Summary
Adveco explores the fundamental differences in commercial heat pump DHW system design, key selection criteria, and strategies for maximising performance and minimising the carbon footprint.
Gary Marshall — Updated June 2026
Heat pumps are now one of the main ways commercial buildings, hotels, hospitals and large residential blocks heat their hot water. But fitting a heat pump isn’t as simple as swapping out a boiler. Get the design wrong and you’ll pay for it, either in upfront cost, running costs, or a system that can’t keep up with demand. This guide covers how commercial heat pump hot water systems work, what they cost, and how to design one properly.
What is a commercial heat pump hot water system?
A commercial heat pump hot water system uses an air source heat pump (ASHP) to heat water for a building’s hot water supply. Rather than burning gas or running an electric element, a heat pump moves heat from the air outside into the water, using the same reverse refrigeration cycle as a fridge or air conditioner. This makes heat pumps far more efficient than direct electric heating. But commercial hot water has to meet strict, often heavy demand, hotels, hospitals and leisure centres all need hot water on tap, all day, so meeting that demand well takes proper design, not just a heat pump bolted onto the existing pipework.
Dynamic vs storage design, and the preheat vs direct heating decision
Every commercial domestic hot water (DHW) system falls into one of two design approaches. Dynamic systems use a high heat input and low storage volume, heating water quickly and continuously so the supply doesn’t run cold, which suits high-demand buildings with little room for storage tanks. Storage systems use a large volume of stored hot water and a smaller heat input, drawing down the stored water to meet demand and then reheating it gradually, which suits buildings that want a low-energy system with enough buffer to handle sudden spikes in demand. Which approach you choose affects the size, cost and complexity of everything downstream, including the heat pump itself.
Once you know whether you need a dynamic or storage-led system, the next decision is how the heat pump does its job, and there are two main strategies.
Preheat systems. use a smaller, low-temperature ASHP to raise water to around 40°C, with a secondary heat source, usually an efficient electric after-heater, doing the final lift to the temperature you need. Because the heat pump only has to reach 40°C, it can run in its most efficient range, giving a COP (coefficient of performance) around 2.6. This needs a smaller, lower-cost heat pump, often around 23kW, but more storage space, since the preheat happens in advance of demand. It works best for peaked demand with a fairly low background load.
Direct (full) heating systems. use a high-temperature ASHP to heat water straight to its final temperature, typically 60°C, in one step. This needs a bigger, more powerful heat pump, often around 90kW, and running at a higher flow temperature brings the COP down slightly, to around 2.5. It needs a smaller storage volume, often around 1,000 litres, and suits buildings with continuous, steady hot water demand, though it costs more upfront because the heat pump has to be larger.
Here’s how the two approaches stack up side by side:
Preheat system | Direct (full) system | |
Final water temp reached by ASHP | ~40°C, topped up by electric after-heater | ~60°C, heat pump does all the work |
Typical ASHP size | Around 23kW | Around 90kW |
Typical COP | Around 2.6 | Around 2.5 |
Storage volume needed | Larger | Smaller, e.g. around 1,000 litres |
Upfront cost | Lower (smaller heat pump) | Higher (larger heat pump) |
Best suited to | Peaked demand, low background use | Continuous, steady demand |
Space needed | More, for larger storage tanks | Less, for storage; more for larger plant |
In practice, preheat systems with a smaller heat pump and larger storage tend to work out as the more cost-effective and efficient option overall, because the heat pump spends more of its time running at its most efficient temperature.
Cost, refrigerant choice and getting the most out of your system
Three things drive the cost of a commercial heat pump hot water system: the heat pump itself, the storage tanks, and the electrical and plumbing infrastructure needed to connect it all. A preheat system with a 23kW ASHP costs less upfront than a direct system with a 90kW ASHP, but needs more space and a larger storage tank to make up for the smaller heat pump. Running costs come down to efficiency: a higher COP means more heat delivered for every unit of electricity used, so it’s worth weighing the slightly lower upfront cost of a direct system against the better long-term efficiency a preheat system usually delivers.
Refrigerant choice affects performance, safety and environmental impact too. R32 is the most common choice today, with a medium Global Warming Potential (GWP) and low flammability, making it a safe, well-understood option. R290 (propane) is gaining ground for high-temperature systems, with better thermal properties that suit heat pumps working at higher flow temperatures, though it’s flammable and needs stricter installation protocols and a properly trained installer. As regulations tighten around high-GWP refrigerants, expect to see more commercial systems move to hydrocarbons like R290 through the late 2020s and into the early 2030s.
A heat pump’s COP isn’t fixed, it changes with the flow temperature you’re asking it to produce and the temperature of the air outside, which is why efficiency tends to drop in cold weather. A few design choices help keep efficiency high across the year: size the heat pump correctly, since an oversized ASHP costs more upfront and rarely runs in its efficient range, so pair a correctly sized heat pump with adequate storage instead; design for the lowest flow temperature the system can get away with, since lower flow temperatures mean a higher COP; use the heat pump for preheating rather than the whole heating job, so it spends more time running efficiently; and build in redundancy with simple controls, so the system stays reliable and doesn’t rely on complex logic that’s more likely to go wrong.
Heat pumps also need outdoor space, airflow and, in built up areas, careful attention to noise. Acoustic performance and physical footprint both need to be part of the design from the start, particularly on urban sites where the heat pump might sit close to neighbouring buildings or public space. And it’s worth being clear on the carbon picture too: heat pumps are low carbon, not zero carbon. A heat pump’s carbon footprint depends on its COP and on how much carbon is in the electricity grid at the time it’s running. A well designed preheat system, with its higher overall COP, is usually the most cost-effective and lowest-carbon option, since it gets the most heat pump efficiency and only tops up the last few degrees with electric heating.
Which buildings suit commercial heat pump hot water systems?
Heat pumps work well across most commercial building types, but the right design depends on the demand pattern. Hotels and leisure centres, with predictable peaks around morning and evening, often suit preheat systems with good storage. Hospitals and buildings with round the clock demand often need a more continuous, higher-capacity approach. Large residential blocks and offices sit somewhere in between, and usually benefit from a proper site survey before committing to a design.
Adveco designs commercial hot water systems for buildings across the UK, including full ASHP and preheat solutions. Our services cover site surveys, metering, system design, nationwide supply and support, and full commissioning, so the system you end up with is sized correctly from day one.
Frequently asked questions
What’s the difference between a heat pump and a boiler for hot water. a boiler generates heat directly by burning fuel or using an electric element. A heat pump moves existing heat from the outside air into the water, using far less energy to do it, though it works best at lower flow temperatures than a boiler.
How much hot water storage does a commercial heat pump need. it depends on the system. A preheat system typically needs more storage, since the heat pump only partially heats the water in advance. A direct system heating water to its final temperature usually needs less, sometimes as little as 1,000 litres for a mid-sized building.
What’s a good COP for a commercial heat pump hot water system. a COP around 2.5 to 2.6 is typical for well designed commercial systems. Preheat systems tend to sit at the higher end, since the heat pump runs at a lower, more efficient flow temperature.
Can heat pumps meet hot water demand in hotels and hospitals. yes, with the right design. Hotels usually suit preheat systems built around predictable peak demand, while hospitals, which need hot water continuously, often need a system sized for steady, round the clock output.
