nautic boiler extra heating coil

[Mike Adams]

I have a 40 litre nautic boiler with only one heating coil. It has an immersion heater that dosen't work and I have never used. Rather than change the calorifier for one with two heating elements so I can connect up the webasto that does the central heating I was thinking of either fabricating a coil that could be inserted in place of the electric heating element or buying one. I seem to have a vague recollection that these were available in some form but I can't find any. Anyone done this or similar?

[Tony Brooks]

As long as the Webasto and the boiler are open vented and the  engine is not involved I can't see any problems apart from the possibility of heated water passing through the non-operating boiler.

 

The solar hot water suppliers sell a coil like you describe and it may even have an immersion heater in it.

 

Edited to add - both could probably share the same expansion tank.

Edited May 3, 2020 by Tony Brooks

[David Mack]

https://www.ebay.co.uk/itm/272972899295

[Ex Brummie]

Such a coil can be easily made with 10mm copper wrapped around a suitable core to achieve the item in David Mack's post, with an immersion blanking plug fitted with a couple of 10mm bulkhead fittings. Much cheaper than £80.

There used to be a product called Hot Rod that was used in the 70's and 80's to convert immersion heaters to water systems, but not seen one for years.

[Mike Adams]

Thanks. The problem is that the hole with the heater in is only 1" 1/4 BSP  much smaller than the domestic ones and I am not sure of the minimum bend radius for 10mm pipe to make a coil. Anything smaller probably wouldn't allow sufficient flow. I am thinking of 6 lengths or however many I can fit in of 10mm into a brass boss at either end with drillings to make a continuous coil. I could thread one end to screw into the tank. I need a few lockdown projects!

[ditchcrawler]

8 hours ago, Mike Adams said:

I have a 40 litre nautic boiler with only one heating coil. It has an immersion heater that dosen't work and I have never used. Rather than change the calorifier for one with two heating elements so I can connect up the webasto that does the central heating I was thinking of either fabricating a coil that could be inserted in place of the electric heating element or buying one. I seem to have a vague recollection that these were available in some form but I can't find any. Anyone done this or similar?

I saw one and posted details a couple of years ago, it was to put solar heat into the calorifier.

[Tracy D'arth]

5 hours ago, Mike Adams said:

Thanks. The problem is that the hole with the heater in is only 1" 1/4 BSP  much smaller than the domestic ones and I am not sure of the minimum bend radius for 10mm pipe to make a coil. Anything smaller probably wouldn't allow sufficient flow. I am thinking of 6 lengths or however many I can fit in of 10mm into a brass boss at either end with drillings to make a continuous coil. I could thread one end to screw into the tank. I need a few lockdown projects!

Here you are,

https://www.ebay.co.uk/itm/1-1-4-BSP-Hot-Water-15mm-Rod-Coil-Heating-Immersion-Calorifier-Solar-Marine/123719920362?hash=item1cce482aea:g:SesAAOSwU6RdQEpW

 

TD'

[Mike Adams]

Thanks TD looks suitable but maybe it is only a couple of these at £3.95 from screwfix?

[Tracy D'arth]

3 hours ago, Mike Adams said:

Thanks TD looks suitable but maybe it is only a couple of these at £3.95 from screwfix?

A good bit longer I think and you will have problems getting elbows tight enough on the turn at the bottom. There is a guy in Warrington on ebay who makes hot rods any length using these flexible copper sections and end feed fittings, all brazed together into a standard 2 1/4 BSP brass blanking  plug. But I don't think he could do it with the smaller marine flange.

The price for that marine one on ebay is not too bad considering.

[Ex Brummie]

If you use this 15mm one, you will need a valve on the return to balance/restrict it so that the water has chance to do the job you want.

[WotEver]

18 minutes ago, Ex Brummie said:

If you use this 15mm one, you will need a valve on the return to balance/restrict it so that the water has chance to do the job you want.

I don’t follow that logic. The slower the water flows through the loop, the cooler it will get. Have it moving through quickly and it will surely be hotter?

[Mike Adams]

I've decided I am going to have a go at fabricating one myself using 4 lengths of 15mm pipe 20 inches long to fill the full length of the horizonal cylinder. I will make up a brass boss with a 1 1/4" inch thread at one end and a plain one at the other end with cross drillings in both bosses to get a continuous loop and solder the pipes into each boss. I will post a picture when I've made it.

Cheers!

[Ex Brummie]

3 hours ago, WotEver said:

I don’t follow that logic. The slower the water flows through the loop, the cooler it will get. Have it moving through quickly and it will surely be hotter?

Just like a central heating system, the flow needs to be matched to the heat exchange capacity so that hot water does not flow too quickly through the coil, otherwise it imparts no heat to the load. 

[WotEver]

17 minutes ago, Ex Brummie said:

Just like a central heating system, the flow needs to be matched to the heat exchange capacity so that hot water does not flow too quickly through the coil, otherwise it imparts no heat to the load. 

Nope, I’m not seeing it. You have a tank of cold water and you put a coil of hot water into it. The cold water is heated by the fact that it’s in contact with the hot coil. How does the speed of the hot water flowing through the coil affect that heat transfer?

[WotEver]

If you were passing the cold water through a coil in a hot tank in order to heat the coil then I could see why you’d want to slow that flow, but not this way round. 

[Ex Brummie]

You need to balance the system so that the coil does not take everything from the Webasto leaving cold heating. Water will always take the line of least resistance and this arrangement will provide an easier route. The system needs some thinking out and some form of manual diverter/mixing valve may be needed so that the OP can prioritise his requirements.

[David Mack]

21 hours ago, Tracy D'arth said:

A good bit longer I think and you will have problems getting elbows tight enough on the turn at the bottom.

I notice the ones on eBay have elbows at the bottom which fit inside the tube, rather than the normal outside. I assume the guy uses 10mm end feed elbows (or some other odd size) inside 15mm pipe and brazes them together, since it's unlikely to be a close enough fit for solder.

[Tracy D'arth]

2 hours ago, David Mack said:

I notice the ones on eBay have elbows at the bottom which fit inside the tube, rather than the normal outside. I assume the guy uses 10mm end feed elbows (or some other odd size) inside 15mm pipe and brazes them together, since it's unlikely to be a close enough fit for solder.

They will be 12mm elbows, possibly a street elbow into an ordinary one to save length. They will be brazed, solder would be a poor job in this situation.

TD'

[WotEver]

11 hours ago, Ex Brummie said:

You need to balance the system so that the coil does not take everything from the Webasto leaving cold heating. Water will always take the line of least resistance and this arrangement will provide an easier route. The system needs some thinking out and some form of manual diverter/mixing valve may be needed so that the OP can prioritise his requirements.

All the more reason to pass it through the cylinder as fast as possible, assuming that it's plumbed in series with the rads.  Obviously, if it's a parallel connection then the whole thing will need to be balanced, but not for the reason you quoted in post 10.

[Jon57]

12 hours ago, David Mack said:

I notice the ones on eBay have elbows at the bottom which fit inside the tube, rather than the normal outside. I assume the guy uses 10mm end feed elbows (or some other odd size) inside 15mm pipe and brazes them together, since it's unlikely to be a close enough fit for solder.

12 hours ago, David Mack said:

I notice the ones on eBay have elbows at the bottom which fit inside the tube, rather than the normal outside. I assume the guy uses 10mm end feed elbows (or some other odd size) inside 15mm pipe and brazes them together, since it's unlikely to be a close enough fit for solder.

Possible this kind of fitting 

[Mike Adams]

The 'hole' through which the unit needs to fit is only 39mm. Maybe a 12mm one, if you can get it would fit.

[Jon57]

29 minutes ago, Mike Adams said:

The 'hole' through which the unit needs to fit is only 39mm. Maybe a 12mm one, if you can get it would fit.

2 x 15mm Street elbows butched might do it.? Worth a try for only £2

[Mike Adams]

Started working on this last night. 15mm seems to large so going with 12mm. I have made one end now to make the other.

 

[Tracy D'arth]

1 hour ago, Mike Adams said:

Started working on this last night. 15mm seems to large so going with 12mm. I have made one end now to make the other.

 

Very nice bit of brass turning. It must be lovely to have access to a decent lathe.  How are you doing the bottom end? Same way with a recess pipe to pipe under a screw on cap ?  Flow down 2 and back up 2?

[Mike Adams]

I was going to have a single loop, twice up and down, using two cross drillings at the other end and one on this end which gives about 80 inches of pipe. I don't know if it better to have two parallel paths as most calorifiers just have a single coil.