Efficiency (or not) of thermal stores??

[delberto]

hi folks,

I'm buying a new build house in N.I that has an oil fired condensing boiler and a room sealed wood burning stove with a back boiler and both heat sources serve to supply a thermal store which in turn serves the central heating and DHW via internal coil heat exchangers. (The brand is maxi pod from N.I)

I'm a chippy by trade so am after some expert insight into why a thermal store (DHW supply) is rated as only 3 stars on a sap/EPC assessment.
The oil burner/wood burner combo gets 4 stars for the heating side which comes through the heat store too...
The only thing that I can guess at is the heat store also has an electric immersion element fitted and if that is only switched on to assist with the DHW demand then the more expensive electric energy required 'might' be the answer but I'd appreciate any insight from the experts.
Of the 2 other houses built at the same time with the same DHW systems one also gets a 3 but one gets a 4...

Any thoughts? (Apart from me getting a life)

 

[Dan Robinson]

Standing losses and the electric immersion combined I would have thought. But with an oil boiler, a thermal store is probably best.

Consider zoning your heating with Evohome.

 

[delberto]

Hi Dan,

The heating is already fairly well zoned I think... It has 3 zones for the under floor heating downstairs (hall/WC, lounge, kitchen/dining) and a separate zone on floors 1 and 2 controlled by a room stat and thermostatic valves on all rads. I guess the heat store acts as the bypass. I'll look up evohome.

Having looked up the thermal store the makers say it far exceeds building regs for insulation but I wonder if it is worth adding more to reduce the standing losses that you mention?
Also just remembered that one of the 3 showers has an electric shower fitted which I guess may also affect the overall rating (but that is not mentioned in the SAP CERT).