Installing Stove with Back Boiler

[smileypete]

A is correct! Large tees and reducers sounds good.

 

What sort of pump will be used? These days there are 12V circulation pumps from £16ish on Ebay, worth having a spare at that price. With the pump it's best to have the outlet pointing up so it 'self bleeds'.

 

The small pumps aren't all that powerful, if so ideally have the pipes with a bit of a slope towards either radiator or backboiler so air can't get trapped, the angle the boat sits in the water will probably do OK if they're run parallel.

 

Same for the pipes to the header tank, would help to have a small slope towards the tank so trapped air can escape there, but it's not so critical as the pumped part.

 

Some people have the pump on a 'pipe thermostat' so it only runs when the backboiler outlet pipe is hot, a strap on cylinder stat can usually be used here.

 

cheers, Pete.

~smpt~

Edited August 21, 2014 by smileypete

[Staarek]

A is correct! Large tees and reducers sounds good.

 

What sort of pump will be used? These days there are ones from £16ish on Ebay, worth having a spare at that price. With the pump it's best to have the outlet pointing up so it 'self bleeds'.

 

The small pumps aren't all that powerful, so best have the pipes with a little slope towards either a radiator or backboiler so air can't get trapped, the angle the boat sits in the water may help here.

 

Same for the pipes to the header tank, they should have a small slope towards the tank so trapped air can escape there and the system 'self bleeds'.

 

cheers, Pete.

~smpt~

 

Plenty of great advice! Many thanks Pete.

I bought one of these pumps that is used in solar installations, it was around 40 quid from ebay, 12l/h head of 3 m. I will test it and get bigger one if needed. Regarding the pipe entering the header tank from the top, does it actually have to be going all the way to the bottom of the tank or is it ok as long as the end is submerged in water?

[Paul G2]

I'd go for something like this:

 

Based on adequately sized gravity rads near or next to the stove, and more distant rads on a pump.

 

That way you can choose to have all the heat going to the saloon if you wish, and are not reliant on a pump and it's 12V supply.

 

cheers, Pete.

~smpt~

 

 

You can get the real © symbol by holding down the Alt key then typing 0169, assuming you have a Windows machine.

[smileypete]

 

Plenty of great advice! Many thanks Pete.

I bought one of these pumps that is used in solar installations, it was around 40 quid from ebay, 12l/h head of 3 m. I will test it and get bigger one if needed. Regarding the pipe entering the header tank from the top, does it actually have to be going all the way to the bottom of the tank or is it ok as long as the end is submerged in water?

 

Best have it ending say 1" below the very top edge of the tank.

 

The idea is that if the system boils, the water is pushed back into the tank, not up in the air like a geyser! Can also be helpful to have a loose fitting lid on top of the tank to help reduce evaporation.

 

A pump with 12l/min will be plenty, might even be scope in future to slow it down to reduce power use and any noise, though best get things up and running first.

 

 

 

 

You can get the real © symbol by holding down the Alt key then typing 0169, assuming you have a Windows machine.

 

Ta that is useful to know © Alt 248 is another useful one.

 

cheers, Pete.

~smpt~

Edited August 21, 2014 by smileypete

[Staarek]

 

Best have it ending say 1" below the very top edge of the tank.

 

The idea is that if the system boils, the water is pushed back into the tank, not up in the air like a geyser! Can also be helpful to have a loose fitting lid on top of the tank to help reduce evaporation.

 

A pump with 12l/min will be plenty, might even be scope in future to slow it down to reduce power use and any noise, though best get things up and running first.

 

 

 

Ta that is useful to know © Alt 248 is another useful one.

 

cheers, Pete.

~smpt~

 

Thanks again Pete, I will report back to let you know how did it go once I'm done.

[Staarek]

Ok so I got everything in place. The stove works a treat and I love it. The back boiler doesn’t seem to be doing anything though. I bled the system and it seems that the water circulates but the rad stays cold. The pipes immediately after the back boiler don’t seem to be getting warm. Yesterday I had the fire on for about 5 hours and no joy. I’ve got it connected as in drawing “A”. Any suggestion will be appreciated.

Thanks!

[smileypete]

Does the backboiler start to heat up if the pump is switched off temporarily?

 

Could be the weather is quite mild so the stove is running at a low output. Usual way to control the pump is with a cylinder stat fixed to the pipe near the top backboiler outlet, saves power when the stove is low.

 

cheers, Pete.

~smpt~

Edited September 23, 2014 by smileypete

[Staarek]

Does the backboiler start to heat up if the pump is switched off temporarily?

 

So you have 1 rad pumped from the backboiler, what's the output of stove and backboiler in kW, and the size of the rad, is it a single or double rad, kW if known?

 

Could be the weather is quite mild so the stove is running at a low output.

 

cheers, Pete.

~smpt~

 

Hi Pete and thanks for your post.

 

I didn't try to have the stove on without the pump running as I wasn't sure if it was safe. I will try today/tomorrow though.

The backboiler is rated at 1.2kw and so is the rad. It is 3 Column Radiator 600mm x 600mm. There is quite a bit of piping too, but I'm still surprised that pipes coming out from the boiler are not even getting warm.

 

The boiler is Arada unit (picture attached)

(return is connected to the lower point)

I was thinking, would it be viable to close the valves at the radiator for a while to see if the pipework is getting warm? Would that be safe?

[smileypete]

Sorry yes, you mentioned the backboiler and rad kW back at the start.

 

Should be fine to turn the pump off for a bit, feel the backboiler top outlet pipe to check if it gets hot. All a thermostat will do is turn the pump on and off automatically according to the temp of the top outlet pipe. If it's starts to boil you'll definitely know as the backboiler will make a kettling/banging sound.

 

Best to leave the rad fully open as it's the only one. One other thought, any antifreeze used should be premixed before filling though the pump might do that OK.

 

ETA: If you'd prefer a bigger proportion of heat going to the backboiler, something that may help a little is to line either side of the stove (left and right) with more firebrick or equivalent fire board, though best check with Arrow to see if they think it's OK to do.

 

cheers, Pete.

~smpt~

Edited September 23, 2014 by smileypete

[Staarek]

Sorry yes, you mentioned the backboiler and rad kW back at the start.

 

Should be fine to turn the pump off for a bit, feel the backboiler top outlet pipe to check if it gets hot. All a thermostat will do is turn the pump on and off automatically according to the temp of the top outlet pipe. If it's starts to boil you'll definitely know as the backboiler will make a kettling/banging sound.

 

Best to leave the rad fully open as it's the only one. One other thought, any antifreeze used should be premixed though the pump might do that OK.

 

cheers, Pete.

~smpt~

 

Perfect, thanks Pete, I will try that. I premixed antifreeze before I filled the system up as I heard it doesn't mix well once in the pipes.

[smileypete]

If you want to get as much heat as poss the the radiator, would also help to lag the pipes between backboiler and rad, just the 9mm foam lagging should do fine though a bit unsightly unless 'boxed in' with ply etc, maybe leave the pipe exposed where you want a little background heat like loo/bathroom.

 

cheers, Pete.

~smpt~

Edited September 23, 2014 by smileypete

[Staarek]

If you want to get as much heat as poss the the radiator, would also help to lag the pipes between backboiler and rad, just the 9mm foam lagging should do fine though a bit unsightly unless 'boxed in' with ply etc, maybe leave the pipe exposed where you want a little background heat like loo/bathroom.

 

cheers, Pete.

~smpt~

 

Cheers Pete. I will run some more tests and see if the rad is getting warm at all. I'm thinking that maybe the stove might just need to run hotter. I'm looking to insulate some parts of the pipework (ones that running in the engine compartment and under the bow) I would prefer to leave the rest uninsulated as in the end the heat is staying inside the boat. Also I'm not over convinced about the pump, I'm looking into getting one for Webasto/Eberspacher as these ones are designed for similar applications. One I've got at the moment is for solar applications and I'm thinking that maybe it's not suitable.

[Staarek]

I managed to run some tests yesterday and it turned out the back boiler is getting hot when the pump is off. I also tried to reduce the flow of the pump (partly closing the ball valve installed after the pump) and the pipes were starting to get warm.

 

I was thinking to do the following:

• Replace the antifreeze with just water as it should be easier for the back boiler to heat up water than antifreeze.
• Insulate all the pipes (19mm thick or more) and the header tank
• Reduce the flow of the pump a bit (not with partly close valve as the pump won’t last long that way but maybe with lower voltage delivered to the pump?

 

Any suggestion will be appreciated. Thanks!

[smileypete]

For lagging 9mm or 13mm poly foam will do, much bigger won't save that much more, but not too close to the stove due to fire risk. The header tank, and its feed and vent pipes should stay cold so no need for insulation there.

 

Reducing the speed of the pump or leaving out the antifreeze won't make any difference to the backboiler output. If the pump is bit annoying switching in and out, then running it at lower speed could be helpful.

 

For a thermostat there's also the small non-adjustable normally open (N.O.) button thermostats for a few £, could have one switching the pump on low speed at around say 60°C and one switching full power at say 80°C:

 

http://www.ebay.co.uk/sch/i.html?_sacat=0&_sop=15&_nkw=no+thermostat&rt=nc&LH_PrefLoc=2

 

To slow the pump down, could use a resistor, even a 12V 8W to 20W filament bulb, or a cheap PWM controller might do OK:

 

http://www.ebay.co.uk/sch/i.html?_sacat=0&_sop=15&_nkw=no+thermostat&rt=nc&LH_PrefLoc=2

 

cheers, Pete.

~smpt~

Edited September 24, 2014 by smileypete

[Staarek]

Thanks Pete. I will do some work on it during weekend and report back.