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Combi or conventional system if I want the ultimate shower experience??

Discussion in 'Plumbing and Central Heating' started by Iknowcraig, 9 Mar 2018.

  1. Iknowcraig

    Iknowcraig

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    hi all, I am looking at buying a place that needs renovating. I will be getting a new boiler installed and will be refitting two new bathrooms and a new cloakroom. Seeing as the whole system will be new, I wanted to get advice on what the ultimate setup would be? Whenever we go to posh hotels the showers are always amazingly powerful and I’d love to have that experience at home.

    I’m under the inpression that even a 40kw Combi might struggle to deliver the flow to achieve this with two bathrooms? I know this is dependant on mains water pressure, but even with good pressure would this be up there with the flow I could achieve with a gravity fed system and top of the line pump?

    I’m happy (and likely to have to) re-pipe the system from the stopcock up so have free reign over what setup to go for!

    We would be putting in a large main bathroom with big freestanding bath and rainfall shower along with a good sized ensuite with rainfall shower. I have two daughters (babies) so am sure in future the hot water will be in high demand!

    I am leaning towards a regular condensing boiler and vented system with the biggest tanks I can get at the moment, with a top of the line 4.5 bar shower pump providing the pressure for the house. Is this the best choice?

    Thanks for any advice!
     
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  3. oldbuffer

    oldbuffer

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    1. If you have the mains pressure for it (say 2 bar dynamic (pressure measured with one mains connected cold tap running) and 25 litres per minute, AND if your water supply is reliable (i.e. not cut off more than, say once per year) then you are unlikely to beat a sealed central heating system with un-vented hot water system on a 250 to 300l cylinder.
    2. Otherwise, the regular boiler, adequate cold and hot water storage and a good shower pump as you suggest would probably be best.
    3. It would be prudent to look at the sort of showers you are going to get, and see what flow they provide at given pressures before deciding on the size of pump. You could start by looking at the pressure requirement of 2 x 20lpm rainfall showers and size the pump accordingly. You might also want to look at the cost of water required to run showers with any higher flow rates.
    4. Make sure cold water storage cistern and hot water cylinder are sized to provide the flow rates you require for a reasonable amount of time before they run dry.
    5. My personal preference is for heat only boilers on a sealed system, so that the all the ancillaries, pumps, bypasses, expansion vessel etc are external to the boiler, meaning you are not tied to the manufacturer for replacements. Make sure the boiler you like can be attached to a sealed system, but I think virtually all modern ones can be.
    6. Depending on property layout, you could use a combi boiler to provide hot water to the kitchen, and still run a vented or un-vented hot water system for the rest of the house off the central heating output.
     
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  4. Iknowcraig

    Iknowcraig

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    Thanks for your great reply!

    I will certainly have a look at the pressure once we are in the house before making any decisions. One other factor that may come into play is cost - not that I am concerned about cost as such, but in the sense that I am happy (and keen) to do as much work as possible myself and would only want to pay professionals where absolutely necessary - i.e installing the new boiler. So would having a un-vented system (bill & tank) installed add lots to the cost compared to getting just a regular boiler installed and then me installing all the rest of the pumps, tanks, pipework etc myself?

    With regards to sizing the system, is there any guidance online about the size of tanks required to feed two showers etc? Im imagining I would just go for the biggest hot tank I could get as I would want such powerful showers!
     
  5. Dan Robinson

    Dan Robinson

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    Can't argue with the advice above. A ccombicombi boiler has its place, but never where the word "ultimate" is a prerequisite.

    However, a combination boiler running a kitchen or local shower whilst driving a cylinder fit the main bathrooms can be a good option in some buildings.
     
  6. oldbuffer

    oldbuffer

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    1. You need to check flow rate as well as pressure. You can have high pressure with a pathetic flow rate if there are restrictions in the system.
    2. You can install water pipework for:
    2a. Central heating (including the radiators).
    2b. Cold water services and domestic hot water. However, if going the un-vented route their are certain pipework elements you can't do.
    3. You cannot install:
    3a. Any gas related pipework.
    3b. The boiler flue, or any part of the flue system.
    3c. You cannot hang the boiler on the wall.
    3d. The cylinder itself, its expansion vessel (if required)l, combination valve, d1 or d2 pipes and various other fittings for an un-vented hot water cylinder .
    4. Remember that if there are any problems with items you have installed, not only will you have to put it right (yourself or by paying someone) you may also have to pay for delays caused to the installer.
    5. Any problems with items you buy will be yours to rectify, again with potential delay payments to the installer.
    6. There's quite a lot of calculation required to size the boiler, hot water cylinder and cold water storage tank:
    6a. The boiler needs to satisfy the heat loss requirements of the property (plus about 10% for "warm up");
    6b. It also needs to satisfy water heating requirements, which depend on type of cylinder (ordinary, fast recovery), and size of cylinder.
    6c. The hot water cylinder and cold water storage cistern need to be sized depending on anticipated usage. If you've got 2 x 20lpm showers running, a ten minute shower will use 400 litres. Assuming roughly 2/3rds is hot water suggests a 300 litre cylinder. However, this calculation needs to be done specifically for your property, and expected usage, and allow for hot and cold water temperatures.

    I'd strongly urge you to get a good plumber / heating engineer on board early on. He or she will explain clearly what the options are, what works they would wish to do, and thus what areas you could undertake. Expect to pay for this advice. If you get it by going out for quotes, you probably won't get a detailed breakdown of costs.
     
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  7. Iknowcraig

    Iknowcraig

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    Thanks for this, I understand I would need a professional for the installation of the boiler itself and anything gas related or as pat of an unvented system, this is why I am leaning towards a vented system as I can then install everything beyond the boiler. The house has an existing vented system in place so I may be able to reuse some elements of this although I would likely be putting the new cylinder in a new location and a new cold water tank due to the age of the property.

    I would actually prefer to install the system myself as this is likely to be my "forever" home, so I would like to know it inside and out and have the ability to fix it.
     
  8. dishman

    dishman

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    @oldbuffer

    How many plumbers would think you were mad if you asked for a heat only boiler but set-up as a sealed system with external expansion and pump? I never thought of that as an option but I like it.
     
  9. bernardgreen

    bernardgreen

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    two hot water cylinders.
     
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  11. dilalio

    dilalio

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    @Iknowcraig
    - I commend your enthusiasm but wonder if this may all be a pipe-dream (pun intended ;)).

    How much experience have you with system design, pipe sizing, layout and actual installation?
    It is both a science and an art form in itself!
    It all sounds like fun and full of promise at his end of the journey, but get any of it wrong and you’ll have no end of issues and be far from the ultimate shower!

    Consider a dedicated space (plant room) for the main components rather than trying to squeeze them into hidden parts at various locations; work out pipe sizes, runs and fittings to keep heat loss down and flow rates up; beware thermal transfer across closely routed pipes of different uses; ponder over a secondary return, separate towel rail circuits with summer control, up/down heating zones, UFH... and it goes on!

    Oh, and Ultimate showers need ultimate drains :D
     
  12. Iknowcraig

    Iknowcraig

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    Thanks for your reply! I don't have any experience with system design, layout etc but do have a bit of plumbing installation experience, so the physical part of actually installing the system I think I would be fine with, the planning side I would need to do plenty of research on. I would imagine there are fairly template installations for varying sizes of houses that differ little? I have a blank canvas so can keep the layout fairly simple. Or do you think the planning/layout side of things is completely beyond an amateur? (I would put in plenty of research before embarking on it if that helps?!)

    The idea of a vented system appeals to me as I believe I could install everything past the boiler myself so save money and I would then be completely familiar with the system for any repairs in future. Although the idea of a sealed system with unvented cylinder does seem a bit more appealing now I have researched it. Would this kind of system cope with the demands of 2 high power showers and taps around the house provided my mains pressure was good enough? Also if the mains supply is a small bore would having a new supply installed help with this?
     
  13. dilalio

    dilalio

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    1. Perform test on incoming main: standing and working pressure and FLOW.
    2. Consider replacing main with at least 25mm mdpe... as near to UV cylinder as poss if going that route.
    3. Accumulators/booster pumps can be installed if carriers supply is poor at their stopcock.
    4. Pipesizing is important for baths/showers.
    5. Even vented HW with CWSC’s be quickly depleted by pump(s) before rising main can recover reservoir.
     
  14. dishman

    dishman

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    Question: Is 22mm pipe still relevant in a pressurised system as it is vital in a gravity fed system for hot water (for baths and showers)?
     
  15. dilalio

    dilalio

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    Depends on the flow rate possible with the outlets... baths definitely 22 as fillers are usually 3/4 or 22 inlets, showers usually 22 if tappings are 22 or 3/4 if not then just bring 22 nearby and reduce down in wall.
     
  16. For good shower flow consider a recessed thermostatic mixer-divertor valve.Something like the bristan bright range (15mm compression connections).The mixer with 3 knobs.

    Powered by an unvented hot water cylinder (your water mains supply flow/pressure will need checking for suitability) and a decent gas boiler (y).
     
  17. Keithmac

    Keithmac

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    Quite an important point and I bet often overlooked unti it's too late..
     
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