The Efficient Home Forum

Hello,

I am currently having a house in the process of being build by a developer. I am thinking to go for the Evohome system and have been reading to get familiar with the system, however I still have a couple of questions.

First of all, the developer plans to install a Ariston Clas One boiler. I have not been able to find whether this boiler is OpenTherm or not. Any advice about this?

The second question is about the underfloor heating. Downstairs will be underfloor heating in one zone. Upstairs all rooms will be having a radiator. When it comes to controlling the underfloor heating I see special regulator valves available. On another forum however I came across the solution to add a HR92 valve before the underfloor heating distribution block. Is this a good solution in case the underfloor heating has only one zone? In case it is not, why is it not a recommended solution?

Thanks in advance for any reactions.

Ariston uses its own BUS communication instead of OpenTherm, so you won't get the best benefit with evohome out of this particular boiler.

If your downstairs is going to be just the one zone of UFH, I personally would have a 'mixed' UFH circuit using a T87RF, HM80, mixing valve and pump. This will give you the ultimate control over a single zone of UFH. More details on the HM80 and mixing valves are here - https://theevohomeshop.co.uk/31-mixed-circuit-controls

A HR92 Radiator Controller wasn't really designed for UFH and certainly won't be able to give the necessary flow rates through a 15mm valve that is required for larger UFH areas. I am not going into too much detail over this, as this is a heating installer or developers job to work this out.

Thanks for the very quick reply.

Regarding the boiler and the suitability with OpenTherm. Is it still worth considering Evohome in your opinion, and in which way would a On/Off system be suitable instead?

All depends on the size of house, etc but evohome uses an 'aggregated' demand from all the items on the system to control the boiler by OpenTherm or TPI. In a normal S Plan Plus situation, you have multiple on/off controlling devices calling for demand on the same boiler and this is by no way the best way to do things.

IMO, on/off control is both old and outdated, so it is not really the control system you need to rethink here, its the boiler...

I am not actually sure if changing the boiler is still an option. I will be asking this for sure though.

In case I have to work with the current setup, you mentioned in the previous post that I wouldn't get the best benefits from Evohome with this boiler. What is unclear for me is even if the Ariston boiler doesnt support OpenTherm, can the OpenTherm Evohome Thermostat still be used? Or not at all?

I am struggling to understand the different combinations of a modulating boiler, OpenTherm boiler, On/Of thermostat and OpenTherm thermostat. If you could give me some advice what is compatible to what and how it impacts the regulation I would be really grateful.

Have you seen this? (https://theevohomeshop.co.uk/content/21 ... me-with-it) Pretty much sums up OpenTherm and the advantage of it verse on/off.

So in a nut shell if the boiler is not OpenTherm then it can't use OpenTherm controls, however evohome can still control your boiler with TPI control (on/off switching relay) but this will cost you about 10-15% on your annual fuel bill verse OpenTherm.