High Heat Retention Storage Heaters

At the time of writing, the methodology for EPC assessments of existing dwellings is RDSAP 9.94. This updates to RDSAP 10 on 15th June 2025 and a significant methodology overhaul from RDSAP to the Home Energy Model (HEM) is proposed for 2026. In addition, government consulations indicate future changes to the format of EPCs and minimum rating levels required for private rental properties. Methods for improving EPC ratings may therefore change in the future.

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, often due to the absence of a main gas supply, and as a product have undergone some technical developments 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 in the assessment.

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 of this specific paragraph (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 it should be recorded in the EPC assessment as a fan-assisted storage heater, and you won't get as much of a gain in EPC rating as you might have expected.

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

The following table shows modelled EPC ratings for my house when different types of storage heaters are used as the main source of heating.

In each case, only the specified type of storage heater is present. There's no mix of different heater types.

This is a 1950s mid-terrace house (see our Case Study 2 page for more info)

Note that for this modelling, hot water is provided by a normal sized Hot Water Cylinder with 50mm foam insulation and dual immersion heaters operating on dual rate electric:

My EPC rating improves as I change to a more modern variant of storage heater.

Interestingly, when electric storage heaters are the only 'Main Heating' source, the EPC rating does not seem to be affected by the presence of un-heated habitable rooms or electric Secondary Heating. This is in contrast to the presence of these things in combination with other heating systems such as gas boilers. See our Heating Systems page for more information.

From the table we can see that moving from Modern Slimline Storage Heaters to 'High Heat Retention Storage Heaters' would take me from 48E to 59D.

That's an increase of 11 SAP points for my property.

The gain for your property though will differ. Contact a local energy assessor to advise about any rating changes for your specific property.

There are a couple of possible recommendations that can appear on an EPC for storage heaters:

New or Replacement Storage Heaters (a)

• This recommendation is considered when the main heating in the property is currently provided by 'Old Large Volume' or 'Modern Slimline' storage heaters.
• This recommendation is triggered when mains gas is not available at the property (mains gas meter not present).
• If hot water heating is provided by a cylinder with single immersion, or from solid fuel secondary heater then the recommendation is for High heat Retention Storage Heaters and dual immersion water heating, using large cylinder with 50mm factory applied insulation.
• If hot water heating is instead provided by any other system then the recommendation is for High Heat Retention Storage Heaters and controls.

New or Replacement Storage Heaters (b)

• This recommendation is also considered when the main heating in the dwelling is supplied by electric room heaters, or electric ceiling heating, or if no heating system is present.
• This recommendation is then triggered when mains gas is not available, and hot water heating is provided by a cylinder with a single immersion, or from solid-fuel secondary heater or no hot water system present.
• The recommedation is for High Heat Retention Storage Heaters, 7 hour offf-peak tarif, with dual immersion water heating, large cylinder with 50mm factory applied insulation.

Maybe you're interested in replacing your storage heaters to improve your EPC rating because you're selling your property or perhaps you want to get a C band rating in advance of the increased MEES targets touted for 2028/2030 and the changes to EPC metrics and methodology proposed for 2026.

If so, what options might you have? You could:

• HHRSHs - Upgrade your existing storage heater(s) to High Heat Retention Storage Heaters (HHRSHs) - only 1 might be required, plus panel heaters (see below)
• Gas Boiler - Remove the storage heaters, get gas connected to the property and fit a gas boiler and radiators / underfloor heating
• Oil Boiler - Remove the storage heaters and fit an oil boiler and radiators / underfloor heating
• Air Source Heat Pump - Remove the storage heaters and fit an air source heat pump with radiators / underfloor heating
• Electric Panel Heaters - 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 much 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 are looking for 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 of 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 a target temperature, compared to storage heaters which charge up using only cheap rate electricity during the night.

If you fancy an interesting read related to this kind of matter, follow these links to Leicester Trading Standards, who reached a compromise agreement with Fischer Future Heat UK Ltd and Premier Radiators Ltd, including undertakings and a redress fund for consumers. This was in response to complaints about the supply of electrically heated radiators or panels. The undertakings include not making certain claims about energy savings without qualifications. 

https://www.leicester.gov.uk/business/trading-standards/?vAction=fntUp

https://www.leicester.gov.uk/media/wwtpatcj/signed-undertakings-2022.pdf

Back to EPCs though, and to illustrate the reduction in EPC rating when you remove all your storage heaters and replace them with electric panel heaters, here are the modelled EPC ratings for my house (a 1950s mid terrace):

So, if I were to move from 'modern slimline storage heaters' entirely 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.

This compares to an increase in rating of 11 points to 59D if I my 'Main Heating' system was changed to High Heat Retention Storage Heater(s), or 20 points to 68D if I were to install a condensing gas combi boiler and radiators instead.

Having said this, and still being an advocate for storage heaters over panel heaters any day of the week, if you do find yourself in this situation where you have fitted panel heaters everywhere in a dwelling, notice the behaviour that we describe in one of the sections below about upgrading the heating in the living room to a High Heat Retention Storage Heater and having electric panel heaters elswhere in the property. This might be a path to recover your EPC rating (although it offers poor financial economy for the occupant in the long term).

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 Recommendation on your EPC if you currently have earlier types of storage heaters, and there is no gas meter present at the property.

When you see a recommendation on your EPC for High Heat Retention Storage Heaters, an estimate of the cost will be provided, but 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. When fitting High Heat Retention Storage Heaters they have typically been connected to both a peak rate and an off-peak rate electrical supply whereas previous models of storage heater were usually connected to just a single off-peak electric supply. Installation would therefore commonly involve providing an additional peak electricity connection to each position where an older storage heater was being replaced with a HHRSH. Fan Storage Heaters would have had both already however.

More recently though, some models of HHRSH can be connected via a single, peak-rate supply - see notes later on this page - and this can make installation cheaper.

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 a similar cost.

High Heat Retention Storage Heaters will need to be sized via a Heat Loss calculation for the area they heat, and your electrician would normally work this out for you. You may find that if you have an old but large storage heater, you might need to replace it with two HHRSHs. The largest Dimplex Quantum HHRSH (150/150RF) for example can store 23kWh and is just over 1m wide. That's somewhat smaller than some of the older, large, storage heaters.

In terms of recording High Heat Retention Storage Heaters in an EPC assessment, at the time of writing there's some interesting behaviour that becomes evident.

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.

However, with storage heaters, including of course High Heat Retention Storage Heaters, those things don't appear to affect the rating.

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:

In all these combinations, my EPC rating would appear to stay the same.

So, firstly, we notice that with HHRSHs as the only 'Main Heating' source in the EPC assessment, adding more than one HHRSH does not vary the EPC rating (Panel heaters can only be recorded as a 'Main Heating' source if they are the only type of heating in the property, otherwise they are recorded as a source of Secondary Heating).

Also, the presence of unheated habitable rooms appears not to affect the rating.

Lastly, the presence of electric panel heaters recorded as secondary heating does not appear to affect the rating either.

A combination of perhaps one HHRSH plus electric panel heaters in other rooms could be a cheap 'upgrade' path to increase an EPC rating, perhaps in a small property such as a 1 bed rental flat.

You might consider putting a High Heat Retention Storage Heater in the living room (the 'Main Heating' system needs to heat the living room) and use electric panel heaters in other rooms such as the bedroom, in order to keep renovation costs down.

This would be fine for the EPC rating but in reality if you wanted to reduce the long term running costs for the occupant you'd probably consider HHRSHs instead of those additional panel heaters.

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 and electric panel heaters to reach a C band target on a flat in a building with solid brick walls.

The above behaviour works in part because electric panel heaters are not recorded as a 'Main Heating' system in an EPC assessment unless they are the only form of heating.

Lastly, bear in mind the situation where you put a High Heat Retention Storage Heater in the living room, but elsewhere you also have another form of heating in the property that is also considered a 'Main Heating' system but which costs more to run. This could be an older type of storage heater for example, and in this case both types of heater would need to be allocated a proportion of heating in the assessment. For example this might be 50% each if they both heated the same amount of floor area each. This would bring the EPC rating down, compared to only having HHRSHs present, because that older storage heater costs more to run.

Note that despite the behaviour detailed above with HHRSHs and unheated habitable rooms and electric secondary heating, you do still need to ensure that sufficient heating capacity is provided in the property overall in order to maintain the heated condition of the whole living space.

Moving forwards, there are some updates to the EPC assessment methodology for existing dwellings coming up in the near future - one is the update to RDSAP 10 due on the 15th June 2025, and the other is the move to the Home Energy Model in 2026. We await to see whether this behaviour remains the same after these updates.

In addition, changes away from a single rating metric on domestic EPCs, to multiple metrics which are also planned for 2026 will almosrt certainly change overall approaches to meeting MEES requirements in the future.

Finally, as I regularly mention, it is very important to contact a local energy assessor to model your particular property, with any changes you have in mind before proceeding with any works. This will ensure you work from a position of relative certainty regarding any EPC rating outcomes you have in mind.

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 in particular, 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 consider this as an option, even if you think it's not a viable one.

This of course won't take you down the ideal long-term path of reducing carbon emissions, but it could serve as a half-way point whereby you could move to a heat pump next time round.

Currently, as I write this in 2025, domestic EPCs are purely centered around the running costs of a dwelling (for heating, lighting and domestic hot water) rather than CO2 emissions. This is in contrast to EPCs for non-domestic (ie commercial) buildings which are centered around CO2 emissions instead.

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 (circa £200 in 2016 iirc), 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 will then know for sure. You might be surprised at what's possible.

As many properties with Storage Heaters as their main heating source are unlikely to have gas present, installing a heat pump could be an attractive option.

A full system will require the installation of central heating pipes around the property along with either radiators or underfloor heating but space for a modern hot water cylinder is likely to be present already.

The resulting EPC rating is likely to be very good in comparison to old storage heaters, although under the current methodology, possibly not quite as good as a condensing gas boiler, depending on the model of heat pump.

With a £7,500 grant currently available via the Boiler Upgrade Scheme (BUS) this could be an attractive option.

Thanks go to Daniel who got in touch to let me know that there are some models of High Heat Retention Storage Heater that can be connected to a singe (peak-rate) electric supply, rather than having two separate peak and off-peak electrical connections.

An example is the Dimplex Quantum RF series which from series 9 can be configured this way. Information is available on the Dimplex website about that facility here:

https://help.gdhv.co.uk/support/solutions/articles/79000141048-how-do-i-wire-a-qmrf-for-single-supply-

Essentially, with this model, the connections for the peak and off-peak supplies can be looped together at the heater so that a peak-rate supply is effectively fed into both connections on the heater.

This kind of installation relies on the property having a fixed time-period, off-peak energy tariff with 'whole home switchover' whereby all wiring in the property utilises the off-peak rate when available.

A 'charge settings' screen on the heater can then be manually configured with the times that you want the heater to charge up. These times need to correspond to the times of cheaper rate electricity that you receive from your energy supplier.

Note however the guidance on the Dimplex website about timings when we change in and out of British Summer Time, and being aware of whether your energy supplier's cheap electricity rates also shift forward and back by an hour, or not.

If you have a High Heat Retention Storage Heater connected in this way, it might be wise to let your assessor know in advance, otherwise they may express some surprise when they notice the single electrical supply cable. This could cause an assessor to question whether the HHRSH operates on dual rate electricity or not.

Although this might not necessarily be required, the assessor could take photographs of the 'charge settings' screen on the heater to satisfy themselves, and any potential auditor, that the heater only charges during off-peak hours.

If you have a storage heater of any kind, it would be wise to double check that you are on a 'dual rate' electricity tariff. You can confirm this by either; two rates being visible on the electricity meter, or on a recent bill.

This is something that an energy assessor will look for during an assessment. If you cannot confirm the meter is able to show two rates, do locate recent electricity bills, and present these to the assessor to support the choice in the assessment of dual rate electricity being available at the property.

If an energy assessor is not able to record the electric meter as being 'dual-rate' then the EPC rating will be affected.

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