Britain’s hard-to-heat homes and aging housing stock

Introduction

The UK has some of the oldest housing stock in Europe, with 37% of homes built before 1946. These older homes are often poorly insulated and hard to heat, losing warmth much faster than modern buildings. Studies show a typical UK home can drop 3C in just 5 hours on a cold day (20C inside, 0C outside), about three times the heat loss seen in better-insulated homes in Germany or Norway. To make matters worse, the uptake of efficiency improvements has stalled; the installation of insulation and other energy-saving measures has fallen by around 90% since 2013.

This form of heat leakage and energy inefficiency not only leaves residents uncomfortable but also drives up energy bills and emissions.
Here we cover the challenges of retrofitting heating and hot water systems in Britain’s aging, hard-to-heat homes, and how specifiers can design in more ‘retrofit ready’ solutions that improve efficiency, comfort and sustainability of their housing stock.

Many of Britain’s buildings were built when coal fires and minimal insulation were standard, resulting in damp, leaky homes which are among Europe’s most costly to heat. As of 2023, an estimated 13% of English households (3.17 million) were in fuel poverty under official metrics.
Social housing residents often live in some of the least efficient properties and end up spending 17.3% of their income on heating, roughly the equivalent of two months’ pay. Cold, under heated homes affect health and wellbeing, contributing to issues like respiratory illness and excess winter deaths, while high bills force families to choose between “heating or eating.” Cold homes cost the NHS around £1.4 billion each year in related health and social care impacts.

Improving these homes is a national priority. The UK has committed to reaching net zero carbon by 2050, and home heating (mostly from gas boilers) accounts for a significant chunk of emissions. Efficiency targets are looming; for instance, all social housing in England must reach at least EPC Band C by 2030. Progress is being made and the share of social homes rated A-C climbed from 23% to 52% in the last decade, but there is still a long way to go. Meeting these goals means retrofitting millions of homes with better insulation, low-carbon heating systems, and smarter hot water solutions. This is a massive undertaking, and social housing landlords, architects and specifiers are at the forefront of figuring out how to upgrade Britain’s aging housing stock at scale.
Upgrading older housing stock is essential for social housing providers working to deliver safe, healthy and sustainable homes for every resident.

Key challenges of retrofitting heating & hot water:

Replacing a fossil fuel boiler with a heat pump or other modern heating system isn’t straightforward in older properties. Specifiers and installers face practical challenges in retrofitting heating and hot water systems for ‘hard-to-heat’ homes:

Space constraints: Many UK homes (especially smaller houses and flats) simply lack space for bulky new equipment. For example, about 80% of British households still use combi boilers that provide instant hot water and thus have no hot water cylinder at all. When you try to retrofit a heat pump (which requires a hot water tank), you hit a wall: Where can the cylinder go?
In a typical two up, two down house that runs on a combi boiler, finding an indoor spot for a hot water cylinder is extremely challenging. Airing cupboards and lofts are often too small or already in use. This lack of space is a constraint that can make it hard to switch to heat pumps or other systems requiring hot water storage.

Disruption and practicality: Heating retrofit can be invasive and time-consuming. Old radiators need upsizing for low-temperature heating, pipework layouts may need changes, and installing a heat pump involves finding room for both the outdoor unit and indoor cylinder.
Social housing providers report that heat pump retrofits are more complex than simple boiler upgrades, often requiring greater skill and more time, which means more disruption to tenants during the works.

Legacy building constraints: Older buildings come with thick solid walls that are expensive to insulate, electrical systems that may need upgrading for new loads, or legacy constraints that limit modifications. These factors can constrain what heating systems can be installed or how well they perform. A Victorian terrace retrofitted with a heat pump will still struggle if it remains poorly insulated, requiring either an oversized heat pump or supplementary heating (like electric radiators) in cold snaps.
Specifiers need to plan holistic retrofits (fabric & heating systems together) to truly solve hard-to-heat issues.

Cost and energy performance gaps: A major concern in retrofitting heating is ensuring affordability, both upfront and ongoing. Electric heat pumps can drastically cut carbon emissions, but if the home is draughty or the system isn’t optimised, running costs could increase.
“Spark gap” (cost difference between electricity and gas) is a real worry for fuel poverty and makes some housing providers hesitant to go all-electric. Bridging this gap requires careful design: maximising efficiency (through insulation, proper sizing, and controls) and using smart tariffs.

Hot water storage issue: Even if the space heating issue is resolved with a heat pump, providing sufficient hot water in a retrofit scenario introduces another challenge: where to store it?
Heat pumps operate most efficiently with stored hot water, but as noted, most British homes weren’t built with a hot water tank cupboard (especially those that have enjoyed the convenience of combi boilers for decades). Installer surveys and reports (e.g. by Nesta) highlight that finding space for a cylinder is one of the biggest hurdles when moving from a combi to a heat pump system.

It’s not just inconvenience – lack of hot water storage can derail an otherwise viable low-carbon retrofit.

This means specifiers need to look for smarter ways to supply high-flow rate hot water without sacrificing half a closet for a giant tank.

However, there are modern solutions to each of these issues.

Focus on social housing: Efficiency upgrades and resident impact

Retrofitting is particularly urgent and challenging in the social housing sector. Councils and housing associations often manage large portfolios of aging homes, including high-rise blocks and post-war estates that are notoriously hard to heat.

The goal isn’t just hitting a target; it’s about improving comfort and reducing bills for tenants who are often on low incomes. Upgrades that lower energy use directly combat fuel poverty. In fact, research by the National Housing Federation found that bringing all social homes up to EPC A-C could save residents £700 million per year in energy costs (roughly £567 per household annually).

However, most social homes are small, rely on combi boilers, and have no existing hot water tanks, so switching them to heat pumps en masse means solving the cylinder problem at scale.

Designing retrofit-ready solutions: What specifiers should consider

Retrofitting Britain’s old homes is achievable with planning and the right technologies. For specifiers, whether housing consultants, energy assessors, building services engineers, or architects, the key is to design heating and hot water systems that are “retrofit ready” – meaning solutions that are flexible, space efficient, and future proof.

What are some strategies and innovations in the retrofit scene?

Fabric first: A retrofit-ready design doesn’t treat heating in isolation. The first step is always to improve the building fabric: insulation, draught proofing, double glazing, to reduce the overall heat demand of the home. Specifiers can use tools like SAP or the upcoming Home Energy Model to simulate how fabric upgrades combine with new heating systems.
For example, adding internal wall insulation in an old solid-wall home might cut heat demand by 30%, meaning a smaller and cheaper heat pump could suffice.

High-temperature heat pumps (HTHP): One barrier to retrofitting heat pumps is the need to replace radiators; traditional radiators sized for a boiler might be undersized for a low temp heat pump (see: low vs high-temperature heat pumps). However, high temperature heat pumps (HTHPs) using refrigerants like R290 propane can supply water at 70-75C, much closer to boiler temperatures. This can reduce the need to change radiators or pipework in a retrofit.
HTHPs do use a bit more electricity than standard low-temp 50C models, but they address a major friction point and can be a smart choice for certain hard-to-insulate properties, which makes up most social housing flats.
Specifiers can evaluate whether HTHPs can enable a swap without extensive heat emitter upgrades; if so, it might simplify the project and lower upfront costs (even as we keep an eye on long-term running cost implications).

Heat networks and communal solutions: For tower blocks of flats, connecting homes to a district heating network can be an efficient retrofit solution. Instead of individual heat pumps in every flat, a centralised energy centre (which could use large heat pumps, waste heat, or other sources) supplies multiple dwellings via insulated pipes. While heat networks require infrastructure investment, they are an attractive way to retrofit high-rise buildings or estates where one can leverage scale.

Load shifting: One opportunity to combat bills with electric heating (heat pumps, direct electric, etc.) is by using time-of-use tariffs and thermal storage to “load shift.” This warms up your home or your hot water when electricity is cheapest and greenest (say, overnight or midday when renewables are abundant).
Demand-side response programs and smart tariffs in the UK (like Octopus Agile or Economy 7) can significantly cut running costs if the heating system is designed to take advantage of them.

Advanced hot water storage technologies:

We circle back to the hot water cylinder challenge, because it’s a pivotal issue in retrofits.
Recognising that, a simple solution is compact thermal batteries that can replace the cylinder altogether. Our Thermino thermal batteries use phase change materials (PCM) to store heat in a much smaller volume than water can – in fact, up to four times smaller than an equivalent hot water cylinder. For instance, a 210L hot water cylinder (common in a 3-bed home) can be replaced by a heat battery roughly a quarter of that size. And despite its small size, a PCM heat battery delivers high-flow hot water on demand, by releasing heat from the PCM into a heat exchanger. The result is a unit that fits where a bulky tank would never go. This kind of solution directly tackles the space constraint issue: even if a home has no airing cupboard, a compact heat battery might slide under the kitchen worktop or fit in a small closet.

Mains pressure hot water comfort: Importantly, with Thermino heat batteries, households (vulnerable social housing tenants in particular) still get reliable, on demand hot water at mains pressure for power showers or baths. Traditional hot water cylinders carry efficiency and maintenance penalties that are magnified in hard-to-heat homes. A standard cylinder loses heat throughout the day, typically on the order of 1-2 kWh of heat loss per day as “standing losses,” even with decent insulation. In an inefficient home, those losses effectively leak into the ether (or help heat the house a bit, but often at the wrong time of day). Over a year, that can amount to 300-700 kWh of wasted energy.
Our Thermino range of heat batteries, in contrast, are highly insulatedwith vacuum insulation panels, which result at least 50-75% lower heat loss than a traditional hot water tank. That translates to lower bills.
Also, because our heat batteries store <15L of hot water at any time, there’s very low risk of Legionella bacteria growth, so they don’t require the periodic energy-intensive, high-temperature anti-Legionella cycles that hot water cylinders do. This is ideal for social landlords who otherwise need to schedule regular checks on cylinders aross their portfolio.

Specifiers will be pleased to know that from an installation perspective, fitting a Thermino is straightforward. The installation time is typically shorter than a like-for-like cylinder plus boiler swap, meaning projects can be completed faster.

Compact thermal storage is the missing puzzle piece that allows specifiers to confidently design future-proof homes.
A heat pump (or even a modern electric storage heater) plus a Thermino battery (ePlus, xPlus or TS) can replace a combi boiler, delivering both efficient heating and high-performance hot water, even in a small flat. Combine that with solar PV to drive self-consumption and good insulation and you’ve transformed a hard-to-heat house into a warm, efficient, and future-ready home.

For specifiers, the key is to stay informed about modern solutions, from high-temp heat pumps, heat networks to thermal batteries, and to take a holistic approach that considers both the building fabric and the building services.

If you’re looking to future-proof the heating and hot water in an older building, or want to learn more about integrating thermal storage into your retrofit projects, check out our resources and case studies for specifiers, or contact our team for a personalised assessment of your project.

Frequently asked questions (FAQs)

Why are Britain’s homes so hard to retrofit?
Most were built before insulation standards, with no space for cylinders or modern heating systems.

Does poor insulation affect heat pump efficiency?
Yes, draughty homes make heat pumps work harder and reduce performance.

Can heat pumps work in older or social housing?
Yes, with good design, high-temperature models and compact storage make it feasible.

Why is hot water storage a challenge in retrofits?
Most homes with combi boilers have nowhere to fit a hot water cylinder.

What makes Thermino ideal for retrofit projects?
It’s up to four times smaller than a cylinder, needs no maintenance on the appliace, and is quick to install at scale.

Is Thermino eligible for Boiler Upgrade Scheme funding?
Yes, it qualifies as ancillary equipment when paired with an MCS-installed heat pump.