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

Screwdriva

Greetings all,

Thought I'd share the real world before/ after consumption data from our household after we replaced our 5 year old Worcester Bosch Greenstar with a Viessmann 200-W System boiler.

In a nutshell, we are consuming ~31% less gas YoY with the only other variable being the replacement of our large K22 radiators on the ground floor with a wet UFH system. Comfort levels have greatly increased & the boiler should pay for itself during its 12 year warranty. 

If we were to do it again, our green goals would have prompted us to go for a Vaillant AroTherm+ ASHP installation given that we are a well insulated, Solar PV household. But if you are firmly in the market for a gas boiler, I haven't found any other boiler that can match the V200 on burner efficiency, modulation ratio, advanced weather compensation etc. 

Hope this helps in your search! 

MattMattMattUK

Condensing gas boilers set up properly operate in a 95-97% efficiency range. Unless the pervious system was not set up properly then there is no way that a 30% reduction in like for like usage would be possible, that would have meant the older boiler would have needed to be operating at around 60% efficiency, which is low even for a non-condensing boiler. 

Two things stand out, one you had an entirely new central heating setup, underfloor heating generally creates a perception of warmth greater than the actual air temperature, secondly is the data does not make consistent sense, your usage in 21/22 is largely flat, where as 22/23 it is highly variable and whilst the unseasonably warm November appears to be a factor, the other months make little sense. 

Netexporter

Did you install the UFH at the same time as the new boiler?

Screwdriva

MattMattMattUK said:

Condensing gas boilers set up properly operate in a 95-97% efficiency range. Unless the pervious system was not set up properly then there is no way that a 30% reduction in like for like usage would be possible, that would have meant the older boiler would have needed to be operating at around 60% efficiency, which is low even for a non-condensing boiler. 

Two things stand out, one you had an entirely new central heating setup, underfloor heating generally creates a perception of warmth greater than the actual air temperature, secondly is the data does not make consistent sense, your usage in 21/22 is largely flat, where as 22/23 it is highly variable and whilst the unseasonably warm November appears to be a factor, the other months make little sense. 

I've learnt not to view things with a binary lens as I get older. 

1) The Worcester Greenstar Ri was definitely an inefficient boiler. It could not modulate below 6kW, had no weather compensation and was set up on an S plan. It also had no DHW cylinder temperature control, unlike the V200 which stores our hot water at 50 degrees C 6 days a week.  

2) The data is based on actual average monthly temperatures for both years. On milder days, the V200 modulates down to an output of 2.1-3kW for most days, which is half the old boiler's peak modulation capability. This is when savings near 50%. On the coldest days, observed gas savings are closer ~20% when it is outputting between 4-5kW to compensate for the property's heat loss of ~5.2kW at -2C.

Where the V200 excels is the out of the box capability to support two different heating circuits at 2 different flow temperatures and control PDHW temperature separately as well. When a boiler can do all of this using weather compensation curves instead of room influence, it's hard to see a scenario where 20%+ savings are not achieved.  

Netexporter said:

Did you install the UFH at the same time as the new boiler?

Yes. Same time. Video of installation here. 

jennifernil

We went for the less expensive and not so fancy 100-W heat only model, a 32kW version, in May 2022 , and added a tado control system in January 2023.  Previous boiler was a 34 year old Potterton Neataheat, so fairly inefficient but still working fine, and had never had anything wrong with it.  Heating an area of approx 210 sq m in central Scotland, stored HW in vented cylinder.  We are retired, so at home a lot.

Over our first 12 months our gas use reduced from 28000 kWh to 18000 kWh, so roughly 35%.    It has been colder lately than this time last year, so possibly too many variables to see exactly how a full 12 months with both new boiler and new  controls will compare,  but we are very pleased so far, and enjoying the more precise control the tado gives us.  

Netexporter

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.

markin

Google "You'll find that a water underfloor heating is typically 25% more efficient than traditional central heating and works at a much lower temperature which means it is cheaper to run."

So the boiler could be the 5% better, It will have far more time at the better condensing temps of 25c-40c vs rads.

Here's the thread on the install.
https://forums.moneysavingexpert.com/discussion/6345707/going-green-er-with-a-viessmann-200w-heating-efficiency-home-improvements

Screwdriva

markin said:

Google "You'll find that a water underfloor heating is typically 25% more efficient than traditional central heating and works at a much lower temperature which means it is cheaper to run."

So the boiler could be the 5% better, It will have far more time at the better condensing temps of 25c-40c vs rads.

Here's the thread on the install.
https://forums.moneysavingexpert.com/discussion/6345707/going-green-er-with-a-viessmann-200w-heating-efficiency-home-improvements

I'm aware of the benefits of UFH. Sadly, these would only apply to the ground floor (1/3rd of the property).

My point really is that the radiators are simultaneously being run at a slightly higher (40 degrees) flow temperature + the hot water is being stored at the lower temperature and that the boiler modulates itself to levels no other boiler can, based solely on outside temperatures. All while having a 98% DIN rated efficient burner.

If all that equates to "5% better", I'll eat my hat.

MattMattMattUK

Having read your previous posts as well as the reply above, I am out.

markin

Screwdriva said:

An early preview of what to expect this winter perhaps? August was the first month the cylinder immersion heater wasn't used (given Agile Outgoing prices.) The follow are the actual measured consumption figures YoY:

August 2021 - 20 metre units/ 640 kWh used for DHW
August 2022 - 13 metre units/ 415 kWh used for DHW

Consumption patterns were largely the same. The only variable was pipe lagging. It's clear the Viessmann 200-W has yielded gas consumption savings of ~35% for DHW. If my maths is correct, at the new price cap tariff, this would translate to a savings of £400 per annum for hot water.

Did this hold out to be true?

Screwdriva

markin said:

Did this hold out to be true?

You mean PDHW savings? I haven't calculated the £ amount but the ~35% reduction in gas usage for hot water has remained constant since that post.