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Conventional, system or combi for renovation project

Discussion in 'Plumbing and Central Heating' started by LozM, 9 Mar 2021.

  1. LozM

    LozM

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    Hi we live in a 1950's detached house with a conventional boiler system with the two tanks in the attic, hot water cylinder in the airing cupboard and boiler in the garage. We have never had any problems with it in 10 years lived here but about to do two storey extension which at the end will leave us with 4 bedrooms and 4 bathrooms. Only one of the bathrooms will have a bath, there will be 3 showers, two existing ones are electric (cold mains fed) and the 3rd is up for grabs depending on what system settle on. There will be 14 radiators and two zones of wet underfloor heating.

    The two gas people round so far (firm we have used in past and the builders gas contractor) both started off saying going for system boiler with unvented tank and then in the end settled on a 35/40kw combi boiler. I have read quite a bit on the difference between the 3 systems (conventional, system, combi) but was after some real world experiences. We have 2 young children and intend on staying house a long time so whilst money is always a consideration I am really after doing the best thing for the house.

    A lot of people I know seem to settle on system boiler but seems you can still run out of hot water and appreciate pressured for hot water but the pressuring in itself could find leaks in what is likely to be very old plumbing so failing to see the advantages but seems what everyone is doing. Given we already have the tanks in attic then can't see the advantages of system over conventional other than more moving parts to go wrong.

    When I go on some of the manufacturer websites they won't even recommend a combi boiler for size of house although guess not taking into account the bathrooms could have electric showers.

    Gas men have said with 40kw combi then could easily run couple of hot taps no issues and the electric showers take up the slack and 14 radiators no issues. Have read that 40kw could be overkill on the heating side so not most efficient. My experience of combis is that as they work a bit harder more prone to failure but seems things have moved on and that many come with 10 year guarantees.

    Anyone been in similar situation and what would people recommend, any help greatly appreciated.

    Lawrence
     
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  3. bernardgreen

    bernardgreen

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    A system boiler has most of the essentials like pump(s) and valve gear etc crammed into the boiler casing. A heat only boiler with pump(s) and valve gear external may take up a bit more space but will be easier to maintain, service and repair.

    As for combi boilers, NO This is old but still valid information LINK
     
  4. Razor900

    Razor900

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    Before you get any answers we would need to know the incoming flow rate and pressure on your water main. You may be looking at stored water in some way if you have 4 bathrooms
     
  5. oldbutnotdead

    oldbutnotdead

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    One option which few think about is combi plus tank, might work very well for your setup.
    Bit of extra dhw plumbing needed, use combi water for 1 of the showers (ensuite will be least likely to clash with kitchen tap use), use tanked for main bathroom & one other shower, keep 1 electric shower in the least-used location. Any combi can pull this trick, Intergas are designed for it.
    EDIT This route requires careful design so many of the box-shifters won't be interested/will do a poor job.
    EDIT 2 Prob need at least 300l cylinder to run both bathrooms properly
     
  6. Razor900

    Razor900

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    Intergas aren't specifically designed for this
     
  7. muggles

    muggles

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    As above, need to know your mains pressure & flow rate before specifying a system. An unvented cylinder would be an ideal solution but there's no point having one if your mains can't keep up. Equally, you'll not run 4 bathrooms off a combi, and you'd notice a significant difference in performance even running 2 showers together.
     
  8. DIYnot Local

    DIYnot Local

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