Octopus Agile & Heat Pump Costs | Phil Steele

Octopus Agile & Heat Pump Costs

In this episode of Energy Unwrapped, I sit down with Phil Steele from Octopus Energy to talk about Octopus Agile, heat pump running costs and the wider shift to smarter home energy.

We get into how my own renewable setup has evolved over the years, from solar and battery storage through to EV charging, a Mixergy hot water cylinder and finally a heat pump. That leads into a broader discussion about how households choose between tariffs like Octopus Agile, Intelligent Octopus Go and Cosy, and how those decisions change once you add heat pumps, batteries and electric cars into the mix.

One of the biggest themes in the conversation is that heat pump running cost is not just about COP. Efficiency matters, but tariff choice, battery strategy and when you use electricity can make an even bigger difference. We also talk about proper heat loss calculations, why some homes get oversized heat pumps, and why getting the design right from the start matters so much.

What we cover in this episode

• how Energy Stats UK started with Octopus Agile data

• my journey from solar to battery, EV, smart hot water and heat pump

• how to think about Octopus Agile vs Intelligent Octopus Go vs Cosy

• why a heat pump can make your winter electricity demand jump

• how a proper heat loss survey should be done

• why air change assumptions can lead to oversized heat pumps

• how monitoring helps you understand real heat pump performance

• why COP matters, but cost on a time-of-use tariff matters more

• how smart tariffs and smart controls are changing the game for homeowners

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Full Transcript

Below is the full transcript for this episode, lightly edited for readability.

How Energy Stats UK Started with Octopus Agile

A big part of this episode is the backstory behind Energy Stats UK and how it began with a simple interest in Octopus Agile data. I explain that the first page on the site went live in July 2019, after I started pulling tariff data from the Octopus API and building something useful from it. What started as a nerdy interest in regional Agile pricing grew into a wider project covering more smart tariffs and more household energy tech.

From Solar Panels to Battery Storage, EV Charging and Heat Pumps

We then talk through how my own home setup has evolved. It started with 5.1 kW of solar, then battery storage, then EV charging, then a Mixergy smart cylinder, and finally a 5 kW Vaillant heat pump. That progression matters because it shows how one bit of renewable tech often leads to the next. Solar gives you the first taste of self-generation, then batteries and tariffs change how you use electricity, and eventually the whole home starts to shift towards electrification.

Why Smart Hot Water and Mixergy Changed the Setup

Before the heat pump went in, I installed a Mixergy cylinder as part of a staged move towards electrification. That made it possible to soak up more spare solar and make much better use of off-peak electricity. We talk about why smart hot water storage is underrated and how it helped bridge the gap between having solar and eventually moving to a heat pump.

Heat Pump Controls, Havenwise and Better Decisions on Flow Temperature

The episode also covers how my heat pump is controlled. I explain why I use Havenwise alongside the Vaillant system and how it can make more granular decisions about target flow temperature by using more data points, including current room temperature and where the temperature needs to get to next. It is a good example of how software and control strategy can improve performance without changing the hardware itself.

Heat Pump Monitoring and Why Built-In COP Figures Can Mislead

Phil and I also get into heat pump monitoring, including why built-in performance figures are not always as accurate as people think. I explain how I use OpenEnergyMonitor and why proper metering of temperatures, flow rate and electrical consumption matters if you want trustworthy COP data. It is one thing to see a number on an app. It is another to know that the number is based on good quality inputs.

Octopus Agile vs Intelligent Octopus Go vs Cosy for Heat Pumps

One of the most useful parts of the conversation is around tariff choice. We discuss how different homes will land in different places depending on whether they have an EV, battery storage, a heat pump, or all three. For some homes, Intelligent Octopus Go makes sense because of the cheap overnight charging and convenience. For others, especially where heating is the bigger opportunity, Cosy may look more attractive. The wider point is that there is no single best tariff for every house. The right answer depends on the equipment you have and how you use it.

Why Heat Pump Electricity Use Jumps in Winter

We also touch on a really important reality for heat pump owners: winter electricity demand rises sharply. Even with batteries, once the colder weather arrives the electrical load from heating becomes much more noticeable. That is one reason why the tariff conversation matters so much. A setup that looks great in summer can look quite different once the heat pump is working hard through winter.

Heat Loss Calculations and Why Some Heat Pumps Are Oversized

A large section of the episode focuses on heat loss calculations and why they matter so much. I explain how a proper survey should be done room by room, looking at fabric losses and ventilation losses, then designing the system around a realistic outdoor temperature for the property’s location. We also talk about how poor assumptions around air changes can lead to oversized systems, larger radiators than needed, and worse performance overall. This is one of the most important sections for anyone planning a heat pump.

Air Tightness, Ventilation Losses and Better Ways to Measure a House

Related to that, we discuss some of the testing I have been doing around air tightness and ventilation losses, including pressure-based tests and CO2 decay methods. The reason this matters is simple: the standard assumptions used in some heat loss calculations can be far too cautious, which then pushes system sizes up unnecessarily. Better data gives you a better design.

COP or Cost: What Really Matters for Heat Pump Owners?

Towards the end, we get to the core question: COP or cost? My answer is that both matter, but if your goal is cheaper running costs then tariff choice can outweigh small COP improvements. I talk through my own hot water analysis and the conclusion that all the little efficiency gains in the world do not beat simply running on a much cheaper time-of-use tariff. If you can do both, great. But for many homeowners, getting onto the right tariff is the bigger win.

Final Thoughts on Agile, Heat Pumps and Smarter Energy Use

This episode really comes down to one idea: smart energy is about more than one product. Solar, batteries, EVs, heat pumps, hot water storage and tariffs all interact. The households that do best are usually the ones that treat these things as part of one system, rather than trying to optimise each one in isolation.

About the Energy Unwrapped Podcast

Energy Unwrapped is my podcast about renewables, home electrification and how energy technology works in the real world. You can browse all episodes, platform links and future updates on the main Energy Unwrapped Podcast page.

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