High Heat Retention Storage Heaters

At the time of writing the methodology for EPC assessments of existing dwellings is RDSAP 9.94. The much anticipated RDSAP 10 update is due in Q1 2025 and a significant methodology overhaul from RDSAP to the Home Energy Model (HEM) is proposed for 2026.

Storage Heaters are often seen as an attractive option for properties that don’t have a mains gas supply available.

In the absense of a more economic fuel type, storage heaters make the best use of electricity they can by heating up high density bricks during the night time when lower cost electricity is available, and releasing that heat throughout the day.

Although somewhat less than ideal from a domestic EPC rating perspective due to the high cost of electricity as a fuel type, they are fitted to numerous properties, and as a product have undergone some development over the years.

Early storage heaters were large bulky unattractive boxes, modern ones became thinner and more attractive, and included automatic charge controls, and then fan assisted storage heaters became a regular recommended upgrade on EPC certificates a few years ago,

Nowadays, High Heat Retention Storage Heaters are the best performing variant, and are likely to be seen in EPC recommendations if you already have earlier types of storage heater in your property.

They have additional insulation so that heat is retained in them longer than a conventional storage heater. The extra insulation helps keep the outside of the heater cool while it's not in use. They also have features to further increase energy efficiency such as adaptive start and open window detection.

In order to successfully enter a High Heat Retention Storage Heater in an EPC assessment, the Energy Assessor needs to locate the specific make and model from a list in the Product Characteristics Database (PCDB), hosted by the Building Research Establishment (BRE).

If your device is not on the list, it cannot be entered as a High Heat Retention Storage Heater.

To check if a particular model is listed in the PCDB, click on the link below and go into the High Heat Retention Storage Heaters section:

https://www.ncm-pcdb.org.uk/sap/searchpod.jsp?id=17

At the time of writing this section (Sep 2024), there are only 45 available models of HHRSHs currently listed in the PCDB:

• Dimplex Quantum: QM050, QM070, QM100, QM125, QM150, QM050RF, QM070RF, QM100RF, QM125RF, QM150RF
• Creda Quantum: CQH 070, CQH 100, CQH 125, CQH 150
• Heatstore Quantum: HSDQ 070, HSDQ 100, HSDQ 125, HSDQ 150
• Heatstore Dynamic HHR: HSDHHR050, HSDHHR070, HSDHHR100, HSDHHR125, HSDHHR150
• Gabarron Ecombi HHR: ECOHHR10, ECOHHR20, ECOHHR30, ECOHHR40
• Gabarron Solar HHR: SOLARHHR10, SOLARHHR20, SOLARHHR30, SOLARHHR40
• Stiebel Eltron: SHF 2000, SHS 2400, SHS 3600, SHF 3000, SHS 2000
• Haverland Eco-Joule-1: SHV1700HHR, SHV2250HHR, SHV3400HHR
• Fischer Elektrostore: HHR16, HHR25, HHR34

If the heater you are looking to install is not on this list then your EPC rating won’t be better than if you had 'standard' storage heaters present.

As a minimum, you need to have a High Heat Retention Storage Heater fitted in the main living area of your property - such as a living room.

The new labour government of 2024 has indicated their intention to tighten the the MEES requirement for rented properties to Band C by 2030. Perhaps you're interested in updating or upgrading your storage heaters to improve your EPC rating because of this legislation.

If so, what do you do? You could:

• Upgrade your existing storage heaters to High Heat Retention Storage Heaters (HHRSHs)
• Remove the storage heaters, get gas connected to the property and fit a gas boiler and radiators / underfloor heating
• Remove the storage heaters and fit an oil boiler and radiators / underfloor heating
• Remove the storage heaters and fit an air source heat pump with radiators / underfloor heating
• Rip out the storage heaters and fit electric panel heaters instead because you’ve seen a very convincing advert on social media from a company saying that their peak-rate electric panel heaters are very efficient and better than storage heaters

We'll consider some of these options here:

There are companies that actively advertise, particularly on social media, trying to sell panel heaters to people that currently have storage heaters and want something 'better'.

They try to dupe you into purchasing their products by describing them as highly efficient electric panel heaters. Here's an example marketing ploy:

"Electric Radiators offer a modern, energy efficient heating solution for any space. Unlike traditional radiators, electric radiators provide 100% conversion of energy to heat, precise temperature control for each room and the latest energy saving technology, ensuring optimal comfort and reducing energy wastage."

In reality, if you replace all your storage heaters with electric panel heaters, whatever the company tells you, your EPC rating will fall. This is beacuse the panel heaters use peak rate electricity for heating during the day, and it will therefore cost more to maintain the property at the same temperature, compared to storage heaters which charge up using only cheap rate electricity during the night.

The following table shows modelled EPC ratings for my house, if I had storage heaters or panel heaters as the only type of heating. This is a 1950s mid-terrace house (see our Case Study 2 page for more info - note there is no form of Secondary Heating present in the property and for the modelling hot water is provided by a normal sized cylindeer with 50mm foam insulation and dual immersion heaters):

So if I were to move from 'modern slimline storage heaters' to 'electric panel heaters' as the only form of heating in my property, this would reduce my EPC rating from 48E to 39F. That's a drop of 9 SAP points.

In contrast, moving to 'high heat retention storage heaters' instead would take me from 48E to 59D. That's an increase of 11 SAP points.

Always contact a Domestic Energy Assessor and ask them what effect any proposed changes might make to your EPC rating. It's important to do this before you make any chages.

There are many factors that contribute in the calculation of an EPC rating and if you want to hit a particular target you need to be working from a position of certainty rather than hoping you'll get the rating you want.

This option will be listed as a Recomendation on your EPC if you currently have earlier types of storage heaters.

When you see a recommendation on your EPC for High Heat Retention Storage Heaters, an estimate of the cost will be provided. You should carry out due diligence and get a worked estimate from an electrician, particularly if you want more than one fitted.

Currently, as an example, Dimplex Quantum High Heat Retention Storage Heaters are listed on the Internet with a retail price of around 1,000 GBP each, and that's just for one heater without installation.

Installation is an additional cost, and the heater might require additional wiring when replacing older storage heaters. High Heat Retention Storage Heaters generally require both a peak rate and an off-peak rate electrical supply, for each heater. Previous storage heaters are likely to only have had an off-peak electric supply present.

If you need to replace/install several storage heaters then the cost will mount up quickly, and you may then want to compare with another type of heating system that could increase your EPC rating even further for similar cost.

High Heat Retention Storage Heaters will need to be sized via a Heat Loss calculation for the area they will heat. Your electrician would normally work this out for you.

In terms of recording High Heat Retention Storage Heaters in an EPC assessment, there are some interesting points to notice.

Thinking back to other heating systems for a moment, such as a gas boiler, we recall that to maintain the best EPC rating you would normally make sure all of the 'Habitable Rooms' in the property are heated by that boiler, and any form of peak-rate electrical heating (panel heaters, fixed fan heaters, electric towel rail radiators etc) are removed - See our Heating Systems page for more information about this.

If you have a High Heat Retention Storage Heater however, those things appear not to affect the rating like they would with say a gas boiler.

To demonstrate this, in the table below I model my house (as described in our Case Study 2 page), but with High Heat Retention Storage heater(s) declared as the Main Heating source, together with unheated habitable rooms and electric panel heaters as secondary heating, in differing combinations:

Notice that the EPC rating appears to stay the same.

It would appear that adding more than one HHRSH does not vary the EPC rating.

Also, the presence of unheated habitable rooms appears not to affect the rating, and neither does declaration of electric panel heaters as secondary heating.

Even if I add Main Heating 2 as an earlier type of storage heater, so that we have a combination of one HHRSH, and one older type of storage heater, the assessment software I am using (Elmhurst Energy's RDSAP Go app for iOS) does not allow me to assign a percentage of heat to that older type, and so the assessment rating stays the same at 59D.

This combination could be the case in say a 1 bed flat where you install a HHRSH in the living room and retain an older type of storage heater in the bedroom to keep the renovation costs down.

I first became aware of this behaviour after reading a very intelligent case study on the 'EPC Home' website here:

https://epchome.co.uk/coventry/epc/case-study/e-rating-to-c-rating/

I'd thoroughly recommend reading their case study as it delves into U values for walls when modelling and fitting internal wall insulation, and combining that with High Heat Retention Storage Heaters to reach a C band target on a flat in a building with solid brick walls.

There are some updates to the EPC assessment methodology for existing dwellings in the near future - one is the update to RDSAP 10 due in Q1 2025, and the other is the move to the Home Energy Model in 2026. Whether this behaviour with HHRSHs will stay the same will need to be seen.

Despite the behaviour detailed above with HHRSHs and unheated habitable rooms and electric secondary heating, you still need to ensure that sufficient heating is available in the property overall in order to maintain the condition of the living spaces.

Finally, do contact a local energy assessor to model your property before proceeding with any changes. This will enable you to work from a position of certainty regarding EPC rating outcomes.

You won’t see a recommendation on your EPC to upgrade from a storage heater to a gas combi-boiler unless you have a gas supply to your property and a gas meter in the meter box.

If you don't have gas, it might be possible to get it connected to the property, so do include this when considering your options - and you could fit a condensing gas boiler and radiators or underfloor heating system.

This of course won't take you down the ideal path of reducing carbon emissions, but currently domestic EPCs are more centered around the cost of the fuel for heating rather than the CO2 emissions. This is in contrast to EPCs for commercial premises which are centered around CO2 emissions.

If you do get a gas boiler system installed including radiators, at least you would be further down the path to swap that gas boiler out for a Heat Pump next time round.

I was in this position with my property, which had old electric storage heaters back in 2015. The EPC rating was 43E. There was no gas supply to the property, although evidence of a previous gas meter was visible under the stairs.

We contacted the local supplier who fitted a new gas supply connection for a very low cost, and we then fitted a gas combi boiler with radiators. This brought our EPC rating up to 68D, one point short of a C-Band rating.

If you have a flat, with no gas present, it might be harder, particularly if you are not on the ground floor. Do still enquire with local suppliers though as you can then know for sure. You might be surprised at what's possible.

This could be more of an option compared to installing gas to a property that currently has electric storage heaters.

Click here to return to our 'Improve Your EPC' main page, and see if there is another way you could improve your EPC rating.