Hot Water

[Hudds Lad]

i was just having a ponder about hot water on the boat. when we were onboard during Storm Ciara, or whatever the one was that came directly after it, and couldn't get out of the marina we kind of struggled for hot water.

 

normally we'd be running the engine whilst moving which provides a nice full tank of hot which is still nice and toasty the next day, so i've never really thought much about it when static.

whilst on shorepower at the marina i ran the immersion heater for about half an hour, which gave "warm" not hot water. useless for greasy washing up. guessing i didn't run it long enough.

i'm unsure if running the Alde boiler for the heating gives a tank of hot, i'm assuming it would but we rarely use it as it burns gas for fun.

 

so, long story short, lets say you have a calorifier tank of average boat-size (no idea what capacity of ours is), how long would you guesstimate to produce a tank of hot from;

a) engine running whilst cruising

b) immersion heater

c) central heating

 

just after ballpark figures from your experience, ta.

[David Mack]

A standard domestic water heater is usually 3kW. The types fitted to boats are often 1kW, in order to keep the current taken from the shore supply down. That means a given size of tank on a boat is going to take three times as long as its house counterpart to heat up. Add to that the effect that if your calorifier is under a cruiser stern the starting point is going to be water and not much above freezing on a day like today, whereas in a house the water will start at room temperature.

 

The Alde on Belfast drinks gas, but will heat enough water for a good shower in about half an hour with the radiators turned off.

[Mad Harold]

On my last boat it had a Morco gas instant water heater.

Used for washing,washing up and showers.

Didn't think it's gas consumtion was excessive,but I used to turn the pilot light off when not required.

 

[Alan de Enfield]

17 minutes ago, Hudds Lad said:

b) immersion heater

 

It will depend on the size of the tank (Cauliflower) and the thermostat settings.

 

I have set the the thermostat on our cauliflower to 85 degrees, it is a 65 litre tank and I set the timer to 2 hours.

After that there is sufficient (almost) boiling water for washing the pots, and at least couple of showers

 

 

 

Edited February 2, 2021 by Alan de Enfield

[dmr]

Lots of variables. We are liveaboards so the calorifier is never colder than warm, starting from stone cold would take quite a bit longer.

 

The engine takes maybe a couple of hours to get the water really hot. I suspect for the first few minutes it actually takes heat out of the calorifier to heat itself.

The Alde is for emergencies only and takes ages to make warmish water.

We have a vertical calorifier and a short immersion heater in the top so it makes hot water quite quickly but not very much of it, only the top gets hot..

 

..............Dave

[Hudds Lad]

part of the problem is the calorifier is horizontal and in the engine bay i suppose.

 

no idea what temp immersion is set at, only control for it i know of is a switch under the steps  

 

i was just thinking if say engine took two hours for a full tank, would boiler and immersion be comparable or longer?

like i said, just pondering and wondering what similar setups performed like.

appreciate i can't furnish much detail. but you know, shareboat, lockdown, that sort of thing  

[rgreg]

39 minutes ago, Hudds Lad said:

...

 

so, long story short, lets say you have a calorifier tank of average boat-size (no idea what capacity of ours is), how long would you guesstimate to produce a tank of hot from;

a) engine running whilst cruising

b) immersion heater

c) central heating

 

just after ballpark figures from your experience, ta.

a) 2 hours

b) 1 hour

c) 1 hour (Alde to calorifier only) 

 

[nicknorman]

2 minutes ago, Hudds Lad said:

part of the problem is the calorifier is horizontal and in the engine bay i suppose.

 

no idea what temp immersion is set at, only control for it i know of is a switch under the steps  

 

i was just thinking if say engine took two hours for a full tank, would boiler and immersion be comparable or longer?

like i said, just pondering and wondering what similar setups performed like.

appreciate i can't furnish much detail. but you know, shareboat, lockdown, that sort of thing  

Assuming the immersion heater is 1kw then the engine is likely to heat it quicker - I would expect plenty of piping hot water after an hour’s running, whereas an hour on a 1kw immersion, starting from cold, will only give you warmish. But on the other hand, it is much cheaper and calmer to heat the water from the immersion, if you have shore power. If you are on the boat for a while and on shore power, you can leave the immersion switched on because they have a built in thermostat.

[Tonka]

Quote from screwfix

Whether the water from an electric immersion water heater is too hot or too cold, it can be easily adjusted as it is thermostatically controlled. The protective cap over the connections to the immersion heater is normally held in place by a nut or screw. ...

 

may be worth a look

[jonathanA]

I'd have put a & b the other way round.

 

Assuming the usual 1kw immersion. Mine takes easily a couple of hours o  immersion 55l surecal horizontal under the bed

 

Cross posted with nickn. 

Edited February 2, 2021 by jonathanA

[mrsmelly]

We have a large cauliflower and BY FAR the best way if on hook up is the immersion heater. Mains electric is virtualy free and makes it a no brainer. I leave my immersion on 24/7 365 we also have a fridge and freezer both on summer or winter 24/7 365 and the mrs uses the large washing machine 2/3 times a week. There is telly leccy kettle and lots of other kit and the most it ever costs is 60 quid a month or if you like 2 quid a day. I have used a timer on the immersion and can get another 15 quid a month off that but I leave it on now.

[ditchcrawler]

From this about 3 hours https://www.sust-it.net/immersion-heater-energy-calculator.php?fu=20&cu=uk

[Onewheeler]

Both the engine and the Webasto get our water hot enough for a shower or washing up in about twenty minutes. Roughly an hour from either to get to the tank being more or less fully up to temperature.

[Jen-in-Wellies]

Around two to three hours from coldish with a backboiler from a squirrel stove. A similar time from solar thermal hot water, depending on the weather. It isn't working too well today...

[blackrose]

11 hours ago, Hudds Lad said:

 

a) engine running whilst cruising

b) immersion heater

c) central heating

 

On my boat the 60 litre calorifier is in the cabin and I have a 1kW immersion heater so it's:

 

a) 40 mins

b) 90 mins

c) when my eberspacher worked I think it used to take about 45 mins - an hour

 

10 hours ago, Tonka said:

Quote from screwfix

Whether the water from an electric immersion water heater is too hot or too cold, it can be easily adjusted as it is thermostatically controlled. The protective cap over the connections to the immersion heater is normally held in place by a nut or screw. ...

 

may be worth a look

 

But make sure it's not live before taking the cap off!

[Ex Brummie]

Just think, The average kettle now has a 2kw element and takes 3 mins to heat a litre. The element is also in the bottom so

it heats all the water. 

A boat calorifier with a 1kw heater has a 1ft element, so in a vertical calorifier will only heat up about 1/4 of the capacity. If you take no water out, then you will get some transference down to the other 3/4 of the cylinder. 

If your calorifier is horizontal, then you heat up more of your capacity, but if the outlet is halfway up the cylinder like some I've seen, then you only ever draw cooler water than you have at the top.

As the americans say, do the math.

[Alan de Enfield]

29 minutes ago, Ex Brummie said:

A boat calorifier with a 1kw heater has a 1ft element, so in a vertical calorifier will only heat up about 1/4 of the capacity.

 

That may be true is the element was fitted into the top of the cylinder, but that is not how they are fitted.

 

As you can see on mine, the element is very close to the bottom of the cyliner and hence heats all of the water. (Just like a kettle)

 

 

[Boatingbiker]

The norm is to use a 2 hour heat up or recovery time to heat the contents of the calorifier from typically 10 deg C to 65 deg C and the  heating coil within the calorifier will be sized accordingly.

 

To calculate the required heat input in kW is given by the following equation 

 

Heat input (kW) = calorifier capacity in litres X constant (4.2) X Temperature difference between hot water temperature at outlet and  cold fill temp (typivally 65 -10) all divided by recovery time in seconds.

 

Therefore for a 200 litres calorifier, cold water in at 10 and Hot water out at 65 and 2 hour recovery = 200 X 4.2 x (65-10) / 2 x 3600  = 6.4 kW

 

Increasing the available energy input from a primary source will not necessary reduce the time taken as it depends upon the coil fitted by the manufacturer. 2 hours is the norm used by most manufacturers but can be changed at design stage  

 

 

Following on from above , if you want to calculate the time taken to heat the water then

 

Time (seconds) = calorifier capacity x 4.2 (constant) x tempature difference all divided by heat input in kW

 

ie TT = 200 x 4.2 x 55  /   6.4  = 7218 seconds  divide this by 3600 = 2.0 hours

 

 

Hope this helps

Edited February 3, 2021 by Boatingbiker

[Sea Dog]

18 hours ago, Jen-in-Wellies said:

Around two to three hours from coldish with a backboiler from a squirrel stove. A similar time from solar thermal hot water, depending on the weather. It isn't working too well today...

I'd have thought you'd be OK with all that lovely insulation on your roof, Jen!

 

[Boatingbiker]

post deleted

 

Edited February 3, 2021 by Boatingbiker
post combined with earlier post

[doratheexplorer]

19 hours ago, rgreg said:

a) 2 hours

b) 1 hour

c) 1 hour (Alde to calorifier only) 

 

This is not my experience.

 

55l surecal calorifier.

 

1kw immersion at least 1.5hrs

 

Engine about an hour.

 

Alde  - this is a bit more complicated.  I've done a lot of experimenting with gas use.  So - on full power (number 7 on the dial), with the rads turned off - about 45 minutes.  However, the Alde guzzles gas on number 7, so I never use it that way.  I've found maximum efficiency is at around 5 on the dial, and at that setting the Alde takes just over an hour (1hr10min roughly), but uses far less gas.

 

In terms of cost, immersion is cheapest as long as the marina hasn't added cost to the unit price.  Alde, surprisingly, is not far behind, as long as you use it at its best.  Engine, by far the most expensive way (probably best part of a litre of diesel), but you do get some battery charging too.

 

All these time vary slightly according to the temperature of the water in the tank at the start.

 

Edited February 3, 2021 by doratheexplorer