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CH boiler replacement, comments/advice please including on Hive and alternatives.

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  • ThisIsWeird
    ThisIsWeird Posts: 7,935 Forumite
    1,000 Posts Second Anniversary Name Dropper
    silvercar said:
    Our hive controls when the heating and hot water are on or off. The actual temperature of the water in the rads/ water from the taps is controlled by the boiler. When the heating is scheduled on by the app, the hive room thermostats turn it off if the thermostat reaches the required temperature. 
    You can have 6 on and offs each day, with different temperatures for each. So we have a slightly lower temperature in the early morning and early afternoon than we do late evening. Other times it is set very low for frost protection, but never reaches that low.

    Advantages for us is the ability to switch the heating on or off when we are out and to turn the heating off when we are on holiday, knowing we can turn it on before we arrive home.
    Thanks for that.  There doesn't seem much difference in cost between a Hive and a programmer + room-stat - provided it's reliable.

    Go 'Smart'. For gawds sakes go Smart.
    It would be stupid not to.
    Even a Hive is multiple times better than a conventional programmer-timer, even a Prog Stat.
    Smart is awesome.
  • Rollinghome
    Rollinghome Posts: 2,729 Forumite
    Part of the Furniture 1,000 Posts Name Dropper
    Hi Rollinghome.
    The Vaillant is one of many reputable makes, so if you like this model, and it fits in the space most neatly and easily, then great. They will all be significantly more efficient than your current beast.
    I have to agree that a Heat Pump would be a very risky install here, given all you've said about the insulation levels. There is simply no reason to be cold, or to have energy bills that will be similar - or possibly even higher - than what a modern gas boiler will provide, especially when it'll cost more and look more ugly.
    That leaves the controls. You have an E850?! Wow. Stick it on eBay... Someone will want it to replace a defunct one, but it'll have no place with your new boiler :smile:
    The Hive is one of many Smart systems, and it'll transform the control you'll have over your CH and DHW. However, you should go for a model that uses the Vaillant protocol, as this will squeeze out a bit more efficiency. Not sure what's recommended, but - yes - they will do what you suspect; full control over the timings for your CH, with whichever temp you want for each time slot. Instant override from your phone. Going out for the day? Just turn the CH down, and then back up by phone as you head home. Smart is fab.
    You might even consider adding Smart TRV heads on the most regularly used rads, such as in bedrooms. That'll then control them to just come on for a bit before bedtime, and again before you wake up - and off (or right down) at other times. Instant savings.
    A quick surf suggests Vaillant uses eBUS, and have their own VSmart controls, but no idea what it's like, or alternatives. Should be quite researchable.


    Yes, a brand spanking new E850 still in it's box. Too good just to put the kettle on in the mornings. I'm not into Ebay but will certainly take a look.   I've also got a lovely brand new SMC Commander pump in its box. Would be sure to outlast any modern one.  Both pressies to my wife during her 40 years in an architects practice.  More useful than samples of bricks.
    Thanks for your views on the Hive and other suggestsions.  I'm just writing out a flexible quote for an installer so will probably suggest the Hive and leave the techie compatability details to them..  
    I'm not going to install this system myself though I have installed a couple of full systems back in the day when they weren't so fussed about us amateur DIYers blowing up the street, and under instruction from my wife on the proper way to spec radiators etc.
    Would have been nice if the boiler had gone down in July instead of January. Was on my to-do list 10+ years ago. :)
    I have a Hive myself, and like it, but I wouldn't recommend it for the Vaillant as this boiler will accept a more nuanced control which should add a couple more % efficiency.
    The essential difference is that the Hive will give you full control over times and temps, and is nice to use, but 'all' it'll ultimately do is turn the boiler on and off at your chosen times, a bit like a better version of your existing room stat.
    An eBUS, or Opentherm, or other more advanced Smart control will do a bit more; as the required temp approaches, it'll inform the boiler that it's 'close', and tell the boiler to turn down to match this reduced demand. So, instead of on...on...on...on...ok, off...off...off...right, on...on...etc, it'll be like, on...on...ooh, getting close, back off, turn down, eeeassssyyy now, that's it, hooooold it...niiiice, ookkaaay, turn it back up a bit more...
    So, it'll not only mean fewer ones and offs for the boiler, but it'll try and keep the boiler more in the 'condensing' area for longer = more efficiency.
    It would be silly to not go for this - all these Smart controls cost a similar amount in the first place.
    Thanks for that TIZ! I'll do a bit of googling.  I'd better be quick as I've already emailed the possible/likely installer and Mrs R is dropping hints about it getting a bit chilly.

  • bob_a_builder
    bob_a_builder Posts: 2,357 Forumite
    Part of the Furniture 1,000 Posts Name Dropper
    Google Nest (smart stats) support OpenTherm
    https://support.google.com/googlenest/answer/9259109?hl=en-GB
  • FreeBear
    FreeBear Posts: 18,163 Forumite
    Tenth Anniversary 10,000 Posts Name Dropper Photogenic
    Google Nest (smart stats) support OpenTherm
    https://support.google.com/googlenest/answer/9259109?hl=en-GB
    Unfortunately, Vaillant doesn't support OpenTherm.
    But if you are open to hacking code, there are a number of interfaces & solutions available.
    Her courage will change the world.

    Treasure the moments that you have. Savour them for as long as you can for they will never come back again.
  • ThisIsWeird
    ThisIsWeird Posts: 7,935 Forumite
    1,000 Posts Second Anniversary Name Dropper
    Ask Vaillant themselves what's best. 
    They may have discontinued VSmart, and now have myVaillant, but not sure - it's far too complex to follow.
    Just nuts having different protocols.
    I understand Tado used to include eBUS, but no longer do!
    Double nuts.
  • Albermarle
    Albermarle Posts: 27,754 Forumite
    10,000 Posts Seventh Anniversary Name Dropper
    I think you need to be clear on the hot water situation.
    Gravity fed is very old fashioned, and I think you should be at least looking at the HW being a pumped system as well.
    Or as already mentioned you could move to an unvented system for CH and HW.
    This would mean no more tanks in the attic and mains pressure for showers etc.
    However you would need a new HW tank, and it will mean more cost/pipework to install as it is a more specialised job to install them.
    Even if you stick to a vented system, it would probably be a good idea to have a new HW tank anyway, if yours is quite old. Just replacing a hot water tank like for like ( but a more modern well insulated one is not such a big/costly job.

    Despite you having a four bed solid wall house, the boiler you have picked seems more powerful than necessary at 25KW. It looks like it can only modulate down to 6KW so will use more gas than a smaller boiler. 
    We have a 4 bed semi with solid walls. Double glazed, but some of it quite old. Open fire and draughty hallway.
    Our 18 KW boiler copes with no issues. 13 radiators + hot water.
    Yes it is a bit old-fashioned now, so with the new boiler the system will be fully pumped. The only time gravity feed feed was a blessing was if the pump fails. And pumps don't fail if you get a good one.
    I'm sticking with an unvented "regular boiler" system because I don't want any additional stress on an old system I would get from a closed system combi or system boiler.  With a combi, I'd get much lower water pressure because we have a raised storage tank and very low mains pressure.
    Our old boiler is 80 btu so 25 Kw is very similar and big enough for a fast warm up when we come to a cold house with big rooms.  The next size down for that model is 18Kw.

    OK, it probably helps us that there is someone in the house pretty much every day in the Winter, so the house never really gets that cold, even overnight. Also the only 'big room' is the hallway/stairs, which we live with being on the cooler side. 
  • FreeBear
    FreeBear Posts: 18,163 Forumite
    Tenth Anniversary 10,000 Posts Name Dropper Photogenic
    Rollinghome said: Our old boiler is 80 btu so 25 Kw is very similar and big enough for a fast warm up when we come to a cold house with big rooms.  The next size down for that model is 18Kw.
    The size of the boiler doesn't really affect how fast a house will heat up. If you want fast warm up, you either fit large radiators, or increase the flow temperature. Where bigger boilers come in to their own is reheating the hot water tank, but only if the cylinder has a suitably large enough coil. My old boiler was rated at ~12kW and would heat a tank of water from cold to ~50°C in under an hour.
    For heating, I'm rarely putting 7kW in to the radiators (have a heat meter monitoring flow).
    Graph from this morning - Peak output was 6.9kW from a Viessmann 050 30kW combi.
    Her courage will change the world.

    Treasure the moments that you have. Savour them for as long as you can for they will never come back again.
  • Rollinghome
    Rollinghome Posts: 2,729 Forumite
    Part of the Furniture 1,000 Posts Name Dropper
    I think you need to be clear on the hot water situation.
    Gravity fed is very old fashioned, and I think you should be at least looking at the HW being a pumped system as well.
    Or as already mentioned you could move to an unvented system for CH and HW.
    This would mean no more tanks in the attic and mains pressure for showers etc.
    However you would need a new HW tank, and it will mean more cost/pipework to install as it is a more specialised job to install them.
    Even if you stick to a vented system, it would probably be a good idea to have a new HW tank anyway, if yours is quite old. Just replacing a hot water tank like for like ( but a more modern well insulated one is not such a big/costly job.

    Despite you having a four bed solid wall house, the boiler you have picked seems more powerful than necessary at 25KW. It looks like it can only modulate down to 6KW so will use more gas than a smaller boiler. 
    We have a 4 bed semi with solid walls. Double glazed, but some of it quite old. Open fire and draughty hallway.
    Our 18 KW boiler copes with no issues. 13 radiators + hot water.
    Yes it is a bit old-fashioned now, so with the new boiler the system will be fully pumped. The only time gravity feed feed was a blessing was if the pump fails. And pumps don't fail if you get a good one.
    I'm sticking with an unvented "regular boiler" system because I don't want any additional stress on an old system I would get from a closed system combi or system boiler.  With a combi, I'd get much lower water pressure because we have a raised storage tank and very low mains pressure.
    Our old boiler is 80 btu so 25 Kw is very similar and big enough for a fast warm up when we come to a cold house with big rooms.  The next size down for that model is 18Kw.

    OK, it probably helps us that there is someone in the house pretty much every day in the Winter, so the house never really gets that cold, even overnight. Also the only 'big room' is the hallway/stairs, which we live with being on the cooler side. 
    I think that's it. Every house is different in layout, position, and how it's used.  British Gas "advisors" may pretend they can calculate yours needs by the number of radiators or beds, but it's nonsense.  One 12k BTU rad in a room gives out as much heat as six 2k BTU rads, if not necessarily as efficiently, and what you need will depend on the temperatures you want and a bunch of other factors.  We've got rads ranging between 5k btu and 13k.
    A good architect will have an engineer calculate heat losses by measuring every surface and use a heat loss coefficient table to calculate the heat-loss, and the heat-gain from adjacent rooms. The table will list every type of material including the exact composition of walls, floors, glazing, etc and be used to calculate the needs for a specified internal temp at a specified minimum outside temp.  And then a fairly arbitrary figure is added to allow for raising the temperature in a specified time.   Which might be why British Gas may think just counting rads will do.
    Or you can use a calculator like https://www.bestheating.com/btu-calculator to make a stab at it, without really knowing their methodology.
    It looks like a pain to choose a smart system without reliable in-depth reviews etc that I don't have time to read.  So I'll go for a cheap Hive that I can always replace with something better if warranted.
    Thanks to all for their suggestions.

  • FreeBear
    FreeBear Posts: 18,163 Forumite
    Tenth Anniversary 10,000 Posts Name Dropper Photogenic
    Rollinghome said: Or you can use a calculator like https://www.bestheating.com/btu-calculator to make a stab at it, without really knowing their methodology.
    I prefer the Stelrad basic heat loss calculator - Punched in the same numbers in both, and got totally different answers. For a 4x4x2.4m bedroom with 2.5m² of uPVC DG Low-E windows, one external 9" solid brick wall, heated room below, and insulated loft above.
    Best Heating says 2240BTU (668W), whilst Stelrad says 4130BTU (1210W). Quite a big difference !
    Her courage will change the world.

    Treasure the moments that you have. Savour them for as long as you can for they will never come back again.
  • Rollinghome
    Rollinghome Posts: 2,729 Forumite
    Part of the Furniture 1,000 Posts Name Dropper
    edited 11 February at 2:34PM
    FreeBear said:
    Rollinghome said: Or you can use a calculator like https://www.bestheating.com/btu-calculator to make a stab at it, without really knowing their methodology.
    I prefer the Stelrad basic heat loss calculator - Punched in the same numbers in both, and got totally different answers. For a 4x4x2.4m bedroom with 2.5m² of uPVC DG Low-E windows, one external 9" solid brick wall, heated room below, and insulated loft above.
    Best Heating says 2240BTU (668W), whilst Stelrad says 4130BTU (1210W). Quite a big difference !
    A cynic would point out that Stelrad are selling radiators and the bigger they are, the more expensive.

    There was a time when central heating installers would give a quotation that guarantees specific temperatures in each room for a specific outside temperature. Such as 21 degrees for lounge, 55 or 60 for bedrooms etc. with outside temperature of 2 degrees say.  The specific requirements for insulation would also be given. For retail installations, that's not done now.
    But as you say, it depends on who you ask.  There are several sites supposedly giving accurate calculations for boiler size based purely on number of bedrooms. Regardless of whether it's a cosy terrace on the south coast with tiny rooms, or a rambling old detached rabbit-warren with huge rooms and high ceilings high on the moors.

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