Going green(er) with a Viessmann 200W (& heating efficiency home improvements)

Screwdriva

BUFF said:

OK, the Worcester 18Ri can't modulate down to the same level as that Viessman but it can certainly do load & weather compensation with the right controls (e.g. WB EasyControl).
If it was installed according to the specified conditions (Viessman will have similar) a 10 year warranty was available & certainly current 18Ris are compatible with a 20% H2 blend (same as the 100-W). Your WB will have been made in England though, albeit assembled from many parts that probably were not.

It just seems to me that you are probably spending £2k plus junking a perfectly serviceable boiler (with it's embodied carbon) for something which whilst theoretically a bit better is still going to take many years to pay for that minor improvement?

A 10 year warranty wasn't available in 2017 but a 7 year was. I don't believe our Ri is compatible with any H2 but if you find anything that says the 2017 era models were, please do share. 

We don't have EasyControl and don't see the point of investing further in an older boiler to get additional functionality. We do plan to sell the boiler on. 

BUFF

Screwdriva said:

BUFF said:

OK, the Worcester 18Ri can't modulate down to the same level as that Viessman but it can certainly do load & weather compensation with the right controls (e.g. WB EasyControl).
If it was installed according to the specified conditions (Viessman will have similar) a 10 year warranty was available & certainly current 18Ris are compatible with a 20% H2 blend (same as the 100-W). Your WB will have been made in England though, albeit assembled from many parts that probably were not.

It just seems to me that you are probably spending £2k plus junking a perfectly serviceable boiler (with it's embodied carbon) for something which whilst theoretically a bit better is still going to take many years to pay for that minor improvement?

A 10 year warranty wasn't available in 2017 but a 7 year was. I don't believe our Ri is compatible with any H2 but if you find anything that says the 2017 era models were, please do share. 

We don't have EasyControl and don't see the point of investing further in an older boiler to get additional functionality. We do plan to sell the boiler on. 

It's going to be years yet (probably post 2030) before H2 gets mixed into the mains nationwide not least because of all the millions of existing installs that can't use it.. You could easily ask WB if your 18Ri is compatible with 20% H2 as the current production is.
Do you already have the Nest? If you don't, the EasyControl is cheaper than the Nest so you could gain much of the extra efficiency/functionality for your existing install for relatively little outlay (it's also compatible with digital TRVs [albeit only Bosch afaik] which Nest isn't) ~£200 instead of £2000.

Meatballs

What distance pipe centres are you going for?

Every HP engineer I've spoken to always says 100mm, but the guy I have been speaking to said you couldn't get anymore heat out than 150mm...

Screwdriva

ABrass said:

It says extruded polystyrene. That means an R value of around 3.5 for 18mm. In reality you'll get half that or less as it's notched for the pipes. If the pipes are 12mm then you'll have 6mm of material between your hot water and the slab.

Working out the heat loss calculation isn't trivial but there's going to be a lot being dumped into your concrete slab. I'd see if I could find someone who can model it before I spent money on it.

XPS is good insulation, PIR is better but the difficulty is the thickness you need to get near modern standards for a retrofit property.

Thanks to your input, the heating engineer has agreed to replace the 18mm with 25mm solid boards.  If you have a specific product in mind, I can suggest it to him. If not, we'll likely go with the 25mm XPS board (linked below).

https://www.thefloorheatingwarehouse.co.uk/product/thermrite-25mm-solid-floor-insulation-panel-tile-direct-4-grooves-at-150mm-centres/

Thank you very much for sharing your thoughts. 

ABrass

I'd go for PIR boards, Celotex or Kingspan etc. They're slightly higher performing.

Cardew

I have 2 Viessman boilers, a combi and a conventional boiler with weather compensation, both with a 10 year warranty.

I am a little puzzled by the claimed advantages of a lower modulation figure of the Viessman. I suspect it would not be possible to easily calculate how long the Viessman spends at the theoretical 3kW.

There will be an advantage of the low modulation level in keeping the boiler in condensing mode. However a boiler that 'only' modulates down to, say, 5kW won't keep firing(for the same heating load) and will stop firing for a period. i.e it won't be using an extra 2kW for the whole time the Viessman is outputting 3kW.

I would have thought the savings would be marginal.

Screwdriva

ABrass said:

I'd go for PIR boards, Celotex or Kingspan etc. They're slightly higher performing.

I am struggling to find a strong 25mm PIR board with the prefabricated grooves in them. 

ABrass

Screwdriva said:

ABrass said:

I'd go for PIR boards, Celotex or Kingspan etc. They're slightly higher performing.

I am struggling to find a strong 25mm PIR board with the prefabricated grooves in them. 

They probably don't make them. If XPS exists then it's still pretty good.

Screwdriva

ABrass said:

They probably don't make them. If XPS exists then it's still pretty good.

Yes, this is the only one I could find. All others are just polystyrene (EPS?), which I'm still unsure about.

https://www.thefloorheatingwarehouse.co.uk/product/thermrite-25mm-solid-floor-insulation-panel-tile-direct-4-grooves-at-150mm-centres/

Screwdriva

Quick update - we've gone with the 16kW 100-W compact boiler (vs. 19kW). Translation: a 49 minute hot water cylinder recharge time.

Also, the Worcester Bosch 18Ri boiler can only modulate down to 6kW (not 5.5 as previously shared), and has a 50 db sound level (44db for the the Viessman)