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

Waywardmike

Screwdriva said:

Reed_Richards said:

@Screwdriva, what's your annual gas usage?  In my old house it was 19500 kWh per year, averaged over 15 years.  This was a 4-bedroom house in Cambridgeshire, built in the 1960s and we used gas for heating and hot water.  I had an Atag gas boiler, which was very advanced for its time.

Pre all improvements, including the boiler replacement, our gas consumption was ~22500 kWh. Now, after improvements and receiving the EPC A rating, we consume ~12500 kWh for heating, cooking and hot water, with dramatically increased comfort levels. 

Is this not the average gas usage in the UK?  Again, not knowing how many occupants are in the house maybe you shouldn't be average, but surely an 'A' rated house should be well below average?

Screwdriva

Waywardmike said:

Is this not the average gas usage in the UK?  Again, not knowing how many occupants are in the house maybe you shouldn't be average, but surely an 'A' rated house should be well below average?

There are several factors that affect gas consumption including size of the property, the number of occupants and what has been described as "lifestyle". These have remained constant. 

A 35% larger, certified Passivehaus I know of consumed 604kWh of electricity for heating/ cooking/ hot water in 11/2023 (they have a 5 kW Arotherm+, MVHR & 9kW Solar PV). During the same month, we consumed 1734 kWh of gas (1734/4 = ~433 kWh if we had a heat pump with a SCOP of 3). One would think we should have dramatically higher energy consumption and that they would barely consume any?

Only way to be sure there's nothing needlessly heatlossy going on is a heat loss assessment with an infra red camera, which is next on the list of to dos.

JSHarris

Screwdriva said:

A slightly larger, certified Passivehaus I know of consumed 604kWh of electricity for heating/ cooking/ hot water in 11/2023 (they have a 5 kW Arotherm+ & 9kW Solar PV). During the same month, we consumed 1734 kWh of gas (1734/4 = ~433 kWh if we had a heat pump with a SCOP of 3). One would think we should have dramatically higher energy consumption and that they would barely consume any?

That sounds as if it's outside the Passivhaus energy limit to me.  To meet the Passivhaus certification requirement the total energy input over a year must not exceed 15kWh/m² total floor area.  That's a tough target to meet, as it includes all the energy used, not just heating, cooking and hot water. Allowing for seasonal variation (using PHPP and generic UK climate data, so there will be a small error) that figure of 604kWh implies that their house is very large, almost mansion-sized.  For comparison, our non-PHI certified 1400ft² house used 294kWh total energy input during November 2023.

Screwdriva

JSHarris said:

 For comparison, our non-PHI certified 1400ft² house used 294kWh total energy input during November 2023.

Agree - I expected their consumption to be significantly lower despite the 2400ft² size - I have checked their consumption and certification to be sure - I suspect it needs further "tweaking" of the heat pump settings.

More often, these variances in results highlights that, to me atleast, averages are an average method of evaluation. If the infra red camera doesn't pick up anything obvious, the 10K kWh reduction in gas consumption is likely as good as it will get for us. 

Reed_Richards

@Screwdriva, presumably your A-rated EPC predicts the power requirements for heating and hot water; what does that say?

Screwdriva

Reed_Richards said:

@Screwdriva, presumably your A-rated EPC predicts the power requirements for heating and hot water; what does that say?

Just under 10K kWh for heating and hot water (not cooking), of which 7.5K kWh for heating. 

JSHarris

Reed_Richards said:

@Screwdriva, presumably your A-rated EPC predicts the power requirements for heating and hot water; what does that say?

I'm not at all convinced about the accuracy or veracity of the EPC process.  I used PHPP when designing our home, although I didn't bother with PHI certification as it would have added a significant extra cost burden for no tangible benefit (other than bragging rights, if someone was so inclined).  My EPC certificate is a joke, literally, as the suggestions it offers for energy saving improvements are ludicrous.  Apart from the fact that we live at the bottom of a steep valley (which makes a wind turbine a non-starter, even if we did have acres of space for the thing to get clean air), the whole SAP process was simply bizarre.  It annoyed me having to fork out several hundred pounds for this worthless bit of paper, just because of some very poorly structured government dictat.

Look at this and have a good laugh at the improvement suggestions (those used to looking at returns on investment might find it particularly amusing!)  I should add we have solar water heating, we use the solar panels to heat our thermal battery that provides hot water - this "didn't compute" in SAP . . .:

Reed_Richards

Screwdriva said:

Reed_Richards said:

@Screwdriva, presumably your A-rated EPC predicts the power requirements for heating and hot water; what does that say?

Just under 10K kWh for heating and hot water (not cooking), of which 7.5K kWh for heating. 

So what you are using now is within the margins of error for the EPC estimate but what you were using before you got the new boiler was over twice as much.  I'm pretty sure the EPC assessment, which is very broad brush, would not have recognised the difference between the two boilers.  Why do you think your previous energy usage was so much greater than the EPC value?  To me it seems mysterious.  

Screwdriva

Reed_Richards said:

So what you are using now is within the margins of error for the EPC estimate but what you were using before you got the new boiler was over twice as much.  I'm pretty sure the EPC assessment, which is very broad brush, would not have recognised the difference between the two boilers.  Why do you think your previous energy usage was so much greater than the EPC value?  To me it seems mysterious.  

I was pleasantly surprised to find the EPC process rewards points things like weather compensation, hot water cylinder control, underfloor heating, Solar PV generation capacity and aspect (South facing vs. East facing) etc. 

As as far the reasoning goes, I think it's the combination of improved insulation, increased emitter surface area and a boiler that can maximize capitalization on both. 

Reed_Richards

@Screwdriva, is it documented somewhere what things do get you points on your EPC?  I would be very interested to know.  

With regard to Weather Compensation, you could have a boiler that can do Weather Compensation wired to a third party controller that can do Weather Compensation and still not have Weather Compensation if the controller setting is wrong.  But perhaps you just win points for the boiler, whether or not the Weather Compensation feature is operational?  Could your previous boiler not do Weather Compensation?  It was a feature of the boiler I installed in 1998, I would have thought that you would have made sure any boiler you bought had it