Unvented Cylinder size for Bathroom

Discussion in 'Plumbers' Talk' started by asmith890, May 20, 2022.

  1. asmith890

    asmith890 Member

    Hi all,

    We plan on installing a small unvented cylinder at our home for the bathroom only (1 bath and 1 rainfall showerhead).

    Does anyone know what size cylinder we should buy? We already have a combi for the CH and downstairs hot water so it’s just for the bathroom. I was thinking 120L but I’m worried that’s not enough if we have 2 showers, one after the other. Or bath then shower.

    The main reason for doing this is we want a powerful rainfall shower and better flow from the bath. Currently our mains water pressure is 1.5bar and the shower is struggling. The bath also takes a long time to fill. We have a good flow rate of 22L/min cold mains but 12L/min hot water from the combi which is correct for the spec of boiler. I was going to go down the accumulator route as a second option.

    I would guess that it’s best to go for an indirect cylinder and pipe it from the combi rather than a direct cylinder? Thank you for any advice.
     
  2. andy48

    andy48 Screwfix Select

    1. The average bath uses around 90 litres of water, give or take 10 litres. Of the 90, about 65 litres will be hot.
    2. A five minute shower uses about the same amount of water, and again about 65 litres will be hot. A five minute shower is unlikely in anyone under the age of 40.
    3. On the above basis you would be a little short of hot water for a bath followed by a shower.
    4. A fast recovery cylinder would help, but is unlikely to be the full answer.
    5. Personally I'd go for a 180 - 210 litre hot water cylinder.
     
    asmith890 likes this.
  3. asmith890

    asmith890 Member

    Thanks for the info. We definitely don’t want to be short. How “fast” are the fast recovery cylinders in heating up the water again?

    I’m guessing the unvented cylinder is pressurised to no more than 3 bar? Or are the pressures and flow rates the same as the incoming cold mains? We thought about a direct cylinder but I would have thought they cost more to run as opposed to indirect off the combi boiler. Thank you
     

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