Cabin heat from engine

[Pizzazz]

I am considering installing a heating system on my 31' sailboat. Since I sail in California, the primary use of the system will be to raise the temperature by 10-15 degrees F during the night while at anchor or a mooring (mostly for the kids). I ruled out non-diesel heaters (carry separate fuel, exhaust piping, too much effort for little gain). Diesel heaters make sense but they are expensive, noisy and there is always the question why carry a separate engine when there is the main propulsion engine that sits mostly unused.

So I came up with the following system. I have a 13 hp Yanmar diesel with a heat exchanger and a 6 gallon hot water heater. I would install an additional 40 gallon water tank under the starboard settee in series with the water heater, a couple of radiators and a small water circulation pump. Running the engine under way will heat 46 gallons of water to, say 140F. Assuming I target 70F cabin temperature, I would have about 27,000 BTUs stored in the system which is equivalent to running a typical household 1,500W space heater for about 6 hours (much more than I typically need). Then, while at anchor I could just circulate the hot water with the small inline pump.

Do you think this would work? On the plus side, I see a simple and cheap installation (just hoses and the water tank), increased tankage (I have always wanted more fresh water), convection heating (better since you do not lose the heat if you open the hatch for a few minutes), the option to use the water heater when docked with AC to warm the boat without running the 1500W heater all night long.

On the minus side, the engine will heat the water under load but likely not at idle. One way to fix this is to install a bypass hose from the water pump to the engine exhaust (either manual or thermostat driven) that will bypass the raw water cooling circuit until the 46 gallons of water is heated, then will open the raw cooling water loop - kind of dangerous but doable. I have not done the calculations but I believe the 13 hp engine will heat 46 gallons of water rather quickly. I do not think the additional tank needs to be insulated but this should also be a consideration.

Any feedback is much appreciated.

Pizzazz

[Lepke]

It will pay to insulate the tank. HW tanks have poor insulation. I have a 50 gallon. Turning it off when there is no need saves about $30-40 a month in port. Plumbing draws the heat out even when no water is moving unless it's well insulated.
The tank water won't be drinkable if the plumbing/engine ever had antifreeze.
I have a hydronic system with a boiler and 10 gallon tank. Without reheating, the tank last about 2 hours heating 1 cabin. So maybe you'd get overnight with 40 gallons. Insulating, the boat, plumbing, boiler all made big differences for me.

[Pizzazz]

Thank you for sharing your experience. Very helpful. I discussed this system with someone at Raritan today and came up with some improvements. Since the Raritan heater employs an internal heat exchanger, I will just tee off the hot water from there. This way the water in the 40 gallon tank will stay potable (it never touches the engine coolant). Basically, all I am doing is expanding the 6 gallon water heater to 46 gallon with an additional tank. I will need to install some check valves but that is relatively easy.

The key to maximizing the performance of the system is the maximum achievable water temperature (may be I can go do 160F), insulation as you suggest and the efficiency of the heat transfer from the engine to the Raritan heater. The last one depends heavily on the ability to bypass the engine heat exchanger raw water circuit. Ideally, this would be achieved with an adjustable thermostat which will open the raw water circuit once the hot water in the heating circuit reaches 160F or whatever I decide to use. Do you know what is the max hot water temperature you are running your boiler at?

[Snowpetrel]

I wouldnt want to drink the water after its been heated, to much risk of nasty bacteria breeding inside it as it heats up and cools down. But I think its a good solution to storing and using some of the waste engine heat. Ive often wondered if heating a diesel tank would also work as themal heat storage, or would the diesel be degraded by the heat?

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[El Pinguino]

After a day of motoring in a cold climate I just open up the engine room so that big hot bit of iron can share its warmth with the rest of us. Bonzer place to dry gloves as well....

Mind you I consider 12C/54F to be ideal... 70F is positively tropical...

[FSMike]

Was on a boat once with a settee across from the oven. Owner turned on the oven when he cooked dinner up to 300* IIRC and let it cook with a couple of feet of heavy chain inside it. When he was through cleaning up after dinner, which is when it was usually getting cold, he turned off the oven and opened its door. The chain radiated heat for hours.

[treefarmer]

have you considered a small solid fuel stove?
a few small peices of some form of solid fuel burning for a short period would not only warm the bodies but also the souls.
fair winds

[a64pilot]

Your idea will work if your willing to add the complication.
You do not want to turn off the raw water though, it's needed to cool the exhaust as I'm sure you don't want to dry stack a Sailboat, but other than that, I see no problem.
I bet though that you will have to run your engine longer than you think you will.

The water will still be potable I believe just as the water coming out of a regular hot water heater is, all your doing is expanding your hot water heater to 46 gls and tieing it to a bus heater or similar, correct? You will still use hot water every now and again for washing hands or something, thereby continuously replacing the water, keeping it from becoming stagnant?

[a64pilot]

If you live at a dock then of course you can start out with hot water.
I have found that if my water heater is hot already from being heated electrically, the engine warms up much faster as of course the engine pulls heat from the heater, not the other way around, so now if I know we are going out in a couple of hours, I turn the hotwater heater on.

[alctel]

Originally Posted by Pizzazz

I am considering installing a heating system on my 31' sailboat. Since I sail in California, the primary use of the system will be to raise the temperature by 10-15 degrees F during the night while at anchor or a mooring (mostly for the kids). I ruled out non-diesel heaters (carry separate fuel, exhaust piping, too much effort for little gain). Diesel heaters make sense but they are expensive, noisy and there is always the question why carry a separate engine when there is the main propulsion engine that sits mostly unused.

Have you checked out the drip diesel heaters like the newport? Quiet, warm, don't draw any power (aside from a 12v fan) and the fan gives amazing cozy atmosphere to the cabin

[rognvald]

Pizazz,
As a small boat owner myself, do you think this is a bit of overkill for a 31 foot boat ,in your proposed system, with the added complexity of pumps, radiators, plumbing, and tankage? Many Americans are wary of diesel heaters but European sailors and fishermen have been using them for many years with a great track record. If you use a floor-mounted Reflex unit from Denmark(Model 66M), you only need an exhaust pipe and a flue(no inlet pipe). They are bullet-proof, dependable and well-made and will perform up to a 15 degree heel. Here's a site for some additional information. Good luck and safe sailing.
Toplicht › Online-Shop › heating & cooking › diesel heater

[Pizzazz]

That is the idea, to expand hot water storage from 6 to 46 gallons and circulate the water from the bigger tank through the smaller tank heat exchanger. I could even install a valve to separate the two tanks once warmed up so that I get hot water from the smaller tank and heat from the larger tank (avoiding the cold/hot mixing as long as possible).

Regarding the raw water bypass, I will just bypass the engine heat exchanger and will feed the raw water from the pump into the mixing elbow to allow the cooling of the exhaust.

I see now the complication of having to operate two valves to charge the system but I still like the concept of capturing excess engine heat vs. producing new heat in a separate heater or stove. Next, I will do a test run with the raw water bypass to see how long it takes to warm up the 6 gallon tank on idle speed before going ahead.

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[zeehag]

for my smaller boats , in winter i used oil lamps with excellent results in cabin heating in so cal.
they are pretty also.

[1affiah]

Another consideration is weight. How will your boat handle with another 350++ pounds of water, plumbing, etc? Maybe list to one side, or "heavy in the butt"?

[Stu Jackson]

Originally Posted by Pizzazz

Regarding the raw water bypass, I will just bypass the engine heat exchanger and will feed the raw water from the pump into the mixing elbow to allow the cooling of the exhaust.

This is possibly the very worst idea I have ever read on a boating forum and I've been participating for over 15 years.

Why?

What's your engine worth to you? They are VERY expensive to replace. VERY.

Never interrupt the exhaust cooling system. Never.

I am an HVAC engineer, so I know about heat transfer.

If you want hot water for a bus heater when you're motoring, do this:

Cabin Heater - c34.org

If you want heat when the engine is off, buy a catalytic propane heater or a diesel heater.

Adding that additional hot water will take over four hours to heat from your engine. Why? 'Cuz it takes almost a half an hour to heat six gallons when your engine is at cruising speed (this is empirical from 18 years of experience). Do the math. 6=1/2 hour. 46/6=7.666 half hours.

What's your entire engine worth to you?

And even if you do manage to store it, it won't last as long as you think, because HVAC heating systems are based on the continual heating of the medium to maintain the basic water temperature. You'll be starting out with a full heated tank, but it's temperature will drop as it's used for heating. That's why the water in water heaters gets cold after it's been used up: the engine is OFF.

I rarely get this negative about any issues that come up on a boating forum, but in this case I'm trying to save you from yourself, since you seem to have worked hard to ignore the previous replies and warnings.