Hydronic Heater (for hot domestic water)

[Diverrob]

Good Day

I am considering buying a Chinese diesel hydronic heater to heat the coolant in the engine and circulate it through the hot water tank so I can have hot water at anchor without running my generator (Honda 2000W). Has anyone done this before and if so would you recommend a particular brand either to use or to stay away from. Not looking to use it for cabin heat as I have an Espar D4 air heater already. I have a Mainship 34T with a 6 gallon water tank that is already plumbed to be heated by the engine. Thanks

 

[Lepke]

I don't think there is a difference in Chinese brands. Many truckers use them, but with constant use they don't last as long as European brands. I have one in my pickup with a remote, so I can deice the windows in winter. And the engine starts better.

 

[Bmarler]

I’ve always wondered why more people don’t heat domestic water with a hydronic heater.
I have a loop on my espar system just for that purpose. In summer I need to close the other loops so the boat doesn’t heat up, but a small dedicated unit for hot water should work well.

 

[MV Moira]

We had a Webasto hydronic unit in our sailboat for 25 years, plumbed to heat water and to heat the cabin through several radiators with a selector valve. It worked fine, would make water hot enough for showers in about 15 minutes. The only significant maintenance I can recall to the heater was that after maybe 10 years the diesel exhaust vent rusted out and the unit had to be replaced.

Edit: The Webasto antifreeze/coolant circuit did not touch the engine coolant circuit at any point. It was its own free-standing circuit that only heated the cabin and domestic hot water.

 

[Diverrob]

I’ve always wondered why more people don’t heat domestic water with a hydronic heater.
I have a loop on my espar system just for that purpose. In summer I need to close the other loops so the boat doesn’t heat up, but a small dedicated unit for hot water should work well.

Do you use the same coolant in the heater as your engine and do you run it through the engine as well as your hot water tank? I was thinking that I would use the system to run through the engine as well as the water heater. That way there would be no need for an expansion tank in the heater loop.

 

[DDW]

The Safety Police will tell you not to run the engine coolant through the water tank heat loop. The reason is, ethylene glycol antifreeze is extremely toxic, and if there is a pinhole leak in the heat loop, your domestic water will poison you. This is why hydronic systems that use waste engine heat have a secondary heat exchanger: now you'd have to have two faults to die, one in the water tank and one in the heat exchanger.

I have had a heat exchanger go bad, and mix the engine and hydronic loop coolants, so it does happen.

In the hydronic loop you are supposed to use propylene glycol antifreeze for this reason: it is relatively non-toxic. There are propylene glycol coolants sold for engine use, so one solution is simply to change your engine coolant to that and do as you suggest.

 

[Jeff F]

Do you use the same coolant in the heater as your engine and do you run it through the engine as well as your hot water tank? I was thinking that I would use the system to run through the engine as well as the water heater. That way there would be no need for an expansion tank in the heater loop.

Do you really want to keep the engine at the same temperature as the HW? I don't think this is a good plan. It'll take a lot more energy, and put a lot of heat into the ER

I have a hydronic system that provides HW, but the engine loop and HW loop are separated, for good reason

 

[rslifkin]

The Safety Police will tell you not to run the engine coolant through the water tank heat loop. The reason is, ethylene glycol antifreeze is extremely toxic, and if there is a pinhole leak in the heat loop, your domestic water will poison you. This is why hydronic systems that use waste engine heat have a secondary heat exchanger: now you'd have to have two faults to die, one in the water tank and one in the heat exchanger.

I have had a heat exchanger go bad, and mix the engine and hydronic loop coolants, so it does happen.

In the hydronic loop you are supposed to use propylene glycol antifreeze for this reason: it is relatively non-toxic. There are propylene glycol coolants sold for engine use, so one solution is simply to change your engine coolant to that and do as you suggest.

I've never seen that as a big concern on systems that run engine coolant through the water heater. As an example, my engines have 13 psi pressure caps on the cooling systems. Unless I depressurize it, the fresh water system never gets below 40 psi. So a failure would force water into the engine coolant and out the pressure cap rather than putting coolant into the hot water tank. Plus consuming hot water is generally not advised anyway. The only reason I don't have the water heater plumbed to an engine is to avoid the extra complexity and failure points in the cooling system.

 

[Diverrob]

Do you really want to keep the engine at the same temperature as the HW? I don't think this is a good plan. It'll take a lot more energy, and put a lot of heat into the ER

I have a hydronic system that provides HW, but the engine loop and HW loop are separated, for good reason

I was going to add a couple valves to isolate the engine from the loop but this would mean also adding an expansion tank to the system. On your system can the engine heat the hot water or is it only on the hydronic and electric systems? I suppose having it on hydronic/electric only would not be the end of the world at the end of the day.

 

[Diverrob]

I've never seen that as a big concern on systems that run engine coolant through the water heater. As an example, my engines have 13 psi pressure caps on the cooling systems. Unless I depressurize it, the fresh water system never gets below 40 psi. So a failure would force water into the engine coolant and out the pressure cap rather than putting coolant into the hot water tank. Plus consuming hot water is generally not advised anyway. The only reason I don't have the water heater plumbed to an engine is to avoid the extra complexity and failure points in the cooling system.

That’s a good point, my cap on the engine is 15psi and the domestic water is significantly higher than that (30-40 I believe). I was thinking of adding a couple isolation valves to isolate the engine when not in use but this will also require an expansion tank. Having the engine coolant go through the hydronic system will ensure I have three option for hot water (engine, hydronic and electric). I appreciate all the comments, it makes me consider other options!

 

[Jeff F]

I was going to add a couple valves to isolate the engine from the loop but this would mean also adding an expansion tank to the system. On your system can the engine heat the hot water or is it only on the hydronic and electric systems? I suppose having it on hydronic/electric only would not be the end of the world at the end of the day.

Mine has the furnace circulate its own coolant, with one heat exchanger for the engine coolant and one heat exchanger for HW. So engine heat gives HW, but indirectly.

Valves would work I guess. Thinking out loud here, but an alternative would be to put the heater in its own loop with the WH, and add a heat exchanger to that loop to capture engine heat. You might need to add a small circulation pump as well, depending on the heater.

 

[Lepke]

My main engines and hydronic heating is tied together, but can be isolated. The advantage is cruising the engines heat the boat. And in cold weather the engines can be preheated before starting.
My hot water tank is heated by electricity or a coil in my diesel stove and is a separate system. My inverter can heat the water, but I only do that when cruising because I have alternators dedicated to the inverter bank.

 

[Bmarler]

Do you use the same coolant in the heater as your engine and do you run it through the engine as well as your hot water tank? I was thinking that I would use the system to run through the engine as well as the water heater. That way there would be no need for an expansion tank in the heater loop.

I do not. I have a separate expansion tank in the pilothouse for the entire system. My system is only used for heating the boat. 4 zones, two heated towel bars, de-misters for the pilothouse windows, etc…I could connect the engine but it would take btu’s away from the boat heating.
Some people recommend not to connect to the engine coolant without using a separate heat exchanger, but I think it could be effective. After all, the small hydronic heaters are marketed as engine preheat systems.

 

[Diverrob]

I do not. I have a separate expansion tank in the pilothouse for the entire system. My system is only used for heating the boat. 4 zones, two heated towel bars, de-misters for the pilothouse windows, etc…I could connect the engine but it would take btu’s away from the boat heating.
Some people recommend not to connect to the engine coolant without using a separate heat exchanger, but I think it could be effective. After all, the small hydronic heaters are marketed as engine preheat systems.

Yes the one I am looking at is sold as an engine heater so antifreeze should work with it just fine. I have no aspirations of adding zones as I have an air heater already with the ducts already in place and works well for our winters on Vancouver Island. I will do a bit more research on the requirements of an expansion tank and see what comes up. I am leaning to simply running the heater through the same lines as the current setup with the engine coolant and add isolation valves to separate the engine from the loop when not needed. The reason for this is having the option to pre-heat the engine would be a nice option to have when it actually does get below freezing here.

 

[ksanders]

On a couple boats I heated potable water with the hydronic heating system.

I did not heat engine blocks, as it was unnecessary, but having hot water at anchor was fantastic!!!

 

[ksanders]

message deleted incorrect thread

 

[boomerang]

To the OP, @Diverrob , I'm curious whether or not you went ahead with your plan of installing a hydronic heater on your boat. I, knowing pretty much nothing about that type of a system but knowing we didn't want to run the generator every time we wanted hot domestic water for showers and dishes on our trip South, did all of the research I could do in the few weeks we had before leaving and bought a Chinese 5 Kw unit to try. Now that the trip is behind us , my wife and I both realized that for us and our style of cruising, it was one of the best additions we could've added to our boat.

 

[Diverrob]

To the OP, @Diverrob , I'm curious whether or not you went ahead with your plan of installing a hydronic heater on your boat. I, knowing pretty much nothing about that type of a system but knowing we didn't want to run the generator every time we wanted hot domestic water for showers and dishes on our trip South, did all of the research I could do in the few weeks we had before leaving and bought a Chinese 5 Kw unit to try. Now that the trip is behind us , my wife and I both realized that for us and our style of cruising, it was one of the best additions we could've added to our boat.

I have not pulled the trigger on this yet but will be trying to get it installed over the winter. I have a source locally for the heater and I believe the rest of the parts can be sourced at the local chandler. I am glad to hear that you think this is a good addition to your vessel, I think having basically hot water on demand would be fantastic especially because I want to expand our winter cruising.

 

[Greg QS]

run the genset or diesel heater still burning fuel. is it worth the upgrade? just for hot water no. Piggy back on a heat system OK,yes.

 

[Diverrob]

run the genset or diesel heater still burning fuel. is it worth the upgrade? just for hot water no. Piggy back on a heat system OK,yes.

So I partially agree with you, the issue for me is that I don’t have a dedicated gen set. I only have a Honda 2000W and when it’s out and running to heat water it’s loud if you are with others in an anchorage.

 

[boomerang]

run the genset or diesel heater still burning fuel. is it worth the upgrade? just for hot water no. Piggy back on a heat system OK,yes.

We burned 7 quarts of fuel in the diesel heater over the course of 2 weeks. That wasn't a continuous run but we started it every evening after anchoring for domestic hot water and to hear the boat, every morning to heat the boat and often times during the day for cabin heat. Thank goodness I have the ability to fabricate and install parts and the components. Otherwise, the economy of the diesel heater wouldn't be so glowing.

 

[Bmarler]

I think a small dedicated hydronic system for the water tank is a smart solution. It could be completely automatic if wired properly.
Hot water at the tap is a big deal for most women. Having to plan to make hot water is a pain for them. Making my wife’s life easy is important. When I do things like that it buys me points to use later for things I want.

 

[Greg QS]

So I partially agree with you, the issue for me is that I don’t have a dedicated gen set. I only have a Honda 2000W and when it’s out and running to heat water it’s loud if you are with others in an anchorage.

Well if you don't have a genset the yes. Watch out for those honda gas gensets. They are not ignition protected and vent fumes out of the gas tank. I have seen people store them in the bilge. Humm where do the gas vent fumes go. Had a buddy that kept one in the bilge of a diesel boat. Noting in a diesel boat is ignition protected. Some people just don't think.

 

[C lectric]

Just my opinion but do not heat the engine cooling water unless you want trouble.with a overheated engine. Keep the two separate.

Just my opinion and I don't care who disagrees with me.