Juliette Fletcher, Data Scientist at Energy Systems Catapult, compares heating demand in real homes and shows why heat pump smart controls and new heating habits matter most when temperatures fall

The UK has plans to install 450,000 heat pumps a year by 2030, and that shift from gas boilers will see big changes in how we use energy at home. But how much extra demand they will place on the electricity grid? Used well, a heat pump’s daily demand looks very different from a traditional gas boiler’s, and households making the switch will need to adjust their heating habits to get the best results.

We analysed smart meter data from homes in our Living Lab to see how heat pump optimisation helps reduce energy demand when a cold snap hits. Here’s what we found.

What homes did we look at?

Of the 2,300 Living Lab participants who currently share their smart meter data with us, we selected 241 homes for our analysis based on their heating system:

– 41 homes with ‘optimised’ air-to-water heat pumps. We selected these as they share heating usage data with us via Homely

– 200 homes with gas boilers for comparison. We selected these from our much larger pool of gas heated homes, because they had the highest quality smart meter data. (This is one of the four off the shelf data sets available from the Living Lab).

Our approach

We plotted half-hourly winter profiles for gas and heat pump heated homes, split into weekdays and weekends. The Homely heat pumps had their own energy monitoring so we could separate electricity used for heating from the rest of the home’s use.

We then compared a cold winter week with a more typical one to see what happens to heat pump demand when the weather turns colder.

Gas boilers: the familiar morning and evening peaks

Of the UK’s nearly 30 million homes, around 85% use natural gas for heating, so most of us have built our heating habits around what works best for a gas boiler: quick, on-demand heating, switched on when we need it – often in the morning and evening.

Our data shows exactly that: two peaks a day. One when people wake up, between 6am and 8am, and one in the evening when they return home, typically between 3:30pm and 7:30pm.

Of course, not every home follows this pattern. Homes occupied all day tend to use gas steadily between the morning and the evening (an ‘all-day’ pattern), while others add a midday spike (a ‘three-peak’ pattern). Both still use far more gas by day than overnight.

Heat pumps: flattening the curve

Heat pumps work best when they run steadily at a lower temperature. Keep the old habit of switching the heating off throughout the day and then blasting it back on when the house feels cold, and the heat pump has to work flat out to catch up.

That creates big spikes in electricity use, much like the morning and evening peaks you get with gas boilers.

Used in an ‘optimised’ way, the daily profile looks much smoother. All the homes in our sample use the Homely app and heat pump optimiser, which helps make this ‘low and slow’ approach easier. Homely adjusts the heating to the weather and works with time-of-use and dynamic tariffs, shifting more of the heat pump’s work into cheaper periods. Put simply, the system does the planning, so households don’t have to.

This keeps the home comfortable and avoids the sudden bursts of high energy use that happens when a heat pump is treated like a gas boiler. It’s good news for the grid too, with less pressure at peak times.

There’s no sharp evening peak. That suggests heating is no longer directly triggered by people coming home. Instead, the system is managing comfort in advance while avoiding peak tariff prices. There’s still a morning spike (between 4am and 6am) as the system ramps up to the daytime “comfort” setting but it’s earlier than with gas boilers, which may reflect the optimiser making use of cheaper overnight electricity.

What happens when it gets cold?

Previous analysis of the coldest days of the year, based on smart meter data from a larger group of heat pump homes, found that consumption can be three times higher than on mild days, with pronounced afternoon peaks that could put much greater stress on local networks. Our data shows optimised heat pumps significantly reduce these spikes and the amount of energy used.

We compared optimised heat pump demand on the first Monday of December, which was a relatively mild day with temperatures hovering around 10°C, and the first Monday of January when it was  below 0°C for much of the day.

As temperatures fall, peak daily heat pump electricity use was around 75% higher on the colder day, which just shows how closely demand follows the weather. As heat pumps become more common, this weather-driven demand will play a growing role in how local networks and the national system plan for cold snaps.

Our data shows the value optimised heat pump systems give consumers and the energy system: they spread the extra cold‑weather demand fairly evenly across the day instead of creating sharp peaks and lead to a much smaller rise in energy use than unoptimised systems.

Why this matters: think slow cooker, not kettle

Switching from a gas boiler to a heat pump works best when households change how they think about heating. Gas boilers are designed for quick bursts of high heat, so many of us turn them up and down to match what we need right now.

Heat pumps are more like a slow cooker than a kettle. They deliver steady, lower temperature heat over time and work best when left running for longer periods. They shouldn’t be controlled with an on/off room thermostat, like a gas boiler. The best approach is using controls that measure indoor and outdoor temperatures to set how quickly the home heats up. That takes installer experience, and households need to know what to expect from a lower-temperature system. Get it right and the home will be more comfortable.

Optimisation of heat pumps matters most during cold snaps when the colder it gets the harder the heat pump works to keep homes warm. Heat pump optimisation won’t stop demand rising but it can help reshape it, spreading demand more evenly across the day and easing the pressure on local grids. As heating electrifies, this kind of smart, flexible operation won’t just be helpful, it will be fundamental to keeping our energy system stable.

The value of real-world data

Understanding how heat pumps perform in real homes is exactly why the Living Lab exists. Over 5,000 diverse UK households share their energy data and trial new products, services and policy innovations – helping us understand changing energy demand, consumer needs and system impact.