Webasto and Calorifier sizing

[Colin Brendan]

Hi,

 

I have a Webasto Thermo Top C 5.2 KW, and need to replace my Calorifier. I primarily want to use this Webasto for hot water (rads are secondary).

 

Any recommendations for a calorifier size/make that would:

 

A: Give me a shower in 30 mins (I know! How long's a piece of string... right!) - happy to turn rads off to make this happen

B: Allow the Webasto to run in summer without rads for 30 mins without short cycling (I will stick a rad on if I have to but would prefer not).

 

Thanks for any help!

Edited January 26, 2023 by Colin Brendan

[Tony Brooks]

The largest you can fit in. Any reputable make. I suspect there are cheaper alternatives that are just as good to Surecal.

[ditchcrawler]

You could even run the Webasto through both coils if you don't want to use the engine to heat the water

[Colin Brendan]

3 minutes ago, Tony Brooks said:

The largest you can fit in. Any reputable make. I suspect there are cheaper alternatives that are just as good to Surecal.

If it's a big calorifier won't it take longer to heat?

2 minutes ago, ditchcrawler said:

You could even run the Webasto through both coils if you don't want to use the engine to heat the water

Will consider this but I like the engine backup.

[rusty69]

4 minutes ago, Colin Brendan said:

If it's a big calorifier won't it take longer to heat?

Yes

[Tony Brooks]

12 minutes ago, Colin Brendan said:

If it's a big calorifier won't it take longer to heat?

Will consider this but I like the engine backup.

 

I suspect it will take longer to cool down. You will get hot water at the top of the calorifier long before it is all hot.

[David Mack]

13 minutes ago, Colin Brendan said:

If it's a big calorifier won't it take longer to heat?

First you need to know the flow rate, water temperature and duration of your shower, together with the calorifier maximum water storage temperature. Then you can work out what size calorifier you need to hold sufficient hot water for your shower. Then you can look at the heat output of your webasto and the maximum heat transfer rate of the calorifier heating coil to see whether the water can be heated in the required 30 minutes.

Or you can just install the largest calorifier that will fit.

[Colin Brendan]

13 minutes ago, Tony Brooks said:

 

I suspect it will take longer to cool down. You will get hot water at the top of the calorifier long before it is all hot.

Not worried about it cooling down - I guess I'm after a calorifier that will:

 

A: Absorb enough of the 5.2Kw output for 30 mins without causing the heater to step down

B: Give me a shower at the end of that 30 mins (or even before)

10 minutes ago, David Mack said:

First you need to know the flow rate, water temperature and duration of your shower, together with the calorifier maximum water storage temperature. Then you can work out what size calorifier you need to hold sufficient hot water for your shower. Then you can look at the heat output of your webasto and the maximum heat transfer rate of the calorifier heating coil to see whether the water can be heated in the required 30 minutes.

Or you can just install the largest calorifier that will fit.

Yeah I guess that's exactly what I was asking - happy with guesses or peoples experience if they can't provide a precise calculation

 

Edited January 26, 2023 by Colin Brendan

[Tony Brooks]

Sorry, I am out. To a degree it will depend upon the relative temperature of the coil and domestic water so the time will alter throughout the year. Once having looked up the formulae I might be able to work it out for you, but I feel there are too many unknowns.

[Colin Brendan]

I suppose a starting point would be what are surecals coils rated at? Can't seem to find that info.

Or:

• does anyone have a thermotop C?
• How big is your Calorifier?
• How long before you can have a shower?
• Do you have to keep a rad on in summer to stop it short cycling before you get a shower out of it?

[matty40s]

As someone who fits Webastos, you really do need another heat dump rad on the circuit(even a towel rail) to take some of the heat otherwise almost all Webastos I have fitted would cut to short cycle fairly quickly.

It is recommended by Webasto if that helps.

[magnetman]

Triple coil 60 litre two large coils and one small coil. Run the two large ones with the Webasto and the small one with the engine circuit. 

Add one double radiator somewhere in the shower room area..

 

I made that all up but I bet it would work. 

 

Uxbridge boat centre used to do these to order. I expect they are quite expensive though so may not be all that feasible. 

Edited January 26, 2023 by magnetman

[rusty69]

2 minutes ago, magnetman said:

Triple coil 60 litre two large coils and one small coil. Run the two large ones with the Webasto and the small one with the engine circuit. 

Add one double radiator somewhere in the shower room area..

 

I made that all up but I bet it would work. 

 

Uxbridge boat centre used to do these to order. I expect they are quite expensive though so may not be all that feasible. 

When you say large coil, do you mean large bore, long length or both? 

[magnetman]

Bore. I don't know if they do custom length. Two coils had fittings to adapt to 22mm pipe and one had fittings to adapt to 15mm. 

[matty40s]

Edited January 26, 2023 by matty40s

[system 4-50]

2 hours ago, Colin Brendan said:

I suppose a starting point would be what are surecals coils rated at? Can't seem to find that info.

Ask surecal.

I would guess that a big cauliflower would be less likely to immediately short cycle than a small one as having a longer coil(s)??

[ditchcrawler]

57 minutes ago, matty40s said:

Only problem is, its vented not pressuered

[matty40s]

17 minutes ago, ditchcrawler said:

Only problem is, its vented not pressuered

I'm quite sure there are capable individuals with skills beyond ours...

[Colin Brendan]

On a slight tangent - anyone had any joy with something like this? 

 

https://www.butlertechnik.com/webasto-motor-home-plate-heat-exchanger-with-mixer-valve-4111209a-p1516

[David Mack]

43 minutes ago, Colin Brendan said:

On a slight tangent - anyone had any joy with something like this? 

 

https://www.butlertechnik.com/webasto-motor-home-plate-heat-exchanger-with-mixer-valve-4111209a-p1516

To use your webasto as an instantaneous shower? I would have thought the heat output a bit on the low side, unless you are happy with a cool shower or a low flow rate.

[matty40s]

8 hours ago, Colin Brendan said:

On a slight tangent - anyone had any joy with something like this? 

 

https://www.butlertechnik.com/webasto-motor-home-plate-heat-exchanger-with-mixer-valve-4111209a-p1516

Your boat engine will not be working hard enough for you to benefit much from this. You would probably have to install a valve system to shut off the skin tanks whilst you have a shower and then switch it back as soon as you are out of the shower. What a faff.

There is a reason 95% of boats are plumbed how they are....it works.

[GUMPY]

I've found with a vertical calorifier and an immersion heater in the top the quickest way to get enough hot water for two showers is to use the immersion for 10-15 minutes. Uses about 20Ah from the battery bank. Works every time for us😱

 

[ditchcrawler]

3 hours ago, Loddon said:

I've found with a vertical calorifier and an immersion heater in the top the quickest way to get enough hot water for two showers is to use the immersion for 10-15 minutes. Uses about 20Ah from the battery bank. Works every time for us😱

 

Wait for post saying its mad to heat with electricity, it will kill your batteries in minutes, etc.

[David Mack]

5 hours ago, matty40s said:

Your boat engine will not be working hard enough for you to benefit much from this. You would probably have to install a valve system to shut off the skin tanks whilst you have a shower and then switch it back as soon as you are out of the shower. What a faff.

There is a reason 95% of boats are plumbed how they are....it works.

The link posted above is suggesting it is used to heat the shower water directly from the webasto/radiator circulation.

 

[GUMPY]

1 hour ago, ditchcrawler said:

Wait for post saying its mad to heat with electricity, it will kill your batteries in minutes, etc.

20Ah is 6% of my nominal battery capacity hardly a problem when the overnight capacity is only down to 89%🤔

As it happens I shower in the evening when the water is hot from our days boating😱