Hot Water when the calorifier goes cold?????????????

[Gazza]

We have a Moody Eclipse with a Volvo raw-water cooled engine fitted with a calorifier (and immersion heater for shore power); we get reasonably hot water after the engine has been running, but, inevitably, after a few hours the water isn't hot. Given that we have the luxury of a good size shower facility in the heads, I'd like to have a method of generating hot water on demand.

Our previous boat (Vancouver 32) had a gas heater in the heads, but these seem to have fallen out of favour, presumably for safety reasons; fitting one would probably be slightly awkward given the layout in the heads. I know that some people advocate using an inverter connected to the immersion heater, but I'm wondering about the drain on the batteries ( 2x 110ah for domestic use).

The thought occurred to me that using a small petrol generator wired into the immersion heater might be an answer, but I'm not sure what output would be needed or indeed how long it might need to run - I'm sure I'm not alone in being very irritated by boats running generators for hours in quite anchorages.


Any thoughts/experiences would be useful - thanks.

 

[Hoolie]

Get used to cold showers?

 

[AngusMcDoon]

Electric heater off an inverter powered by the batteries is a non starter. Heating water requires far too much energy. A 2 kilowatt generator will heat enough water for a shower in 45 minutes or so.

 

[CLB]

Depends on the size of your immersion. Last boat had an 800w one and I used a 1kw genny to heat water. Current boat has 1500w immersion and genny is now no good. Choice is bigger genny or smaller immersion.

 

[Plum]

We have a Moody Eclipse with a Volvo raw-water cooled engine fitted with a calorifier (and immersion heater for shore power); we get reasonably hot water after the engine has been running, but, inevitably, after a few hours the water isn't hot. Given that we have the luxury of a good size shower facility in the heads, I'd like to have a method of generating hot water on demand.

Our previous boat (Vancouver 32) had a gas heater in the heads, but these seem to have fallen out of favour, presumably for safety reasons; fitting one would probably be slightly awkward given the layout in the heads. I know that some people advocate using an inverter connected to the immersion heater, but I'm wondering about the drain on the batteries ( 2x 110ah for domestic use).

The thought occurred to me that using a small petrol generator wired into the immersion heater might be an answer, but I'm not sure what output would be needed or indeed how long it might need to run - I'm sure I'm not alone in being very irritated by boats running generators for hours in quite anchorages.


Any thoughts/experiences would be useful - thanks.

My calorifier now gives warm enough water for a shower the following morning after fitting some decent insulation.

Www.solocoastalsailing.co.uk

 

[CrikeyChris]

We have a Moody Eclipse with a Volvo raw-water cooled engine fitted with a calorifier (and immersion heater for shore power); we get reasonably hot water after the engine has been running, but, inevitably, after a few hours the water isn't hot. Given that we have the luxury of a good size shower facility in the heads, I'd like to have a method of generating hot water on demand.

Our previous boat (Vancouver 32) had a gas heater in the heads, but these seem to have fallen out of favour, presumably for safety reasons; fitting one would probably be slightly awkward given the layout in the heads. I know that some people advocate using an inverter connected to the immersion heater, but I'm wondering about the drain on the batteries ( 2x 110ah for domestic use).

The thought occurred to me that using a small petrol generator wired into the immersion heater might be an answer, but I'm not sure what output would be needed or indeed how long it might need to run - I'm sure I'm not alone in being very irritated by boats running generators for hours in quite anchorages.


Any thoughts/experiences would be useful - thanks.

Eberpacher, Webasto and Planer manufacture diesel water heaters. The first two are expensive, the Planar's are cheaper although perhaps threatened by much cheaper Chinese units. Coolant passes thru the heater and either goes thru a coil in a colorifier or it can go thru a small heat exchanger which promises something akin to hot water on demand - but be aware these heaters do take 5 or so minutes to warm up properly.
I have a Planar 4kw feeding into one of two coils of a 30L calorfier. Not without issues plumbing all this in and units are a bit noisy and of course the glow plugs and pumps use electricity.
In a way I regret not getting a bigger unit and using it for space heating as well as for hot water.
The planar units are about 5-6 hundred pounds and you will need some radiator pipe, some valves etc and a dual coil tank (if you still want to take advantage of the engine heat.
From your description of your battery bank I do not think it is possible to heat sufficient water using them.

 

[ghostlymoron]

Showers on a boat? What's wrong with wet wipes? (Except plastic content of course)

 

[cegri]

- Check the isolation of your hot water tank. Ours keep the water warm enough for almost 24 hours. (Make sure no one uses hot water when washing their hands etc... Most don't realise they spent hot water if they use the hot side of the tap for a few seconds.)

- 1200 Watt heating element heats our tank to warm in 10 minutes, hot enough for shower in 15 minutes. (with 2000 Watt inverter) Our 600 Watt solar panels recharges in a few ours. Still, we use this option rarely.

 

[AntarcticPilot]

A 1kw immersion heater will draw about 83 amps at 12 volts (watts = volts times amps). WIth 2 110Ah batteries, you're going to use all the available capacity to run the immersion heater for an hour, presumng the batteries are fully charged to start with.

The specific heat of water is 4.16 kiloJoules per Kilogram - that is, it requires 4160 joules to raise the temperature of a kilogram of water by 1 degree C. Therefore, to raise the temperature of (say) 20 kg by (say) 30 degrees C will take 4160x20X30 - that is, 2,496,000‬ Joules. A watt is a Joule per second, to a 1kw heater will take 2,496 seconds (41.6 minutes) to heat the water by 30 degrees. SO, heating a tank of water is going to totally flatten your batteries, and that's assuming the tank is perfectly insulated - which, of course, it isn't.

In other words, heating water from your battery bank is going to use all your available battery capacity to heat one tank of water. The only viable way of doing that would be to run the engine while operating the immersion heater - which rather defeats the object of the exercise!

 

[ostra4]

Our hot water tank is 40 litres, very well insulated and fitted with a 1200 watt immersion heater, to get a full tank of hot water takes ages if we are at anchor using main engine, If we want quick hot water I have a 2kw Honda which heats tank in about 20 mins . I'm very aware of keeping use to a minimum to avoid annoying others and also place the genny on a rubber Matt to keep noise down, it's certainly not quiet but 15-20 mins and all is done .....plus a few further minutes if wife wants hairdryer on .....,! Iv rowed away from the boat to check and it doesn't seem bad and probably better than main engine churning away for much longer. Easiest solution would be leave the wife at home !

 

[RupertW]

We are looking at using solar power. Our element is 1.5kw at 230v so plan is to buy a 110v invertor for it alone to reduce the amps and wiring needs ( but double the time of course), and aim only to raise it by a few degrees (sea temp is 25-30 and air temps often a lot higher), and as the batteries go into float by 11am if we are not sailing and using nav lights and autohelm then this should do enough to add 10 degrees I think.

Will buy a cheap invertor to test this out. Won’t work in the Winter but we tend to be in marinas and AC then.

 

[Trident]

Electric heater off an inverter powered by the batteries is a non starter. Heating water requires far too much energy.

I beg to differ - we make 40l every day of scalding hot water using a 2Kw inverter - we do have 1400w of solar and wait until lunch time when the batteries are full and then we can run it effectively for hours if need be just from the solar input without training the batteries at all - they stay on float charge mode the whole time ... Without solar just doing it from battery reserve would be a bad idea of course

 

[maby]

I think that the answer depends very much on how often you are going to need to heat it up away from shore power. The best solution is one of the diesel powered water heaters as described above. Those will give you virtually unlimited supplies of hot water in a convenient package that you can run whenever you want - but they are quite expensive to buy and install.

If this is an infrequent requirement, then a small electric generator is probably the best way to go. Check the power rating of your immersion heater - swap it for an 800w unit if necessary. Then buy a small petrol suitcase-style generator, make up a suitable cable to connect it to your shorepower socket and run it on the foredeck or swim platform. Don't go for the cheapest gennies - they are noisey and bulky. But for less than £500 you should be able to get a decent performance, quiet genny that will do everything you want and will also be available for other things.

 

[lw395]

You can get a used/refurbished diesel water heater for £300 or so, or you can take a chance on one from a scrapper.
That gives additional benefit if you add a couple of heater matrices.
In the UK that is a good way to extend your season IMHO. In fact I think the economics of a cruising boat in the UK without heating look quite dodgy!
On a bigger boat, a proper built in generator is an option.
The oddball option I've not actually seen done on a boat is to add a second or really big alternator. Then the main engine can work reasonably hard and heat the water fairly quickly.

 

[AngusMcDoon]

I beg to differ - we make 40l every day of scalding hot water using a 2Kw inverter - we do have 1400w of solar and wait until lunch time when the batteries are full and then we can run it effectively for hours if need be just from the solar input without training the batteries at all - they stay on float charge mode the whole time ... Without solar just doing it from battery reserve would be a bad idea of course

Ok, I'll rephrase it. Electric heating using the battery bank the OP described is a non starter because as has been shown, it will flatten them completely.

 

[Homer J]

Slight thread drift here but.... given the huge amount of energy required to heat water.....if I drink a couple of litres of ice cold water per day will I be able to eat more Frey bentos pies without weight gain?

 

[cegri]

Slight thread drift here but.... given the huge amount of energy required to heat water.....if I drink a couple of litres of ice cold water per day will I be able to eat more Frey bentos pies without weight gain?

https://www.wired.com/2010/11/the-physics-of-zero-calorie-ice-cream/amp

 

[AngusMcDoon]

Slight thread drift here but.... given the huge amount of energy required to heat water.....if I drink a couple of litres of ice cold water per day will I be able to eat more Frey bentos pies without weight gain?

Yes, but not a lot. It's a recognised effect the one way that helps biffas lose weight is to live in a cooler house. The cold water drinks effect might be minimal though. Food is quite concentrated energy if high fat.

 

[Hoolie]

We are looking at using solar power. Our element is 1.5kw at 230v so plan is to buy a 110v invertor for it alone to reduce the amps and wiring needs ( but double the time of course), and aim only to raise it by a few degrees (sea temp is 25-30 and air temps often a lot higher), and as the batteries go into float by 11am if we are not sailing and using nav lights and autohelm then this should do enough to add 10 degrees I think.

Will buy a cheap invertor to test this out. Won’t work in the Winter but we tend to be in marinas and AC then.

Four times the time actually. For a 230v element at 110v both the current and the volts are halved so watts are one quarter.

 

[lw395]

Four times the time actually. For a 230v element at 110v both the current and the volts are halved so watts are one quarter.

It's not exactly so, because the lower power means the heater element will run cooler, so have a lower resistance than at 230V.
It might be wise to be getting the water hot enough to kill legionella?