Over the last few weeks, I’ve been working through the Heat Geek course (Enlightenment, Awakening & Mastery), and I’ll be honest with you, it has completely changed how I look at air source heat pumps installations. I’ve completed the first two courses and am on Mastery now and the one thing that has astonished me is just how much complexity and depth there really is when it comes to planning and installing a heat pump system.
I thought I had a fairly good grasp (theoretically) of what was involved in an installation with a lot of sweeping, top-line assumptions, but the deeper I go into the course, the more I realise just how much maths, careful planning and system design goes into making these machines work efficiently.
And looking back at our own installation, it now makes complete sense why our system has been underperforming. We have a SCOP of just 2.7.
The Installer Who Didn’t Believe in Maths
When our system was being fitted, the commissioning engineer (who also oversaw the wider project) struck me as an arrogant individual, and we’ve had several run-ins since. He made it very clear that he thought installing an air source heat pump didn’t require much thought. His approach was cavalier at best, and dismissive at worst.
Despite coming to our property several times, not once did I see him or his team actually sitting down to plan the system in detail. There was no sign of calculations being done, no sign of pipe runs being sketched out, no radiator outputs being worked out. It was all a case of “we’ve done this before and it should be OK.”
But as the Heat Geek course makes painfully clear, that’s not how low-temperature heating systems work. You can get away with “rule of thumb” methods when installing a gas or oil boiler because they run at 70-80°C flow temperatures, which masks inefficiencies and bad design choices. With heat pumps, you can’t get away with it. Every assumption comes back to bite you, and the result is a system that underperforms year after year.
Why the Maths Matters
One of the biggest revelations for me during the course has been just how much maths goes into a properly designed heat pump installation… complicated maths and calculations.
For instance, you need to know the lengths of pipework running to each radiator or underfloor heating circuit. You need to understand the friction losses that those pipe runs create. You need to know the pressure drops across different parts of the system. And you need to size your distribution and circulation pumps accordingly.
Even if you don’t know exactly what’s hidden in the walls or under the floors, you still have to make assumptions and you still have to calculate. Without those numbers, you’re essentially designing blind.
And here’s the key point: a circulation pump that’s too small won’t move enough heat around the system. A pump that’s too big will just waste energy and potentially add noise. The only way to get it right is by doing the sums.
That applies not just to pumps, but to radiators, emitters, volumisers, expansion vessels, pipe sizing… the whole lot. Heat pumps are unforgiving systems. If the installer hasn’t done the numbers, the system is never going to perform as it should, unless they get lucky, and you don’t want to be relying on luck if you’ve just spent upwards of £10,000 on a new heating system.
What Our Installers Got Wrong
In our case, the mistakes started right at the beginning. There was no proper room-by-room heat loss calculation. Instead, the installers took a vague look at the property and sized the system based on little more than guesswork, and fitted the biggest unit they had, an 18kW heat pump.
The result? Two years down the line, the installers admitted their mistake and we had to upgrade a significant number of radiators, swapping K2s for K3s, just to get some rooms to a comfortable temperature.
But the radiator saga wasn’t even the most frustrating part. Every time we complained about certain rooms not reaching temperature, or about the system struggling in cold weather, the installers’ solution was always the same: “we’ll put in a bigger circulation pump.”
That was their go-to answer, time and again. We now have four fitted. It was complete guesswork. Not once did they stop to consider pipe runs, pressure losses or friction. They never measured, never tested, never calculated. And unsurprisingly, the bigger pumps didn’t fix the problems. All they did was mask some of the symptoms while driving down the overall efficiency of the system, increasing our running costs.
It was like watching someone try to fix a car by just installing a bigger and bigger engine, without ever looking at whether the tyres are flat or the brakes are seized.
And the sad thing is, despite us pointing this all out to them, they still think they did a good job.
Why Our SCOP Is So Poor
Looking at it now, I can see exactly why our SCOP is just 2.7. On paper, our heat pump should be achieving well over 3.5 (perhaps even closer to 4) if it had been designed correctly. That’s a huge difference in running costs and carbon savings.
But because the system wasn’t designed with proper maths:
- The emitters were undersized.
- The radiators were never balanced properly.
- The flow rates were (and still are) wrong.
- No calculations were done to figure out how to heat the index circuit (which to this day struggles to come to temperature)
- The buffer tank is a horror story.
- More and more circulation pumps were added based on guesswork leading to higher running costs.
Every one of those mistakes chips away at efficiency. Add them all together, and you’re left with a system that performs well below par.
What the Heat Geek Course Teaches
The thing that strikes me most about the Heat Geek course is just how formula-driven it is. There are equations for every aspect of system design:
- How to calculate radiator outputs at different flow temperatures.
- How to calculate if a radiator/room will come to temperature when it drops below freezing outside.
- How to work out pipe sizing based on flow rates and acceptable pressure drops.
- How to map heat loss accurately room by room.
None of it is guesswork. None of it is left to “gut feel.” It’s engineering, and engineering is numbers.
That’s why it frustrates me so much to look back at our own installation. Because the knowledge exists. The formulas exist. The training exists. But too many installers either don’t know it, don’t care or don’t bother to apply it. I’m not saying Heat Geek is the holy grail, but it’s evident to me that if you want an efficient low temperature heating system you need do the maths, otherwise it’s purely guesswork.
And homeowners like me and hundreds of others on the forums are left footing the bill, both financially and environmentally, for systems that don’t deliver what they should.
What Homeowners Should Do
So here’s the most important part of this article: my advice to any homeowner who is considering a heat pump, or who is in the middle of having one installed.
If your installer comes to your house and starts making assumptions, whether it’s about heat loss, radiator sizing, flow rates or pipework, that is a massive red flag.
Heat loss calculations are not optional. They must be done. Radiator sizing is not something you can “eyeball.” It needs numbers. Pump sizing is not something you can fix later with trial and error. It needs to be calculated.
And as a homeowner, you are absolutely entitled to see those calculations. Any installer who has been properly trained should be able to show you the maths. They should be able to explain, in clear terms, how they arrived at the numbers. They should be able to demonstrate that the system has been designed, not just thrown together.
If they can’t (or won’t) then walk away. Find someone who will.
Because here’s the truth: maths doesn’t lie. When the numbers are correct, they give a reliable picture of how the system will perform. If the installer has done the work, you can have confidence that your heat pump will deliver. If they haven’t, you’re gambling with thousands of pounds of your money and years of your comfort.
So, doing the Heat Geek course has opened my eyes to what system design should look like and what it entails. It’s made me realise just how badly our own installation was handled. And it’s made me determined to help other homeowners avoid the same pitfalls.
Heat pumps are fantastic pieces of technology when they’re installed correctly. But they’re not plug-and-play. They require maths. They require planning. They require attention to detail. The require design.
So my biggest piece of advice to anyone reading this is simple: ask your installer to show you the maths. Don’t settle for vague answers. Don’t accept “we’ve been doing this for years” as reassurance.
Because when it comes to heat pumps, assumptions cost money. Calculations save it. And in the end, a system designed with numbers will always outperform one built on guesswork.