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Should I recalculate my heat pump's SPF? My renewable heat incentive journey part 2

Posted by Tasha Kosviner on 4 July 2014 at 9:03 am

As the owner of an air source heat pump who received a renewable heat premium payment grant prior to 20 May 2013, I am in the second tranche of applicants being invited to apply for the renewable heat incentive

The date from which the group is eligible to apply – July 9, 2014 – is fast approaching so I have been examining the eligibility criteria with a renewed vigour. I have had my green deal assessment and I have – through gritted teeth! – ensured that my loft insulation is up to the required 250mm. 

But the other question that has been on my mind is whether I should have my seasonal performance factor (SPF) recalculated. As I outlined in this blog, the SPF is the efficiency rating assigned to your heat pump. This rating is based on the required temperature of the water flowing through the system. The lower the flow temperature required (in order to keep the house comfortably warm), the higher the system’s efficiency; the higher the system’s efficiency, the higher your SPF; and the higher the SPF, the higher your RHI payments.

At the time my heat pump was installed, and up until the launch of the renewable heat incentive in April, installers used a variety of different methodologies to decide a heat pump’s SPF. Because Ofgem is unable to ascertain the accuracy of these different methodologies, it has been decided that for the purposes of RHI, a heat pump’s SPF should be deemed to be the minimum 2.5, and your payments are set accordingly. 

If you think your heat pump is more efficient that this, you can decide to have your SPF reassessed using the new industry standard, set by the MCS and outlined in their heat emitter guide. This is the standard by which all SPFs are now calculated and has been in use since RHI launched in April 2014. 

The question is, should I? The reassessment takes all day and can be expensive – I’ve heard of one installer charging £250 – and the possible gains through an increase in RHI payments could be marginal.

I called my installer for advice and the short answer he gave me was that no, it wouldn’t make much difference to my rating. Firstly, since my system is linked to a combination of underfloor heating and radiators, it’s not as efficient as one run purely with underfloor heating.

Secondly, since my home is well insulated, the amount of renewable heat needed is fairly low (RHI is designed to make payments based on the amount of renewable heat generated ie the heat demand of the house).

 Thirdly, even if my SPF went up marginally to say SPF3 this would only equate to an increase of around £40 a year. Since he charges £150+VAT for the assessment, it would take nearly four years to make it back and then with only three years left to run on my scheme my total gain for going through the hassle of reassessment would be a relatively small £120 spread over years four to seven. 

Further questioning of experts connected with the Microgeneration Certification Scheme standards for heat pump efficiency, reveals that in most cases an SPF of 2.5 is a good achievement for an air source heat pump although ground source heat pumps, provided they are connected to a system capable of heating effectively at lower flow temperatures, are likely to achieve 3.5 or higher. 

I think I’ll be sticking with 2.5 then. 

This is the second installment in my RHI: a personal journey series. You can read the first installment here. I will shortly be posting on my experience of the application process too so watch this space. 

More information

YouGen guide to the RHI

YouGen guide to heat pumps

From the blog

How is the SPF of my heat pump calculated? (Sept 2013)

If you have a question about anything in the above blog, please ask it in the comments section below.

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9 comments - read them below or add one

Gilly Jones

Gilly JonesComment left on: 11 August 2014 at 9:02 am


I put a  tweet out and Eco Living UK offer this service. You can find a local branch searching our online directory.



report abuse left on: 7 August 2014 at 8:58 am

I am also looking for somebody to do an SPF calculation for my existing GSHP. I am not able to find anybody at present. If anybody knows of one then please let me know.

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RachComment left on: 23 July 2014 at 9:16 pm

Installer responded already. Ofgem correct! Our GSHP SPF is 4.1. Thank you Ofgem for spotting this error. Think our current application now needs to be rejected and a completely new application made. Email sent to Ofgem asking them to confirm next steps.

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RachComment left on: 23 July 2014 at 8:48 pm

Dear Tasha

Progress has been made. Sheepish installer completed calculation after pressure from head office. Charge £150 inc. which seems standard for existing customers. Application completed and straight into review! SPF calculation duly provided. Latest development today - Ofgem technical team reckon the calculation is wrong at 3.4, they think it has been calculated on ASHP basis not GSHP as it should have been, which would give a 4.1 SPF. If this is the case I need a new calculation and to make another RHI application.

Have left a message and sent an email to our installer, no response as yet. Obviously no idea which is correct!

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Tasha Kosviner

Tasha KosvinerComment left on: 16 July 2014 at 11:37 am


Make sure your installer uses the MCS heat emitter guide to do the calculations. This involves them doing a room by room assessment of your property. Ofgem will not accept an SPF recalculation in any other format and you will need to prove that the heat emitter guide methodology was used.

Out of interest, how much are they charging you for the recalculation?



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RachComment left on: 14 July 2014 at 7:56 pm

Good news, my installer is now cooperating. We'll see if the SPF calculation arrives in a couple of days as promised!

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RachComment left on: 10 July 2014 at 3:44 pm

Tasha, thank you for your response. I've been online looking for alternative MSC installers to approach for the SPF calculation and unfortunately most seem only interested in dealing with existing customers. One accepting non existing customers has a waiting list of 3 months and is charging £600.00 + VAT for the privilege!

I will keep trying but if anyone knows a company providing a reasonable service please let me know.

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Tasha Kosviner

Tasha KosvinerComment left on: 10 July 2014 at 11:50 am

Hi Rach

Having spoken to Ofgem about this, the answer is that a) no, unfortunately there is no obligation on your installer to carry out a reassessment and b) yes, you can approach any MCS-registered installer. 

I hope that helps. I'd be interested to hear how you get on.

Tasha (editor)


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RachComment left on: 9 July 2014 at 2:59 pm

We have a legacy GSHP and think it will be worth our while to have the SPF calculated for our system before making the RHI application (even though our house is well insulated). However our problem is that our installer is not responding to requests to carry out an SPF calculation! Not sure where that leaves us - are our installers obliged to carry out the calculation or can we approach any MCS registered installer?

Anybody else encountering similar problems?

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