Combi Boiler / Showers

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    • #274687
      MasterPlumbers
      Keymaster

      What size Combi Boiler would be good enough for an average sized house with 8 radiators, bath/shower, washer etc..(and how much)

      Is it ok to link a mixer shower to a combi boiler and does it affect the rest of the system and vice versa.

      Does a 9.5kw electric shower give a decent flow rate.

      Any help would be grateful…cheers

    • #290188
      DP
      Participant

      quote:


      Originally posted by JMC:
      What size Combi Boiler would be good enough for an average sized house with 8 radiators, bath/shower, washer etc..(and how much)

      Is it ok to link a mixer shower to a combi boiler and does it affect the rest of the system and vice versa.

      Does a 9.5kw electric shower give a decent flow rate.

      Any help would be grateful…cheers


      To say the boiler is to be connected to eight radiators means nothing. The radiators have an output in Btus or Kwatts. Smallest combi will be rated at 80,000 Btu or 20 Kwatts. This output is chosen to give an acceptable flow rate of hot water; say 9 litres at temperature rise of 35 degrees Centigrade. Yes, it will give you a good flow at the shower, but beware, open other taps/ faucets and you end up dividing the flow rate or end up reduced flow rate depending upon where the other hot water draw off is.
      Bigger combis give improved flow rates with possibility of multiple supplies (say two drawoff points)
      If multiple simultaneous draw off points are to be used, then a storage combi will be the answer.
      Combi boiler is essentialy a boiler that heats the radiators until hot water demand is made. At this point the boiler gas rate goes to maximum and the radiator water is diverted to secondary heat exchanger that heat the water that you can rinse you mouth with. The problem here is that water sufficient for only one draw off point at a time is possible because of the size of the burner and main heat exchanger. While these can be made bigger to improve Hot water delivery, end result is not satisfactory for multiple hot water delivery.
      Improvement on this is Storage combi which preheats water. When a hot water demand is made, this stored energy will deliver water that will fill a bath in three minutes recovering in eight to ten minutes

      Storage combi is usually fitted with presure reducing valve which will give a reasonably steady flow with two or three faucets open (will effect flow if bath taps are open)

      Flow rate from a combi will be as good as if not better than the 9.5Kw shower. Remember inlet water temperature effects what the outlet temperature is to be. Lower inlet temperature will need to be in the boiler or the 9.5Kw shower longer for an acceptable temperature in the winter.

    • #290189
      Guest
      Participant

      I’d just like to thank the person who replied to my questions… It was very helpful…cheers

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