surprised that a single heater was able to suck down the engine temperature. That makes O C Diver's thermostat sound like an even better idea.

I'm also wondering if switching from the usual 5/8" hose to 3/4" might eliminate the need for a circulation pump. My engine (FL120) seems to have a valve on the side of the engine where the hose returns from the water heater. Does anyone know if that is intended to reduce the flow through the system?
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Old 10-27-2015, 06:47 PM   #6
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I have my water heater on a loop that runs with the engine coolant and it goes through a heat exchanger that feeds the bus heater.

Once the water heater is up to temp, it is well isolated and saps little heat.

I can regulate the flow to the bus heater through a couple ball valves, the circumstances pump is this tiny solar job that is just perfect.
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Old 10-27-2015, 09:42 PM   #7
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Quote:
Originally Posted by Doug H View Post
I'm also wondering if switching from the usual 5/8" hose to 3/4" might eliminate the need for a circulation pump. My engine (FL120) seems to have a valve on the side of the engine where the hose returns from the water heater. Does anyone know if that is intended to reduce the flow through the system?
Yes, you definitely want to use larger diameter hose going to the water heater even if the ports on the engine are only 1/2". The water pump pushes coolant in different directions and too much frictional line loss will reduce or stop the flow of coolant to the water heater. My water heater has likely 15' hose runs (30' total loop) and would probably not flow if the hoses were 1/2".

Quote:
Originally Posted by psneeld View Post
..... the circumstances pump is this tiny solar job that is just perfect.
I also use a circulating pump designed for solar heat applications. Think it draws around 1 amps at 12 volts.

Ted
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Old 10-29-2015, 08:19 AM   #8
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An added circ pump will allow faster water circulation , more heat faster , and with the engine on , the electric is no problem.

One sometimes overlooked use for the setup is heat,AFTER the engine is shut down.

The circ pump and box heater fan are not a large electric draw.
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