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New Boiler / Cylinder Sizing

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  • 26-05-2020 10:33am
    #1
    rob w
    Registered Users Posts: 1,111 ✭✭✭


    Hi,

    Having some renovation work done and plumber has provided a quote based on new gas boiler and cylinder spec'd himself - just wanted to check the sizes are adequate.

    We are in a 4 bed house (approx 150sq m), 2 bathrooms (1 with shower, 1 with shower over bath). House has cavity insulation, attic space is well insulated and ground floor will be insulated shortly.

    Plan is for 10 rads, 3 UFH zones (60sqm total). Currently there is 2 occupants in the house.

    A 26kW System boiler with a 120L Indirect cylinder has been spec'd - I was expecting larger, but maybe it is not required

    Can anyone advise if this sounds about right?

    Thanks


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    #2
    Dtp1979
    Registered Users Posts: 12,736 ✭✭✭✭Dtp1979


    Boiler seems a tad big. Cylinder too small. If you want a bigger cylinder then ask for one.


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    #3
    rob w
    Registered Users Posts: 1,111 ✭✭✭rob w


    Dtp1979 wrote: »
    Boiler seems a tad big. Cylinder too small. If you want a bigger cylinder then ask for one.

    I will, just wanted to get some opinions, that's all!


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    #4
    roy rodgers
    Registered Users Posts: 1,492 ✭✭✭roy rodgers


    Sounds like a veissmann and a gledhill cylinder going in.
    Them cylinders have an excellent coil for rapid recovery of your water so size wise could work if it's a 4 pipe boiler..


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    #5
    [Deleted User]
    Posts: 0 ✭ [Deleted User]


    roy rodgers wrote: »
    Sounds like a veissmann and a gledhill cylinder going in.
    Them cylinders have an excellent coil for rapid recovery of your water so size wise could work if it's a 4 pipe boiler..

    If you were fitting a unvented with a 26kw+ coil would you chose to fit 120l.

    I would normally see 210l or 300l fitted in a house with that hot water demand.


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    #6
    roy rodgers
    Registered Users Posts: 1,492 ✭✭✭roy rodgers


    gary71 wrote: »
    If you were fitting a unvented with a 26kw+ coil would you chose to fit 120l.

    I would normally see 210l or 300l fitted in a house with that hot water demand.

    A 120 litre be too small for a unvented system some of them pumps are throwing out massive litres/min.
    But when I was going to school we were told to size a cylinder was to be 30 liters a day on a vented system.
    But now a days we have to factor in pumps, rapid recovery coils, high performance insulations and energy costs.
    I would rather see a rapid recovery coil on my cylinder than having to over size a cylinder to have enough hot water for the dwelling. Less water to heat =more money for home owners.


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    #7
    [Deleted User]
    Posts: 0 ✭ [Deleted User]


    roy rodgers wrote: »
    A 120 litre be too small for a unvented system some of them pumps are throwing out massive litres/min.
    But when I was going to school we were told to size a cylinder was to be 30 liters a day on a vented system.
    But now a days we have to factor in pumps, rapid recovery coils, high performance insulations and energy costs.
    I would rather see a rapid recovery coil on my cylinder than having to over size a cylinder to have enough hot water for the dwelling. Less water to heat =more money for home owners.

    Good point about the flow rates I’m used to unvented not being pumped.

    The problem at times with hot water priority is the home owner can complain of losing heating so I haven’t decided is it better to have a system boiler with similar characteristics of a combi or store more hot water with less cycling but longer re-heat times.


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    #8
    roy rodgers
    Registered Users Posts: 1,492 ✭✭✭roy rodgers


    gary71 wrote: »
    Good point about the flow rates I’m used to unvented not being pumped.

    The problem at times with hot water priority is the home owner can complain of losing heating so I haven’t decided is it better to have a system boiler with similar characteristics of a combi or store more hot water with less cycling but longer re-heat times.

    Personal I think is to have it as close to the charactersistics of a combi boiler. Buts it's a catch 22 for us to get it right and to understand the house holds demand is a key factor. I would take in to account the age of kids and how much longer they are going to be living in the house for before sizing a cylinder..
    Yes future prove if it's a young couple starting out with the possibility of kids within the next 10 years but if it's a couple with kids grown up and moved on I'd inclined to just go with what their needs at this moment.
    Them standard gledhill envofoam cylinders have a 15kw coil now so even from cold they be hot enough for showers after 30 mins. And when this is explained to the customer about the re-heat times they get a better understanding of what way is best to use it for less cost.
    But yes its horses of courses..


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    #9
    John.G
    Registered Users Posts: 3,474 ✭✭✭John.G


    Tank in Tank cylinders are also available which apparently give almost combi like output, a 130 litre Smartline will give a continuous flow rate of 10.97 LPM at 40C or 5.55 LPM at 60C (=8.9 lpm@40C) so once one shower is finished the boiler can go back to CH mode almost immediately since little or no reheat is required if the boiler is configured for priority hot water demand.


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    #10
    rob w
    Registered Users Posts: 1,111 ✭✭✭rob w


    Thanks for the discussion on that lads, have a bot of research to do now. Plumber will be over next week so will discuss with him then.

    Im not sure if the cylinder spec'd is a Gledhill as mentioned in the above posts, but I know the boiler is an Ideal Vogue 26kW (rather than the Veismann mentioned above). I'll chat more with the plumber next week about it all!


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