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

Screwdriva

70sbudgie said:

My head is a bit fuzzy at the moment, so sorry if this is a daft question...

I think you are implying that the improved modulation is the reason for the fantastic savings. Doesn't this suggest that both boilers, old and new, were massively oversized? And the new one perhaps slightly less so? Does you new boiler ever output its max rating - or close to it? What savings could be achieved simply by correctly sizing the boiler?

The previous boiler was 18 kW unit which could modulate down to 6 kW. The replacement V200 is a 19 kW unit - a feature of the V200 range is that all of them can modulate down to 2.1 kW, essentially nullifying the risk of oversizing. 

The new V200 has never exceed an output of 5 kW, even when it was - 5C outside last December. 

I believe the modulation capability combined with the advanced weather compensation controls that force the boiler to modulate and the higher burner efficiency all contribute to the savings I've shared on Page 16. 

paul991 said:

Roughly what does it cost to install underfloor heating per square meter in a existing concrete floor?

We removed our old wood flooring (donated) and poured self leveling screed first -> 25mm grooved XPS UFH boards + 15mm piping -> another layer of screed -> S2 Tile adhesive -> Tiles

Roughly £215 per sq metre. 

Reed_Richards

Screwdriva said:
he previous boiler was 18 kW unit which could modulate down to 6 kW.  The replacement V200 is a 19 kW unit - a feature of the V200 range is that all of them can modulate down to 2.1 kW, essentially nullifying the risk of oversizing. 

The new V200 has never exceed an output of 5 kW, even when it was - 5C outside last December. 

If it uses 5 kW  at -5 C and you heat your house to 20 C then it will only need 2.5 kW at 7.5 C and 2 kW or less for any outside temperature greater than 10 C.  Therefore the lower limit of its modulation range (2.1 kW) is insufficient to stop it having to cycle at outside temperatures of 10 C or above.  That's not necessarily a bad thing so long as it constrains itself to long cycle times (as per your HeatGeek reference from a few posts back).

The relatively low heat requirement of your house is a clue as to why your old boiler was so inefficient by comparison with the new one.

delgarno

This is an excellent thread and thank you to @Screwdriva and everyone else who contributed.

I’m considering something very similar and have kicked off a new thread.  Would love comments to help me!

https://forums.moneysavingexpert.com/discussion/6466197/another-going-greener-with-viessmann-200w-efficient-heating-system-design-questions

Reed_Richards

@Screwdriva has moved over to the Energy board with a reprise of this topic: https://forums.moneysavingexpert.com/discussion/6491452/viessmann-200-w-gas-boiler-the-most-efficient-boiler-sold-in-the-uk/p1