Tash and Bex Posted September 18, 2019 Author Report Share Posted September 18, 2019 2 minutes ago, ditchcrawler said: I think you would be sailing very close to the wind with a lot of faith th a pressure switch and a pressure relief valve at 21 psi max pressure. please expand? Link to comment Share on other sites More sharing options...
Paul C Posted September 18, 2019 Report Share Posted September 18, 2019 (edited) 19 minutes ago, Tash and Bex said: a calorifier is running at 25psi in most cases, which is around the same pressure as a non vented domestic system. the issue really comes if the prv fails, they don't half go boom if they boil up.... PRVs tend to fail safe, ie they open at a lower pressure than design. Dirt builds up around the valve opening and prevents a reliable seal. To fail closed, the spring would need to become jammed or some other moving part seize. I can't see that happening if its regularly used. But if it does, normally a plastic pipe would either split or a joint would fail, so it would leak and drop the pressure. There may be a bit of steam/condensation, and an amount of hot water, but nothing more dangerous than that. I'd not worry about safety aspects of a calorifier failing, just the inconvenience/cleanup factor. I think we're on the same page re: likely pressures though. Typically a PRV is 3 bar; and a 12V water pump typically has a 25-30psi cutout. 14psi = 1bar (approx) Edited September 18, 2019 by Paul C Link to comment Share on other sites More sharing options...
Tash and Bex Posted September 18, 2019 Author Report Share Posted September 18, 2019 4 minutes ago, Paul C said: PRVs tend to fail safe, ie they open at a lower pressure than design. Dirt builds up around the valve opening and prevents a reliable seal. To fail closed, the spring would need to become jammed or some other moving part seize. I can't see that happening if its regularly used. But if it does, normally a plastic pipe would either split or a joint would fail, so it would leak and drop the pressure. There may be a bit of steam/condensation, and an amount of hot water, but nothing more dangerous than that. I'd not worry about safety aspects of a calorifier saving, just the inconvenience/cleanup factor. generally yes, a split tank is the most dramatic outcome, and I have no concerns whatsoever about pressurised HW systems! Link to comment Share on other sites More sharing options...
ditchcrawler Posted September 18, 2019 Report Share Posted September 18, 2019 8 minutes ago, Tash and Bex said: please expand? Well a domestic vented tank has a pressure rating of 50 ft head of water, that is only about 21 psi so if you used one of those on your pumped system you would need to drop the pressure by 4 psi and also find a pressure relief valve to suit. Maybe something like one of these would be better/safer https://www.telford-group.com/tempest-stainless.html Link to comment Share on other sites More sharing options...
MtB Posted September 18, 2019 Report Share Posted September 18, 2019 (edited) Well the obvious solution is to fit a big standard MEGAflo. (Google it) heated by whatever method you currently heat your calorifier. These are household mains pressure hot water cylinders, topographically identical to a calorifier but big enough to fill a bath. Edited September 18, 2019 by Mike the Boilerman 1 Link to comment Share on other sites More sharing options...
peterboat Posted September 18, 2019 Report Share Posted September 18, 2019 (edited) 35 minutes ago, Paul C said: PRVs tend to fail safe, ie they open at a lower pressure than design. Dirt builds up around the valve opening and prevents a reliable seal. To fail closed, the spring would need to become jammed or some other moving part seize. I can't see that happening if its regularly used. But if it does, normally a plastic pipe would either split or a joint would fail, so it would leak and drop the pressure. There may be a bit of steam/condensation, and an amount of hot water, but nothing more dangerous than that. I'd not worry about safety aspects of a calorifier failing, just the inconvenience/cleanup factor. I think we're on the same page re: likely pressures though. Typically a PRV is 3 bar; and a 12V water pump typically has a 25-30psi cutout. 14psi = 1bar (approx) I have had a spit cauliflower, expansion vessel and prv failed it was a right mess! Newark cylinders repaired it for me. The pressure vessel and prv are now in cupboard with the cauliflower Edited September 18, 2019 by peterboat Link to comment Share on other sites More sharing options...
Tash and Bex Posted September 18, 2019 Author Report Share Posted September 18, 2019 43 minutes ago, ditchcrawler said: Well a domestic vented tank has a pressure rating of 50 ft head of water, that is only about 21 psi so if you used one of those on your pumped system you would need to drop the pressure by 4 psi and also find a pressure relief valve to suit. Maybe something like one of these would be better/safer https://www.telford-group.com/tempest-stainless.html a vented tank is at atmospheric pressure, it's vented! Link to comment Share on other sites More sharing options...
Tash and Bex Posted September 18, 2019 Author Report Share Posted September 18, 2019 31 minutes ago, Mike the Boilerman said: Well the obvious solution is to fit a big standard MEGAflo. (Google it) heated by whatever method you currently heat your calorifier. These are household mains pressure hot water cylinders, topographically identical to a calorifier but big enough to fill a bath. yes, that would be a solution, however I would struggle to site it, hence it would need to be horizontal and even then would be inconvenient. also, if I have a system running the same capacity of storage as the bath it would only ever need to get to bath water temperature, a domestic unvented calorifier seems a bit overkill.....Now if I had a widebeam it would be a different story Link to comment Share on other sites More sharing options...
bizzard Posted September 18, 2019 Report Share Posted September 18, 2019 (edited) Tinkin outside da box-boat. Mount bath upon bricks on towpath. Fill with canal water. Light a fire of sticks beneath it. Wait one hour precisely to heat up. Jump in with toy boat or duck. Edited September 18, 2019 by bizzard 1 Link to comment Share on other sites More sharing options...
MtB Posted September 18, 2019 Report Share Posted September 18, 2019 27 minutes ago, Tash and Bex said: yes, that would be a solution, however I would struggle to site it, hence it would need to be horizontal and even then would be inconvenient. also, if I have a system running the same capacity of storage as the bath it would only ever need to get to bath water temperature, a domestic unvented calorifier seems a bit overkill.....Now if I had a widebeam it would be a different story Get one made then to whatever size and format you want it to be then. Won’t cost much more than an off-the-shelf one. Domestic unvented cylinders start at about 80 litres. Think out of the box!! Link to comment Share on other sites More sharing options...
Tash and Bex Posted September 18, 2019 Author Report Share Posted September 18, 2019 1 minute ago, Mike the Boilerman said: Get one made then to whatever size and format you want it to be then. Won’t cost much more than an off-the-shelf one. Domestic unvented cylinders start at about 80 litres. Think out of the box!! lol, you consider that using a hot water cylinder as a.....hot water cylinder represents out of the box thinking? domestic unvented cylinders aka calorifiers seems rather firmly in the box to me, but I appreciate your suggestion Link to comment Share on other sites More sharing options...
Paul C Posted September 18, 2019 Report Share Posted September 18, 2019 I'm not sure you're thinking outside the box; you just want someone to agree that your idea of an unvented plastic tank, raised to tepid temperature, will be okay. Link to comment Share on other sites More sharing options...
Tash and Bex Posted September 18, 2019 Author Report Share Posted September 18, 2019 Just now, Paul C said: I'm not sure you're thinking outside the box; you just want someone to agree that your idea of an unvented plastic tank, raised to tepid temperature, will be okay. well, raised to bathwater temperature, but yes, essentially, the advantages of such a system outweigh any other choices as far as I can tell Link to comment Share on other sites More sharing options...
stegra Posted September 18, 2019 Report Share Posted September 18, 2019 Might be possible to get a square hot water tank custom made to fit in the space where you originally planned. Google brought up this company that supplies bespoke tanks in all shapes and sizes: http://www.gasapplianceguide.co.uk/Bespoke hot water cylinders.htm Link to comment Share on other sites More sharing options...
Tash and Bex Posted September 18, 2019 Author Report Share Posted September 18, 2019 1 minute ago, stegra said: Might be possible to get a square hot water tank custom made to fit in the space where you originally planned. Google brought up this company that supplies bespoke tanks in all shapes and sizes: http://www.gasapplianceguide.co.uk/Bespoke hot water cylinders.htm thanks, I will look into it Link to comment Share on other sites More sharing options...
Paul C Posted September 18, 2019 Report Share Posted September 18, 2019 "be aware, water is more often than not stored in a cylindrical vessel for good reason." 1 Link to comment Share on other sites More sharing options...
Tash and Bex Posted September 18, 2019 Author Report Share Posted September 18, 2019 Just now, Paul C said: "be aware, water is more often than not stored in a cylindrical vessel for good reason." yes, in a pressurised system cylinders have a much better resistance to splitting and deforming, but I would contest your supposition that water is more often stored in cylinders as I live on a rather long stretch of canal which seems to be rather reasonable at storing water, domestic supply tank is frankly some kind of crazy polygon and my fish tank is a cube. I think the "good reason" you allude to is that it's much much cheaper to make cylindrical pressure vessels than any other shape. Link to comment Share on other sites More sharing options...
David Mack Posted September 18, 2019 Report Share Posted September 18, 2019 1 hour ago, ditchcrawler said: Well a domestic vented tank has a pressure rating of 50 ft head of water, that is only about 21 psi 55 minutes ago, Tash and Bex said: a vented tank is at atmospheric pressure, it's vented! Not necessarily! A domestic vented tank could be fitted 50 feet lower than the header tank which feeds it, on which case the pressure in the tank would be a 50 ft head above atmospheric pressure. Link to comment Share on other sites More sharing options...
Onewheeler Posted September 18, 2019 Report Share Posted September 18, 2019 42 minutes ago, bizzard said: Tinkin outside da box-boat. Mount bath upon bricks on towpath. Fill with canal water. Light a fire of sticks beneath it. Wait one hour precisely to heat up. Jump in with toy boat or duck. When I were a lad, we had a galvanised steel bath. Filled it from kettle and saucepans on t'gas cooker every Friday night. Youth of today don't know they've been born etc... Link to comment Share on other sites More sharing options...
smiler Posted September 18, 2019 Report Share Posted September 18, 2019 4 hours ago, Tash and Bex said: very little, we have a permanent city centre mooring now. I have been trying to work space in for a larger domestic unvented calorifier, but I just can't, unless I were to use it horizontally and even this would be a push You don't have room for a 2nd/larger calorifier but do have room for an extra 200 litre plastic tank? KISS Thinking outside the box for a moment.... 2nd/larger calorifier and go for a good cruise once a week on bath-night. It is a boat afterall, not a flat. Link to comment Share on other sites More sharing options...
Alan de Enfield Posted September 18, 2019 Report Share Posted September 18, 2019 16 minutes ago, Paul C said: "be aware, water is more often than not stored in a cylindrical vessel for good reason." Is it so the water doesn't get stuck in the corners ? Link to comment Share on other sites More sharing options...
Paul C Posted September 18, 2019 Report Share Posted September 18, 2019 (edited) Well yes it comes down to cost, but a side effect of your novel rectangular unpressurised tank is that it will bulge and if installed eg snugly underneath a bed, break the furniture around it. I know we're talking about low pressures but still, with thinnish plastic, it will distort. Ask any balloon artist who makes more intricate pieces than simple sausage dogs, etc. If you went for a much thicker tank, and/or some kind of metal framework to suppress this, then fine - but then its going to get more costly. The key aspect is the pressure - I know you've said its vented, therefore completely unpressurised, but I think if its well ventilated then there will be a horrendous inefficiency due to losses as it gets warmer. So, you want a little pressure, just a few psi would be okay. That could be achieved without a PRV, simply by having the vented outlet up a narrow tube, around roof height on the boat. Its certainly possible to do it. I'd focus more on the heating source - do you already have a gas or diesel water (and/or space) heater? They're quite expensive, around £2k but it tends to be a once-off install and a piece of equipment which is very useful (in siuations where you don't, or don't want to, run the engine as in a traditional single coil calorifier). I'd spend a little more and go for bigger rather than smaller, if you've not bought one of these yet. ETA - just reviewed the OP, I see you have a Webasto, that should be fine but obviously it will take some amount of time to heat up a bath-full of water. Edited September 18, 2019 by Paul C Link to comment Share on other sites More sharing options...
Tash and Bex Posted September 18, 2019 Author Report Share Posted September 18, 2019 Just now, smiler said: You don't have room for a 2nd/larger calorifier but do have room for an extra 200 litre plastic tank? KISS Thinking outside the box for a moment.... 2nd/larger calorifier and go for a good cruise once a week on bath-night. It is a boat afterall, not a flat. I appreciate your calling me stupid, however allow me to explain. A 200L water tank can be pretty much any shape you desire, a fairly flat tank would be easily to install under the floor of the wardrobes. A domestic hot water cylinder of any description has a diameter it seems of 510mm minimum, and would be difficult to site 200L of water weighs well, 200kg and will certainly affect ballast, if I were to implement my plastic tank idea, the tank would be on the same side as the bath, and as only one of these vessels would be full at anytime, ballast can be allowed for. The plastic tank would not be allowed to refill until the bath was emptied thus negating the dynamic ballasting issues. A DHW tank based system will cost around £600 more than the plastic tank system, not a problem if it has £600 of extra value to the system, but I am not in anyway convinced it will 12 minutes ago, David Mack said: Not necessarily! A domestic vented tank could be fitted 50 feet lower than the header tank which feeds it, on which case the pressure in the tank would be a 50 ft head above atmospheric pressure. ah yes I take your point, but if i mount my water tank 50' above the boat I would struggle with bridges! Link to comment Share on other sites More sharing options...
MtB Posted September 18, 2019 Report Share Posted September 18, 2019 31 minutes ago, Tash and Bex said: well, raised to bathwater temperature, but yes, essentially, the advantages of such a system outweigh any other choices as far as I can tell The main advantage of this is it would make a truly first class fast breeding ground for legionella. Link to comment Share on other sites More sharing options...
Tash and Bex Posted September 18, 2019 Author Report Share Posted September 18, 2019 8 minutes ago, Paul C said: Well yes it comes down to cost, but a side effect of your novel rectangular unpressurised tank is that it will bulge and if installed eg snugly underneath a bed, break the furniture around it. I know we're talking about low pressures but still, with thinnish plastic, it will distort. Ask any balloon artist who makes more intricate pieces than simple sausage dogs, etc. If you went for a much thicker tank, and/or some kind of metal framework to suppress this, then fine - but then its going to get more costly. The key aspect is the pressure - I know you've said its vented, therefore completely unpressurised, but I think if its well ventilated then there will be a horrendous inefficiency due to losses as it gets warmer. So, you want a little pressure, just a few psi would be okay. That could be achieved without a PRV, simply by having the vented outlet up a narrow tube, around roof height on the boat. Its certainly possible to do it. I'd focus more on the heating source - do you already have a gas or diesel water (and/or space) heater? They're quite expensive, around £2k but it tends to be a once-off install and a piece of equipment which is very useful (in siuations where you don't, or don't want to, run the engine as in a traditional single coil calorifier). I'd spend a little more and go for bigger rather than smaller, if you've not bought one of these yet. ETA - just reviewed the OP, I see you have a Webasto, that should be fine but obviously it will take some amount of time to heat up a bath-full of water. i do have a webasto, but i am thinking of adding a second, a 5KW webasto will heat 150l with a 40c rise in around 40 minutes. they are commonly available from breakers yards now, as they are fitted to many diesel cars. I can get a working one for around £50! In terms of tank expansion, I am considering a tank very similar to my waste tank, and whilst doubtless this does distort when full, it's not by much. it will be interesting to see if 40 degree water has a similar effect! 1 minute ago, Mike the Boilerman said: The main advantage of this is it would make a truly first class fast breeding ground for legionella. indeed, I refer you to my many earlier posts on in this thread which mention that Link to comment Share on other sites More sharing options...
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