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Seasonal performance factors and RHI: should I get a reassessment?

Posted by Tasha Kosviner on 9 May 2014 at 9:50 am

You've had a heat pump installed (prior to the launch of the RHI), you've had your green deal assessment, you've got your MCS certificate and you're poised to apply for the government's newly-launched renewable heat incentive (RHI) scheme.

But hold on - what's this? A question in the application about whether you want to use your deemed SPF of 2.5 or another figure. What does that even mean? You thought this was supposed to be simple, right?

Well yes it was, but then Ofgem realised that paying incentives based on the type of renewable heat installation you have, wasn't simple either. In order to make the incentives work properly they needed to look at not just the type of technology you have installed, but also at the efficiency of that installation. 

The efficiency of a heat pump installation depends on the temperature the water in the pipes needs to be maintained at, in order to have a warm home. And this depends hugely on both the efficiency of the heat emitters you use - for example radiators or underfloor heating - and on the heat demand of a room. To put it bluntly, if you connect an air source heat pump to traditionally small radiators in a room with three outside walls and as many windows, it's going to require a whole lot of heat to keep it warm. If you connect it up to an underfloor heating system in a room with a single, triple-glazed, south-facing window, then you'll need much less energy to heat it. 

Thus the SPF or seasonal performance factor was born. The SPF assigns an efficiency rating to your heat pump based on the required temperature of the water flowing through it. The lower the flow temperature, the more efficient your system and the higher your SPF.Crucially, the higher your SPF, the higher your RHI payments will be.

In new systems, that is in systems installed after the launch of RHI on 9 April 2014, the SPF is assessed using the MCS's heat emitter guide and the figure you find on your MCS certificate will be the one you can use in your RHI application. 

But for legacy systems, that is systems installed before the 9 April launch, your SPF will probably have been 'deemed', or fixed, at the relatively low 2.5. This is because prior to the launch, there was not an industry standard for calcuating SPF so Ofgem have no way of checking your installer's SPF calculations for accuracy. 

In order to get a more accurate - and potentially higher - assessment of your system, you will need to get a reassesment of your home.

The reassessment will involve your installer coming out to do a room by room assessment of your property. Each room will be assigned a heat loss calculation and then the installer will look at the means you have employed to emit heat into that room - for example outsized radiators, traditional radiators or underfloor heating. Those figures will then be used to arrive at the SPF calculation. 

The calculation you are given will be based upon the heat demand and heat loss calculations of the least efficient room in your house so be warned - your home can be let down by the use of just one ineffecient radiator, in a sea of otherwise underfloor-heated rooms. 

As a very broad guide, if your heat pump is linked up to underfloor heating in a highly insulated house, it is possible that your SPF will be considerably higher than 2.5; if it's linked to traditional radiators, and you have minimal insulation over the minimum requirement, it's likely that 2.5 won't be far off. Ground source heat pumps are likely to achieve higher ratings than air source heat pumps. 

Robert Meeks, a commercial sales manager for ICE Energy which has installed over 11,000 heat pumps, has come up with these figures to give an idea of what a higher SPF rating might mean for a typical 3-bedroom property.

A typical 3-bedroom property has an annual heat consumption of 20,000kWh. At an SPF of 2.5 the renewable energy component of this is 12,000kWh. But with an SPF of 3.4, the renewable energy component is 14,120kWh. In this case, upgrading the SPF to 3.4 would yield an additional 2,120kWh of additional renewable energy. If you have a ground source heat pump it would result in an increase to your RHI payments of £398.56 per year at a rate of 18.8p/kWh, or £2789.92 over the seven years of the scheme. For an air source heat pump, this would result in an increase of £154.74 a year, or £1083.32 over seven years. 

Remember though that there are lots of variables and the only way to know for sure what your SPF is is to get the assessent done. 

Whether you choose to get an assessment or not will probably depend on you balancing the likely increase in SPF - and consequently your RHI payments - against the cost of getting the assessment done. I've heard of one company that is charging £240 for the assessment. However, apart from that upfront cost, there is minimal risk involved: if you do get an assessment done and it comes out at below 2.5, Ofgem tell me you can always ignore it and opt for the deemed SPF of 2.5 in your application.

More information

YouGen guide to renewable heat initiative

The domestic renewable heat initiative: your questions answered

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

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13 comments - read them below or add one

Caitlin Moran

Caitlin MoranComment left on: 10 September 2014 at 3:44 pm


Sorry for the late response, Gilly put a  tweet out and Eco Living UK offer this service. You can find a local branch searching our online directory.

Hope this helps

Caitlin - YouGen Team

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flipflops13Comment left on: 9 September 2014 at 11:46 am

hi we have decided to have our SPF report but can only find the company linked to ice energy (Home survey reports) They are quoting £240 to do the SPF.  I can not find anyone local who are providing them, has anyone any suggestions please?

We have tried the local green deal asserssors but have had no luck and would just like to compare charges/service

many thanks

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DSComment left on: 14 July 2014 at 6:10 am

The MCS heat emitter guide is based on Leeds weather, so presumably you will be disadvantaged if you live in the south and getting a bumper payment if you live in Scotland.

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Tasha Kosviner

Tasha KosvinerComment left on: 9 July 2014 at 2:56 pm

Hi AJSmith

Have a look at this blog which gives further information about the SPF question in relation to renewable heat incentive. 

The general feeling seems to be that 2.5 is not a bad result for an ASHP. However, if you feel there is a problem with your system then you should discuss it with your installer. 

They are obliged under the renewable energy consumer code to provide an installation that is suitable for the setting. 

Let us know how you get on!


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AJSmithComment left on: 7 July 2014 at 9:38 pm

We have a legacy system ashp system and am not sure whether it's worth having the SPF calculated or whether to accept the 2.5 default.

Our supplier (in my opinion) over designed the system as it always overshoots on heating (we request 18 degrees, it provides 22 degrees). I don't believe the supplier took account of the insulation & air tightness levels we were going to achieve with our refurbishment.

We have underfloor heating to all areas, a Hitachi Yutaki-M 6kw ashp, a 100 litre buffer tank for the underflor heating and a 300 litre unvented cylinder.

Our supplier wants £222 to provide an SPF based on their original calculations or £354 to re-calculate the SPF based on the as-built structure.

Any thoughts on whether it is worth having the SPF calculated?

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neilpaigntonComment left on: 26 June 2014 at 10:31 pm

As a legacy install once I had the Green Deal advice assessment which included an EPC report for £150. One day later the certificate numbers arrived and I completed the online RHI application and was accepted on the scheme.

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kit henson

kit hensonComment left on: 26 June 2014 at 9:13 am

Thank you Tasha

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Tasha Kosviner

Tasha KosvinerComment left on: 23 June 2014 at 1:26 pm

Hi Kit 

Further to the below, I've talked with MCS and no, although there has been pressure from installers, it doesn't look like there's going to be any further guidance on this. 

The current guidance states that all heated areas need to be taken into account when looking at SPFs and that a heating system should be designed so that all areas are heated to between 16-21 degC.


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Tasha Kosviner

Tasha KosvinerComment left on: 23 June 2014 at 1:08 pm

Hi Kit

There hasn't been any update that I'm aware of although I am in touch with MCS about it. I'll be sure to post as soon as I hear something.

In the meantime, it might be worth have a chat with your installer though and asking their opinion. They will have an idea of how flexible they can be with the assessment as per my reponse to stuart below... 

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kit henson

kit hensonComment left on: 20 June 2014 at 4:45 pm

Hello Tasha

just wondered if you had an update on this issue - has the guidance been altered in terms of the spf calculation? i am holding off getting mine done in case there will be a more favourable basis to cover bathrooms/hallways etc which currently will drag the number down



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stuart smith

stuart smithComment left on: 12 May 2014 at 1:01 pm

Thanks Tasha


Very helpful; lets hope there is guidance soon as if I have to upgrade small conventional rads in small rooms and corridors I would need to get this organised before making an applicatiopn for the RHI





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Tasha Kosviner

Tasha KosvinerComment left on: 12 May 2014 at 11:18 am

Hi Stuart

Your SPF will be assessed according to the worst performing room, so yes, technically if your bathroom is the least efficient, then that's where your rating will fall down. So yes, a larger radiator in the bathroom would be the best solution for obtaining the best SPF. 

If your bathroom is an en suite, there may be an argument for your assessor treating it as one room with the adjoining bedroom since it's unlikely to be a room that is continuously heated, the biggest draw on heat will be when the extractor fan is on and the rest of the time the door may be open onto the bedroom.

This issue is something that I'm told the microgeneration certification scheme (MCS) are looking at, as things like en suites, hallways, seldom used basements etc may all disproportionately skew SPF ratings. Additional guidance is currently being considered - keep an eye on this blog for further updates. 


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stuart smith

stuart smithComment left on: 10 May 2014 at 12:44 pm

Hi Tashs


Interesting blog but also worrying. I have fan assisted low temp rads except for conventional rads in bathrooms (the manufactures say they shouldn't be put in bathrooms). Will I have to install larger rads in the bathrooms so as to allow the heating to be adequate in those rooms at a temp flow of 40 degrees and so as to get a SPF over 2.5 (I'm aiming for 3.4)?


Your comments would be appreciated.







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