water heating options

[PabloC]

Hi, I'm looking for some advice on the options I have to heat the water (showers/sinks, not raditators). I've been a live-a-board for three years, mostly in a marina. When I have cruised I've made the most of the engine heated hot water on the days we've moved, and on the days we haven't, just made do with either the remaining tepid water or boiled water on the hob for washing up etc.

 

Now I'm starting to CC, I'm looking into some different options. The boat has an immersion heater and calorifier which I run directly from the shoreline when in the marina. I don't have a gas water heater.

 

I'm looking for the simplest solution. I know I could fit a gas heater but with the layout of the boat and where the pipes (both water and gas) run it would be a bit of a pain to fit. I've looked into a solar dump, but have no idea of where to start with fitting that when usually the immersion heater is powered directly off the shoreline - I wouldn't want to lose that option.

 

Would the simplest solution be to run the immersion off a generator? I've also seen these - https://www.whisperpower.com/diesel-generators which seem to be able to be permanently fitted in an engine bay. Although they look expensive and maybe overkill?

 

Also, I've heard mixed opinions on whether it's a good idea to run the engine on idle to heat the water. It's an 2004 Isuzu engine, if that makes any difference.

 

Any thoughts you have would be appreciated! 

[MtB]

Gas water heater usually. But if this is impractical I’d say a diesel Webasto to heat the cailiflower. 

[LadyG]

I have a stove with back boiler.

An Isuzu 33 with 70amp alternator.

A Webasto.

I generally have enougn water to shower and  wash.dishes in winter. 

I light stove most nights so water generally warm

I can run engjne for thirty minutes to replace shower and washing water.

Or the Webasto for thirty minutes to keep water warm. The batteries then need to be charged to replace elecricity. This can take eight hours per week with engjne in winter I make sure engine is regularly serviced. Oil and filter change 250 hours, API CC.

I try to economise on electricity.

I use a laundeŕette.

I keep stove with back boiler ( gravity fed),  running 24/7 in winter. It is on for a few hours per evening three months if the year. A large kettle oould sit on stove top or on cooker top.

I think a generator would only help if you need to charge batteries but not to heat water, too many inefficiences, and a faff to set up every day. You would not be popular if you run generator all day. You need to buy petrol, where would you safely store generator and petrol?

Probably better to move boat every week.

 

 

 

Edited April 26 by LadyG

[booke23]

The standard setup these days is to have twin coil cauliflower, with one coil heated by the engine and the other by a Webasto/Ebbersplutter (along with radiators), as well as an immersion heater. 

 

How much solar do you have? You need quite a lot to consider a solar dump, and it will only produce significant amounts of hot water for half the year anyway. 

[David Mack]

What is your space heating? If you have radiators it is fairly straightforward to add a circuit for a twin coil calorifier.

[Stilllearning]

22 hours ago, PabloC said:

Hi, I'm looking for some advice on the options I have to heat the water (showers/sinks, not raditators). I've been a live-a-board for three years, mostly in a marina. When I have cruised I've made the most of the engine heated hot water on the days we've moved, and on the days we haven't, just made do with either the remaining tepid water or boiled water on the hob for washing up etc.

 

Now I'm starting to CC, I'm looking into some different options. The boat has an immersion heater and calorifier which I run directly from the shoreline when in the marina. I don't have a gas water heater.

 

I'm looking for the simplest solution. I know I could fit a gas heater but with the layout of the boat and where the pipes (both water and gas) run it would be a bit of a pain to fit. I've looked into a solar dump, but have no idea of where to start with fitting that when usually the immersion heater is powered directly off the shoreline - I wouldn't want to lose that option.

 

Would the simplest solution be to run the immersion off a generator? I've also seen these - https://www.whisperpower.com/diesel-generators which seem to be able to be permanently fitted in an engine bay. Although they look expensive and maybe overkill?

 

Also, I've heard mixed opinions on whether it's a good idea to run the engine on idle to heat the water. It's an 2004 Isuzu engine, if that makes any difference.

 

Any thoughts you have would be appreciated! 

I think if I understand  what you say, I'd just keep with the hot water calorifier run by the engine. On days you don't move you just have to run the engine, which will charge batteries and give you hot water. I used to always moor up, then shower with the engine still running, then having dressed etc, turn the engine off. This gave me a tank full for future needs. If you have crew with you, get them to shower before you moor up, thus getting them clean, and the calorifier refilled with hot before you moor.

[PabloC]

23 hours ago, MtB said:

Gas water heater usually. But if this is impractical I’d say a diesel Webasto to heat the cailiflower. 

Thanks. I've taken a look at how they'd be fitted into the system and it doesn't seem too difficult.

 

22 hours ago, LadyG said:

I have a stove with back boiler.

An Isuzu 33 with 70amp alternator.

A Webasto.

I generally have enougn water to shower and  wash.dishes in winter. 

I light stove most nights so water generally warm

I can run engjne for thirty minutes to replace shower and washing water.

Or the Webasto for thirty minutes to keep water warm. The batteries then need to be charged to replace elecricity. This can take eight hours per week with engjne in winter I make sure engine is regularly serviced. Oil and filter change 250 hours, API CC.

I try to economise on electricity.

I use a laundeŕette.

I keep stove with back boiler ( gravity fed),  running 24/7 in winter. It is on for a few hours per evening three months if the year. A large kettle oould sit on stove top or on cooker top.

I think a generator would only help if you need to charge batteries but not to heat water, too many inefficiences, and a faff to set up every day. You would not be popular if you run generator all day. You need to buy petrol, where would you safely store generator and petrol?

Probably better to move boat every week.

 

 

 

Thanks for the reply. And you find running the engine without moving is fine?

 

20 hours ago, booke23 said:

The standard setup these days is to have twin coil cauliflower, with one coil heated by the engine and the other by a Webasto/Ebbersplutter (along with radiators), as well as an immersion heater. 

 

How much solar do you have? You need quite a lot to consider a solar dump, and it will only produce significant amounts of hot water for half the year anyway. 

Thanks. I have 800w solar. It looks like I'll go down the diesel heater route. Although I only have a single coil calorifier so I'm presuming I'd need values to isolate the engine when it's running.

 

8 hours ago, David Mack said:

What is your space heating? If you have radiators it is fairly straightforward to add a circuit for a twin coil calorifier.

I have a multi fuel stove which is plenty for the size of boat. There are radiators fitted but they were previously set up via a heat exchange and small pump coming from the engine - quite a unusual set up but it seemed to work for the previous owners. I've never used them though. I tracked all the piping today and it seems quite a simple fit for a diesel heater by taking out the heat exchange/pump set up.

 

57 minutes ago, Stilllearning said:

I think if I understand  what you say, I'd just keep with the hot water calorifier run by the engine. On days you don't move you just have to run the engine, which will charge batteries and give you hot water. I used to always moor up, then shower with the engine still running, then having dressed etc, turn the engine off. This gave me a tank full for future needs. If you have crew with you, get them to shower before you moor up, thus getting them clean, and the calorifier refilled with hot before you moor.

Thanks for the reply, you're correct - The days I'm cruising is no problem, plenty of hot water. On the days I'm not, I'm going without at the moment. Running the engine on idle on occasion. It's only because I've heard running the engine idling for 45-60 minutes can be damaging that I limit how often I do this.

[David Mack]

6 minutes ago, PabloC said:

I have a multi fuel stove which is plenty for the size of boat.

Fit a back boiler to heat the water and maybe also the radiators. Together with a solar dump system that should provide year-round hot water.

Edited April 27 by David Mack

[Stilllearning]

40 minutes ago, PabloC said:

Thanks. I've taken a look at how they'd be fitted into the system and it doesn't seem too difficult.

 

Thanks for the reply. And you find running the engine without moving is fine?

 

Thanks. I have 800w solar. It looks like I'll go down the diesel heater route. Although I only have a single coil calorifier so I'm presuming I'd need values to isolate the engine when it's running.

 

I have a multi fuel stove which is plenty for the size of boat. There are radiators fitted but they were previously set up via a heat exchange and small pump coming from the engine - quite a unusual set up but it seemed to work for the previous owners. I've never used them though. I tracked all the piping today and it seems quite a simple fit for a diesel heater by taking out the heat exchange/pump set up.

 

Thanks for the reply, you're correct - The days I'm cruising is no problem, plenty of hot water. On the days I'm not, I'm going without at the moment. Running the engine on idle on occasion. It's only because I've heard running the engine idling for 45-60 minutes can be damaging that I limit how often I do this.

In my opinion, with a modern diesel, relax and run it just above tickover, charge the batteries and have hot water.

[Tony Brooks]

40 minutes ago, Stilllearning said:

In my opinion, with a modern diesel, relax and run it just above tickover, charge the batteries and have hot water.

 Rather than that, if you have an ammeter for the domestic bank, run it at the speed that gives maximum charge. With LA batteries, the charge will drop after perhaps 20 minutes and continue to drop, so you can slow the engine down to maintain maximum charge. That way, you maximise the load the alternator puts on the engine.

[MtB]

Please, don't run your engine at all when moored next to other boats that are occupied.

 

It may be permissible under the terms of your licence but its not good manners, IMO.

 

 

 

 

Edited April 27 by MtB
Finesse it

[booke23]

2 hours ago, PabloC said:

Thanks. I have 800w solar. It looks like I'll go down the diesel heater route. Although I only have a single coil calorifier so I'm presuming I'd need values to isolate the engine when it's running.

 

You probably need slightly more solar for an effective solar dump.....you would get some heating from it but it might not be worth the faff with 800w. People with solar dumps usually have well over a kilowatt of solar. 

 

Yes you can go down the valve route to isolate the engine/heater. Although you do hear of webasto's on a single coil system without valves, it could be a real pain to retrofit. You'd loose a bit of heat to the engine with this setup and it could be problematic with pressurised engine cooling systems. 

[blackrose]

I have twin coil calorifier from engine/Webasto, 1kW immersion heater which I can use on sunny days from solar panels/lithium batteries and instant gas water heater. I also have a 2.8kW generator so if I'm using it to run the battery charger on dull days in winter I can switch on the immersion heater at the same time. 

 

The more options you have the better. 

[JoeC]

15 hours ago, PabloC said:

There are radiators fitted but they were previously set up via a heat exchange and small pump coming from the engine - quite a unusual set up but it seemed to work for the previous owners. I've never used them though. I tracked all the piping today and it seems quite a simple fit for a diesel heater by taking out the heat exchange/pump set up.

I have a heat exchanger and pump fitted to my engine to heat the radiators in winter when the engine is running. I also have a Webasto connected to the same radiator circuit so you may find your current setup could be used should you install a diesel heater. There are some posts on here about installing heat exchangers.

[MtB]

13 hours ago, booke23 said:

You probably need slightly more solar for an effective solar dump.....you would get some heating from it but it might not be worth the faff with 800w.

 

I think it would be worthwhile. I helped a mate design and install a solar dump onto 1200W of panels over winter and it came on stream working well late feb or the beginning of March, I can't quite remember. The less solar you have, the later in the year it will come on stream and the sooner in Autumn it will stop working so more is always better, but a little will always be useful in the summer. 

 

 

[blackrose]

On 26/04/2025 at 20:34, booke23 said:

How much solar do you have? You need quite a lot to consider a solar dump, and it will only produce significant amounts of hot water for half the year anyway. 

 

I'm still unaware of a solar dump system from a MPPT which can switch on/off a mains immersion heater. Is there some sort of simple relay system which could be set up? The only system I've seen requires replacing the mains immersion heater with a 12v immersion and they can be problematic depending on how easy the mains immersion is to get out.

[booke23]

1 hour ago, blackrose said:

 

I'm still unaware of a solar dump system from a MPPT which can switch on/off a mains immersion heater. Is there some sort of simple relay system which could be set up? The only system I've seen requires replacing the mains immersion heater with a 12v immersion and they can be problematic depending on how easy the mains immersion is to get out.

 

Me neither, and you’d think there would some sort of system to do this. I knew a guy with a manual system that worked well…..basically he had a 1kW mains immersion that could run off the inverter which he would manually turn on mid morning in the summer once his LFP’s were fully charged. Even then he had a heavy duty dimmer type switch on the immersion so he could vary the power as it was rare his solar could actually produce the full 1kW….as the sun got higher he could turn up the immersion. It’s not ideal in that it needs watching closely and constantly fiddling with, but it did produce pretty much all the hot water he needed for 8 months of the year. I think he had about 1.8kW of solar.   

 

[IanD]

1 hour ago, booke23 said:

 

Me neither, and you’d think there would some sort of system to do this. I knew a guy with a manual system that worked well…..basically he had a 1kW mains immersion that could run off the inverter which he would manually turn on mid morning in the summer once his LFP’s were fully charged. Even then he had a heavy duty dimmer type switch on the immersion so he could vary the power as it was rare his solar could actually produce the full 1kW….as the sun got higher he could turn up the immersion. It’s not ideal in that it needs watching closely and constantly fiddling with, but it did produce pretty much all the hot water he needed for 8 months of the year. I think he had about 1.8kW of solar.   

 

 

You can do this automatically with some inverters/combis; on the Victron Multiplus/Quattro you can connect a 230Vac immersion heater to the second AC output (which is relay switched), and use an assistant to turn the relay on and off according to SoC -- in my case, 99% and 95%. I have 2.1kWp of solar and a 2.5kW immersion to make sure it can absorb all the power even in full summer sunlight. Once the hot water is up to the immersion cutout temperature the heating stops.

[booke23]

17 minutes ago, IanD said:

 

You can do this automatically with some inverters/combis; on the Victron Multiplus/Quattro you can connect a 230Vac immersion heater to the second AC output (which is relay switched), and use an assistant to turn the relay on and off according to SoC -- in my case, 99% and 95%. I have 2.1kWp of solar and a 2.5kW immersion to make sure it can absorb all the power even in full summer sunlight. Once the hot water is up to the immersion cutout temperature the heating stops.

 

Now that sounds ideal.

[DShK]

On 27/04/2025 at 19:47, MtB said:

Please, don't run your engine at all when moored next to other boats that are occupied.

 

It may be permissible under the terms of your licence but its not good manners, IMO.

 

 

 

 

No dogs barking, unpleasant smells, loud talking or laughing above a titter either! 

 

The only time it has ever caused me a bother is when a hire boater was basically abreast of me in coventry basin, running his engine at 11pm. I had a quiet word.

Edited April 29 by DShK

[Alan de Enfield]

38 minutes ago, IanD said:

..........to the second AC output (which is relay switched), and use an assistant to turn the relay on and off according to SoC

 

 

Is that the same as a Butler ?

[IanD]

39 minutes ago, Alan de Enfield said:

 

Is that the same as a Butler ?

 

[LadyG]

On 27/04/2025 at 17:45, David Mack said:

Fit a back boiler to heat the water and maybe also the radiators. Together with a solar dump system that should provide year-round hot water.

My stove is unbranded.with gravity fed back boiler, It will heat a little radiator in bathroom, and the fat pipes running to the calorifier are warm, so boat is dry.,, but im not convinced keeping the desired temp throughout the boat is easy. I use the Webasto radiators early morning and in spring/ autumn and for hot water. The s/f stove is not readily adaptable, it takes a few hours to warm up.

Edited April 29 by LadyG

[blackrose]

17 hours ago, booke23 said:

 

 I knew a guy with a manual system that worked well…..basically he had a 1kW mains immersion that could run off the inverter which he would manually turn on mid morning in the summer once his LFP’s were fully charged. 

 

That's what I do most days if I'm at home and it's sunny. My inverter has no problem running the 1kW mains immersion. 

 

Today I ran my washing machine and then switched on the immersion for about an hour and a half to get a full tank of water. 

 

The lithium batteries were at about 85% SoC this morning, went as low as about 70% and were back to 85% this evening. 

 

I guess I could just use the timer on my immersion heater on days I'm away from the boat if the forecast is for sun, but if it clouds over I don't really want to use the batteries to heat water.

Edited April 30 by blackrose

[Alan de Enfield]

3 minutes ago, blackrose said:

My inverter has no problem ruining the 1kW mains immersion. 

 

Would it not be worth changing it so it doesn't ?