Adding engine heat for hot water

[Seevee]

Anyone converted their water heater to run on engine heat as well as electric?

That's seems to be quite popular on a lot of boats.

I've got a 375hp Yanmar. Need to check the heater.

If you've done this mod, please comment.

 

[Wxx3]

My Raritan comes with inlet and outlet for the heater hose connection.
Hardly a conversion.

 

[psneeld]

Mine is heated by engine coolant.

 

[johnrupp]

Most marine water heaters come with a heat exchanger built in for this purpose. Great to have hot water while and after motoring. If you hook yours up put a tempering/mixing valve on the outlet. Set valve to 120/140 degrees. Without valve your hot water will be at temperature of engine coolant. 180 plus degrees. This can cause severe burns.

 

[DavidM]

Unlike sailboats, most trawlers and i think all Mainships were delivered from the factory without the engine's coolant system hooked up to the water heater.

It is fairly easy to hook up your engine's coolant system to the hot water heater. I suspect you have the Yanmar 6LY engine. Look at the attached pic which gives the location of the fittings on the engine. These are BSP or JIS spec threads, but US 3/8" NPT male to hose barb fittings are close enough. Remove the plugs and replace with the hose barb adapters.

Then run 3/8" heater hose from the fittings to the heater coolant inlet and outlet hose barbs and hose clamp both ends. Refill with antfreeze and start the engine. Let it run with the coolant fill cap off and as it heats up add coolant. Sometimes you have to go out and really put a load on the engine to get all of the air out. Feel the new hoses and when they are hot then the air is out and coolant is circulating. Replace the filler cap.

As others have said you can add an anti-scald valve to temper the very hot water temperature. They are available at home stores.

David

 

[kthoennes]

Our 1996 Mainship 370 came standard with engine-heated hot water, but we have the fiberglass tennis shoe model, the floating Clorox bottle model, not the trawler style so maybe the trawlers didn't.

 

[Seevee]

Great info, thanks!
For the anti scald valve, assume that bypasses the flow into the heater when it gets to xxx temp?

Can someone post a link to one that would be similar to what I'd need?

 

[Brooksie]

The anti-scald or tempering valve referred to above does not work by stopping the coolant flow to the heater rather by automaticly mixing water from your cold water tank to maintain the setpoint temperature of the hot water.

These work great in shoreside use because there is an unlimited supply of cold water to temper the hot with. Aboard however, the cold water is at best room temperature or if the tank is located in the engine space, the cold water can be,well, hot. Thus the tempering valve does not work well aboard.

There are valves, non-electric, that work as you describe. Defoss/Danfoss is a large supplier and there are always several on ebay for resonable $

 

[78puget-trawler]

Have shoreside and engine source as well.

 

[Insequent]

My hotwater has 3 heat options: AC from shorepower, engine coolant & heat exchanger and Webasto hydronic system & heat exchanger. Not difficult to configure.

 

[FF]

"For the anti scald valve, assume that bypasses the flow into the heater when it gets to xxx temp?"

Factory valves on the heater usually simply shut down the circ water to the heater.

An anti scald valve (not a tempering valve) will also shut off the hot water if it can not be delivered at the temperature selected due to a lack of cold to mix.

You want an anti scald valve that works for the entire fresh water system.

 

[psneeld]

There are valves that regulate coolant water into the heater based on the hot water temperature inside the tank. Had one on my last water heater.

Then there are mixing valves that are on my new one...this is what the manufavturer says..."Every Isotemp tank features a safety mixing valve that regulates the temperature of the water coming out of the tank so that water heated to 160+ degrees will not scald boat owners or their guests".

 

[Larry M]

Great info, thanks!
For the anti scald valve, assume that bypasses the flow into the heater when it gets to xxx temp?

Can someone post a link to one that would be similar to what I'd need?

Here are a few Sure Marine has listed.

Honeywell AM100-1LF Sparco Thermostatic Mix Valve, 1/2" Female NPT

Honeywell AM100-UPEX-1 Sparco Thermostatic Mix Valve, 1/2" PEX Fittings

 

[rwidman]

Unlike sailboats, most trawlers and i think all Mainships were delivered from the factory without the engine's coolant system hooked up to the water heater...........

I'm not too sure about that. I've only owned two boats with water heaters but both used engine coolant to heat water while underway.

If the water heater has the heat exchanger, using excess engine heat provides an excellent source of hot water.

 

[bayview]

The good thing about a faucet mixing valve is that because the tank water gets so hot when mixed with cold water it becomes the equivalent of a much larger tank since so little hot is used.

The mixing valve for the entire hot water system seems a good idea.

Each engine maker has recommended ports for this use. generally it is important to use the proper outlets.

 

[rwidman]

The good thing about a faucet mixing valve is that because the tank water gets so hot when mixed with cold water it becomes the equivalent of a much larger tank since so little hot is used.

This is true and a much better solution than limiting the flow of engine coolant.

As a practical matter, we seldom have anyone on our boat besides ourselves and when we do, it would be rare for them to use hot water. We don't have the recommended mixing valve but we are cautious with the hot water, knowing how hot it can be. If we were travelling with guests or children, the mixing valve would be important.

 

[CaptTom]

Here are a few Sure Marine has listed.

Honeywell AM100-1LF Sparco Thermostatic Mix Valve, 1/2" Female NPT

Honeywell AM100-UPEX-1 Sparco Thermostatic Mix Valve, 1/2" PEX Fittings

This is similar to the one I use, both at home and on the boat. Works great. Frankly you can accomplish the same thing right at the faucet, just mix hot & cold to your liking. Then you have the option to hit those greasy dishes with the super-hot stuff direct from the water heater.

We went with the mixing valve when we started having friends with children on board. Adults can figure out how to work a faucet, or deal with the consequences. But I don't want to any kids hurt on my boat!

 

[kchace]

I know my trawler came with engine coolant to hot water heat exchanger factory installed.

As others have said, a mixing valve is crucial and having that setup with water heated to engine coolant temperature allows the hot water to stretch much further.

Ken

 

[psneeld]

Of all the ways a kid can hurt themselves on a boat, I see my own kids who grew uo on boats who never scalded themselves and now my grandkids who I dont see left unsupervised in the shower/bath that hot water is an issue.

While the engine heat can be a lot, the hot water on my boat heated from the engine is only 15 degrees or so above dockside.

Those that run diesels up above 190 or 200, then I can see the worry.

 

[yachtbrokerguy]

A few engine mechanics have said to me that they do not like to see the engine coolant running to a hot water heater due the possibility of failure of one of these hoses. If you overheat a very expensive diesel engine the cost to rebuild is very high. If you are running a generator anyway like we do in Florida most of the time for air conditioning, they say it is not worth the risk for hot water. Shut off valves might be a consideration to have on the extra coolant lines closed when not needed.

 

[porman]

Our Mainship came with engine heated hot water. However I'm in the process of installing a Webasto hydronic system and now run the engine coolant through a heat exchanger that heats the water heater. I also installed one of the Honeywell valves to regulate the hot water temperature. Sure Marine has been assisting with this and they are the best to work with.

 

[Seevee]

A few engine mechanics have said to me that they do not like to see the engine coolant running to a hot water heater due the possibility of failure of one of these hoses. If you overheat a very expensive diesel engine the cost to rebuild is very high. If you are running a generator anyway like we do in Florida most of the time for air conditioning, they say it is not worth the risk for hot water. Shut off valves might be a consideration to have on the extra coolant lines closed when not needed.

Very good point, but with a proper set up and hoses check, as well as the hot water heater, how high is the risk? I'd hope very low.

I've had several with my smaller boats without issue. I did replace a heater once because of rust, but never had a coolant failure with the engine.

However, not having hot water for a quick rinse off while or after running for awhile is priceless, and cranking the genny would be a pain.

Any others had failures?

 

[psneeld]

Very good point, but with a proper set up and hoses check, as well as the hot water heater, how high is the risk? I'd hope very low.

I've had several with my smaller boats without issue. I did replace a heater once because of rust, but never had a coolant failure with the engine.

However, not having hot water for a quick rinse off while or after running for awhile is priceless, and cranking the genny would be a pain.

Any others had failures?

Not very high....personally never heard of engine damage from a water heater plumbing problem.

Not saying it doesnt happen, but with proper install andgood PM...a lot more to worry about.

However, risk management teaches us that if you have to run a generator a bunch...that might be the better way.

 

[AusCan]

A few engine mechanics have said to me that they do not like to see the engine coolant running to a hot water heater due the possibility of failure of one of these hoses. If you overheat a very expensive diesel engine the cost to rebuild is very high. If you are running a generator anyway like we do in Florida most of the time for air conditioning, they say it is not worth the risk for hot water. Shut off valves might be a consideration to have on the extra coolant lines closed when not needed.

Good idea. I've installed valves to isolate engine coolant from the water heater along with a bypass valve.
This was after one of my first trips in rough water when my engine overheated due to the hot water tank shifting slightly and kinking the coolant hose.

The valves are also useful as manual temperature control for the hot water.

 

[rwidman]

A few engine mechanics have said to me that they do not like to see the engine coolant running to a hot water heater due the possibility of failure of one of these hoses. .........

If this was really a risk, you wouldn't see heat exchangers in water heaters and boat manufacturers wouldn't manufacture them this way. The risk of a hose breaking is pretty slim if you use quality hose suitable for the purpose and route it in a safe manner.

There's probably a greater risk of the heat exchanger failing and contaminating the potable water with engine coolant but that's still a very, very small risk. There are millions of boats out there with this system and not a lot of reports of failure.

 

[Lepke]

I have a hydronic system. When running I can use the engine heat from one or both engines, my wood stove or pellet stove with a series of valves to send heated water thru the boiler. All is plumbed with pipe except short hose connections to the engines. Valves are installed so the system can be isolated in sections in case of a leak. The boiler is diesel fired and can use more than 5 gallons a day in really cold weather. That's why the pellet stove.
I found diesel the most expensive follow by electricity, wood (unless I cut, split and haul) and then pellets. When you figure the chain saw, vehicle and time, wood isn't cheap.

 

[CaptTom]

A few engine mechanics have said to me that they do not like to see the engine coolant running to a hot water heater due the possibility of failure of one of these hoses. If you overheat a very expensive diesel engine the cost to rebuild is very high. If you are running a generator anyway like we do in Florida most of the time for air conditioning, they say it is not worth the risk for hot water. Shut off valves might be a consideration to have on the extra coolant lines closed when not needed.

Very good point, but with a proper set up and hoses check, as well as the hot water heater, how high is the risk? I'd hope very low.

Any others had failures?

Certainly if you run the genset all the time anyway, the engine coolant loop would be unnecessary. Not the way I cruise, and not the way I want to cruise.

I did once have a hose fail in a water heater coolant loop, and it did drain most of the coolant into the bilge. A support had come undone and the hose fell to where it was chafing on the tiller arm.

Not a big deal. I could smell it right away, and was able to patch it up, top off the coolant and be on my way.

Hopefully you'd always have a way to detect an overheat condition, even if you weren't where you could smell the anti-freeze, long before the engine was destroyed.

I just don't see any negatives. I'd plumb in shutoff valves if I was that worried about it. I have one installed, only because I was working on that area anyway. Putting in another one at the other end of the run hasn't made it to the top of my list yet. Come to think of it, it's not even ON the list at this point.

 

[sunchaser]

A few engine mechanics have said to me that they do not like to see the engine coolant running to a hot water heater due the possibility of failure of one of these hoses. If you overheat a very expensive diesel engine the cost to rebuild is very high. If you are running a generator anyway like we do in Florida most of the time for air conditioning, they say it is not worth the risk for hot water. Shut off valves might be a consideration to have on the extra coolant lines closed when not needed.

Tucker

Yes a hose failure can cause damage. But, given the number of coolant hoses around my motors they all can . Just part of the ER checks when under way. You're spot on with the shut off valve point. This is my approach. But our valves are easily accessible.

I have not jumped on the tempering valve band wagon. But I do tell guests that the forward head and shower have very hot water. Kinda like don't walk in the street barefoot on an AZ summer day. Even the two year olds get it.

 

[bayview]

All vehicles have engine heat systems and we dont worry about them. Surely boat owners inspect their ER more than their cars.

 

[Xsbank]

My boat has a dedicated heat exchanger, then the loop to the water tank is completely separate. If the loop fails, no effect on the engine. The water circulates just fine by thermal loop, there is no pump but I always have plenty of hot water. This is definitely belt-and-suspenders, I will probably remove the heat exchanger and sell it! Too much plumbing!