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

Screwdriva

MeteredOut said:

I'm not claiming the new boiler is not giving you savings - it patently is - I'm stating you cannot, with the evidence you have provided, state is almost exclusively the reason for the 31% savings.

Exclusively the reason for 31% savings? Perhaps. The nuance here is the V200 is capable of taking advantage of the new emitter setup better than the unit it replaced and arguably, better than any other boiler available on the market. If we had not installed UFH and kept the 1800X600 K2 radiators in situ, we would have had a single household radiator circuit running at 40 degrees flow. 

Would that have led to slightly reduced savings? Perhaps. But it would be disingenuous to suggest the difference would be significant.

MeteredOut said:

To reduce the flow temperature to 40C (compared to your <60C previously), and keep the same radiators, would obviously either mean a colder house (although I note the EPC A rating) or the boiler requiring to run for longer to maintain the same temperatures as before.

Incorrect. The K22 radiators were large enough to heat the entire floor at 40 degree flow while maintaining a comfortable 20 degree room temperature across the household. The installer (Heat Geek Elite) performed these calculations prior to quoting for the job. 

FreeBear

Screwdriva said:

MeteredOut said:

It wasn't implied. It was stated as fact, which IMO was pretty disingenuous.

If we had replaced the K22 radiators with UFH while preserving the Worcester Greenstar 18Ri boiler, would we have achieved anywhere close to the shared savings? (IMO, it is disingenuous to suggest that would be remotely possible).

If you look at the manufacturer's specifications for the 18Ri, I suspect you would have got pretty close. After all, the 18Ri is not particularly old and has a very similar SAP rating as the Viessmann.

What is disingenuous is to claim massive savings from just a boiler swap when substantial changes have been made to the heating system and the weather has been significantly different. And that is assuming no alterations to the heating schedules or thermostat set points.

Screwdriva

FreeBear said:

If you look at the manufacturer's specifications for the 18Ri, I suspect you would have got pretty close. After all, the 18Ri is not particularly old and has a very similar SAP rating as the Viessmann.

What is disingenuous is to claim massive savings from just a boiler swap when substantial changes have been made to the heating system and the weather has been significantly different. And that is assuming no alterations to the heating schedules or thermostat set points.

If you watch the video linked on Page 1, you'll find the installer specifically ruling out the savings you believe possible with the old boiler entirely. The average temperatures for each month are on display for all to see. And again, flow temperatures for UFH vs. K22 rads would have differed by 5 degrees at a maximum. 

To suggest that this would amount to a significantly different outcome highlights a limited understanding of low temperature heating design. 

MeteredOut

MeteredOut said:

To reduce the flow temperature to 40C (compared to your <60C previously), and keep the same radiators, would obviously either mean a colder house (although I note the EPC A rating) or the boiler requiring to run for longer to maintain the same temperatures as before.

Incorrect. The K22 radiators were large enough to heat the entire floor at 40 degree flow while maintaining a comfortable 20 degree room temperature across the household. The installer (Heat Geek Elite) performed these calculations prior to quoting for the job. 

The fact that you admit to running the system at <60C (at least for some period of time) makes me think there's a fair dollop of confirmation bias at play here.

As I said, no-one can say for sure that you did not get a 31% benefit purely by swapping the boiler, but I don't believe you've provided the evidence (or an explanation) that that was the case.

But, its great that its worked for you and it certainly have provided an option for those that might be in the market for a new boiler. I just wouldn't want someone to replace their own 5 year old one that is in fine working order on the basis of this thread, and expect the same savings as you've documented here.

Screwdriva

MeteredOut said:

The fact that you admit to running the system at <60C (at least for some period of time) makes me think there's a fair dollop of confirmation bias at play here.

I've admitted to the old boiler flow temperature being <60C flow in 2021 and the Viessmann running the radiator circuit at 35-40C flow. Not sure where you see the dollops of bias, but those are the facts.

MeteredOut said:

I just wouldn't want someone to replace their own 5 year old one that is in fine working order on the basis of this thread, and expect the same savings as you've documented here.

While I did replace (and sell on) our 5 year old boiler, I have not suggested anyone do the same on this thread. Nor have I stated anyone should expect exactly the > 31% savings we achieved, but simply that we did achieve this measured result. The end outcome will always depend on the heating setup the V200-W will provide heat to (insulation levels, emitter size and type etc.).

That said, I would definitely expect considerable and comparable savings for households that are well insulated and have the right emitter set up, when paired with the V200 over other comparable boilers, as none offer the combination of functionality and capabilities out of the box .

JSHarris

At our old house I had a condensing gas combi installed, about 20 years ago, to replace an old non-condensing system boiler.  There was a small saving in running cost (mostly from having got rid of the old and inefficient hot water tank), but it was disappointing. 

I spent some time monitoring flow and return water temperatures and measuring the flue gas temperature, then set about adjusting the boiler to try and ensure it stayed condensing for longer.  This relatively simple change gave a massive efficiency improvement, easily around 30% over the as-installed setting.  Main problem was that the installer just didn't understand, or couldn't be bothered, to set the new boiler up to be efficient.

If anyone wants to do this, then the key temperature to watch is the return to the boiler in heating mode.  This determines the condensing efficiency, as the return water recovers heat from the flue gases before they are expelled.  If this is too high the boiler won't run in full condensing mode and will be significantly less efficient.

Only physical change I had to make was to replace one living room radiator for a thicker, finned, one, that was better able to heat the room with the lower temperature flow.  As it turned out that radiator needed replacing anyway, as it was starting to corrode along the lower edge.

To sum up, I can easily understand why a new boiler that's been setup to optimise condensing performance can give a big saving.  However, there's every chance that just adjusting an existing condensing combi could result in a similar improvement, at a very much lower cost.

Screwdriva

JSHarris said:

To sum up, I can easily understand why a new boiler that's been setup to optimise condensing performance can give a big saving.  However, there's every chance that just adjusting an existing condensing combi could result in a similar improvement, at a very much lower cost.

To a point, yes. Prior to replacing the boiler, we reduced flow temperatures to < 60C and adopted a half dozen largely insulating measures around the household, which led to a 25% reduction gas consumption the year before. The measures and result are documented here. 

The savings from the Viessmann 200-W are incremental i.e. over and above the savings achieved from adjusting our 5 year old Worcester Bosch's flow/ return temperatures to the lowest possible setting. 

Reed_Richards

By and large, if you are doing scientific experiments to find out what causes what then you only change one variable at a time.  There's a technique called Response Surface Methodology that allows you to change several variables at once but you have to make multiple experiments with multiple changes of variables to deconvolve what causes what.  @Screwdriva changed multiple variables in going from their old to their new heating system and whilst you can conjecture about what caused what, there can never be proof without more experiments with further changes of variables.  That leaves much scope for argument, as we see.

JSHarris

That's a very good point, @Reed_Richards and one that we are probably all guilty off when jumping to conclusions about cause and effect.  I installed an ASHP here, and initially its performance was very disappointing.  Took me several days of changing one setting at a time, then measuring to see if there was any performance difference, to pin down the cause.  It turned out that although the unit was badged Glowworm, which made me think it was a UK product (given that Glowworm was a brand associated with boilers) in reality it was made by a US company, Carrier, and actually manufactured in Italy.

This was very relevant, as all the settings assumed climatic conditions that were very different to the relatively mild, but often rather wet, UK winter weather.  After a lot of faffing about, and some help from Carrier themselves, I managed to find settings that really improved performance a lot.  As installed, with the factory internal settings (which are password protected to stop users fiddling with them) the coefficient of performance (COP) was only about 2.0.  After tweaking it I managed to get the average winter COP up to 3.5, a very useful gain.  Has made me wonder if  part of the problem with the bad press associated with heat pumps may be related to them being installed with the wrong settings.  Glowworm knew nothing at all about this when I contacted them, and were generally unhelpful, whereas Carrier just provided me with all the factory documentation, passwords, how to adjust the climatic settings etc.

Waywardmike

After reading through this thread I can't help but go back to original post and wonder how you use so much gas to begin with and even now, with an 'A' rated house.  Are there 10 of you living there? Do you throw massive dinner parties where you cook for long periods of time?

I'm in a leaky 4 bed >100 year old detached dormer bungalow with uninsulated solid walls on the ground floor, 9' ceilings and a PIV system pumping cold air into the hallway (small sacrifice considering it essentially cured our condensation issue overnight).  We use less gas than you even after your savings.  We don't cook with gas though and have an iboost so our boiler is essentially off over the late spring/summer early autumn.  We've had a battery the last couple of years so the iBoost doesn't doo much now in the darker months as the battery has PV priority.  Our boiler and cylinder are only 4 years old but made by Ideal so hardly 'high end' and I would assume has none of the fancy tricks the Veissmann has.  I'd probably argue ambient temperatures in London are higher than here, slightly North of London, so our heating system has to work harder.

Confirms what I believe about the EPC system of rating houses, it's pretty useless.

Here is our gas usage for those months if anyone's interested?

Nov   478.8

Dec 1839.1

Jan  2211.5

Feb 1410.6