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

[SG]

Aside from the conservation of energy law less inefficiencies observations above -- i.e., you'll not get less than the capacity of. 1500 watt heater (many boats water heaters are 1250 watts), Etc. -- what would you do?: recirculate your potable water in a dedicated loop back to the hot water heater tank? You can't mix the water with something that would or could tTaint and still safely drink it. You could return it back to your water tank. Then essentially turn turn your water tanks into heat storage tanks. That would be fraught with problems.

I could go on, but I in answer to the questioned asked: practically the answer is, NO

 

[JimInPB]

I guess that you could mount the water heater near a berth & strip the insulation off the heater to let heat escape out into your sleeping area, or something like that, but I think that Skipper already hit the nail on the head. Just get a plug in electric heater. I like the oil filled type.

https://www.walmart.com/ip/Mainstay...MI3tbWsrju3QIVB1SGCh3JqwgTEAQYAyABEgIAr_D_BwE

https://www.homedepot.com/p/1500-Wa...iant-Portable-Heater-Grey-HD904-A7Q/205210318

https://www.lowes.com/pd/De-Longhi-1500-Watt-Oil-filled-Radiant-Tower-Electric-Space-Heater-with-Thermostat-Energy-Saving-Setting/50094370?cm_mmc=search_google-_-Rough Plumbing and Electrical-_-Dsa_ple_173_smart Home & Security-_-&k_clickID=4f76c467-ec88-4872-a4f5-540d14986ed3&gclid=EAIaIQobChMI3tbWsrju3QIVB1SGCh3JqwgTEAAYASAAEgK6-_D_BwE

 

[Mikem]

We use a Pelonis oil filled heater on our boat as well and it works just great. I think in the winter I set it on medium (900 watts of 600 and 1500 selections) and set the thermostat somewhere in the middle. Unless we have a really cold snap, we don't have that many days below freezing in a typical winter, the boat stays in the low to mid 50s. So when we come aboard and crank up the diesel heater (Webasto hydronic) the boat warms much quicker. Also, after docking I remove an engine panel and the heat from the engine wafts quickly through the boat.

 

[907Juice]

Also, after docking I remove an engine panel and the heat from the engine wafts quickly through the boat.

You said wafts

 

[jssailem]

water heater would limit your heat output a lot compared to diesel

@VisionPNW Kloudie is on the correct track to answer your query.
You can do what your thinking but the tools will cost you more to operate than the heat provided. This is measured in BTU’s British Thermal Units. And the cost to produce them.
Your wabasto Diesel heater produces more BTU’s per dollar of fuel than the water heater, or the engine.
The engine, while motoring about the Sound, is producing extra energy and the heater shown is able to tap into that “excess heat energy “ and redirect it to warming your cabin. Care is needed in tapping into this apparent ‘free’ heat. Your engine needs a certain amount of heat to run efficiently. Tap too much off be water heating or cabin heating and your Diesel engine starts to not run effectively and now your impacting the reason you started the motor, to get from point A to point B.
It is a balancing act of compromise.
Best resource to warm your toes on the boat from December to February a Diesel forced air heater or boiler designed for the task. Most fun, a significant partner under blankets.

 

[Skipper]

But we're not talking about your boat. We're talking about his boat, a 32 footer.
The WM, or other same heater under other brands, will do a fabulous job warming a 32 foot cabin. 1500 watts and an efficient safe design. Even in freezing temps, 30 minutes and you're settled. An hour and you're toasty.
The forward cabin might still be chilly, but when you go to bed you can move the heater. There are outlets forward too. Or sleep in the salon converted double.
I was in Annapolis in a 30 footer for years of winter weekends afloat, and the heater was perfect. In summer, it stows in a cabinet.
Can't be easier.

 

[VisionPNW]

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.

I have the same system that has a loop of hoses running from the diesel furnace, through radiators, and the heat exchanger on my water heater. Those hoses (carrying antifreeze) also connect to the engine/water heater loop so I have engine heat as on option to heat my hot water (and theoretically the whole boat) as well.

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...

Currently I don't have a thermostat setup. The furnace is run by a timer and consumes 0.16 gal/hr. In the coldest of winter in the Seattle area, I could see using a gallon or so a day. This adds up quick and I've run the tank dry a few times which we all know how difficult it is losing the prime and having to bleed and reprime anything diesel powered. I've never run out at a convenient time either! 5 or more gallons of diesel a week also adds up quickly. I was just looking to expand my options.
Leaving a 1500w heater on 24 hrs a day would only cost $3.85 a day, but running the diesel furnace (on full time) would be $11.50.

I think I'll be doing something like a hybrid of both and only using the diesel furnace to get me going up to temp and a small heater to maintain.

 

[Stu Jackson]

Aside from the conservation of energy law less inefficiencies observations above -- i.e., you'll not get less than the capacity of. 1500 watt heater (many boats water heaters are 1250 watts), Etc. -- what would you do?: recirculate your potable water in a dedicated loop back to the hot water heater tank? You can't mix the water with something that would or could tTaint and still safely drink it. You could return it back to your water tank. Then essentially turn turn your water tanks into heat storage tanks. That would be fraught with problems.

I could go on, but I in answer to the questioned asked: practically the answer is, NO

This is the correct engineering answer based on the OP. The engine coolant is used to heat the domestic drinkable water, two separate circuits.

Hello Below discussed his system a week or so ago: diesel hydronic heater tapped into engine coolant circuit with fan powered radiators. Heats the boat and makes hot water. This is the choice one makes between an air system which heats the boat but not the domestic water, and hydronic.

 

[Hello Below]

I think I'll be doing something like a hybrid of both and only using the diesel furnace to get me going up to temp and a small heater to maintain.

Why not a hybrid hot air furnace? Is there such an animal? Is there a marine hot air diesel furnace on the market that also has an electric element in it. Kind of like a WM (Caframo) heater build in. Thus, when shore power is available this system would use the existing duct work to distribute the hot air. Much less heat than a typical diesel furnace (15,000+ BTUs vs 1,500W = 5,000 BTUs) but possibly much less cost as VisionPNW has detailed.

 

[Gunni]

We are about 90 days out from the first boat fire caused by boat heaters. Typically a live aboard in some ancient boat with bad wiring or a space heater and an absentee owner.
https://www.tradeonlytoday.com/industry-news/fire-destroys-boats-annapolis-marina
https://www.wbaltv.com/article/crews-battle-boat-fire-in-annapolis/7098420
https://www.spinsheet.com/butler-marina-boat-fire

Sometimes it is a petrol heater:
http://www.capitalgazette.com/news/ac-cn-boat-fire-river-20180608-story.html

 

[Skipper]

We are about 90 days out from the first boat fire caused by boat heaters. Typically a live aboard in some ancient boat with bad wiring or a space heater and an absentee owner.
https://www.tradeonlytoday.com/industry-news/fire-destroys-boats-annapolis-marina
https://www.wbaltv.com/article/crews-battle-boat-fire-in-annapolis/7098420
https://www.spinsheet.com/butler-marina-boat-fire

Sometimes it is a petrol heater:
http://www.capitalgazette.com/news/ac-cn-boat-fire-river-20180608-story.html

Nowhere in the Annapolis article does it state the cause.
In most cases with an electric heater, it's the boat's corroded resistive wiring that developes heat and then fire.
Even the WM video on their heaters states that they are designed for unattended use. If it's a heater failure in a fire it's likely a non marine cheapo.
Although I'd never leave any heater on high unattended. I used to leave the WM on low 600 watts in the antifreeze mode on a timer for nighttime. That's about it.
Anyway the OP was not about unattended heating so I'm on a tangent...

 

[Ken Cross]

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.

Actually, resistance heat is resistance heat. There is no efficiency improvement to be had with a different resistance heating element. The difference is only how many heating elements you have onboard. It might be a good idea to check how many watts or BTUs the water heater puts out. (1 watt = 3.412 BTU. Watts and BTU are the same things.) If it's an adequate amount of heat it should work fine. Now if your water heater transfers heat outside the boat you loose efficiency only because you are throwing away heat you just paid for. One advantage of using your water heater - safety. It can't light anything on fire as a space heater can.

Ken

 

[Ken Cross]

Aside from the conservation of energy law less inefficiencies observations above -- i.e., you'll not get less than the capacity of. 1500 watt heater (many boats water heaters are 1250 watts), Etc. -- what would you do?: recirculate your potable water in a dedicated loop back to the hot water heater tank? You can't mix the water with something that would or could tTaint and still safely drink it. You could return it back to your water tank. Then essentially turn turn your water tanks into heat storage tanks. That would be fraught with problems.

I could go on, but I in answer to the questioned asked: practically the answer is, NO

There are 2 ways to address this. Recirculate the potable water or connect it to the engine coolant loop with valves. Now you can pull heat out the same way the engine puts it in. both methods would require a recirculation pump, however.

Ken

 

[All U Get]

I'm glad no one suggested burning the compost from their composting toilet. Didn't Roger Long have a wood stove in his boat?

 

[Gunni]

TomY has a wood stove in his boat! He posted up a picture the other day.

 

[catalanc]

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

I asked this very question a while ago and was sternly reprimanded. I am only now peeking out of my room ....

 

[NotCook]

what would you do?: recirculate your potable water in a dedicated loop back to the hot water heater tank? You can't mix the water with something that would or could tTaint and still safely drink it. You could return it back to your water tank.

No, you wouldn't want to do either of these, as you point out. That would be the role of a heat exchanger in the hot water heater. If connected to the engine cooling system, it would already have one in place.

 

[NotCook]

I'm glad no one suggested burning the compost from their composting toilet.

eeeeeeeeewwwweee!

 

[NotCook]

Those hoses (carrying antifreeze) also connect to the engine/water heater loop so I have engine heat as on option to heat my hot water (and theoretically the whole boat) as well.

And presumably if the water heater was plugged into shore power, it would also provide heat through the diesel heater to the whole boat. But, as others have pointed out, it probably would be less efficient than an electric heater. On the otherhand, as you pointed out, the diesel heater cost was about three times the cost of electricity, so might be worth an experiment. Does your diesel system have a separate control for the pump for the heated coolant through the system, or is it only running when the diesel heater is heating?

 

[VisionPNW]

Does your diesel system have a separate control for the pump for the heated coolant through the system, or is it only running when the diesel heater is heating?

Only when the heater is running, but I was thinking of putting in a manual override switch if I decided to go this route.