Viessmann 200-W Gas Boiler - The most efficient boiler sold in the UK?

Screwdriva

Netexporter said:

Interesting video. What is the total build up of that UFH system. I'm looking for one for my gaff. Anything less than 50mm, including finishes, would be a bonus.

Less than 50mm. 25mm insulation board + screed + tile. That's it.

If you need a slightly thinner board, I'd go with this Polypipe 22mm reflective UFH board.  If I was doing it all again, this is the one I'd go for! 

FreeBear

jennifernil said: We went for the less expensive and not so fancy 100-W heat only model, a 32kW version

Very few homes need a 32KW heat only boiler. Looking at the logs for my boiler (Viessmann 050 30KW Combi), it is modulating down to 25% or less when running the heating. So 6-7KW on most days. Flat out, I'm limited by the radiator capacity - ~12KW @ Δt of 50°C. I suspect your mansion would have similar limits.

With so many variables in play, I'm not going to claim that my boiler is more efficient than the old one (it certainly is) or better than another installation based purely on monthly gas consumption. November has been the warmest on record, and we have the prospect of another mild winter - This will reduce gas consumption straight off. A smarter control system or programmable thermostat has the potential to save 5-10%, as will turning the thermostat down.

Netexporter

If you need a slightly thinner board, I'd go with this Polypipe 22mm reflective UFH board.  If I was doing it all again, this is the one I'd go for! 

Thanks. I've been looking at various systems but that looks like it may come closest to what I want/need.

Reed_Richards

With a gas boiler you cannot achieve more than 100% efficiency.  So the thing that amazes me about these results is not the efficiency of the new boiler and heating system but the inefficiency of the old one.  As I recall, the previous boiler was not that old but it must have only achieved an efficiency far less than conventional wisdom would have you believe.  I wonder why?

FreeBear

Reed_Richards said:

With a gas boiler you cannot achieve more than 100% efficiency.  So the thing that amazes me about these results is not the efficiency of the new boiler and heating system but the inefficiency of the old one.  As I recall, the previous boiler was not that old but it must have only achieved an efficiency far less than conventional wisdom would have you believe.  I wonder why?

Worcester Greenstar Ri has a SAP seasonal efficiency rating of 89.8% - https://www.homeheatingguide.co.uk/efficiency-tables?model=017550

Viessmann 200, rated at 89% - https://www.homeheatingguide.co.uk/efficiency-tables?model=018017 - Marginally less efficient than the WB on paper.

If the old boiler was running at a very high flow temperature (say 75-80°C) and the new one at 45-50°C, That could account for a 10-15% saving. Smarter controls might account for another 5% - Still well short of 30%. Milder weather and changes in lifestyle are more likely contributory factors. Quite likely that similar savings could be achieved without resorting to a new boiler.

Screwdriva

FreeBear said:

Viessmann 200, rated at 89% - https://www.homeheatingguide.co.uk/efficiency-tables?model=018017 - 

https://www.viessmann.co.uk/en/products/gas/vitodens-200-w.html

98% stated in the brochure as well. Their other boilers (V100/ V050) are rated at 94%. 

If the old boiler was running at a very high flow temperature (say 75-80°C) and the new one at 45-50°C, That could account for a 10-15% saving. Smarter controls might account for another 5% - Still well short of 30%. Milder weather and changes in lifestyle are more likely contributory factors. 

1) The old boiler ran at <60 degrees flow measured.
2) The average temperature of the 2022 winter season was actually marginally colder than 2021 but more variable. 
3) The V200 runs nearly all the time, with set back temperatures, unlike the on/ off cycling of the older boiler. No other "lifestyle changes".

Quite likely that similar savings could be achieved without resorting to a new boiler.

Didn't get that impression after reading this heat geek review:

https://www.heatgeek.com/viessmann-vitodens-200-boiler-review/#google_vignette

Reed_Richards

I repeat, to me the issue is not how very good the new boiler and heating system is, but why the old one was so much worse.  If we knew that and there was something that could be changed to make improvements short of replacing the boiler,  then that could help a lot of people

Screwdriva

Reed_Richards said:

I repeat, to me the issue is not how very good the new boiler and heating system is, but why the old one was so much worse.  If we knew that and there was something that could be changed to make improvements short of replacing the boiler,  then that could help a lot of people

If there was something obvious, Urban Plumbers would have disclosed it the video linked earlier in this thread. He starts his episode by talking about how the Greenstar can't be made more efficient. 

Suboptimal boiler + suboptimal plan + suboptimal controls contrasted with the best boiler sold in the UK with everything available out the box (as per Heat Geek review).

Reed_Richards

That's a pity.  In fairness to Urban Plumbers, I'm sure their focus was on the new system and they would have only noted something wrong with the old one if it was glaringly wrong.  

Bendo

Reed_Richards said:

I repeat, to me the issue is not how very good the new boiler and heating system is, but why the old one was so much worse.  If we knew that and there was something that could be changed to make improvements short of replacing the boiler,  then that could help a lot of people

Its pretty obvious isnt it. UFH with low flow temps means it will always be cool enough to condense. The big rads removed would have been only condensing a little or not at all.