2 Nov 2021
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United Kingdom
Ive opened a can of worms by researching the heating system for our refurbishment.

We are having a central heating system installed.
The proposed boiler is a Vaillant ecoFIT pure (think 618 but not definite).
The heating will have 3 underfloor heating circuits for two zones. Builder intends two Honeywell t6360b room stats in each zone, with the third zone being the rest of the house radiators (5 of them); (controlled by a nest).
The non TVR lead radiator is a towel rail in the bath room.
I want a smart heating system but keen to ensure the system is modulating with weather compensation.
I've done some research and see that the boilers modulation ratio is basic at a max of 1:5. This could be improved in sure, seems 1:10 is what should be aimed for.
As we are in the Apple ecosystem so I was pretty keen on Tado for homekit compatibility but am disappointed to see they have removed modulation through BUS control in their new starter kits (v3+) in favour of a cycling system, In addition you need to have the newer bridge to make it Homekit compatible. So using Tado would be a bodge of various old and continental technology.
Its also ambiguous if the Vaillant is compatible as it states on Tado - VRC-410/410s or VRC-420/420s, multiMATIC 700 boiler controller is not compatible. However Vaillant state the boilers are fitted with - Boiler Plus compliant with time and temperature controls – "Install with VRT 15, timeSWITCH 160 and VR 66 wiring centre for the easiest way to meet Boiler Plus". The VR 66 doesnt support eBus so doesn't support modulation......

Im confused- suggestions for a system that is smart, connected and able to modulate with weather compensation? I can change any part of the system still.

Or should I give up and just install the builder system- does nest even modulate the system? It says it does weather compensation.
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Pick a boiler that modulates as low as possible. Like a viessmann. The modulation will happen by the boiler and its own weather sensor.

You will then need a detailed heat loss calculation or survey for the house.

With this you can size radiators (or UFH) to low flow temps and the correct flow rate to be heat pump ready (it's also the smart thing to do).

It's very easy to get this wrong, 99% of plumbers won't know how to do it.

If it's all setup "properly" you won't even need room thermostats or TRVs, that's the goal. Obviously you can include them if you like.

Opentherm is great as an idea but in practice very few boiler manufacturers support the full protocol. Even less controls do aswell (tado is among the best but it's still tricky and not all that worth it when the system is designed and running correctly.).

Flat fee advice can be had from here you will not find any equivalent.
As above, start with a decent boiler with decent modulation, and a decent installer. A great boiler installed badly won't be any better than an average boiler lobbed in by your builders. The Heating Hub or Heat Geek will give you a list of local installers who know their stuff and will be able to advise on the best control strategy as well as the best boiler for your needs. Start by finding a good installer, get a proper heat loss survey done, and then discuss boiler options with your chosen installer.

Radiator and pipe sizing is important too - make sure your radiators are sized correctly for condensing boilers, preferably to run at the same flow temperature as the UFH. Most condensing boilers don't actually condense properly because the radiators are too small, so the boiler has to run too hot to operate in the most efficient way. It's the difference between your boiler running at 95% or 80% efficiency. Similarly, correct pipe sizing can have an effect on the efficency and balance of a system
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As an aside, it would be worth looking at the netatmo system, that is opentherm compatible and so will make the most of modulating boilers, it also has apple home kit compatibility and has individual trv's.

I'm not sure how it all hooks up with under floor heating etc,

As for boiler, the intergas xclusive has good modulation and is compatible with opentherm modulation protocols.

The Honeywell Evo home is probably better suited to your requirements but isn't compatible with apple homekit
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