Heating Hot Water From Engine

I'm attempting to connect my 3208T to a new water heater that has a coil for this. Has anyone had a problem with this and where would you tap off the engine?

I did a search on boatdiesel and the attached pic is what I found. I don't know that engine so I can't say if it is right. The supply port should be on the thermostat housing. Don't know where the return is plumbed.

David

It is right under the heat exchanger on the front of my 3208 T/A. Need a pic?

djmarchand said:

I did a search on boatdiesel and the attached pic is what I found. I don't know that engine so I can't say if it is right. The supply port should be on the thermostat housing. Don't know where the return is plumbed.

David

Click to expand...

That is where it is on my 3306. Right on the tstat housing. I run mine through a heat exchanger with the hot water heater picking up the heat from the exchanger rather than by circulating engine coolant through the water heater.

If you have kids visit, be sure to install an antiscald device in the FW system.

The engine circulates water at 180F+ , and that will be the sink/shower hot water temp after a short while.

OF there is room adding a couple of inches of insulation will keep the water hot for longer after engine shutdown.

We have engine coolant heated water on Willy. We only have a 37hp engine and the water gets too hot.

Thanks, yes my other concern is hot water tank temp getting 180 degree coolant from the engine, but was thinking of installing a temperature controlled value like a zone valve that would close when the hot water tank reached a certain temp and divert the coolant directly back to the engine. I have a similar temp control switch attached to the inverter that turns on a second cooling fan when the inverter reaches 125 degrees. Its located under a dinette seat and its internal fan needs help

Mixing valves are pretty common. Sure Marine, Seattle, sell several different manufacturers.


AM100-1LF - Honeywell-Sparco AM100-1LF - 1/2" NPT Mixing Valve, Lead Free (70&#176F-145&#176F)

Make sure you add a shut off valve at the engine so that when you do not need the hot water you can shut off the coolant line to the heater or heat exchanger. A marine engine mechanic asked me one time if the hot water was worth the risk of a failure in the hot water line that might cause the engine to overheat.

There are both tempering and anti scald valves,

The difference is the anti scald valve will shut OFF the hot water flow if it can nor control the temperature.

Not a place to cheap out as 180F water can do great damage to skin.

Unless you really need the feature of heating hot water with the main engine, I'd avoid doing it. It presents a risk to the engine AND the hot water can be too hot for safety. On small boats where genset use is rare or purposely minimized, ok it can make sense there, but precautions must be taken.

I have seen two engines ruined when coolant was changed for maintenance. An air bubble formed in the water heater loop, then when it got to the engine it air loaded the circulating pump. No flow meant hot coolant did not make it to alarm sensor. By the time operator noticed an issue, engine got hot enough to crack head, manifold and scuff cylinders.

On my personal boat, I do tap off the coolant to run a cabin heater. But the benefits of that massive amount of heat in the cabin tilts the risk/benefit equation. Hot water can be had with a ten minute gennie run, not worth putting my sacred single engine at risk for that.

Just installed an Isotemp SPA 40 water heater. The installation instructions did not call for a check valve in the cold water line. Is it OK without a check valve?

Ski in NC said:

Unless you really need the feature of heating hot water with the main engine, I'd avoid doing it. It presents a risk to the engine AND the hot water can be too hot for safety. On small boats where genset use is rare or purposely minimized, ok it can make sense there, but precautions must be taken.

I have seen two engines ruined when coolant was changed for maintenance. An air bubble formed in the water heater loop, then when it got to the engine it air loaded the circulating pump. No flow meant hot coolant did not make it to alarm sensor. By the time operator noticed an issue, engine got hot enough to crack head, manifold and scuff cylinders.

On my personal boat, I do tap off the coolant to run a cabin heater. But the benefits of that massive amount of heat in the cabin tilts the risk/benefit equation. Hot water can be had with a ten minute gennie run, not worth putting my sacred single engine at risk for that.

Click to expand...

Ski, what about running the coolant through a heat exchanger mounted on the engine? That is my setup and I did it that way to avoid the problem you describe.

On The Rocks said:

Just installed an Isotemp SPA 40 water heater. The installation instructions did not call for a check valve in the cold water line. Is it OK without a check valve?

Click to expand...

I believe the Isotemp has a built-in check valve. At least the 6 gal. one we put on our sailboat did (along with a tempering valve). Great waterheaters, by the way. We wanted to put on on our tug, but we would have had to relocate or install a smaller heater, which we didn't want to do.

our hot water does get very hot. A benefit is that we can get several days of showers while on the hook without turning on the electric heat by mixing in decreasing amounts of cold.. If I were doing it over I would add an anti scald valve at the shower control.

Delfin said:

Ski, what about running the coolant through a heat exchanger mounted on the engine? That is my setup and I did it that way to avoid the problem you describe.

Click to expand...

That's one way to do it, it does reduce the risk to the engine. But does require a pump and head tank.

A normal direct connected loop to the water heater is not that risky at all, its just that it is some risk for little benefit. As long as operator understands the system and pays attention, it is super low risk.

Most HWH have a temp vavle in that if the hot water get to a pre-set temp, the the valve closes the hot engine coolant line.....

>Most HWH have a temp vavle in that if the hot water get to a pre-set temp, the the valve closes the hot engine coolant line....<

TRUE , which means folks wanting cabin heat from a coolant line will need a second line , or removal of the temp shut off setup on the HW heater .

For loads of heat to a box heater it is sometimes necessary to install a centrifugal pump to assist the coolant water flow.

A 180,000+ BTU box heater needs lots of hot water!

This gives a delight as after shut down that hot 2500lb engine can provide heat to the box heater for a good long while.Almost silent , no truck heater smell.

If running at night at slow speed, my box heater can suck out more heat out than the engine is making. I see the coolant temp dropping. And of course I get less heat then, too. Not a problem in daytime as I can pick up the speed a bit.

I would not want to share the loop between a box heater and water heater, the flow would certainly be less. When I want heat, I want as much as I can get. Especially since it is free.. sort of.

Pics 3208 TA

Hey Grinder,

I finally got downstairs to take pics of my 3208. The connections are right under the heat exchanger.

Most fun I have seen is the setup day fishing boats in City Island NY use.

The keel cooler is bypassed and the rail becomes heated so the fishermen can warm their hands .

Free heat indeed!

Thanks for the photos, very helpful. Now if I can only figure out how to connect a diverter valve that will send the coolant directly back to the engine when the hot water heater gets to temp!

Grinder said:

Now if I can only figure out how to connect a diverter valve that will send the coolant directly back to the engine when the hot water heater gets to temp!

Click to expand...

Good idea is to put valves on the hoses at their connection points on the engine just in case one of the hoses between the engine and the water heater blows out while you are underway. It has happened to me and I'm sure to others.

Have never felt the need to cut the hot engine coolant off from the heater once the water heater is up to temp, but such valves should do the trick. May be a pain to get to them to close them depending on your access.

Grinder said:

Thanks for the photos, very helpful. Now if I can only figure out how to connect a diverter valve that will send the coolant directly back to the engine when the hot water heater gets to temp!

Click to expand...

Most HWH I have seen already have this valve installed on theHWH its self...

Alaskan Sea-Duction said:

Most HWH I have seen already have this valve installed on theHWH its self...

Click to expand...

I haven't seen this, is this something new (in the past 4-5 years?). Sounds like a good solution. The mixing valve is also a good idea.

We just learned to live with super-hot water. We do the mixing at the sink or shower faucet, and like BayView said above, I assume that starting out at a higher temperature makes the water stay hot longer.

I love having "free" hot water at the end of (and during) every run. I'd never own a boat without it. To me, it's well worth the risk. I did have the hose between the engine and water heater let go on my last boat (a hanger failed and it was chafing on the steering arm.) I knew pretty quickly and was able to make the repair, refill the cooling system and be on my way. A very small price to pay for all the hundreds of hot showers and clean dishes we've enjoyed over the years.

For those of us with raw water cooling it's quite simple and never gets above 140℉.
One More Time Around: Engine Heat for Hot Water

Thanks, but I feel I definitely need a way to control the hot water going to the heater, the first attempt resulted in the pressure/temp relief valve opening and turning the engine room into a sauna and filling the bilge with hot water. I'm also not excited about 180 degree water running through the hot water system with the possibility of burns even with a mixer valve. I'd like to send the coolant back to the engine with a diverter valve once the hot water tank reached a more comfortable temp like 125.

The Anti scald valve will shut OFF the hot water if it can not control the temperature.
A tempering valve will not.

Perhaps you could install one in the feed to the HW heater , but most folks would prefer the hotter water in the system as it stores longer.

The anti scald valve could be installed in the FW as it leaves the heater , but far more water would be wasted , waiting for the water to get hot at the tap or shower.

Fine Home Building has an article this month on the heated water ,14,000 gallons wasted in the average dirt house in a year and its energy cost in lost heat.

House solution is elegant and changes a $500+ annual waste bill into $5.00 charge, but its not suitable for a boat , unless dockside.

I just installed a couple valves on on the lines going to the heater as well as a bypass line between the two with a third valve. By partially opening the bypass valve, I could control the amount of heat going to the H/W tank. It also allowed me to isolate the lines to the tank if there ever was a leak.
It was all manual adjustment but it worked fine for me.

This what I found on WM

From Isotherm:

Product Description

Designed specifically for marine use, the innovative design of these water heaters represents a welcome departure from traditional upright cylinders and box-like designs of the past. Inner and outer tanks are made of 316 stainless steel, NOT corrosion-prone aluminum. These heaters may be mounted vertically or horizontally and are secured by adjustable stainless steel mounting feet.
Engine water heat exchanger coils are extra long for faster heating and AC heating elements are nickel-coated copper for long life. All models feature polyurethane foam insulation for extra heat retention and incorporate service thermostats set to 160°F. Thermostatically controlled mixing valves prevent scalding, and ensure that water reaches the tap at the temperature you wish. Additional sizes and options available by special order.

• Material: Storage tank and connections: 316 stainless steel; electric heating coil: nickel-plated copper; cover and mounting feet: 304 stainless steel
• Port Sizes: All plumbing fittings are 1/2" NPT, including freshwater and heat exchanger inlets and outlets
• Draw: 6.8A @ 120V AC
• Warranty: One year on labor; two years parts; five-year limited on inner tank

From Kuuma:

With the same ignition-protected design and features as the West Marine water heaters described above, Kuuma water heaters are installed as original equipment on many boats, including Sea Ray, Four Winns, Hunter, Beneteau, and Boston Whaler. Like West Marine water heaters, Kuuma water heaters are protected by a high-temperature limiter with automatic reset. Use of a magnesium anode is recommended to extend tank life.

• Port Sizes: Cold/hot in/out: 1/2" NPT, Engine coolant in/out: 5/8" (for hose)
• Draw: 12.5A @ 120V AC; 6.25A @ 240V AC
• Approvals: ETL
• Warranty: One year against manufacturer defects