Using an existing heat store is compliant with all of the requirement of the “Boiler Upgrade Scheme: Installer Guidance V4.2” and the MSC design standards therefore saves £3,000 on a typical air source heat pump install cost.
An affordable heat store stores up to 17 KW Hr of “Off-Peak” Energy in the form of hot water allowing 14 good hot showers delivered at mains pressure to the consumer at times when electricity is expensive.
An affordable heat store compliments an air source heat pump system and it qualifies as part of an air source heat pump system.
I believe the Affordable Heat Store qualifies as part of an Air Source Heat Pump System after considering the following paragraphs of section 3 of the “Boiler Upgrade Scheme: Installer Guidance V4.2”
Para 3.9 Table One (Fully Compliant)
A heat pump System (with an affordable heat pump as part of that system), will provide heating and hot water- it is therefore compliant.
A heat pump System (with an affordable heat pump as part of that system), is capable of providing all of the hot water and heating – it is therefore compliant.
It is of note that many compliant existing heat pump systems are incapable of heating hot water to the higher temperatures required for legionella control and therefore heat the hot water using immersion heater. An immersion heater can be retained in accordance with Table Two (Clause 3.55)
Para 3.45 (Fully Compliant)
A heat pump must include ancillary plant such as existing radiators, pipes, existing hot water cylinders and immersion heaters, controls etc, all as defined in the BUS scheme guidance. A heat pump on its own cannot provide hot water and heating without ancillary plant and a heat pump absent ancillary plant does not qualify for a BUS grant.
Para 3.46 (Fully Compliant)
This clause states that an ‘air source heat pump’ is not just the the pump but it includes “ancillary equipment”. It further defines ancillary equipment to include hot water cylinders and under para 3.47 that hot water cylinder need not be new.
Para 3.47 (Fully Compliant)
This clause states “An eligible plant’s ancillary equipment does not need to be new and can be retained
from the previous fossil fuel or electric heating system. More detail is given at paragraph 3.55
and table 2.”
Para 3.50 (Fully Compliant)
The heat pump or biomass boiler must provide both space and hot water heating to the property. Para 3.46 and Para 3.47 and Para 3.55 defines a heat pump to be ineligible unless it includes new and existing ancillary plant and that includes an existing hot water cylinder and its existing immersion heater. A heat pump with an affordable heat store is fully compliant.
PARA 3.51 (Fully Compliant)
The heat pump or biomass boiler must be capable of meeting the full space heating and hot water heating demands of the property. Many eligible heat pumps still qualify for BUS despite the requirement to only design the heat pump system to an outside low of -3 degrees centigrade. Many existing heat pumps qualify despite having ancillary immersion heaters which can turn on at 9am in the morning and use electricity at peak demand. An entire heat pump system which includes an existing hot water cylinder and its existing immersion heater if correctly designed will comply with para 3.51. This paragraph stops an installer just heating half a home (say just the bedrooms).
Para 3.54 (Fully Compliant)
A Fossil Fuel System needs to be completely removed but certain heat generating components of the original
heating system can be retained. The retainment of and existing immersion heater as a heat generator plus circulation pumps, solar thermal collectors, and supplementary electric heaters (including immersion heaters) to be retained. Table 2 specifically tells us that a “Thermal Store” can be retained in a air source heat pump system. An affordable heat store is a thermal store.
Para 3.57 (Fully Compliant)
“Where parts are retained, the heat pump or biomass boiler must be sufficient in size, and installed in such a way, that were the retained heat generating components not there, it would be able to provide space heating and hot water to the property on its own.” The only retained heat generating component is the immersion heater so the only requirement is that the immersion heater needs to be replaced. On the assumption the immersion heater is replaced as part of the heat pump install, an affordable heat pump is fully compliant.
OTHER INFORMATION SUPPLIED TO MSC INSTALLERS (Fully Compliant)
The “MSC Heat Pump Design Standards” and in particular “Section 3.4 – Space Heating Design”, within the MSC document, re-interprets the official Oftgem design guidelines in a way not intended by Oftgem.
https://mcscertified.com/wp-content/uploads/2025/01/MIS-3005-D-2025-V1.0.pdf
Whilst the MSC clause 3.4 is ambiguous and conflicts with the official Oftgem Guidance the MSC CLAUSE 3.1 it states that “All applicable legislation and directives must be met in full THE OFFICIAL BUS GUIDANCE SHOULD PREVAIL.
Clause 3.5 recognises that an existing hot water cylinder can be used – An affordable heat store is fully compliant
