Tell me if im missing anything major - backboiler diagram

[WaterMao]

I'm sure I'm about to get ripped to shreds and I'm READY for it. 

 

Background; buying a 42ft trad with no plumbing, leccy or gas fit out. I've made the major decisions regarding solar, batteries etc (on order).

 

I'm wanting to install a back boiler on the puffin villager that's installed and have this as my main source of heating for a calorifier. For safety purposes, I'd have a thermostatically controlled pump going to a small radiator in the bedroom (behind where I'm installing the bathroom, trad layout) and then the header tank at the end of the circuit potentially in the engine room (?). I'm not really arsed about the rad in all honesty so if there's any other way of dumping the excess heat without this going back into the recycled cool water let me know. 

 

I'm planning on doing this as gravity fed, at least in terms of transferring the heat from the stove to the calorifier. I'd probably mount the calorifier somewhere in the kitchen. 

 

My main queries are:

 

- Would a flue mitigate the need for the rad dump, is that doable on gravity fed systems?

- Am I right in my pump placement?

- Am I missing anything major?

- Shall I give up and get a gas boiler?

 

BTW, I'm happy only using hot water when the stove is on, I like cold showers and have a mooring with showers, I also like the simplicity of having the heating system fed by the burner and not too dependent on leccy or gas. I must admit I'm also drawn in by a certain romanticism about the solid fuel stove truly being the "heart of the boat" lol. 

 

Please see my awful diagram below (ignore the "cold water in" and "heat pump" I'm very tired and still trying to understand this properly).

 

Thanks!!

 

 

 

[Tracy D'arth]

So the very short life radiator is heated my the domestic warm water supply at water pump pressure?  With no return pipe? Novel, but totally impractical.

 

How does a high pressure hot water feed into the expansion tank work?

 

Where is the gravity return to the coil in the calorifier?

 

What is the "thermo valve"?. What  is the  purpose of the "temp activated heat pump", presumably running off the electric 240v supply?

[LadyG]

I'm no expert but this looks too complex and prone to failure.

My back boiler (central s/f stove) feeds by gravity to the vertical calorifier which is at the far end, the fat copper pipes feed through the boat, so that all is dry and warm without intervention.

I do have a small bathroom rad which is handy for drying socks, hand towel etc and then there is a loop at the bed head for extra warmth. 

I have a prv at the back of the stove.

There will be lots of ideas on the forum if you use the search facility, top right.

I find that having plenty of hot water on demand,  derived from stove / immersion / engine is very handy for washing up, washing clothes and washing floor. These things are important for cc liveaboards, so I'd think about it from a purchaser's point of view. One day you will want to sell the boat, and you may be limiting your market unnecessarily.

Edited March 6, 2023 by LadyG

[Tony Brooks]

Sorry, but the diagram suggests that you are yet to understand both the domestic (taps & shower) hot water systems, calorifiers, and the central heating.

 

The central heating and domestic hot water NEVER mix.

 

You need four connections on the calorifier: One cold DOMESTIC water IN and the bottom and a DOMESTIC water OUT at the top. A coil in connection FROM the stove to the top of the COIL and a return to the stove from the bottom of the coil. You might have a twin coil calorifier where the second is heated by the engine coolant.

 

I suggest that you draw out the domestic water system and the heating system as two separate diagrams.

 

Pumped central heating systems with stoves are a bad idea, too much opportunity for pump failure with the stove alight. That will lead to lost of steam and scalding water exiting the header tank and possibly an explosion. Try to use gravity circulation.

 

 

Have a look and try to FULLY understand this resource for the DOMESTIC system: Domestic water system

 

Here is just one version of a gravity central heating system. The vent could go into the header tank or through the cabin side/bulkhead to outside.

 

 

Edited to add: stove at back of the boat, so the bow up trim assists rather than fights against gravity circulation. Gravity systems do work with the stove elsewhere but getting nice looking pipe runs and  circulation becomes more difficult.

Edited March 6, 2023 by Tony Brooks

[WaterMao]

Thanks guys, I've defo got a lot to learn 😅

 

I think I was overthinking this a bit, how's this revised version doing?

 

I wanna stick to just having stove as the heating source for water heating for now. I really like @LadyG idea about looping the pipework in the bedroom.

 

I'm feeling this updated version, give me your worst!! (famous last words 🤣)

 

Thanks. 

 

[Tracy D'arth]

Im tired but can't sleep so here goes.

 

You will have water constantly pumping over into the header tank! The pump wont stop! You cannot vent a pressurised system with an open vent.

 

Connect the bottom of the header tank with one pipe onto the gravity flow pipe from the calorifier top coil connection, no vent over the top, totally unnecessary.

 

 You cannot use a steel radiator on fresh water , it will rust away in days. Besides you had no circuit, just a flow pipe.  Same with your loop in the engine room!

If you want a radiator it must go across the flow and return GRAVITY pipes, on the sealed system, with the flow pipe  rising all the way and the return falling.

 

You have not got a clue about plumbing I am afraid.

[Tony Brooks]

Please do as I suggested, read and understand the whole of the section I gave you a link to.

 

For now, you seem to have ignored the advice to draw out the domestic water system separately from the heating system

 

You have ignored my statement that the two systems NEVER mix.

 

For some reason, you have taken no notice of the diagrams I posted and linked to.

 

You have no way of filling or venting the stove (heating) system, so if you ever did get water into i, it would explode soon after lighting the fire.

 

Heating systems (the stove system) needs to run with antifreeze in it to help prevent corrosion Tracy talks about, and antifreeze is poisonous.

 

So, at present, you are highly dangerous to both yourself and others. Goodness knows what you will try to do once you get involved with the electrics. Please either do a lot more study or pay professionals to do the diagrams and work for you.

 

I am disinclined to try to help you much more, as my advice seems to get ignored.

 

PS - without any heat dump rads the stove WILL boil once the water in the calorifier is up to temperature AND the water coming out of the hot taps is very likely to flash off into superheated steam when you turn them one on - that is if the whole thing did not explode first.

[WaterMao]

On 07/03/2023 at 07:45, Tony Brooks said:

Please do as I suggested, read and understand the whole of the section I gave you a link to.

 

For now, you seem to have ignored the advice to draw out the domestic water system separately from the heating system

 

You have ignored my statement that the two systems NEVER mix.

 

For some reason, you have taken no notice of the diagrams I posted and linked to.

 

Hi Tony sorry for any offence caused. I can confirm I'm not a plumber, I'll take your advice and move to a separate system for pumped hot water, it's a real shame it's unsafe to do anything else tbh. 

 

I've seen other people on the forums who get pumped hot water from heat from a backboiler -> calorifier including someone else in this thread by the sounds of it, which is why I didn't think it'd be an issue. The radiator would just be something I install to excess dump heat anyway and I wouldn't install the backboiler if I couldn't get pumped hot water out of it. I've not lived on a boat but I'd assume the 42"er would be well supplied by the stove alone in any regard. 

 

Thanks again for the assistance I will look to pursue another solution!

 

 

[ditchcrawler]

51 minutes ago, WaterMao said:

Hi Tony sorry for any offence caused. I can confirm I'm not a plumber, I'll take your advice and move to a separate system for pumped hot water, it's a real shame it's unsafe to do anything else tbh. 

 

I've seen other people on the forums who get pumped hot water from heat from a backboiler -> calorifier including someone else in this thread by the sounds of it, which is why I didn't think it'd be an issue. The radiator would just be something I install to excess dump heat anyway and I wouldn't install the backboiler if I couldn't get pumped hot water out of it. I've not lived on a boat but I'd assume the 42"er would be well supplied by the stove alone in any regard. 

 

Thanks again for the assistance I will look to pursue another solution!

 

 

You do get pumped hot water, the cold gets pumped in on the blue line to the right of the diagram and the hot comes out of the red under pump pressure

[Bod]

1 hour ago, WaterMao said:

Hi Tony sorry for any offence caused. I can confirm I'm not a plumber, I'll take your advice and move to a separate system for pumped hot water, it's a real shame it's unsafe to do anything else tbh. 

 

I've seen other people on the forums who get pumped hot water from heat from a backboiler -> calorifier including someone else in this thread by the sounds of it, which is why I didn't think it'd be an issue. The radiator would just be something I install to excess dump heat anyway and I wouldn't install the backboiler if I couldn't get pumped hot water out of it. I've not lived on a boat but I'd assume the 42"er would be well supplied by the stove alone in any regard. 

 

Thanks again for the assistance I will look to pursue another solution!

 

 

Please understand, the water heated by the backboiler, is a closed circuit.  The hot water at the tap has been heated by the heat exchanger contained in the hotwater tank, and is taken from the boats water tank.

The two waters, back boiler and tap water never mix.  One has antifreeze added, the other is fully drinkable.

 

Bod

 

[ditchcrawler]

Is this drawing any help to you 

[Tony Brooks]

1 hour ago, WaterMao said:

Hi Tony sorry for any offence caused. I can confirm I'm not a plumber, I'll take your advice and move to a separate system for pumped hot water, it's a real shame it's unsafe to do anything else tbh. 

 

I've seen other people on the forums who get pumped hot water from heat from a backboiler -> calorifier including someone else in this thread by the sounds of it, which is why I didn't think it'd be an issue. The radiator would just be something I install to excess dump heat anyway and I wouldn't install the backboiler if I couldn't get pumped hot water out of it. I've not lived on a boat but I'd assume the 42"er would be well supplied by the stove alone in any regard. 

 

Thanks again for the assistance I will look to pursue another solution!

 

 

 

No one I have ever known gets pumped hot DOMESTIC water from the back boiler.

 

Once again - look at the diagram Brian posted - the stove heats water that is passed through the COIL in the calorifier and back to the stove.

 

The hot COIL heats the water in the body of the calorifier.

 

The domestic water pump pushes cold water into the bottom of the calorifier that in turn pushes the hot water out of the top and out of the hot taps.

 

The stove water and the domestic water never mix.

 

 

Unless you run the stove for maybe an hour or so and then put it out, or if you run all your hot domestic water each time the calorifier contents are up to temperature, you WILL boil the water in the back boiler. It takes a given amount of energy to raise the temperature of the water in the calorifier so if you keep pushing more heat in from the stove the water will boil. The only way to avoid it is stop the stove producing more heat - put it out or drain hot water off, so the stove can heat more cold water - or provide another  way to get rid of the heat that is no longer required, hence the need for a or some heat dump radiators.

 

If you do not believe this, do the thermal calculations involving water volume, temperatures and specific heat of water & antifreeze mixture.

 

Brian's diagram does not address the need for a PRV, accumulator or expansion vessel. There is a lot more to this than stove, calorifier and rads.

 

[magnetman]

You could get hot water directly off the fire if you weld a tube in through the firebox instead of using a boiler. put it at a slight angle. Thick wall stainless steel 1 inch bsp tube should do it. 

. Pump fresh water through it slowly into a storage vessel until you have enough hot water then stop the pump and gravity drain the system. 

 

Would need experimenting and obviously needs to be open vented preferably outside the boat. 

 

The thing is that the little stainless pipe will exchange quite a bit of heat but it won't go crazy. 

 

I've not tried out this theory as do not have need for hot water but the little DIY fire I have on one of the boats does have a slightly angled 1" bsp stainless tube through it for this purpose in case of need in future. 

 

I'm pretty sure it would work. You would be supplying a controlled amount of water using a pwm speed controller on the pump. 

 

It would need to be attended to obviously so may be more interaction than most people would want. 

[ditchcrawler]

2 hours ago, magnetman said:

You could get hot water directly off the fire if you weld a tube in through the firebox instead of using a boiler. put it at a slight angle. Thick wall stainless steel 1 inch bsp tube should do it. 

. Pump fresh water through it slowly into a storage vessel until you have enough hot water then stop the pump and gravity drain the system. 

 

Would need experimenting and obviously needs to be open vented preferably outside the boat. 

 

The thing is that the little stainless pipe will exchange quite a bit of heat but it won't go crazy. 

 

I've not tried out this theory as do not have need for hot water but the little DIY fire I have on one of the boats does have a slightly angled 1" bsp stainless tube through it for this purpose in case of need in future. 

 

I'm pretty sure it would work. You would be supplying a controlled amount of water using a pwm speed controller on the pump. 

 

It would need to be attended to obviously so may be more interaction than most people would want. 

I basically do that, I have  a Dickenson Cooker with a stainless steel water heating coil, ie. a bit of bent pipe in the hot area. As its stainless pipe I connected it directly to the calorifier rather than going through the coils. The engine now goes through the lower coil and I draw heat out via the other coil to a radiator in at the end of the boat. Works well, water heats faster and with the engine running I can heat the radiator as well if I want to without the stove alight 

[magnetman]

Is the Dickinson running all the time ? 

 

 

[ditchcrawler]

2 minutes ago, magnetman said:

Is the Dickinson running all the time ? 

 

 

This time of the year when we are boating, sat as home at the moment, In the spring Autumn it goes on and off on a daily basis, and other times on if its required for cooking. 

[WaterMao]

Thanks for the help guys!

 

@ditchcrawler That diagram is really helpful, I 'get it' a lot better now. 

 

@Tony Brooks I understand where the confusion lies, when you said "no pumped hot water" I thought you meant its inadvisable to use a backboiler as a calorifier heat source all together. Thanks for clarifying

 

One question I do have is, on most of the backboiler units I've seen there's only two valves for pipework, one hot out and one cold return, the diagram looks as though it'd require 3. I was thinking, could the calorifier go at the back of the chain of rads and work "like a radiator" (in terms of its placement in the circuit), instead of being at the front end, therefore avoiding the need for 3 outlets on the backboiler? Then, if I wanted to just heat the calorifier as priority, I could isolate the rads to ensure the heat travels to the calorifier at the back, and open them again once hot to dump the excess heat. Only issue I can see with this is that (I imagine) the pump would be working pretty hard to get the water to the back of the boat, up the pipework, through the calorifier and back into the hot taps, or are narrowboat pumps 'ard enough to hack it? 

 

The idea about the pipe going straight through the heat source is interesting and probably would be cheaper, but I have concerns about trying to drill through a cast iron stove, I've heard they don't like it as their quite brittle, could be wrong though. 

 

Overall though, hope restored! Thanks again!

[Tracy D'arth]

You do not need 3 connections to the boiler, just a tee in the return. Plumbing is not your forte at all is it?

The calorifier is just like a big radiator but needs a corresponding larger pipe. The order that they are connected is immaterial providing that the pipe sizes are correct.

[MtB]

8 hours ago, WaterMao said:

One question I do have is, on most of the backboiler units I've seen there's only two valves for pipework

 

I very much doubt that. There should never be valves fitted in the back boiler pipes.

 

If there are valves that can be closed, a potential bomb has been created. Do NOT, EVER fit valves on the pipes connecting into back boiler.

 

 

[Tony Brooks]

8 hours ago, WaterMao said:

One question I do have is, on most of the backboiler units I've seen there's only two valves for pipework, one hot out and one cold return, the diagram looks as though it'd require 3. I was thinking, could the calorifier go at the back of the chain of rads and work "like a radiator" (in terms of its placement in the circuit), instead of being at the front end, therefore avoiding the need for 3 outlets on the backboiler? Then, if I wanted to just heat the calorifier as priority, I could isolate the rads to ensure the heat travels to the calorifier at the back, and open them again once hot to dump the excess heat. Only issue I can see with this is that (I imagine) the pump would be working pretty hard to get the water to the back of the boat, up the pipework, through the calorifier and back into the hot taps, or are narrowboat pumps 'ard enough to hack it? 

 

1. The diagram was one I had handy that I drew in response to a different question. It does give the impression that there are three pipes in the boiler, but there are not. The layout required the cold return pipe to pass behind the boiler.
 

2. I have advised that you do a bit of studying, there are other diagrams on the internet. Do not try to work from a single diagram you have found online because each boat is different. Once you settle on your final layout of stove, rads & calorifier you adapt the diagrams to suit.

 

3. If you are concerned about the power of the domestic water pipe then do the main DOMESTIC pipe runs in 22mm pipe rather than 15mm, but the domestic water pumps are fine on 72ft boats with 15mm pipe. The pipes that carry stove hot water may well have to be in 28mm pipe to minimise the friction reducing gravity circulation. Plastic pipes expand and sag when hot so any pipes connected to the STOVE are best in copper.

[WaterMao]

@MtB Thanks for the clarification. Two outlets? Holes? lol I get what you mean though.

 

@Tracy D'arth Nope 🤣. I've got until mid May to work this out (when my boat arrives to where my mooring is). 

 

@Tony Brooks That's really helpful, thanks. I've drawn this one out, I know it won't be perfect but hopefully along right lines now :).

 

 

Cheers. 

 

Edited March 14, 2023 by WaterMao
Worked out answer to 2nd query

[Tony Brooks]

6 minutes ago, WaterMao said:

@MtB Thanks for the clarification. Two outlets? Holes? lol I get what you mean though.

 

@Tracy D'arth Nope 🤣. I've got until mid May to work this out (when my boat arrives to where my mooring is). 

 

@Tony Brooks That's really helpful, thanks. I've drawn this one out, I know it won't be perfect but hopefully along right lines now :).

 

One thing I have seen on Ebay is large backboiler solid fuel fires with integrated hot water tank. They look like absolute beasts so I'd have to do some calculations on weight distribution, maybe I'd have to change something in the ballast? Any reason why that'd be a no go (besides weight?).

 

Here's an example of what I mean: Pithers Pither Solid Fuel Stove Stainless Steel + Rare Back Boiler! | eBay

 

Cheers. 

 

 

Still incorrect. The hot DOMESTIC water out will need a pressure relief valve and somewhere for it to vent when/if it opens. The engine room bilge will do for this in most cases. 

 

With the NRV on the domestic cold water inlet to the calorifier you will need an expansion vessel, probably plumbed into the hot domestic out put pipe from the calorifier. This is to protect the calorifier cylinder for regular overpressure.

 

Your red "vent out of boat" will spew water all the time the domestic water pup is turned on. The vent should be at a high point in the STOVE hot to calorifier pipe. It can go to the outside to the top of the header tank.

 

I can think of several reasons not to use such a stove, not least because I can see problems getting the levels for gravity circulation. Depart from what is typical and has been proven over the years at your peril.

[David Mack]

20 minutes ago, Tony Brooks said:

Still incorrect. The hot DOMESTIC water out will need a pressure relief valve and somewhere for it to vent when/if it opens. The engine room bilge will do for this in most cases. 

But this probably comes already fitted to the calorifier.

 

20 minutes ago, Tony Brooks said:

With the NRV on the domestic cold water inlet to the calorifier you will need an expansion vessel, probably plumbed into the hot domestic out put pipe from the calorifier. This is to protect the calorifier cylinder for regular overpressure.

If you have a separate NRV remote from the calorifier inlet you can fit the expansion vessel where you have shown it. But many calorifiers come with a NRV as part of the cold water inlet fitting. Since the expansion vessel has to be downstream of the NRV it is usual to fit it to the hot water out pipe as Tony suggests.

Note also that for the hot water side you need an expansion vessel which is marked as suitable for potable water. Central heating accumulators are essentially the same thing (and cheaper) and are fine on a closed circuit with antifreeze and anti corrosion additive, but will quickly rust away if used on the domestic water system.

Edited March 14, 2023 by David Mack

[Tracy D'arth]

Clueless.  Doesn't comprehend when advised.

 

You cannot have an open vent on the domestic hot water. That's twice you have been told.

No PRV

Primary circuit header tank needs to be on the top of the flow, not half way down the return.

 

At least you now understand that the waters must never mix and that radiators go in the primary circuit.