Changes to MCS 031 System Performance Estimate for Heat Pumps

From the 18 March 2025, system performance estimates will need to be done in a different way. We included a ‘Just the Facts’ explainer in the spring newsletter but this article explains the changes in a little more depth.

What is changing?

The main change is that instead of using heat pump specific SCOP values, generic SPF values dependent on proposed flow temperatures will be used. For an air source heat pump the new SPFs are:

Flow temperature in 0C	SPF
<35	4.0
36 – 40	3.8
41 – 45	3.4
46 – 50	3.1
51 – 55	2.8
56 – 60	2.5
61 – 65	2.5

 

These are lower than the majority of heat pump specific SCOP values that we have been using previously. For example, at 50^oC the average SCOP for heat pumps in the MCS Product Directory is around 3.6 whereas the SPF given in the new method would be 3.1, meaning a 16% increase in the estimate of energy used using the new method vs the old method.

What impact will this have?

In most cases, the new method will result in higher estimated energy usage than the previous calculation method. It also means that specifying a more efficient heat pump that has a higher SCOP won’t be given any benefit within the MCS 031 System Performance Estimate calculation – all systems designed at the same flow temperature will get the same SPF; the only differences being between ground source and air source.

How do running costs compare with a gas boiler using the new SPFs?

The MCS System Performance Estimate has not required installers to provide an energy cost estimate for a while now due to the fact that energy prices are frequently changing and impossible to predict. The new MCS 031 method also removes the requirement to compare estimated energy use of the proposed heat pump system with the customer’s existing system. However, we know that this comparison and running costs in general are important to homeowners.

The new energy price cap prices from 1 April 2025 are:

Fuel	Price per kWh	Daily Standing Charge
Electricity	27.03p	53.80p
Gas	6.99p	32.67p

 

Assuming you are comparing a new heat pump system with a gas boiler that has an efficiency of 0.9, you need the heat pump system to have an efficiency of 3.6 to have a comparable cost. This means that using the new MCS 031 method, you would have to design the system at 40⁰C for the heat pump to come out cheaper to run.

The good news is that several energy suppliers are offering specific heat pump tariffs now. These range in price and complexity, but take the example of the Ovo tariff – the electricity used by the heat pump is charged at a lower rate of 15p/kWh at all times of day. On this tariff you would only need an SPF of 2.0 to come out cheaper than gas meaning a 55⁰C flow temperature will still show savings compared to gas.

The other thing to remember is that if your customer is able to remove their gas connection completely after getting a heat pump installed, they won’t need to pay the daily standing charge for gas. Currently this would save them £119 each year.

Why is MCS 031 changing?

The MCS Heat Pump Working Group proposed these changes because they were concerned that using the SCOP was over estimating real life system performance. In the recent guidance issued by MCS on the new method, they point to the recent Electrification of Heat trial which showed an average measured performance of 2.8. This was a government funded trial involving over 400 heat pumps – the performance data can be found here. Heat pump performance in this study varied massively with the most efficient unit’s performance measured at 4.68. There were also many poor performing systems some of these are flagged as having poor data quality but there are other identifiable issues such as under/oversizing, incorrect pipework sizing or having the weather compensation curve set too high.

However, there is other real world performance data available such as Open Energy Monitor’s ongoing heat pump monitoring project which is currently showing SPFs ranging from 5.0 to the lowest rather than the average being  2.8. All this is to say that all not all heat pumps are the same, not all installs are the same and not all installers are the same. However, the new MCS 031 treats them as though they are.

What else is changing in the new MCS 031?

• Capacity estimates from EPC data

The new method also provides a standard approach to sizing a heat pump from the EPC, meaning the installer is able to provide an indicative performance estimate within an upfront quote, without having to do a full heat loss survey. Note: A full heat loss must still be done prior to installation.

We see this as a positive step in recognising the sales process that installers go through with their customers and formalises a method that many installers are using anyway to give a quick indication of heat pump sizing for customers.

• The new method requires the inclusion of specific wording depending on the proposed emitter system and heat loss per m²

Whether the customer is opting for radiators or underfloor doesn’t make a difference to the SPF (only the flow temp and whether it is ground or air source). However, the combination of the emitter system type and the heat loss of the house require the installer to add a number of notes to the estimate for the customer’s information. These are meant to provide a view of whether what is being specified is likely to operate as designed and prompts the customer to clarify certain things with their installer.

• The new method provides a +/-10% range for the estimated energy use of the system

Providing a range is useful as it gives a clearer indication that what has been calculated is an estimate and therefore not a guarantee of performance.

• The SPF for hot water production has been reduced from 1.75 to 1.70 in line with SAP10.2

The value of 1.70 is provided in SAP 10.2 to be used only when the actual performance of the heat pump in unknown. Where it is known, SAP 10.2 says that you should use the data for the unit, which is the opposite to what the new MCS 031 allows – again reducing the efficiency down to a very conservative estimate. The Product Directory for SAP actually does contain hot water production efficiencies for specific heat pumps, whereas for some reason the MCS Product Directory never has, which is why the previous default value of 1.75 was provided.

What does all this mean for installers?

From the 18 March 2025 installers must provide the new version of the MSC 031 System Performance Estimate to customers. The calculation is now easier to do without doing a full heat loss, however the results will estimate that the heat pump will use more energy than the previous version of the calculation.

But, don’t forget…!

MIS 3005-D section 4.1.4 says that you are still able to also provide an alternative estimate, as long as it can be clearly justified and are not given greater prominence than the MCS estimate.

Therefore, Installer Toolkit users will be able to produce both the old and new estimates for their projects. Heat pump proposals produced by Toolkit following a full heat loss will use the heat pump specific SCOP and also calculate a heat pump specific efficiency for the hot water.

We are also looking at other ways of representing running costs in customer proposals, for example displaying the benefits of using a heat pump specific tariff. Please get in touch if you have ideas on how you would like to present performance and running cost information to your customers.