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WendyH

Hope this is the right board for this question ... I'm planning a simple hot water system for an off-grid agricultural building. Nothing fancy. Straightforward vented hot water cylinder of about 90 litres' capacity. It's to supply hot water to 2 sinks and a washing machine plus underfloor heating for one room in winter only. Pipe runs will be short and straightforward. There are two heat sources. Solar and a 16-litre heat exchanger built into the flue of a wood-fired cookstove. The solar will be indirect as it makes most sense in the context. My question is, would the wood-fired heat source make more sense plumbed direct or indirect? I'm thinking direct, since there is far less chance of boiling a larger volume of water, though with the heat exchanger on the flue, rather than in direct contact with the fire, the chances of it getting excessively warm are much less. I would love to hear opinions on this ... Thanks.
 
Indirect for me. Solar exchanger would be clogged after a few weeks. Hope the hex in the flue isn't something u have dreamed up ! Cooling flue gasses cause them to fall rattler than rise. You will end up with very sooty flue and high levels of co. Surely you would be better off with an old Rayburn or solid fuel back boiler? Or even a gasification log burner.
 
Thanks. I mentioned already the solar would be indirect, so it's just the question over the wood-burner source. I'm aware of the consequences of cooling flue gases and it's taken into account in the design of the stove.
 
What's the heat exchanger made of? Ie do you want rusty water coming out f your taps? I'd think about the above as well, cooling a solid fuel flue is going to lead to tar deposits and possibly
chimney fires, condensation and the risk of a smokey room!
 
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Solar power for two sinks and a washing machine, with a bit of ufh in the winter? Bit overkill, especially with some cobbled together solid fuel heater. Why not just put pv on the roof, electric undersink water heater and a couple of oil filled rads.
 
Solar power will be the sole heat source in summer, so no, it's not overkill in the slightest. It's an essential part of the system. With all due respect to your skills and all, you're not aware of the context and the reasoning that's gone into the design of the system. I'm not looking for people to suggest alternative set-ups here but just to address my question: direct or indirect for the wood-fired heat source?
 
Nostrum - just noticed your reply. It's steel, so valid point and worth considering. Thanks.
 
What material will the feed and expansion tank be made of supplying the Flue heat exchanger?
 
Snowhead - stainless steel for the feed. Expansion tank unspecified as yet because it depends on whether the heat exchanger is plumbed direct or indirect.
 
Use a twin coil indirect open vented hot water vessel. Storage and header cisterns above, The header cistern MUST NOT be the ordinary Plastic type. Need one suitable for solid fuel. The flow and returns to the Hot water vessel would normally be gravity fed, as you require at least one gravity circuit. Another thing to look out for, is that not all modern twin coil vessels are suitable for gravity circuits. Look at your solid fuel appliance very carefully and find out if it has any formal approval, if not look at using a proper wood burner with back boiler. Always use a HETAS registered engineer, they will give you best on site advice for your requirements.
 
Thanks Reg Man. What's your reasoning for suggesting indirect for the solid fuel? Yes, that circuit will be gravity fed and no, I wouldn't dream of using plastic for the expansion/header tank. This installation isn't in the UK, so I can't phone my local HETAS-registered engineer, but I will probably be sourcing the hot water cylinder here because of price and availability. How do I tell whether a cylinder is suitable for a gravity circuit?
 
SimonG - see my original post, viz " The solar will be indirect as it makes most sense in the context."
 
WendyH - make contact with professionals in the country of install they'll be able to answer your questions accurately with the rules and regs pertaining to that country. Might even have been a good idea to mention this in your original post. Although with being on here you intend to biy?
 
What's biy? Bodge it yourself? Yes, we intend to bodge it ourselves, LOL. (And BTW, just because we're not plumbers doesn't mean we're not engineers. Like I said, we're not looking for input on the system, but would just appreciate a bit of advice from those for whom plumbing is more of a speciality.)
 
Engineers, say no more. :)


Honestly though just watch what you're doing, it's not quite as easy as some people make out.

Have a look at the dunsley site (I know it's a neutraliser but have some good diagrams and also the heating innovations web site about the h2 panel. Both overkill but give good diagrams of the layouts.
 
Indirect through a 1" coil for the stove heat-ex (which can be a bad idea for flue gas temps, as has already been said), to stop the the steel exchanger contaminating the water.
You'll want a gravity circuit in min 28mm tube and a heat leak rad @20% of the stove output to sync excess heat. you can valve this off with an N.O 2 port set to spring open when the cylinder is satisfied...

Be careful with this, although Solid fuel and thermosyphons are relatively simple they do need careful planning and installation.
 
in the uk you would want an indirect grade 1 cylinder, with a coil suitable for gravity. most modern cylinders have coils that are designed with small bore high output, gravity requires a different design. grade 1 because its made better, stronger.

you would also need hot water temp controls,(cylinder stat and zone valve) on the gravity circuit and heat leak rad/s.

you will get corrosion from the heat exchanger.

id fit a large thermal store cylinder. your solar will work in the winter to, you wont need much from the solid fuel.
 
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Thanks Pipes Plumbing and AWheating. Solar will contribute in autumn and spring but not for around 10 weeks in winter as the sun disappears behind a mountain ridge to the south. We're aware we won't need a lot of input from the solid fuel, hence designing the heat exchanger into the cook stove rather than space heating, because it will only be run for short periods.
 
Thanks Pipes Plumbing and AWheating. Solar will contribute in autumn and spring but not for around 10 weeks in winter as the sun disappears behind a mountain ridge to the south. We're aware we won't need a lot of input from the solid fuel, hence designing the heat exchanger into the cook stove rather than space heating, because it will only be run for short periods.

Just out of interest where you doing this?
 
Gray0689, as I already said above "Solar will contribute in autumn and spring but not for around 10 weeks in winter as the sun disappears behind a mountain ridge to the south."

And since steveb appears to be employed by the NSA, an answer to the preceding question is redundant.
 
Indirect for me. Solar exchanger would be clogged after a few weeks. Hope the hex in the flue isn't something u have dreamed up ! Cooling flue gasses cause them to fall rattler than rise. You will end up with very sooty flue and high levels of co. Surely you would be better off with an old Rayburn or solid fuel back boiler? Or even a gasification log burner.
Not a expert in solid flues . But to add to this flue will end up
wirh condensation too ( something I have been told from dad )
 
In principle, yes, but it depends on how you build the stove and incorporate the heat exchanger as to how much impact this has. If cooling flue gasses were the only factor in the equation, badeofens wouldn't work as efficiently as they do.
 
Wouldn't it be easier and safer to install aga? Flue mods best done by mfr and on a known system ..

It sounds like your going to be adding a flue hex to a stove not designed or purposely designed for it . I would be intouch with mfr before I did anything. Smoked fish is nice , smoked cakes and dead punters not so.
 
Gray0689, as I already said above "Solar will contribute in autumn and spring but not for around 10 weeks in winter as the sun disappears behind a mountain ridge to the south."

And since steveb appears to be employed by the NSA, an answer to the preceding question is redundant.

And who or what makes this HE for the flu
 
Thanks Reg Man. What's your reasoning for suggesting indirect for the solid fuel? Yes, that circuit will be gravity fed and no, I wouldn't dream of using plastic for the expansion/header tank. This installation isn't in the UK, so I can't phone my local HETAS-registered engineer, but I will probably be sourcing the hot water cylinder here because of price and availability. How do I tell whether a cylinder is suitable for a gravity circuit?
Ok a bit late returning, I think most of this has been answered. The regulations for appliances and flues are supposed to be harmonised with European Standards, I say that is what is supposed to happen but we all know it is not enforce so rigorously in some countries. I think the indirect side of this question is easy to overcome, ask the manufacturer if the off the shelf hot water vessel is suitable for gravity systems, or get a bespoke one made that is suitable. So the other part of the installation relating to the stove heat exchanger and flue. This would worry me, It is going to be nothing but problems and could kill you. With solid fuel appliances and flues, always use an approved appliance and install the flue to the EU standard.
 
Wouldn't it be easier and safer to install aga? Flue mods best done by mfr and on a known system ..

It sounds like your going to be adding a flue hex to a stove not designed or purposely designed for it . I would be intouch with mfr before I did anything. Smoked fish is nice , smoked cakes and dead punters not so.

We're not talking about a pre-manufactured unit here. Masonry stoves and the building thereof might be rare in the UK, but there's a grand tradition of them elsewhere in northern Europe, Russia and the US. The design principles are well proven, scaleable and adaptable and they have a lot of advantages over manufactured metal units. They're WAY more fun to experiment with and build, super-efficient, very controllable, don't rust at the drop of a hat, and don't require a small mortgage to finance. I appreciate your concern, but I've been playing around with woodburners and masonry stoves for years, rebuilding some, building others. I haven't turned myself into toast yet and I have no intention of doing so anytime soon. Thanks for your input guys. My question is well and truly answered.
 
We're not talking about a pre-manufactured unit here. Masonry stoves and the building thereof might be rare in the UK, but there's a grand tradition of them elsewhere in northern Europe, Russia and the US. The design principles are well proven, scaleable and adaptable and they have a lot of advantages over manufactured metal units. They're WAY more fun to experiment with and build, super-efficient, very controllable, don't rust at the drop of a hat, and don't require a small mortgage to finance. I appreciate your concern, but I've been playing around with woodburners and masonry stoves for years, rebuilding some, building others. I haven't turned myself into toast yet and I have no intention of doing so anytime soon. Thanks for your input guys. My question is well and truly answered.

Why ask if your so sure you know what your doing lol
 
If I knew the answer, Gray0689, I wouldn't have asked. But ALL I asked was a simple plumbing question :)
 
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