Stove Back Boiler Installation

[Keajre]

Hello,

 

About to have a chili-penguin stove delivered with a 8000BTU (1.3KWH) boiler which slots in at the back.

 

Was going to use a non-pressured system, but as my calorifier is level with the stove (about 8 metres away) I wont be able to take advantage of gravity circulation. So I was going to buy a small pump, 12v, something like this:

 

http://www.elyboatchandlers.com/12v-central-heating-pumps/jabsco-12v-circulation-pump

 

Is this strictly speaking ok? My concern is, if the pump were to fail while the fire was in full swing then many bad things could happen which I wont list here.

 

Am I better off scraping my back boiler project on the basis that I cannot rely on gravity given the configuration of the stove and tank?

 

Thanks

 

 

[canals are us?]

If you could of heated just the calorifier by gravity what would of happened if the calorifier was already fully heated as the stove had been lit all day and no hot water used, where would the excess heat go too. The calorifier water and stove boiler could boil.

 

If I was doing it I would install a 1.3kw radiator on gravity circulation on an open vented system and then a separate pumped circuit to the calorifier. Of course the piping from the stove would need to rise up to the rad to enable gravity circulation. The rad could be next to the stove.

 

I have 3 rads on gravity using 28 and 22mm copper and a 15mm pumped feed to the calorifior under the bed at the rear. I turn off the rads using the full bore lever valves and then switch on the pump to heat the domestic hot water.

 

Remember you must not block or restrict the cold feed and vent pipe pipework. any lever valves should tee off from the unrestricted main feed and vent pipes from boiler and header tank.

 

If you can't enable gravity circulation I wouldn't bother with the back boiler on safety grounds.

 

James

Edited August 23, 2016 by canals are us?

[Keajre]

Hi James,

 

Really clear information, thanks for taking the time this helps me a lot.

 

When running the main feed between the boiler and the radiator, can angles (45/90 deg) be used? I presume that makes little difference to the gravity circulation? Is it best to insulate the main feed pipes?

 

I see what you mean about tee'ing off from the main feed and using full bore valves to keep the pipe unrestricted, makes sense. 28mm pipe is pretty hefty, how come you use 28mm and 22mm? Is the 22mm for the radiator connector?

 

I guess the only potential for incident would be closing the full bore valves for the radiator and either forgetting to turn the pump on or the pump failing and it not being apparent.

 

I guess electric full bore valves with temp sensor could be a possible.

 

What pump are you using if you don't mind me asking

 

Many Thanks

[nicknorman]

You might consider these pumps:

 

http://shop.solarproject.co.uk/catalog/product_info.php?cPath=2&products_id=10&osCsid=30411fe47bf3a5595ca7687af8359af1

 

Cheap and cheerful but that means you could plumb in 2, one as a backup. I've got one of these pumps for the radiator circuit fed from the engine heat exchanger, and another pumping engine water through a matrix heater at the back (blows warm air onto the steerers feet). 4 years old so far and whilst they don't run that much, they seem to be fine despite the cheap plasticy look.

 

If you were clever you could arrange an automatic transfer system that switched to the backup pump and put on a warning light on to show it was in backup mode. Two pumps in parallel feeding via the low pressure NRVs on that same site would obviate the need for any motorised valves. http://shop.solarproject.co.uk/catalog/product_info.php?cPath=8&products_id=17

 

Just an over-temp switch on the boiler outlet to activate the backup pump.

Edited August 24, 2016 by nicknorman

[Keajre]

Interesting idea, but I want all the output from the boiler to go into the Calorifier, I'd only want heat to flow into a radiator to displace the heat in cases where the stove was on full tilt and the water tank was already fully heated. or did you mean two pumps (and the indicator lights) and no radiator?

 

What about a small grid of 28mm pipes above the stove to act as a gravity circulation system with electronic full bore temperature activated valves. Then equal tee 15mm pipe connected to Calorifier which would have a circulation pump.

 

How big does the heat displacement mechanism have to be to protect the (1.4kw) boiler from damage in the event that circulation pump(s) failed? Surely not really that big?

[nicknorman]

Well presumably you have to be able to dump 1.4 kw but that would only be if the stove was working at full pelt. In terms of selecting a radiator of course the heat energy dumped by the radiator depends on the difference between the fluid temperature and the ambient temperature. So a radiator specced at 1.4kw would be at say 80C fluid temperature and 20C ambient temperature or something like that. Of course you can allow the fluid temperature to go a bit above 80C (but not more than 90, I'd say) in an "emergency" which will increase the heat dumping of the radiator provided the ambient doesn't get too warm.

 

How about this:

 

A 1.4 kw radiator plumbed into a gravity circulation loop. And thus always capable of dumping the excess heat. Td into that (across the radiator) a loop to the calorifier with a pump controlled from 2 temp switches, one to start the pump when the boiler outlet got warm and one to stop it when the water in the calorifier was up to temperature. But have the pump pull the water the "wrong way" ie such that it pulled the hot water along the bottom and the cold along the top so as to kill thermosyphon within the radiator. Would that work? not sure, never tried it! Perhaps you would need a flap valve (not an NRV) in the radiator bit to stop the circulation when the pump was on.

 

Yes you could use motorised valves and/or a second pump for the radiator loop, but my aim is to ensure that with anything failing, the system remains safe hence having the basic low-tech gravity circulation bit.

 

I'm no expert on this by the way, just chucking a few ideas around!

Edited August 24, 2016 by nicknorman

[Keajre]

Hello,

 

Interesting ideas, thanks for sharing.

 

Rather avoid flap valves incase it constricts flow at times when the radiator is trying to displace heat from the boiler. Perhaps does t make a difference not sure.

 

Interesting idea about flowing water the wrong way to prevent thermosyphon with the rad. No idea if that would work.

 

The mind boggles! Have spoken to a stove fitting company. They broadly agree with the above.

 

Scratching my head about where to put the F&E tank. One idea is to use an old metal kettle :-) yup seen it done!

 

Does the expansion tank (F&E) need to be directly above the hot feed? Can it travel down a horizontal pipe? Or will that defeat it's purpose?

 

 

What about a F&E tank on the roof? Or would that be too wild! A pipe through the roof and a small tank there. Struggling with where to put it due to limitations around space near the stove itself

Edited August 24, 2016 by Keajre

[Keajre]

I have found a header tank that would fit inside the boat, since stainless steel one:

http://www.ratsport.com/PBSCProduct.asp?ItmID=9611933

For the heat sink, Would this work, 10 - 12 meters of 22mm cooper pipe made into a sort of towel rail, only would be using a pipe bender not joints to keep restrictions at zero. There are a lot of horizontal pipes in this design idea, which is a concern, I dont have enough experience to know if gravity circulation would function enough under these conditions, any thoughts from anyone?

 

Woudl use mounts all the way along to support the pipe. Haven't done the maths yet, in terms of how much heat woudl be displaced, but will get back to that after, once I know this design will work.

Edited August 25, 2016 by Keajre