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Old 06-05-2014, 07:00 PM   #1
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What size water heater

I'm trying to decide what size of water heater to put in our trawler. We have an 8kw generator.

Size is one consideration but also using a heat exchanger or not. If yes, has anybody ever plumbed the genny to their water heater?

My initial thought is to use a 6 to 10 gallon plumbed to the genny. That way when want hot water it should heat up pretty fast with the electric element plus the heat exchanger from the genny cooling system.

Any thoughts?
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Old 06-05-2014, 08:18 PM   #2
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This was just proposed/discussed in the "What do you do about power?" thread.
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Old 06-05-2014, 08:50 PM   #3
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Thought about this myself. Decided to stick with the heat exchanger on the main engine rather than the generator. With a 1500 watt element my six gallon water heater is hot after 15 minutes. 1500/750 is well within the capacity limits of your 8kw generator even if you have two chargers and a refrigeration system going.

By sticking with the main engine when we do travel the water is hot without running the generator at all.
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Old 06-06-2014, 05:20 AM   #4
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It wouldn't be too difficult to plumb both engine and generator to a single heat exchanger. It would just require opening/closing a couple ball valves to swap over the heat source.
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Old 06-06-2014, 06:19 AM   #5
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Quote:
Originally Posted by Bay Pelican View Post
Thought about this myself. Decided to stick with the heat exchanger on the main engine rather than the generator. With a 1500 watt element my six gallon water heater is hot after 15 minutes. 1500/750 is well within the capacity limits of your 8kw generator even if you have two chargers and a refrigeration system going.

By sticking with the main engine when we do travel the water is hot without running the generator at all.
What size tank to you have? 15 minutes is fine by me. That's a reasonable recovery time.

Right now I have a 20 Gal Raritan with a 1200 watt element and it's recovery is about 40 minutes.
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Old 06-06-2014, 06:21 AM   #6
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It wouldn't be too difficult to plumb both engine and generator to a single heat exchanger. It would just require opening/closing a couple ball valves to swap over the heat source.
That's crossed my mind too.

One setup for extended anchoring, the other for when underway most of the time.
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Old 06-06-2014, 06:56 AM   #7
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It wouldn't be too difficult to plumb both engine and generator to a single heat exchanger. It would just require opening/closing a couple ball valves to swap over the heat source.

Perhaps but it would be better to install 2 FW heaters instead. No cross contamination from the mixed cooling systems and the ability to doubble the load on the noisemaker as desired .

DC solenoid valves could make heater selection a remote operation.
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Old 06-06-2014, 07:10 AM   #8
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It wouldn't be too difficult to plumb both engine and generator to a single heat exchanger. It would just require opening/closing a couple ball valves to swap over the heat source.

Perhaps but it would be better to install 2 FW heaters instead. No cross contamination from the mixed cooling systems and the ability to doubble the load on the noisemaker as desired .

DC solenoid valves could make heater selection a remote operation.
Interesting thoughts.

I saw that Isotherm has tanks that cancan have 2 heat exchanger loops. I could use the genny on one and one of the mains on the other. They also have optional larger elements up to 3kw. I'm thinking that a 10 gallon equipped like that would heat up in no time.
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Old 06-06-2014, 07:38 AM   #9
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What size tank to you have? 15 minutes is fine by me. That's a reasonable recovery time.

Right now I have a 20 Gal Raritan with a 1200 watt element and it's recovery is about 40 minutes.
Six gallon tank with a 1500 watt element. Very hot (too hot for non-mixed water) after 15 minutes.
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Old 06-06-2014, 07:41 AM   #10
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It wouldn't be too difficult to plumb both engine and generator to a single heat exchanger. It would just require opening/closing a couple ball valves to swap over the heat source.

Perhaps but it would be better to install 2 FW heaters instead. No cross contamination from the mixed cooling systems and the ability to doubble the load on the noisemaker as desired .

Several years ago I asked Bob Smith about doing this with my Lehman and my Westerbeke generator. He was adamant in his opposition. The cross contamination of the cooling liquid was his concern.
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Old 06-06-2014, 08:51 AM   #11
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One of those cases where...yeah...better not to for that million to one issue.

But realistically, keep your coolants clean and fresh of the same kind and are the 2 engines gonna know or care?

I would think that a person that goes from anchorage to anchorage every couple of weeks, separated by several days chugging along on the main....it may not be such a bad set up.

Sure things can go wrong...but time after time people here talk about lack of understanding or maintaining a system is the issue...not necessarily the setup.

Then again..if running the genset..why just not use the electric element????... most gensets die from under use not overuse.
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Old 06-06-2014, 08:55 AM   #12
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Six gallon tank with a 1500 watt element. Very hot (too hot for non-mixed water) after 15 minutes.
My experience too....and opinion that depending on boat, people and lifestyle....recovery time can be as important as quantity.
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Old 06-06-2014, 09:48 AM   #13
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It wouldn't be too difficult to plumb both engine and generator to a single heat exchanger. It would just require opening/closing a couple ball valves to swap over the heat source.
I wouldn't suggest it for a person who doesn't fully understand the flow process of their system, or someone who would rather spend the money on another heat exchanger.

Its just what I would do. To avoid the possibility of leaving both valves open, it would be best to use a 3 way ball valve. The risks are easily managed.
Here's one that you could even lock out.

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Old 06-06-2014, 09:58 AM   #14
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Quote:
Originally Posted by Rduval View Post
I'm trying to decide what size of water heater to put in our trawler. We have an 8kw generator.

Size is one consideration but also using a heat exchanger or not. If yes, has anybody ever plumbed the genny to their water heater?

My initial thought is to use a 6 to 10 gallon plumbed to the genny. That way when want hot water it should heat up pretty fast with the electric element plus the heat exchanger from the genny cooling system.

Any thoughts?
To answer the question regarding size...

We have had a 6 gallon unit on smaller boats and found it to be adequate for showering one person. Then let it heat back up and another person showers.

On our current boat we have a 20 gallon unit that uses electric and main engine heating. We've never run out of hot water, even with two people showering during a short time frame.
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Old 06-06-2014, 11:45 AM   #15
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What size hot water heater?

This thread recently talked about water heater size and also using the generator's heat exchanger.
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Old 06-06-2014, 01:54 PM   #16
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What size hot water heater?

This thread recently talked about water heater size and also using the generator's heat exchanger.
Maybe the two threads should be merged. Use this thread's title so nobody has to ask "why would you need to heat HOT water?"
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Old 06-06-2014, 04:22 PM   #17
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Relative to a main propulsion engine, I am not sure the genset generates enough heat to make the plumbing job worthwhile. Heating water is one way to help fully load the genset so if running the gennie for battery charging anyway, no real motivation for reducing the electrical draw by using the genie's coolant heat as well. I'd rather go with a larger volume heater, heated primarily off the main engine(s) and then use the electric heating circuit to load up the genset.
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Old 06-07-2014, 02:49 AM   #18
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Tankless heater is the way to go.
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Old 06-07-2014, 06:51 AM   #19
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Six gallon tank with a 1500 watt element. Very hot (too hot for non-mixed water) after 15 minutes.

IF that is a problem most units have an adjustable thermostat , get out the screwdriver.

Engine or noisemaker HW will usually be near 180F ,not adjustable, enough for caution or a tempering valve in the system.ESP if kids visit!

Folks that run one or more air cond from the noisemaker frequently would appreciate taking 1.5KW of heating load off the unit with a simple heat exchanger loop..

Electric Tankless takes far too many amps , frequently beyond the ENTIRE power output from a smallish noisemaker.

Propane tankless works fine , with the right shower valve setup.
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Old 06-08-2014, 12:04 PM   #20
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Thanks all, I think I'll stick with the 20Gal Raritan I have now and plumb it to one of the main engines and see how it goes this season.
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