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    It came as a surprise to me that there is nothing in the building regulations that disallows connection of a boiler stove to a sealed central heating circuit and a mains pressure (unvented) hot water cylinder. I had read many times on the internet that solid fuel in general had to be connected to a vented system, and that an unvented cylinder was not allowed. I took the trouble to read through the regs, and there was nothing in there prohibiting a sealed system with unvented cylinder heated by solid fuel.

    This seemed like excellent news to me, as it means that I could have all the benefits of a sealed system, lashings of hot water, all with standard components keeping the cost down. The only non-standard item being the stove.

    I found a useful document on the web that backs up my conclusion. Its the "Domestic Heating Compliance Guide" published by the ODPM: www.planningportal.gov.uk/uploads/br/BR_PDF_PTL_DOMHEAT.pdf

    Quoting from the guide:

    "Solid-fuel appliances should not be fitted to sealed heating systems, with expansion vessels, except where specifically permitted by the manufacturer."

    So, all I needed was a stove, specified by the manufacturer for sealed systems and an installer who wasn't outraged by my radical idea. I called a local firm of heating engineers expecting a great deal of skepticism and resistance, only to be greeted with a "no problem, we do it all the time." I confess I felt a bit deflated that my radical idea was actually just run-of-the mill to them! They recommended a particular stove as being the best available for such a system which I had never heard of before:


    I've now got one and it really has to be seen to appreciate how solid and well designed it is!

    So, not only can you connect a back boiler to a sealed system in theory, in practice it's quite common, so common in fact that some manufacturers build it into the specification of their stoves!
    The key is where specifically permitted ie they designed it to do so. Many stoves of UK fireplace design are not designed to do this. A European stove (say pellet) or wood gassification boiler would be designed to operate on a sealed system. This is why thermal stores in the 500lit+ sizes for example 2000lit are made of steel (mild) not copper (softer and at that volume the dia needed would require very very thick & braced cooper). So a steel 2000lit store would ahve a working pressure of 3bar which is a much greater head than the strongest copper cylinder/store would be allowed (max 10m head - 1 bar). Copper would also not be good at that size due to the stress from the shape/vol - it would sag, thats regardless of the head as well as manufacturing difficulty. As in the uk we dont readily expect a 2000 lit store (sealed or unsealed) there is an expectaion that the boiler would only be connected to systems made in soft copper and with a very limited max pressure/head. Therfore there would have been no point in designing a stove boiler jacket capable of operating on sealed systems - with a thermal store.
    Remember the thermal store is on the primary side. A conventional gas or oil boiler sealed system comprises only pipes (small dia) on the primary side, the DHW cylinder is on the secondary side. This again is copper if open vented with a supply tank (max head is again 10m), to go unvented for DHW means stainless steel not just becuse of the strength but because its potable water, if mild steel would be glass lined.
    So its a horse/cart situation we dont have boilers designed becuase there was nothing to connect them to, whereas in places where large sealed primary thermal store systems are expected not surprisingly boiler are desined to operate in closed systems to say 3bar.
    Cheers, Mike up North
    • CommentAuthorcrusoe
    • CommentTimeJan 15th 2009
    Mike: Some good points here. The consensus in the UK domestic plumbing industry - and therefore of most use to forum members here for this type of advice - is that UVHW and woodstoves are a bad marriage. For a fuller discussion of this, see Mark H's current thread.

    The largest store we have made to date in copper has been 1000 litres - for some of the reasons you state. Steel is def the way forward. And with modern inhibitors, the boundaries between materials are coming down.

    One point however: If I understand your comment right, you quote figures from BS gr 3 at 10m head as being the strongest copper cylinder. In fact, Gr 2 (15m head from memory) and others much stronger are available. We have working pressurised copper cylinders capable of in excess of 2m working head, and with PRVs at 3 bar - no problem. Top quality, thick copper, but expensive. Esp when copper hit the prices it did early last year... :(

    Just thought I would clarify.

    Hi, you are right i was generalising about the usual off the shelf cylinders/stores eg DPS / Albion who clearly state the 10m head limit - vented or not - although they only really design for vented. Some of the thinner steel stores are rated only to 1.5 bar but are proofed much higher to about the same as the the 3bar tanks. the problem uis that is you limit to 1,5 bar and you very quickly run out of expansion ullage, particularly if its there is an upstairs as that increases the initial static head. This menas the expnasion vessel gets rather large. So the 3bar tanks are better from that point of view. Although I would not put 3bar down an inherited old pipework system without some checks. but 3 bar max gives you a exp vessel of around 80-120lit which you can live with, 1.5 bar max nearly doubles it so its bigger than most peoples DHW cylinder.

    Cheers, Mike up North
    Another quote from:


    Not only have we learned the it's perfectly acceptable to attach a solid fuel stove to a sealed system if permitted by the manufacturer, but that an unvented cylinder is perfectly acceptable so long as it complies with BS7206 or some alternatives...

    "Minimum provision for new systems...

    b. Unvented hot water storage system products should
    . comply with BS7206 ....
    c. Unvented systems should not be use with gravity circulation."

    Where's that donkey/bull hybrid? It's easy to spot - it goes eeyore from one end and dispenses plumbing advice from the other!
    • CommentAuthorphiledge
    • CommentTimeJan 15th 2009
    If unvented systems cant be used with gravity circulation then what happens in the following situation-
    Its middle of winter and wood stove has been running for a while so its hot. Youve just loaded stove with logs when the door bell goes and its an old friend that wants to go the pub. Out you go, forgetting to shut the stove down. Could be any one of a thousand other distractions but the stove is left to its own devices.

    Then theres a power cut! What happens next?

    As far as I can see the stove will boil very rapidly without pumped circulation. The expansion vessel will be overwhelmed quickly and the pressure releif valve will lift and dump all the steam and water wherever the vent is routed. In the absence of a vented header tank there will be no water in the system and your fire will rapidly overheat and be ruined.

    If I'm missing something then please can someone enlighten me. If not, I think a solid fuel appliance should always be open vented with a gravity heat sink in case of power failure.
    • CommentAuthorcrusoe
    • CommentTimeJan 15th 2009

    No, you're not missing anything. You're thinking laterally....and allowing a margin of error and common sense. Which is enshrined in good solid fuel/woodburning plumbing lore and training.

    Interestingly, I have attended a few scenarios like you describe. Parkrays are favourite, but one with a Franco Belge 75 000 Btu/hr cooker/boiler (a real behemoth) owned by a 'cat lady' in Cornwall...who popped next door during lighting and stayed for a chat with the ashpan door open. The pipe thermostat controlling the pump had been switched off and she forgot to turn it on b4 lighting. It survived, because the system vented and filled as it was designed to do...but I shudder to think of the steam flash should a joint have given out under pressure HAD this been a sealed system.

    If the power cut is widespread, water pumping may be interrupted (it happens) and the cunning little devices designed to introduce cold water into a hot sealed system are as much use as a lead balloon. Stay with a proven, time-tested plumbing system and you won't go too far wrong...depending on your plumber of course.

    For fuller discussion of merits and de-merits on this subject, check MarkH's thread on gas and woodburner - 30 posts to date and interesting reading. Draw your own conclusions.


    • CommentAuthorcrusoe
    • CommentTimeJan 15th 2009
    Tom your comments are becomingly increasingly acerbic and disingenuous - you shouldn't need to do this if you are on solid ground.

    I phoned Mike Barnatt-Millns, or rather he returned my call from his office. These look like good, innovative stoves although I have not fitted any. (I don't know what taking pictures of your installation might prove by the way??) I wrote down his comments, verbatim. While he espouses the cause of woodburning-to-unvented that is not approved under British Standards (as noted previously, some such continental systems are available), he openly ACCEPTS that his views on this matter are not approved of by stove manufacturers or unvented mfrs here in the UK. Re-read that last sentrence. He also strongly RECOMMENDS (while acknowledging that a sealed system would be possible) if you do put stove-to-unvented as per your theory, that this be open-vented. That means a header tank. Sorry...but - as you are staying with horses - that's from the horse's mouth.

    I also took the trouble of calling my local building control office. While I don't need to get building regs permission for most wood/solid-fuel installation activity as I am an approved installer under a controlled scheme (one of those scams you like so much), they were very reticent to concede that they might be able to approve such a hybrid mix. I don't generally find them knowledgeable - but even they knew that.

    Now if I could talk to your firm of installers, tradesman-to-tradesman, I suspect that we would find that, rather than the 'no problem, we do it all the time' attitude you suggest, they were in fact reticent to do this... (to say the least, it is very unusual - and not even recommended by the stove mfr!) ....IF they were approved solid fuel (HETAS) installers in the first place. Please post their contact details - I would love a 4-way chat with them, HETAS and the unvented cylinder mfr, and then to post the precis on this thread.

    Would also be interested to hear your reasoned responses to the questions I posed you in MarkH's thread.

    Best wishes

    The scenario put forward by philedge can happen equally with vented - the f&E tank boils up and fills the bedroom above with steam and sloshes scalding water all over the cupboard. This happend with my old and deparded Rayburn during a storm and a power cut. We were lucky the chimney didnt catch fire as red hot embers were sucked up the chimney. I shoved the burning mass from the fife box into a galvanived bucket with a shovel (very dangerous in hind sight) and when I lifted it there was a deep burnt ring from it on the the Kitchen floor.
    The problem was componded by the lack of power whcih meant that no water supply, so we couldnt simply run the hot taps to dump heat from the gravity cylinder.
    Most boilers have a pump over run faclity where after switching off the pump will intermittantly kick in to shift the residual heat from the jacket, To maintain this in a wood fired gasification boiler you would need a small UPS system or a genny. If you are prone to power outage a small 1kw gen is surprisingly cheap, probably cheaper than it would cost to engineer suitable protection to the system.
    Cheers, Mike up North
    So, we are at last agreed, there is nothing in the regulations anywhere that mandates against the connection of a solid fuel boiler to a sealed system, or an unvented cylinder. In fact the Office of the Deputy Prime Minister produces a handy document outlining the precautions you have to take, which are - the manufacturer must give the OK, and that you must not gravity circulate to the cylinder.

    This is precisely what I have said from the beginning, only to be accused of "unconcious incompetence" by Crusoe, who then suggests I retract what I have said and invites me to become "conciuosly incompetent". He then whines that I am being acerbic! What cheek!

    Philedge is absolutely correct in thinking that in a situation such as he describes, the safety mechanisms will function. When the gravity circuit can no longer cope with the excess heat, the sealed system pressure relief valve will operate. The risks associated with a vented system in such a situation can be much worse as Mike so rightly points out.

    You have to have a gravity circuit that can cope with a slumbering fire in a power cut, and in reality, no stove manufacturer is going to spec their stove for a sealed system unless it is thermostatically controlled. My "heat leak" radiator is ~2kW.

    Crusoe seems to have gone from declaring me incompetent to ringing around all and sundry, including the firm that makes my stove, in his panic to check. He now wants the phone number of the firm of heating engineers who are fitting my stove! I'll make him a deal: if he dismounts from his equine friend (which I now believe not to be a donkey/bull chimera, but an ass), I will ask them to phone him when they next visit my house (which is very soon!).
    • CommentAuthorDantenz
    • CommentTimeJan 16th 2009
    Posted By: Mike (Up North)Hi,
    The scenario put forward by philedge can happen equally with vented - the f&E tank boils up and fills the bedroom above with steam and sloshes scalding water all over the cupboard.

    F&E tank should be covered, lid etc, so sloshing scalding water is a bit of an exageration I say.
    • CommentAuthorcrusoe
    • CommentTimeJan 17th 2009
    The royal 'we' Tom... a consenus of one...you must be getting desperate! Hey, I can't help being tongue-in-cheeky, it's endearing :) Can't remember last time I panicked btw - probably forgetting the anniversary!

    Nothing wrong with checking your facts if someone challenges your beliefs - as an engineer I do it all the time. It's part of the learning curve - you should try it sometime.... or try taking on board the points people keep raising in objection to your argument. See Mark H's post for a list of members who question your MO. Your silence over there in response to my questions is deafening.

    And you say Philedge agreed with you? I took his comments as a sign he disagreed with fitting a WB to an unvented cylinder. Perhaps without getting involved in our tete-a-tete, he might confirm which? If I misread him, I will apologise unreservedly on this post.

    I told the owner of the firm who makes your stove what our disagreement was, to clarify his position. I told him the forum we were on. He knows he is bucking the trend with a WB and Unvented combo and knows clearly most mfrs are not following his example. He also confirmed he recommended a VENTED primary system. Header tank. You somehow espouse a pressurised one, while impying that the installation was tickety-boo and approved by all concerned. This is disingenuity.

    So now unvented systems are safer than vented? Que? (read a plumber's view at yaph.co.uk/unvented/) Based on what? Mike's experience with a defective installation? I believe he will likely confirm that there was insufficient heat-leak output, or possibly if a direct system, a non-ferrous rad or rail hadn't been fitted. This wouldn't otherwise have happened - certainly not to this severity. You are grasping at straws and compounding error here, confirming, if confirmation were needed, your status as an unconscious (note spelling please) incompetent insofar as this topic goes.

    My facts remain posted for members to choose which advice they think sound. While I am a registered unvented installer, like yaph, I have reservations with the technology, and especially its' continued safety when essential maintenance doesn't happen. As people become aware of the many advantages of a Thermal Store - with green credentials, safety, flow rates (and potentially larger storage) all superior to an unvented hot water system, they have some interesting choices available, both in green energy, and keeping their future options open. I am admittedly biased. Because my experiences with them are long-standing and good.

    And crucially - again - a key point in this debate - because something or somebody DOESN'T say you CAN'T do something doesn't mean you CAN or should do it! Ask any apprehended criminal - 'Why were you shoplifting Smithers?' 'Well, m'lud, the shopkeeper didn't say I couldn't....'

    Now if building regs said yes, no problem, you can install an unvented cylinder with a WB, we'd all be doing it. Yet manufacturers in the UK aren't. Likely including the manufacturer of the cylinder you have installed.

    By doing what you have done therefore, according to your own logic above - ie not getting the cylinder mfr's permission to do this, (forgetting the fact that you also have appeared to ignore the stove mfr's advice on fitting a vented primary circuit) you have contravened building regs. Unless of course you can post the cylinder manufacturer's specific approval, or a local building notice showing approval. One or the other is required Tom. Do you have such?

    As far as your installers go, they are implicit in this - if they are HETAS registered, a/c to HETAS, they should not be installing this mix. If they aren't registered, they shouldn't be touching wood or solid fuel stoves in the first place. Rock and a hard place there I'm afraid. But put them in touch by all means - you have the details. As the installation of an unvented cylinder is a notifiable requirement (see above) ask them to have the correct notice and serial no. when they call....and their registration details - HETAS and UDHW. Both are required.

    Thanks to all posters!

    • CommentAuthorcrusoe
    • CommentTimeJan 17th 2009
    Philedge - do I owe you an apology? Heve I quoted you out of context? Please see latest post.

    Online retailer gives boiler stove sealed system advice:

    Some solid fuel appliances that can be fitted to sealed systems:

    Hellfire Combustion Company "Heat Demon"
    Hwam Monet
    Heta Scan-line 580 Aqua
    Heta Scan-line 16 Aqua
    Baxi Multiheat - the full range
    Baxi Solo Innva - all of them!
    All Trianco solid fuel bolers

    You can even buy some on ebay!
    • CommentAuthorcrusoe
    • CommentTimeJan 17th 2009
    Hee hee - and I'm the one supposed to be panicking!!

    Dear reader: Lest there be any confusion, the units mentioned above refer to sealed/pressurised systems here - not unvented cylinders. Not quite sure what Tom's point is, he appears to be trying to re-make a point that is well-established, as per my first post viz: 'The continentals are more advanced than we are on this ..... though I would question the point of the advancement'.

    They've done it for years Tom, and while the continentals started it, it's creeping over here, like many euro-ideas. (this is over at MarkH's thread, btw, not entirely sure why Tom moved it, but I have a pretty good idea!)

    Some good advice on Tom's link above however...(Oh yeah, I listen, read, draw conclusions, like most of the members on the forum :) they say - about sealed (pressurised) systems: 'Most stoves are not suitable to be linked up directly to a pressurised system because with a stove it is possible to boil the water in a boiler...at the moment theses stoves are the exception to the rule.'

    Again, they are NOT talking of unvented hot water cylinders fed by gravity from a WB. My first post again: 'Wood (etc)...cannot legally be connected to a secondary unvented cylinder to provide full gravity (thermo syphon) function....' But the advice on this site IS sound if you are just starting out and need very general advice. They naturally cover their backs in our litigious society by going on to say: '...you should consult an experienced heating engineer to make your final decision.' Now here's where you have to be really careful, cos these experienced guys might just belong to one of those scam things Tom disapproves of, you know, HETAS and the like. :))

    WHY would you WANT a woodburner - in the home - that doesn't give you hot water and/or some space heating in the event of either a pump failure or power cut? Beats me...some apparently seem to want to apply technology for technology's sake. If it ain't broke...

    According to what British standards DO say - not what they don't (!), WBs and unvented gravity hot water systems are a non-starter. They allow sealed systems in some cases - this is primary circuit stuff, not hot water per se. While most British stove manufacturers, and certainly most unvented mfrs, want nothing to do with it due to the inherent and much-increased risk.

    Hyperbole? To keep the mood light and cheery, take a look over at youtube and see what happens when an unvented tank explodes. And you'd want this where? In your house? We saw pics of this during training, but never video! Riveting stuff - and no pun intended...this time.

    Also check out a plumber, yaph's opinion at yaph.co.uk Servicing these systems as I do, I have to concur. And he's talking of a standard unvented system - not a horrible mix of incompatible technologies like WB + UV + SS!! If this type of installation was in my house, with a woodburning stove attached, I WOULD be panicking. Time bombs or what?

    Happy weekend all

    An online retailer giving advice on boiler stoves and unvented cylinders:


    What Crusoe fails to comprehend is that a thermostatically controlled stove, supported by thermostatically controlled zone valves (that fail safe) can completely remove heating from the unvented cylinder (when the cylinder gets to 60c). It is thus emphatically not an uncontrolled heat source. You are not permitted to connect an unvented cylinder to an uncontrolled heat source - obviously!

    This is not just an issue for stoves. To connect solar to an unvented cylinder you have to take similar precautions, because otherwise you would have an uncontrolled heat source! The similarity between solar and solid fuel is mentioned in this helpful document:


    I quote:

    "Solar and Solid Fuel Systems:
    It is possible to use solar panels or a solid fuel boiler to heat an unvented cylinder. The problem with doing this is the need to protect from overheating. System should only be designed by an approved unvented system designer, and may include such features as a heat dump to radiators, as well as additional motorised isolation valves. "

    Traditionally solid fuel installations have been "uncontrolled" and perhaps that is what has lead to the confusion. If an unvented cylinder reaches temperature, the central heating system will simply zone it off and continue with the radiators - whatever the heat source!
    • CommentAuthorJohnh
    • CommentTimeJan 17th 2009
    Tom, in the first link above it states this -

    "A multicoil hot water tank can let you easily connect a stove in to your hot water and heating system. If you have a pressurised system then the stove can be connected to a coil inside the tank and then run on it's own, very simple, vented circuit"

    Doesn't that mean they are recommending that the stove should be connected to an open vented system at some point?

    (I'm not trying to score points here - I'm just getting a bit confused by the discussion)
    Johnh, The point is that it implies a stove can be connected to an unvented cylinder. I didn't link to it in an attempt to get the definitive authoritative statement, just to point out that the idea is not some obscure technical loophole I have found. The issue is that, whether the stove is on its own vented circuit, or working on the overall sealed system of your installation, it must not be uncontrolled.

    Personally, I think the simple incorporation of a stove (ie biomass) into a modern central heating system is good news. I don't quite understand what all the fuss is about. What happens if a zone valve fails on a 50kW oil boiler installation?

    You can get unvented tanks that are safe to 16bar, have a max working pressure of 8bar, on which you might as well set the pressure relief valve to 6bar. Is it actually possible for such a tank to be overheated by a vented circuit set to 3bar?

    In order to have a serious problem with an unvented cylinder set to 6 bar, I guess the following would have to occur:

    1. Power Cut
    2. Failsafe zone valves don't failsafe for some reason
    3. stove thermostat stop working
    4. gravity circuit overwhelmed
    5. sealed system pressure relief valve not work
    6. gravity circulation to cylinder begin despite your efforts to prevent it.
    7. you've filled the fire with enough fuel before going out
    8. you've stayed out long enough for the cylinder to heat from its set 60c to a much higher temperature
    • CommentAuthorandy500
    • CommentTimeJan 17th 2009
    Just been reading this with interest, as I'm going to do a woodburner in our house.
    The UK is a bit behind the times with all this - if you look at the germans for instance, I believe they fit sealed system wood burners as a matter of course, BUT they have more safety controls than we are used to..
    Heat goes to a thermal store which can then dump heat by running the radiator circuit - if you have an unvented cylinder you need to run the bath to heatdump your primary heat store
    Thermostatically controlled primary air to the stove
    Quench coil within the boiler, which flushes cold mains water through a coil to cool the burn if the boiler water goes overtemp.
    UPS connected to boiler circ pump and radiator pump.
    Boiler stove tested and certified to a few bar more than the average UK stove.
    PRV and temperature blow off valves.
    So if they leave the boiler stoked and switch the mains power off before going out for the day, they have backup power. If pump siezes, they have a quench coil, and so on.
    Me - I'm of the opinion a gravity-fed heat dump is essential, whether sealed system, unvented or not.
    Building control always err on the side of caution, if not complete paranoia, so chances of getting them to sign it off are challenging to say the least.
    It's not a HETAS approved method, therefore in the UK you're kind of stuck if you want official approval unless you can make a very good case to your BCO.
    And then there's the house insurance question - they need to be satisfied you haven't installed a 200 litre kettle.
    Dantez, No exaggeration it was practiallcy boiling - made a mess of the ceiling below via the floor. What shade of red have you seen the ccoking plate of a rayburn get to? Whats the biggest bit of athracite youve seen go up the chimmny? IT was very very windy.
    Remember no power ment no incoming mains so running the hot tap exhausted the main tank the whole system was boiled all the way up. Burnt right through through the riddling grate as well.
    Not that i'd use anthacite these days
    Cheers, Mike up North
    • CommentAuthorDantenz
    • CommentTimeJan 17th 2009
    Now solar systems are specifically designed to handle high temperatures with no load conditions. The evaporating temperature of solar fluid is about 140'C so in itself, is able to absorb much more energy before boiling. Also, manufacturer's solar system kits are all what is referred to as, "inherently secure" systems. Yes they have pressure relief valves, temperature sensors, ANTI-GRAVITY check valves built into the pump station on both the flow & return pipes (so no gravity circulation if the pump is stopped) but more importantly, the expansion vessel volume is sized sufficiently large enough to be able to accomodate the complete fluid contents of the system. Thinking about the similarities between solar and wood burner, where both are able to absorb energy into the system regardless of demand makes me think that actually wood burner on sealed system coupled to an unvented cylinder could get approval so long as the system is "inherantly secure". This may therefore, require a stove to have a heat transfer fluid that has an increased boiling point, one that is still able to function even if the stove boiler is in vapour state and where the expansion vessel is sized so as to be able to absorb the whole system fluid contents. That said, I too believe that at present there is general consensus within the heating industry that WB's and unvented don't go together.
    • CommentAuthorMarkK
    • CommentTimeJan 18th 2009
    I hear it is also possible to safely smoke dynamite in certain theoretical conditions.

    I think you two should kiss and make up!
    So for real I have been asked to decide whether to have my 40 KW wood burner (with quench coil) share a vented 2000l Termal Store and Radiator system (meaning big expansion tank in my bedroom up high (no loft)) but more efficient heat transfer from boiler OR have it go through a coil in my TS with its own teenie open expansion tank and the TS radiator system to be unvented with presurised vessel(s). Apparently the costs are similer. My instinct is to save the space in the loft. Is this question relevant to this rather too technical for me thread and if it is, will there be a concensus of advice - or even any advice?

    Any comments gratefully received because I am in over my knowledge level. TS is tank-in-tank type (ie DHW inside its own 340l tank). Boiler and TS will be in basement side by side. Further reliable expert advice is unavailable - long story but I live in Italy is one part of it. Lastly the law, which I will adhere to in this case, states the boiler is to be in an open/vented system. Electricity cuts are common though not usually too long - water outages also occur but so far only in the summer - in general services not robust.
    • CommentAuthorcrusoe
    • CommentTimeJan 18th 2009
    Well it's sunday evening, the long dark tea-time of the soul, heh heh. With that big wind last night a huge Macra Carpa branch fell 40 feet into our communal lane, blocking it, so we have been out with the chainsaws and now have several cwt of pine logs plus a few hundred cones! I never realised cones were so hard to remove - had to use the axe in some cases! Martin Jenkins, wherever you are, I nearly rang you to come have some log therapy... :)

    Brief comments (for me) as in just a mo' I gotta go put some lamb in my mouth (wife insists)...

    Mike: I believe cherry red is at 500-550 c. Customers describe stoves (some thermostatic like the Franco Belge) as seeing the hot plate almost translucent - nearly white, she said. I can't vouch for that, but I'd rather do a bit of whittling any day... :)

    Dantenz: I've never been at a meltdown quite like Mike's - although I have boiled several (vented) stoves safely, some by design - (you can't be in this business 30 years and not be a bit of a pyromaniac) - and some quite by accident. The gravity rads were scalding!

    The anecdotal evidence is undeniable though - the aftermath of a boiling stove isn't pretty, and Mike's description is fairly conservative against some. Terrifying it is, the dark side, hmmmm. Seriously, when the pipes start to bang in a local boiling scenario - a continuous thwaaaang, thwaaaaaaang, you become aware of your mortality and want to run out of the house or hide. When the boiling becomes system-wide, well, you're outa there. A bit similar to the low-pass jet scenario, when everyone ducks and covers their ears...but continuous. Not a hobby most pursue.

    Bear in mind that this scenario occured in the 'fail-safe' open-vented trad British part-gravity system. Which, correctly installed, fails safe by DEFAULT. And can be used in a power cut, water cut, or tax cut. NOT a 'safe-if-it's serviced' (manufacturers' words in the training manual) unvented cylinder and NOT pressed into unwilling service against the manufacturers' instructions. If Mike had had this setup connected at the time of this boil-up, he might not have been telling the tale today

    Interesting and some valid points on solar Dantenz, but because the same principle holds good (sealed/unvented) you can't compare the scale and hence the potential problem in power fail. Thus the training for the two industries - solar and WB/SF - is completely different - I have done both, the latter many times, over many years. It would be like comparing a Nissan Micra to an F1 Honda because both use IC engines. While solar can use gravity principles (Spain etc), it doesn't need such in a power fail. A woodburner does, as you realise.

    Solar can stagnate on the roof all day safely (if wastefully - one of my soapbox topics) due to the small thermal capacity. By contrast, a WB or SF c/heating appliance is capable of massive amounts of heat - to heat a very large house for example - which solar can't unless used as noted, on sunny days using a combo of passive and ST in a house of Passiv + standards. 'Inherently secure' leads me to...

    Andy 500: I would agree that a gravity heat-leak is essential. and while I concur that the 'continentals are more advanced than us' - my first post - (we fitted the odd Tiba and I believe also a Windhager (Austrian) sealed systems in the early 90s - Note: NOT an unvented cylinder) BUT, as per Dantenz' point, they have massive protection (quench coil, back-up power etc etc) and thereby an 'inherently more secure' setup than the system which this debate concerns - ie connecting a (British) woodburner to a (British) sealed system and unvented cylinder. Not that I like even the continental UV/WB setup - these are incompatible technologies which have been engineered around. They do not naturally fit.

    MarkK: I like the idea (no, not smoking dynamite - great analogy for WB+UV by the way, must remember that one for Tom... :) of peace and have been keeping it light as I don't like the personal 'you are wrong, fail to understand, are mislead' style of posting - even if it WERE to come from an experienced installer rather than a theorist with a (wood?) axe to grind. We are after all wasting time debating what is currently a very peripheral part of the WB scene. Problem is, Tom is determined to make this seem like it's a mainline activity in the UK heating industry. I wouldn't mind that delusion if it were just him he was fooling (I think they call this psychological condition 'justification of purchase' - the sort-of diametric opposite of buyer's remorse, where one has to tell everybody how great your new widgit is, especially if somebody else says it isn't).

    But unfortunately he is confusing members with this psuedo-science too. Not that I, as newbie here, am custodian of members' interests, but I do feel bound - and qualified - to put the opposing view, so succinctly stated by Dantenz above, that - and I quote -
    '...there is general consensus within the heating industry that WBs and unvented don't go together.' (End quote)

    While well-informed and willing to question, Dantenz is clearly not, from his language, a heating engineer, nor does he profess to be, yet HE can tell what the prevailing practice is in the industry. Why does Tom think that as a long-standing member of that industry, I somehow can't. It is very disingenuous.

    My persistence with the posting MarkK, is because I, like most UK stove and unvented manufacturers, and the industry I belong to, believe that the mix of technology being espoused by Tom - and especially in its current, UK-embryonic form, is at best, a mismatch, and at worst, a timebomb waiting to happen. Did you go on youtube and see the unvented explosions? Far-fetched? No, I have removed more than half-a dozen gate valves fitted in VENT pipes (open vented) by customers innocently (but so dangerously) trying to stop the vent pipe over-flowing (wrongly positioned cold feed usually the culprit). They do things which you wouldn't believe, in ignorance, life-threatening things. Do you think they won't try and modify a dripping unvented tank too? I wouldn't put odds on it.

    So it's a matter of principle to tell the truth as I and the majority see it. And warn the less technically-adept members of the pitfalls of doing as Tom says. I can't put it any more bluntly than that.

    I didn't bring up the subject of incompetence, Tom did, by telling me I was wrong. If as a professional I am wrong, I am incompetent. As it happens, if I was, I would check my facts and do a mea culpa. I did check my facts, without expecting surprises, and posted the results to confirm rather than retract my comments. That was 'panicking' apparently. So to be clear, I didn't start the altercation, and haven't put a finger-to-keybord in anger. I spoke about it in a tongue-in-cheek way, eggs on faces and such. But it escalated, as these things can.

    Nonetheless, even as the first-abused party, for your sake as peacemaker MarkK, I'll be the first to send him the kiss - 'pwhaa, pwhaa' (down, Tom, it's continental-style) and promise to be nicer to him if he can show me his (legally required) installation certification - cos after all, this is all legal and above board...right? (Not holding my breath here).

    I somehow don't expect any kissssssses back as I have - at least according to members' posts (even on this thread 'The 'truth')- managed to persuade folk of the real facts about this technology. Which was not of course what Tom wanted. I will be posting a final post to show the reality of what REALLY happens when a WB runs away in a Tom-spec WB/UV. Everyone deserves to hear that, having been told (erroneously) that it's perfectly safe. And I reserve the right to respond to further points of course.

    But to show that no ill-will exists, with the moderator's approval, I shall shortly be posting a competition for members, Tom included, to win a FREE place at the UK's first (but not last) 'Eco-Confused' seminar, cutting through the many myths and commercial bias of the alternative energy industry, (note to diary, must add UV to list!), providing real, as-environmentally-friendly -as-possible-solutions, and saving people a lot of time, research and money in the process. Will he enter, that is the question.... :)

    This was suggested to me by CAT members after I presented a 'Future-proof heating' paper at Machynlleth in 2008. It's for the layman and kept humorous and very simple. You can Google it under Ben Shirley. I had a queue of people waiting to ask questions, and could only get to a very few....so we are doing a group thing. It is being held in the Spring on Bodmin Moor in Cornwall. Tickets will shortly be on sale in Clean Slate, the CAT members' journal.

    Because of the dearth (spelling?) of sound, independent advice in the industry, I believe we are going to be heavily oversubscribed, and as I want to keep it small enough for personal involvement and questions, there will have to be more of these - likely once a month. So don't anybody panic if you don't get in to the first. As one of the original woodburning installers (1978 on) and designer of Link-up systems since 1983, I have a unique perspective and experience on alternative energy, peak oil and the future - and it is from this perspective that the agenda has been set.

    Might see you there.

    Regards - and thanks for your peace-making intentions!


    PS: Gotanewlife...can you bear with me, I'm a working guy, will come back to you soonish (Cornish ish!) if you can confirm you're still reading.
    Crusoe, my dear chap, of course I am still here.

    You know I am a chartered personnel manager, an RAF officer, I've got an MA, a project mgt and an IT Service Mgt qual and a new life, in Italy, where none of the afore mentioned makes a scoobies difference. An amateur I am and an amateur I will remain long after I have finished my DIY house renovation. This site, intelligently reviewed and intelligently applied, has and is allowing me to do things greener, cheaper, safer and with less stress and worry - I can't imagine how much harder it would be to become an 'intelligent customer' without it.

    Of course esoteric and theoretical discussions are part of a Forum like this, as are complex specialised discussions where knowledge is assumed, but it is also important that ALL readers know where they stand and posters, amateurs and professionals alike, have a responsibility to readers in this respect, within limits (an idiot will always be able to do something stupid no matter what).

    So you or someone else will answer my question in some way partly or completely, to my satisfaction or not, and I will try to give back as much as I can for I am grateful, even honoured, to be able to share in the extraordinary experience of the Forum's members.
    What a thoroughly invigorating debate.... so is this right then...?

    1. The fact that no matter how complex a stove is you can't shut of the fuel supply makes it prone to overheating
    2. Overheating if linked to a boiler causes potentially explosive pressure and destructive heat to stove and other elements
    3. It is technically possible to design a system to work with a pressurised CH circuit w/ a vented cylinder but your engineer has to really know what he's doing
    4. It is theoretically possible to have use an unvented cylinder as above with all the above WBS, tank, system fail-safes and pressure capacity of the cylinder but
    4a. it is questionable whether the associated risks and costs out way any advantage, possible alternatives including header tank and flat plate heat exchanger.

    Also just to through in a bit (from my own area of expertise as an architect) - Before too much weight is put on the absence of any exclusion of unvented cylinders we should just re cap a little on what the Building Regulations do.... (not meant to be a patronising as it sounds... sorry)

    The Building Regulations are not prescriptive, their text is the little tiny bit of italic text on green background at the beginning of the approved document, they generally talk about reasonable provision.... The Building Regulations APPROVED DOCUMENTS, ie the text of AD J are NOT 'the Building Regulations', they simply describe ways of demonstrating compliance with the Building Regulations. However with something technical like Part J (and increasingly Part L) in terms of getting approval this will be nigh on impossible without complying with the Approved Document guidance.

    Where this is relevant is that essentially the AD J describes how you CAN do something, and is therefore not expected to necessarily include how you CAN'T - so the absence of any ban on unvented cylinders is really to be expected.

    Hope that contributes positively.



    PS: perhaps we should bear in mind that how something said in ones own head when composing a response, but then types out without the benefit of intonation, facial expression, slaps on the back, depositing on the table of another pint etc, etc, can easily be taken the wrong way, and like the the use of a vented cylinder - for safety's sake (!) probabley best not to talk about bulls, asses, donkeys etc... :wink:

    PPS: None the less, Tom I think we could use a fiery (sorry) sort like yourself on board - have you any maritime experience?
    James, I don't share your concerns about sealed systems and unvented cylinders. Is it possible for a sealed system, with pressure relief valve set to 3 bar, to overheat an unvented cylinder at 6bar? Precisely the same safety measures exist on solid fuel and fossil-fuel systems to protect the cylinder!

    Considering sealed systems and back boiler (the topic of this thread), it should be abundantly clear that this is a perfectly acceptable arrangement, bringing with it all the benefits of a standard modern heating system. The ODPM publishes advice on it, the building regs are quiet on it, and I've just received a response from the EST to the effect that they are updating their guidance notes to reflect the fact that stoves and sealed systems are compatible (subject to the manufacturers guidance).

    The good news in all of this is that it is a relatively straight forward way of incorporating biomass into a modern CH system. No need to give up on mains pressure hot water, and no need to compromise the efficiency of your fossil-fuel boiler. Furthermore, you can put your water tank anywhere relative to the stove!

    As for costs, what do you think costs so much? All the CH components are standard.
    • CommentAuthormarktime
    • CommentTimeJan 19th 2009
    Gotanewlife: snip<"... and a new life, in Italy,..." > Ohhh! I thought you got a new wife.

    I'll get my coat. :shamed:

    Posted By: tom.harriganJames, I don't share your concerns

    I was merely trying to summarise the advice from all of the posters not just your comments.

    Perhaps some real life examples of an unvented cylinder with WBS would be good to counter the clear concerns expressed so authoritatively by others...

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