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

Alnat1

Annual gas use up to 20th Mar 22  10,281kWh  Heating, hot water, hob cooking
Annual gas use up to 20th Mar 23  7,193kWh

4 bed detached EPC C (rated before solar installed)

Achieved by turning down boiler temp to 60C, hot water temp to 55C and heating tank for only 40 minutes per day, turning down TRVs in unused rooms and keeping internal doors closed. Pushed an old cushion up chimney. Bought and fitted 2 pairs of thermal curtain linings for living and dining rooms. Total cost £60

Much cheaper than a new boiler and achieved 30% gas savings, almost the same result as you 

michaels

12m to Mar 22 34,241
12m to Mar 23 20,690

Achieved by turning down the thermostat on our veissman 200 weather comp boiler

Reed_Richards

michaels said:

12m to Mar 22 34,241
12m to Mar 23 20,690

Achieved by turning down the thermostat on our veissman 200 weather comp boiler

Wow!  From what to what did you turn the thermostat down?

Magnitio

Average annual gas usage from 2017 to 2021 - 10,336 kWh

Gas usage for 2022 - 5580 kWh

4 bed detatched. Bit more insulation, turned down thermostat, changed hot water cylinder, some use of immersion and electric heater. More clothes and blankets.

Screwdriva

Alnat1 said:

Much cheaper than a new boiler and achieved 30% gas savings, almost the same result as you 

Not really. We had already achieved a 25% savings by doing many of the same things as you have shared before installing the V200. Detailed here. The above savings of 32% come over and above those from simpler measures like those you have shared.

The V200 is similar to a ASHP in that in outperforms in well insulated homes. Safe to also say, our comfort levels have increased YoY. 

michaels said:

12m to Mar 22 34,241
12m to Mar 23 20,690

Achieved by turning down the thermostat on our veissman 200 weather comp boiler

This makes sense. The V200 has an unsurpassed modulation ratio and thrives when it is purring at 12% or a 2.2 kW output.

Reed_Richards

Isn't the implication of your 30% improvement that ordinary condensing gas boilers, which are supposed to 90% efficient, don't achieve that 90% figure?

ABrass

How much of the 30% is down to the boiler, and how much to the improved insulation, larger radiators and underfloor heating?

It's great you're seeing improvement but simplifying it to just the boiler seems to be giving it unfair credit.

Screwdriva

ABrass said:

How much of the 30% is down to the boiler, and how much to the improved insulation, larger radiators and underfloor heating?

It's great you're seeing improvement but simplifying it to just the boiler seems to be giving it unfair credit.

I look at it another way - I could have increased emitter surface area and gained little from it with our old WB which was running at its peak efficiency. By switching to a boiler that can capitalize on the reduced heat loss, we allow for all the previous improvements to be exploited, much like a heat pump would. 

Reed_Richards said:

Isn't the implication of your 30% improvement that ordinary condensing gas boilers, which are supposed to 90% efficient, don't achieve that 90% figure?

It's very likely that the old boiler was running at ~80-85% efficiency. The V200 is a 95% efficient boiler at max modulation. So yes, the increase in operating efficiency, advanced weather compensation curves and the class leading modulation ratio all come together to achieve the incremental 32+% savings (this would likely have been > 35%, were temperatures the same across both years). 

Reed_Richards

But if the old boiler was

Screwdriva said:

... running at ~80-85% efficiency... 

then it's not possible to achieve a 30% improvement!  

Screwdriva

Reed_Richards said:

But if the old boiler was

Screwdriva said:

... running at ~80-85% efficiency... 

then it's not possible to achieve a 30% improvement!  

Sure it is. The lowest the Greenstar could modulate was 6kW. The lowest the Viessmann can modulate is 2.1 kW. Lower output = less gas burnt at a higher efficiency. To highlight my point, even on the coldest day this winter (-5 C), the V200 never exceeded ~ 5kW heat output.

This should help the benefits of increased modulation:

https://www.heatgeek.com/what-is-boiler-modulation/