Electrifying Advice When Electrifying Hot Water

There’s a quiet shift happening in buildings right now, and it’s catching people off guard. As gas is removed, hot water has stopped being a fuel selection exercise and become something else entirely — a question of demand, infrastructure, and how a building actually works. What’s surprising is not the move to electrification. That was inevitable. What’s surprising is the solutions emerging once you follow that logic all the way through.

The expected answer has been clear for some time: centralised heat pump systems as shown above. They align neatly with sustainability frameworks, deliver strong efficiency metrics, and offer a familiar engineering model — plant, tanks, distribution, control. On paper, they are hard to fault.

But buildings aren’t designed on paper alone. Once you bring in structure, space, risers, coordination, cost, and construction sequencing, the neatness starts to unravel. Central systems need room — a lot of it. They introduce weight, require careful management of long pipe runs, and bring with them the ongoing realities of heat loss, recirculation, and maintenance. In new builds, they compete with valuable floor area. In retrofits, they can become almost unworkable. So while they tick the sustainability box, they don’t always pass the geometry, cost, and buildability test.

Rethinking the System, Not the Equipment

That’s where the unexpected shift begins. Across a range of projects, a different approach is emerging — one that at first glance feels completely at odds with what “green” design is supposed to look like. Instead of centralising and storing hot water, some designs are doing the opposite: distributing and eliminating.

Instantaneous electric hot water units are appearing more frequently. Localised. Compact. No storage. No central plant. At face value, it looks like a step backwards — a brute-force electrical solution replacing a highly efficient thermal one. It isn’t. It’s what happens when you stop optimising the equipment and start optimising the system.

The immediate objection is obvious: the electrical load. Instantaneous units demand significant power. But that only becomes a problem if you assume everything operates at once. In reality, buildings don’t behave that way. Hot water usage is inherently diverse — showers, basins, kitchens, all cycling on and off throughout the day. When that behaviour is properly understood and modelled, the assumed peak demand begins to fall away from the theoretical maximum. What looks like a massive load on paper becomes something far more manageable in practice.

At the same time, distributing that load changes the nature of the system. Instead of a central plant cycling large amounts of energy to maintain stored water temperatures, energy is used only when needed, exactly where it’s needed. There are no standing losses from tanks, no continuous recirculation loops bleeding heat through pipework, and no oversized infrastructure trying to anticipate worst-case conditions that rarely occur. The result is a different kind of efficiency — not in how effectively heat is generated, but in how little energy is wasted across the system.

Where Buildings and Electrification Converge

And then there’s the part that rarely gets enough attention: the building itself. Tall buildings, tight risers, complex layouts — these are not minor constraints. They shape what is possible. Centralised systems demand space and pathways that many designs simply don’t have. Instantaneous systems, by contrast, shrink the problem. Less pipework. Smaller risers. No plant rooms dominating rooftops or basements. Space is returned to the building, and with it, value. That matters. Because electrification is not happening in isolation. It’s arriving alongside solar PV, batteries, EV charging, and fully electric buildings. Once that broader electrical ecosystem is in place, the marginal impact of hot water demand changes. Capacity is already being designed in. Diversity across systems improves utilisation. Peak demand becomes something to manage, not avoid. Seen in that context, instantaneous hot water isn’t an outlier — it’s part of a larger shift toward distributed, responsive systems.

So why does it feel so wrong? Because most sustainability thinking is still anchored in equipment performance. It asks how efficient a device is, not how efficient the whole system becomes once it’s installed. It measures COP, energy per litre, theoretical outcomes. What it often misses are the real-world factors: space, coordination, cost, behaviour, and constructability. Heat pumps are technically efficient. That’s not in dispute. But instantaneous systems, in the right conditions, can be system-efficient — and those are not the same thing.

A Shift in Thinking And in Value

This doesn’t mean one approach replaces the other. There are plenty of scenarios where centralised heat pump systems remain the right answer, particularly where demand is continuous and predictable. But there are just as many where they are not — where the building, the brief, or the constraints point somewhere else entirely. What’s changing is not the technology. It’s the thinking. The industry has been conditioned to centralise, store, and optimise plant. Electrification is pushing it in a different direction — to distribute, eliminate, and optimise outcomes. And that’s why these solutions are starting to appear. Because the problem has changed, even if the rules haven’t caught up yet.

The real opportunity sits in recognising that early — in asking the right questions before the system is locked in, rather than trying to fix it later under the banner of value engineering. This is why we engineer value — rather than value engineer later.