How long does hot water stay hot?

[boots]

Hi,

 

we are in the process of looking for our first boat, and one thing that has struck us is that many source the hot water from the engine via a calorifier.

 

Having never used this set up, am wondering how this tends to work out in practice - for example, do you typically have to run the engine every morning to have a shower, or does it stay hot enough from the day before?

 

How long do you have to run the engine to get hot water i) at idle, ii) while cruising

 

does this typically turn out to be a pain in the neck or a non-event?

 

The boat will be used as a weekender / holiday boat. When we just visit for a few hours, then guess the kettle will do!

 

I appreciate that this is almost an impossible question to answer but any experiences would be appreciated.

 

regards,

 

Boots.

[Naughty Cal]

We have an electric immersion heater (for when plugged into shore power) as well as the calorifier. In practise this works fine for us as we prefer to shower in the evening (normally after we have been cruising) and have breakfast at about 10am (after we have been cruising). The only time this has let us down was when we had to wait whilst 2pm for a tide window, this meant we had to boil the kettle to wash the pots. No great hardship really.

[Proper Job]

How long is a piece of string?

 

Most decent foam lagged calorifiers can hold hot water in a usable state for over 24 hours.

 

But it depends on how hot the water gets in the first place and what volume of cold water is introduced in the dormant period. If I've given my engine a good run the day before, I can have hot water for a shower the following morning. However, I have noticed that even using some of the water for hand washing, washing up etc can turn the water in the calorifier tepid if left over night.

 

Obviously the size of the calorifier will make a difference too.

 

As a weekend/holiday boat when you spend most of the time cruising, I don't think you'll have any real problems.

[WJM]

I have a modern Isuzu 'van' engine. I have produced enough hot water for a shower from 20 minutes of engine idling. I also have an electric immersion heater for when I am on the mains and that will heat enough for a shower in half an hour.

 

And after a day's cruising, with engine off at about 5pm, I have a full hot tank the next morning.

 

Overall, getting hot water is not a big deal if you have the right setup.

Edited November 2, 2009 by WJM

[Keeping Up]

I find it takes about half an hour for the calorifier to heat the water. It takes less time if the engine is working hard straight away, because it warms up quicker; I suspect this would make no difference once the engine has reached its full operating temperature.

 

Ours tends to have cooled down overnight, such that you can only sensibly get one shower from it. The second person is just out of luck. I think I may be losing some heat back into the engine due to the water cycling under gravity once the engine has cooled down (I didn't have this problem when the pipes were partly blocked with crud, but then it took two hours to warm up instead)

[Lady Muck]

Ours takes more like 1 or 2 hours to produce hot water. Whether it goes cold overnight depends on the season, in winter it is only lukewarm by the morning, in summer you could get one not particularly hot shower out of it. I think my calorifier could do with better lagging though.

[Naughty Cal]

It depends how much we take out of ours once we have moored up as to wether or not we have hot water the next morning. It is normally hot enough to wash the coffee cups and juice glasses though. Failing that the kettle has been on so will have some hot water in it.

 

Just to add, ours heats up in about 20-30 minutes, but we do have a large engine producing the heat.

Edited November 2, 2009 by Phylis

[nb Innisfree]

Takes us 1.5hrs to get 2 remote 50 lt calorifiers hot, if we then close the valve to the heating coil to prevent back syphon we have 2 hot showers next morning which is about 18 hrs after engine shutdown. In the winter we need to run engine a bit longer or shut it down about 15 hrs before shower.

 

Edited to add that is with a foam lagged calorifier

Edited November 2, 2009 by nb Innisfree

[pugwash61]

How long is a piece of string?

 

Most decent foam lagged calorifiers can hold hot water in a usable state for over 24 hours.

 

But it depends on how hot the water gets in the first place and what volume of cold water is introduced in the dormant period. If I've given my engine a good run the day before, I can have hot water for a shower the following morning. However, I have noticed that even using some of the water for hand washing, washing up etc can turn the water in the calorifier tepid if left over night.

 

 

Sounds very similar to my experiences on my boat, although I use an ebenspacher to heat the water, unless I'm cruising. Then I get a tank for free.

[mayalld]

I have a modern Isuzu 'van' engine. I have produced enough hot water for a shower from 20 minutes of engine idling. I also have an electric immersion heater for when I am on the mains and that will heat enough for a shower in half an hour.

 

And if you turn te immersion on with engine running, drawing 1kw thru the inverter, the engine will be working exta hard, and the water will be hot in 15!

 

We have a large calorifier, and always have oodles of hot (not warm) water for showers in the morning.

[PhilR]

And if you turn te immersion on with engine running, drawing 1kw thru the inverter, the engine will be working exta hard, and the water will be hot in 15!

 

We have a large calorifier, and always have oodles of hot (not warm) water for showers in the morning.

 

Now that does seem an efficient use of fuel - great thinking

[Ray]

As others will know from posts elsewhere on this forum, we can't retain heat in our calorifier overnight if we draw more than about 2 litres the evening before. The suggestion is that the engine, running at around 70 degrees, is not heating the water sufficiently in the first place, so natural loss is what is dropping the temperature overnight.

 

However . . . . .

 

We can also heat the top of the calorifier from the Alde boiler and that is controlled by a thermostat on the calorifier. I tend to turn the Alde on as soon as we board when we stay on the boat on its moorings for the weekend. Although I won't swear to it because I haven't monitored it that closely, I'm 99% certain that at least twice, recently, I've fired up the Alde and the thermostat has eventually turned the boiler off. And then within a couple of hours, the boiler fires up again, because the thermostat has said the water needs heating again. And that's when we've not drawn any water from the calorifier.

 

Something's not right because we have valves that stop any syphoning and, thus, loss of heat that way.

 

We have fitted a pressure reduction valve on the cold water in feed to the calorifier and this does seem to have eased things but we've got so used to working around tepid water in the morning that even when we were away for two weeks recently we didn't think to check in more detail the full effect of this addition.

 

Not withstanding any of the above, we've just had two week's on a friend's unfitted Dutch Barge, which had temporarily had a different model calorifier installed. True the engine was running a lot hotter, but the water was piping hot in the morning, even after we'd washed up the previous evening. Pity we didn't have a shower installed so that we could take full advantage of all that hot water!

[Tam & Di]

We've maybe got more space than some, but we have a 50 gallon foam insulated hot water cylinder and water is ample hot for washing up and showers for 24-36 hours after cruising for even as little as 4 hours. We heat ours from the Gardner when cruising. The alternatives are from the Webasto diesel central heating unit (it becomes the first radiator in the circuit), from a 240v immersion heater either when on shore power, or when the generator is running to give power when we're not plugged in. One thing I did not consider when we set up the system was to use heat from the water-cooled genset.

 

A bit belt and braces (+ safety pins as well), but we often do have other people on board with us.

[alan_fincher]

I agree with PJ's comments, and suspect the biggest key to success is how hot the water is heated by the engine in the first place.

 

Our engine has an 82 degree stat, so can heat the calorifier pretty hot, (with such an arrangement it is good practice to have a thermostatic mixing valve on the output, to mix cold water in at source, and prevent any possibility of scalding at taps, or under shower).

 

If an engine is running with (say) only a 70 degree stat, the amount of hot water that can be drawn off will be significantly less, and an overnight temperature drop will more likely result in even a full tank not being particularly warm.

 

 

Many have said that vertical tanks fare better than horizontal, so I was a bit nervous of fitting the latter. In practice it retains heat better than many other posters say theirs does, (and does not have any non-return valves to stop reverse circulation back through the engine, once it has stopped).

 

Must just have struck lucky, I guess.

[Bones]

I have a vertical cauliflower that sits above the water line. It is 20 years old and well lagged. It takes about 40minutes to get the temperature of its metal casing to 33degrees. The water is still hot in the morning, the evening and warm the following morning. If I get it up to 40degrees it stays hot for a couple of days. However, in winter it stays hot for about 24hours.

[Big COL]

I have a vertical cauliflower that sits above the water line. It is 20 years old and well lagged. It takes about 40minutes to get the temperature of its metal casing to 33degrees. The water is still hot in the morning, the evening and warm the following morning. If I get it up to 40degrees it stays hot for a couple of days. However, in winter it stays hot for about 24hours.

 

How long does cauliflower cheese stay hot for

 

Colin

[Bones]

How long does cauliflower cheese stay hot for

 

Colin

 

 

it being one of my favourite dishes I have absolutely no idea...

 

Now I am hungry.

Edited November 3, 2009 by Bones

[brown]

Vertical and horizontal coliflowers will retain the same heat if no water is drawn off, however the vertical will retain more heat than the horizontal if some of the water is drawn as the cold water has less surface area to mix with the hot. According to Graham Booth anyway.

[Bones]

Vertical and horizontal coliflowers will retain the same heat if no water is drawn off, however the vertical will retain more heat than the horizontal if some of the water is drawn as the cold water has less surface area to mix with the hot. According to Graham Booth anyway.

 

Thanks for that! I was wondering what the difference was!

[Big COL]

Vertical and horizontal coliflowers will retain the same heat if no water is drawn off, however the vertical will retain more heat than the horizontal if some of the water is drawn as the cold water has less surface area to mix with the hot. According to Graham Booth anyway.

 

Not sure I agree with with all of that, however there are other issues to take into consideration. Depending on the design of the hot water plumbing there can be serious heat losses through thermal cycling if the design and installation is not correct.

Also are all calorifiers insulated exactly the same? a varying thickness of insulation coupled with the differing materials of insulation will make a considerable difference.

[Keeping Up]

Our engine has an 82 degree stat, so can heat the calorifier pretty hot, (with such an arrangement it is good practice to have a thermostatic mixing valve on the output, to mix cold water in at source, and prevent any possibility of scalding at taps, or under shower).

Definitely a sugestion worth remembering!

 

I did this, and for a long time I had so many problems that I took the mixer out again. Eventually I discovered that the (very expensive) Caleffi mixer incorporates a safety feature that if the hot water goes above 85 degrees it will shut down, as a safety measure. Unfortunately it starts to shut down before it reaches this temperature, and so it would shut off my hot water supply as soon as the engine had finished heating it! I swapped the mixer to a (much cheaper) simple one from Midland Chandlers, and it performs just fine. So I put the Caleffi under the bathroom washbasin, and it works fine with the pre-regulated hot water supply to give me water on that one tap that is at just the right temperature for washing your hands under the running water.

[WJM]

"And if you turn the immersion on with engine running, drawing 1kw thru the inverter, the engine will be working exta hard, and the water will be hot in 15!"

 

Absolutely brilliant - sheer genius! Thanks!

[blackrose]

Definitely a sugestion worth remembering!

 

I did this, and for a long time I had so many problems that I took the mixer out again. Eventually I discovered that the (very expensive) Caleffi mixer incorporates a safety feature that if the hot water goes above 85 degrees it will shut down, as a safety measure. Unfortunately it starts to shut down before it reaches this temperature, and so it would shut off my hot water supply as soon as the engine had finished heating it! I swapped the mixer to a (much cheaper) simple one from Midland Chandlers, and it performs just fine. So I put the Caleffi under the bathroom washbasin, and it works fine with the pre-regulated hot water supply to give me water on that one tap that is at just the right temperature for washing your hands under the running water.

I also fitted a TMV to the hot water output of my calorifier because I scalded myself a couple of times after running the engine.

 

It worked fine to start with but I've had to take it off a couple of times to remove bits of limescale in the screens which dramatically reduces hot water flow. I'm in a hard water area and it's a real problem. I've seen two people in the marina remove leaking calorifiers and the amount of limescale that they poured out was staggering!

[Chertsey]

Don't forget that a lot of boats will also have a Paloma type instantaneous gas water heater as a back up, and it is still allowed to fit them. The only thing stopping us is not having a suitable place to put one.