Pump for Back Boiler - Recommendations

[Motters79]

Hello all,

 

I would like to plumb a backboiler into my existing radiator circuit. It will need to be pumped and I'm trying to find the best pump for the job. Can anyone recommend a good one that is quiet and efficient without costing a fortune?

 

Thanks

[Tony Brooks]

Not recommending because I have never used one (gravity system) but a fair number have used 12V hot water Solar pumps. A number on Google around £20

Edited August 16, 2020 by Tony Brooks

[Tracy D'arth]

I have always refused to install solid fuel stoves that rely on a pump for circulation. I and many others including the solid fuel advisory board regard such installations as dangerous.

[BEngo]

6 hours ago, Tracy D'arth said:

I have always refused to install solid fuel stoves that rely on a pump for circulation. I and many others including the solid fuel advisory board regard such installations as dangerous.

The OP has an existing radiator  circuit.  It presumably  doesn't have a back boiler, but may or may not be pumped.  There is no info about the heat source.

 

  Adding a pumped backboiler will be a nightmare to balance if both existing and new heat sources are to work properly.

  Much could depend on where in the circuit the backboiler is going to be.

 

Even with a pump, boiling is potentially  quite likely, because of balance/configuration issues

 

N

Edited August 16, 2020 by BEngo

[Tony Brooks]

2 minutes ago, BEngo said:

The OP has an existing circuit, without a pump. 

N

Yes, but is that from a gas boiler or diesel boiler. Both have thermostats and overheat cut-outs unlike solid fuel stoves. It may even be a sealed system that would make a potential bomb if a solid fuel stove is plumbed into it. Not enough info in the post to make much of a reply.

[Motters79]

Hi guys sorry for the delay in replying. Been a busy  few weeks! 

 

To clarify, my existing system is a Webasto in the engine bay feeding a calorifier, 3 double rads down the length if the  boat and a towel rad. 

 

What I hoped to do was to replace my stove for a boiler stove and integrate it into the system. My stove is at the front on the opposite side to the radiator circuit, hence the need for a pump. All my pipe runs for existing rads are at floor level, plus being on the other side to the rad, gravity isn't going to work any way as my bow doors are in the way, and the pipe work has to do 180 degrees on the flat. However I understand the need for a heat leak rad that is gravity fed so I was planning on having a rad on same said as fire about 8 feet away with feed pipe rising gently from stove to just under gunwhale where it would enter the radiator top port. This radiator is at 90 deg to the pipe run however as radiator will  have to hang on the back of my kitchen bulkhead (is this ok and is it on to have a lockshield on both ends of rad?)

 

I was thinking of getting a stove with 4 tappings so that the heat leak rad could gravity feed from one set and the other existing run could be pumped from the other. My webasto set up is currenlty a sealed system but I would change this to vented. Does it matter where I put the header tank? Do I need any kind of over vent into the header tank from the hot feed pipe? 

 

Does my system feasible? Im sure the pumped side will.work fine I'm mainly concearned about getting the gravity part working adequatly.

[Tracy D'arth]

Pet hate, sorry but true.  Dangerous pumped solid fuel fired boilers on boats.

Will your "heat leak" take anything like the full output of the fire?

At least you appreciate that a sealed system would be even more dangerous.

[Motters79]

2 minutes ago, Tracy D'arth said:

Will your "heat leak" take anything like the full output of the fire?

It's a most valid concern. It concerns me hence why Im trying to iron out all the pitfall first.

I'm hoping somewhere very close to full output. The exact  stove has not been decided upon yet but I could fit a 600 × 1200 double rad in that location if necessary.

[David Mack]

Whatever else you do you will need a vent pipe with a continuous rise from an upper boiler tapping, to vent steam if the boiler does boil. Normally this would end at the header tank, so you will need a feed and expansion tank at high level on the same side of the boat as the boiler. 

[Motters79]

1 hour ago, David Mack said:

Whatever else you do you will need a vent pipe with a continuous rise from an upper boiler tapping, to vent steam if the boiler does boil. Normally this would end at the header tank, so you will need a feed and expansion tank at high level on the same side of the boat as the boiler. 

Does this need to be a separate pipe to the one connecting the header tank to the system, or will steam just escape into the header tank provided its connected at a high point near the hot outlet from the stove? I was thinking of connecting the header tank at the end of the rise before it goes into the radiator.

[Higgs]

1 hour ago, Motters79 said:

Does this need to be a separate pipe to the one connecting the header tank to the system, or will steam just escape into the header tank provided its connected at a high point near the hot outlet from the stove? I was thinking of connecting the header tank at the end of the rise before it goes into the radiator.

 

In a stove-backboiler setup, it is common practice to have an expansion tank, or header, It is not a pressurised or sealed system and the header provides space for the heated fluid to expand into, and also provides a reservoir to replace any evaporated fluid, keeping the system fully filled. The main system pipe is 28mm, from the backboiler and return to it. The header pipe is at the end of the run, and usually its highest point, where the fluid is slightly cooler than when it leaves the boiler. The pipe to the header is smaller and only likely to be used by the system for expansion, not flow. 

 

From the backboiler, the 28mm rises; on its way back, it runs downhill. Mine has a rise of about 100mm over 40'. 

 

 

 

I'm not completely sure of the rise feature: Is it to compensate for the rake in the boat, or is it required for the thermosyphon function. Anybody. ?? 

 

 

 

Edited September 1, 2020 by Higgs