Don’t Install a Heat Pump Until You Read This

Mars · 2024-12-15T22:36:31Z

If you’re considering a heat pump or had one recently installed, this article is for you. Our six-year journey with a heat pump has been a rollercoaster of expensive mistakes, lessons learned and a mission to help others avoid our pitfalls. Heat pumps are incredible technology when installed and designed correctly. But when things go wrong, they can become a source of great frustration. Here’s what you need to know to ensure your heat pump journey is a success. The Start of Our Heat Pump Journey Six years ago, after an extensive vetting process, we appointed Global Energy Systems to install our air source heat pump. Global Energy Systems supplied the unit and subcontracted the physical installation to another MCS-accredited company, All Seasons Energy, while maintaining the full contract with us. From the very beginning, it was evident something was amiss. The first three winters were plagued with issues: rooms that wouldn’t heat properly, issues with the controls and higher than expected running costs, temporarily obscured by the cushion of cheap electricity tariffs at the time. Each time Global Energy Systems dispatched a team to address our concerns, we talked ourselves into believing things had improved – perhaps out of desperation to justify the £16,000 investment in the system. But as soon as the next cold spell hit, the same problems reared their ugly heads. In hindsight, it’s glaringly obvious: the installation wasn’t just flawed – it was fundamentally botched from the start. A System That Was Never Designed to Work One of the biggest revelations came years later as we gradually started to educate ourselves on low temperature heating: our system as a whole was never designed to work properly with a heat pump. Instead, it was slapped in to run like a boiler. This critical error was evident from the start, but we didn’t know enough then to question it. The heating services and operations engineer from Global Energy Systems commissioned our system to run on a 45°C set point – a decision that is utterly indefensible if you understand how heat pumps should work. Heat pumps are designed to operate most efficiently at lower flow temperatures: the higher the flow temperature, the more energy they consume, driving up costs and eroding efficiency. Shockingly, when we inquired about weather compensation – a feature that optimises system performance by adjusting flow temperatures based on outdoor conditions – Global Energy Systems outright denied that their heat pump had this capability. This was a blatant lie. Years later, after tinkering with the control panel, we discovered weather compensation settings and heat curve adjustments buried in the system. Global Energy Systems, it seems, had deliberately chosen to run the system at a fixed 45°C, not for our benefit, but to mask deeper issues with the system’s design and performance. As we learned more about heat pumps, we suspected that a proper heat loss calculation and heating design had never been done. When we confronted Global Energy Systems, they admitted it hadn’t. This was a massive blunder. Proper heat loss calculations are the cornerstone of any heat pump installation. Without them, you’re essentially flying blind, which explains the inadequacies of our system. The Saga of Cold Rooms and Circulation Pumps For years, cold spells exposed more limitations of our system. The north end of our house – where the index circuit is – struggled to exceeded 16°C when outdoor temperatures dropped below 3°C. Global Energy Systems' solution? Add more or upsize circulation pumps. We now have four, and they haven’t resolved the problem. Instead, they’ve increased our running costs. When we had our system evaluated by some of the UK’s top installers, their feedback was unanimous: the system had no design and was set up to fail. As Ken Bone explains in the video below, it was essentially running as a boiler replacement with a Delta-T of 20, littered with on/off stats, which is unsuitable for a heat pump. Our house as a whole never had a chance of being heated efficiently.Lessons Learned Insist on a Proper System Design Before installation, double, triple and quadruple-check that your system is designed properly. Ensure every room and heat emitter can hit its target temperature (19°C, 20°C or 21°C, depending on your preference). Get this in writing. These temperatures must be achievable when running weather compensation. Don’t let your installer convince you to settle for a fixed flow temperature. In mild months, this approach wastes energy and money. Understand the Importance of Controllers Heat pumps are fundamentally all very similar at their core: a metal box with pipes, refrigerant and a compressor. The controller, however, is what determines how effectively the system runs and does what you want it to do. In our case, the controller from Global Energy Systems has been dreadful. As we have a hybrid system, it can’t even run weather compensation if we wanted to use th...

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Air Source Heat Pumps (ASHPs)

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JamesPa

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21/11/2025 5:59 pm

@davidnolan22 Inspired by someone on buildhub I asked ChatGPT and Duck.ai (which uses chatgpt and other LLMs) the following question:

"Suppose I have underfloor heating with pipes at 150mm centres buried 15mm deep into concrete that is 100mm thick, sitting directly on damp soil assumed temp at sufficient depth 10C. Suppose that on top of the concrete is say 5mm of luxury vinyl tile and the room above is at 20C. How much heat goes down and how much goes into the room? You may assume, for simplicity, that the heating continues for several months, that the room is infinite is size and that the pipes are supplied with water at 35C"

They used slightly different methods (which they gave) and both had to make simplifying assumptions (unsurprisingly). ChatGPT assumed a room of infinite area, Duck.AI asked me to specify the room size so I gave it 7m square and 10m square. They gave their methods which look reasonable but I haven't verified completely (and Im not sure if I will). In summary ChatGPT says 80% of the heat will go down, Duck.ai says 50% will go down. This is at variance with what UrbanPlumber says here, but his somewhat handwaving argument, for which he admits he has no evidence, makes an assumption which I think is incorrect. However your installer may have based his statement on this, its not the first time I have heard it said.

Frankly I don't know, but I would say that, based on what we have so far, there is at least 50% probability that at least half the heat goes down in an uninsulated UFH arrangement such as yours. If this is correct (and I think you would need to do a finite element simulation to prove it) then it could easily account for your problem.

If you want me to DM you the full conversation with Duck.ai and ChatGPT Im happy to do so. It might be food to ask the exact same question of another LLM that we know doesn't use ChatGPT at all

This post was modified 36 minutes ago by JamesPa

4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.

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