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

MeteredOut

Reed_Richards said:

Screwdriva said:

Following this thread and the very useful comments/ questions shared, I visited my neighbour's property (other side of the semi-detached) and asked if they'd be willing to share their heating bills.

Upon review, and to my surprise, despite having underfloor heating on all 3 floors (we only have it one one) and an oversized 10 year old Worcester Bosch 30 kW System boiler, their gas consumption was between 17-28% higher than our household, depending on the month.

The property layout is identical but we do receive more sunlight as we are South facing. Not scientific but does give the a new boiler a bit more credit. Incidentally, the neighbors have asked me to arrange in introduction to a known Viessmann installer

Just to be absolutely 100% crystal clear, you mean their gas consumption was 17-28% higher than your household used to be before you got the new boiler and made the other changes?

..and what was the annual % difference? A 28% difference in winter months and 17% in summer months will give a different outlook from 17% in winter and 28% in summer.

And have you asked them how often they shower yet?

EssexHebridean

MeteredOut said:

Screwdriva said:

MeteredOut said:

I like the food analogy though. I assume you end up scraping food off your breakfast plate as you grossly overestimated how hungry you were?

More that there were things on the plate simply not worth digesting. 

Reminds me of my daughter when younger - she refused to eat some foods before even tasting them, adamant she did not like them.

How long can we keep this analogy going

Seriously though, I'd be keen to hear the results from a like-for-like replacement by the neighbour, if they plan to do so.

I'm not so fussed about hearing the neighbours results - I am however quite interested to hear what their viewpoint is when the 30% savings they are expecting aren't delivered by the new boiler they have been convinced is the answer to all their prayers... 

Reed_Richards

Screwdriva said:

... despite having underfloor heating on all 3 floors ...

Obviously you would love to have your neighbour verify the capabilities of your boiler model but with underfloor heating throughout, they really ought to consider the option of a heat pump.  Needing only low water temperatures for heating, they could aspire to an SCOP of 4-ish which should be cost-competitive with gas and will go a little way towards saving the planet.  

MeteredOut

Reed_Richards said:

Screwdriva said:

... despite having underfloor heating on all 3 floors ...

Obviously you would love to have your neighbour verify the capabilities of your boiler model but with underfloor heating throughout, they really ought to consider the option of a heat pump.  Needing only low water temperatures for heating, they could aspire to an SCOP of 4-ish which should be cost-competitive with gas and will go a little way towards saving the planet.  

Does that also depend on insulation levels? We have UFH but don't have great in-wall insulation and I'm not convinced swapping our has boiler for a HP would work for us.

JSHarris

MeteredOut said:

Reed_Richards said:

Screwdriva said:

... despite having underfloor heating on all 3 floors ...

Obviously you would love to have your neighbour verify the capabilities of your boiler model but with underfloor heating throughout, they really ought to consider the option of a heat pump.  Needing only low water temperatures for heating, they could aspire to an SCOP of 4-ish which should be cost-competitive with gas and will go a little way towards saving the planet.  

Does that also depend on insulation levels? We have UFH but don't have great in-wall insulation and I'm not convinced swapping our has boiler for a HP would work for us.

Heat pump efficiency is very largely driven by flow temperature, and UFH allows a much lower flow temperature than radiators.  The problem is hot water, as that needs similar temperatures to radiators, so the saving from a heat pump is greater if it only runs UFH heating.  Maximum UFH temperature for a poorly insulated house with a high heat demand is unlikely to exceed 30°C to 35°C.  Ours runs at about 25°C UFH flow (it's mixed down to that from 35°C).

There is a sort of fix for hot water that I used, which is to have a buffer tank heated to the heat pump flow temperature (35°C in our case) and then use that through a heat exchanger to pre-heat the hot water system.  I installed a thermal battery for hot water, which instantly heats it from a cold input, like a combi.  I feed it with pre-heated water from the heat exchanger on the buffer, so it only has to raise the temperature by a few degrees.  This works well, as although the thermal battery uses direct electric heating (at the off-peak rate) the usage is so low that it's not worth worrying about.  It's also simple, with no moving parts.

Screwdriva

Reed_Richards said:

Just to be absolutely 100% crystal clear, you mean their gas consumption was 17-28% higher than your household used to be before you got the new boiler and made the other changes?

No - the neighbour's gas consumption is 17-28% higher than our household in winter 2022/23, the first winter with the Viessmann 200.

EssexHebridean said:

I'm not so fussed about hearing the neighbours results - I am however quite interested to hear what their viewpoint is when the 30% savings they are expecting aren't delivered by the new boiler they have been convinced is the answer to all their prayers... 

Really hoping I get to share the results on here.

Reed_Richards said:

Obviously you would love to have your neighbour verify the capabilities of your boiler model but with underfloor heating throughout, they really ought to consider the option of a heat pump.  Needing only low water temperatures for heating, they could aspire to an SCOP of 4-ish which should be cost-competitive with gas and will go a little way towards saving the planet.  

I suggested an ASHP first, but they were against it as they plan to invest in an air-to-air multi split system in the medium term, mainly for household cooling. 

Reed_Richards

Screwdriva said:

Reed_Richards said:

Just to be absolutely 100% crystal clear, you mean their gas consumption was 17-28% higher than your household used to be before you got the new boiler and made the other changes?

No - the neighbour's gas consumption is 17-28% higher than our household in winter 2022/23, the first winter with the Viessmann 200.

Isn't that a bit odd?  You would think that a big boiler was a bad match to Underfloor heating that needs low water temperatures; it must surely only be able to run in very short bursts.

Screwdriva said:

I suggested an ASHP first, but they were against it as they plan to invest in an air-to-air multi split system in the medium term, mainly for household cooling. 

Well you did the right thing but you can only suggest.  Is there such a thing as a water to air system?  You and your neighbours would be ideally situated for one of those, if it exists.   
    

Screwdriva

Reed_Richards said:

Isn't that a bit odd?  You would think that a big boiler was a bad match to Underfloor heating that needs low water temperatures; it must surely only be able to run in very short bursts.    

As a matter of fact, yes, they complained of excessive boiler cycling. I would imagine that's because of the boiler's inability to modulate.

MeteredOut

JSHarris said:

MeteredOut said:

Reed_Richards said:

Screwdriva said:

... despite having underfloor heating on all 3 floors ...

Obviously you would love to have your neighbour verify the capabilities of your boiler model but with underfloor heating throughout, they really ought to consider the option of a heat pump.  Needing only low water temperatures for heating, they could aspire to an SCOP of 4-ish which should be cost-competitive with gas and will go a little way towards saving the planet.  

Does that also depend on insulation levels? We have UFH but don't have great in-wall insulation and I'm not convinced swapping our has boiler for a HP would work for us.

Heat pump efficiency is very largely driven by flow temperature, and UFH allows a much lower flow temperature than radiators.  The problem is hot water, as that needs similar temperatures to radiators, so the saving from a heat pump is greater if it only runs UFH heating.  Maximum UFH temperature for a poorly insulated house with a high heat demand is unlikely to exceed 30°C to 35°C.  Ours runs at about 25°C UFH flow (it's mixed down to that from 35°C).

There is a sort of fix for hot water that I used, which is to have a buffer tank heated to the heat pump flow temperature (35°C in our case) and then use that through a heat exchanger to pre-heat the hot water system.  I installed a thermal battery for hot water, which instantly heats it from a cold input, like a combi.  I feed it with pre-heated water from the heat exchanger on the buffer, so it only has to raise the temperature by a few degrees.  This works well, as although the thermal battery uses direct electric heating (at the off-peak rate) the usage is so low that it's not worth worrying about.  It's also simple, with no moving parts.

That's the issue we have. The UFH was already in place when we purchased this property, and was commissioned with a 55C flow (at the mixer, as documented in the installers notes  that were left behind). I've managed to reduce that to 40-45C (to help with condensing), but any lower and the house does not get/stay up to temperature in the colder winter days.

JSHarris

MeteredOut said:

JSHarris said:

MeteredOut said:

Reed_Richards said:

Screwdriva said:

... despite having underfloor heating on all 3 floors ...

Obviously you would love to have your neighbour verify the capabilities of your boiler model but with underfloor heating throughout, they really ought to consider the option of a heat pump.  Needing only low water temperatures for heating, they could aspire to an SCOP of 4-ish which should be cost-competitive with gas and will go a little way towards saving the planet.  

Does that also depend on insulation levels? We have UFH but don't have great in-wall insulation and I'm not convinced swapping our has boiler for a HP would work for us.

Heat pump efficiency is very largely driven by flow temperature, and UFH allows a much lower flow temperature than radiators.  The problem is hot water, as that needs similar temperatures to radiators, so the saving from a heat pump is greater if it only runs UFH heating.  Maximum UFH temperature for a poorly insulated house with a high heat demand is unlikely to exceed 30°C to 35°C.  Ours runs at about 25°C UFH flow (it's mixed down to that from 35°C).

There is a sort of fix for hot water that I used, which is to have a buffer tank heated to the heat pump flow temperature (35°C in our case) and then use that through a heat exchanger to pre-heat the hot water system.  I installed a thermal battery for hot water, which instantly heats it from a cold input, like a combi.  I feed it with pre-heated water from the heat exchanger on the buffer, so it only has to raise the temperature by a few degrees.  This works well, as although the thermal battery uses direct electric heating (at the off-peak rate) the usage is so low that it's not worth worrying about.  It's also simple, with no moving parts.

That's the issue we have. The UFH was already in place when we purchased this property, and was commissioned with a 55C flow (at the mixer, as documented in the installers notes  that were left behind). I've managed to reduce that to 40-45C (to help with condensing), but any lower and the house does not get/stay up to temperature in the colder winter days.

40°C to 45°C flow into the UFH seems high.  If I push ours over about 27°C the house has a big overheat swing that takes a day or two to cool off.  The heat pump flow is fixed at 35°C, as it needs to be at least 5°C to 6°C above the highest UFH flow temperature to regulate properly, plus it's handy to pre-heat the buffer to 35°C as the heat pump still works very efficiently at this temperature.  I have heard that there are now electronic mixer valves that allow a lower temperature differential, IIRC they work OK down to about a 2°C difference, which allows the heat source flow temperature to be reduced a couple of degrees or so further.