Can you use your hot water heater to heat your boat?

VisionPNW

VisionPNW

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Dec 4, 2017
79
Hunter 466 Seattle
I have a hydronic system with a diesel powered Webasto furnace. It heats up the hot water to scalding hot and the boat gets really toasty. I'm a liveaboard in the PNW and coming up on colder months so I'm just wondering about the feasibility of using my electric hot water heater instead of the diesel furnace. Has anybody tried this? I think I could probably hook up the circulation pump to work manually or even via thermostat. I'd love to hear what you all think. It might even be cheaper than diesel (and far more convenient than hauling diesel down the dock all the time.)
 
907Juice

907Juice

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Apr 7, 2016
184
Beneteau First 305 Seward, Alaska
I have a heater that works off the engine. I’ll get you a pic this weekend. This’ll be my first winter with it so I don’t know how well it works.
 
Allan12210

Allan12210

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Jan 22, 2008
1,654
Hunter 34 Alameda CA
I asked this question a couple of years ago. Basicly, we have a 1200 Watt heat source while hooked up to shore power. I thought about a circulation system of the hot water through a heater core or radiator with a small fan behind it. This could blow warm air into the boat and a thermostat would cycle the circulation pump on and off. I've seen bits and pieces on Amazon but haven't tried to cobble anything together. There are systems like that for big rig trucks but expensive.
 
justsomeguy

justsomeguy

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Feb 20, 2011
7,993
Island Packet 35 Tucson, AZ/San Carlos, MX
I'm not sure your water heater can put out as much heat as efficiently as the diesel, but if your electric bill is a constant, it may take the edge off of cold mornings.
 
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kloudie1

kloudie1

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Nov 6, 2006
9,894
Hunter 34 Mandeville Louisiana
Yes you can, but the water heater would limit your heat output a lot compared to diesel.. The heater (assuming a normal 6 gallon 120volt heater) can't generate more than three or four thousand BTU .. even the smallest Webasto is 2-4 times better at making heat..
 
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VisionPNW

VisionPNW

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Dec 4, 2017
79
Hunter 466 Seattle
Allan, since I already have the hydronic system, I have the radiators and fans plumbed in and ready to go. I would just need to modify the circulation pump to circulate coolant through the system when the diesel furnace isn't running.
 
VisionPNW

VisionPNW

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Dec 4, 2017
79
Hunter 466 Seattle
kloudie1 said:
The heater can't generate more than three or four thousand BTU
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Thanks for putting this in persepctive. I didn't think about it in terms of heat output capability. I think it would be less efficient than a regular 1500W heater and far more complex.
 
Ron20324

Ron20324

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Jan 22, 2008
8,050
Beneteau 323 Annapolis MD
Charlie Jones s/v Tehani said:
being a smart ass- why would you need to heat HOT water??. Most heat cold water to MAKE it hot. I'll go to my room now :)
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There's always a smart-ass n the room. Actually, if the water in the heater tank is, say 119, the thermostat will heat it to it's 120-140 rating. So, the water heater is, indeed, heating hot water. Now, will you please go to your room?
 
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mz4wheeler

mz4wheeler

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Mar 11, 2015
357
Hunter 33.5 Tacoma, WA
justsomeguy said:
I'm not sure your water heater can put out as much heat as efficiently as the diesel, but if your electric bill is a constant, it may take the edge off of cold mornings.
Click to expand
> but if your electric bill is a constant

But you're electric bill will no longer be constant. It will be MUCH higher now that you're circulating hot water around your boat (which cools it), and force the hot water tank elements to stay on much longer.
 
907Juice

907Juice

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Apr 7, 2016
184
Beneteau First 305 Seward, Alaska
The heater I posted above is off your engine and not water heater. I should work great when the engine is running. But I doubt it will be any cheaper to operate than your furnace.
 
D

dlochner

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Jan 11, 2014
11,430
Sabre 362 113 Fair Haven, NY
VisionPNW said:
It heats up the hot water to scalding hot and the boat gets really toasty.
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Is there a thermostat on the heater to control the water temperature? Household boilers always have a high limit thermostat to prevent over heating. If so, turn the high limit thermostat down.
 
justsomeguy

justsomeguy

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Feb 20, 2011
7,993
Island Packet 35 Tucson, AZ/San Carlos, MX
mz4wheeler said:
> but if your electric bill is a constant

But you're electric bill will no longer be constant. It will be MUCH higher now that you're circulating hot water around your boat (which cools it), and force the hot water tank elements to stay on much longer.
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Some places, such as the docks where I'm at, charge a flat fee for electrical service. No meter at the slip.
I pay a certain amount whether juice gets used or abused. YMMV ;)
 
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NotCook

NotCook

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Dec 29, 2008
805
Treworgy 65' LOA Custom Steel Pilothouse Staysail Ketch St. Croix, Virgin Islands
VisionPNW said:
Allan, since I already have the hydronic system, I have the radiators and fans plumbed in and ready to go. I would just need to modify the circulation pump to circulate coolant through the system when the diesel furnace isn't running.
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Our Webesto diesel heater would be similar. And, our hot water heater has lines coming from the engine cooling system which flows through a heat exchange in the water heater. If you had a similar arrangement, you could tap into those lines to your diesel heater lines, and circulate through the hot water heater. Our systems poth have coolant running through them. I'n guessing yours does, too, with antifreeze in the mix. I don't see why you couldn't do it, assuming your water heater has a heat exchanger for using engine coolant already. Otherwise, I don't think you would want to run actual drinking water through your hydronic system. I assume it has to have antifreeze in it already which, of course, you wouldn't want mixed with your hot water in your water heater.
 
NotCook

NotCook

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Dec 29, 2008
805
Treworgy 65' LOA Custom Steel Pilothouse Staysail Ketch St. Croix, Virgin Islands
We've also contemplated getting a 12V heating element for our hot water heater to use as a dump load for our solar panels, replacing the 110V heating element. We would be more likely to have hot water at any given time with that arrangement. If you could have dual heating elements, you could have both, if you had solar, and heat the water with solar during the day, and only draw shore power at night.

Just curious - I'm sure it varies by what the temp is outside and what you set the thermostat to for your diesel system, but what is the fuel usage rate per hour or per 24 hour period? Inquiring minds want to know...
 
NotCook

NotCook

.
Dec 29, 2008
805
Treworgy 65' LOA Custom Steel Pilothouse Staysail Ketch St. Croix, Virgin Islands
:poke:
Skipper said:
OMG just buy a heater and plug it in./
An electric heater will only blow warm air into one area of the boat. I'm sure his diesel heater distributes the heat throughout the boat. I know that all 4 cabins in our boat are heated (with individual thermostats in each space, I might add)
by the diesel system. Not that we have EVER used it - though, when it gets below 80 here we tend to put on long pants and shirts, and use a blanket.:poke:
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