Halcyan, Highly Commended in the NHDG Big Retrofit Challenge 2026
A retrofit budget goes on the things everyone can see: insulation, windows, heat pumps, new cylinders and controls. Then, in a hard-water area, the water starts coating that brand-new equipment from the day it’s switched on. Nobody writes it into the plan. Nobody measures it. It just quietly wastes energy, increases maintenance and kills equipment, year after year.
That is limescale — The Invisible Enemy — and getting it onto the retrofit agenda is the reason Halcyan exists. So we were delighted when the National Home Decarbonisation Group (NHDG) named Halcyan as one of only four businesses Highly Commended in its Big Retrofit Challenge 2026.
What is the NHDG Big Retrofit Challenge?
The National Home Decarbonisation Group brings together the Tier 1 contractors and energy suppliers who deliver home decarbonisation at scale across every type of UK housing — social, owner-occupied and private rented. To join, a company must directly deliver at least £20 million a year of whole-house retrofit. Its members work on large social housing frameworks and government-funded schemes such as the Warm Homes: Social Housing Fund. These are the people who will carry out most of the country’s home retrofit work.
The Big Retrofit Challenge, run with Futurebuild and Innovate UK, is their search for smaller innovators — UK businesses with a turnover of up to £15 million — whose products or services help make homes warmer, drier and healthier. Six winners were chosen, and they said up to ten further applications could be named Highly Commended, only four were: Halcyan, Showerkap and Trust Electric Heating, Greenworkx.
Why does limescale matter in retrofit?
Whole-house retrofit rightly focuses on heat loss and low-carbon heating: fabric first, then heat pumps, hot water cylinders and controls. But around 60% of UK homes are in hard water areas, and there the hot water side of every system is under constant attack from scale.
Limescale is an insulator — it conducts heat around 300 times worse than the copper in your boiler’s heat exchanger. Even a thin layer makes your boiler burn more gas to heat the same water, which is why UK building regulations require scale treatment in hard water areas (above 200 ppm).
The same applies whatever heats the water. Yet effective scale treatment rarely appears in a retrofit assessment, a PAS 2035 plan or a housing provider’s specification. It’s an energy loss hiding in plain sight.
What usually gets fitted instead — and why it isn’t enough
Where scale is dealt with at all, it’s usually with a cheap inline inhibitor fitted on the boiler feed. It ticks the box. It doesn’t protect the home.
- Boiler only. It protects one appliance and leaves the bathrooms, kitchens, showers, taps and everything else downstream unprotected.
- Short life. Many need cartridges or refills replacing, or simply stop working long before the rest of the retrofit reaches mid-life.
- Qualified results. Read the small print and the claims come heavily qualified by their own makers.
Halcyan takes the opposite approach: one unit near the stoptap treats the whole property, hot and cold, with no refills and a 30-year warranty. That’s why it’s worth changing what gets specified.
Why we entered
Because limescale isn’t on the retrofit checklist, and it should be. We entered for two reasons:
- To be seen by the people who deliver retrofit at scale. NHDG members are exactly who needs to hear this, and a small team like ours can’t buy that platform.
- To secure field trials and case studies. We want to work with housing providers and contractors to gather independent data from real homes, building the evidence retrofit frameworks and government schemes need.
We were open with the judges that this is our biggest challenge: without large-scale, independent field trials, the formal routes into retrofit frameworks are hard to unlock.
What we told the judges
Our application made a simple case:
- Limescale is a hidden energy burden. Scale on heating surfaces wastes significant amounts of energy and shortens the life of equipment, fixtures and fittings, increasing the carbon footprint of every home.
- Halcyan tackles it for the whole property. One unit, fitted near the stoptap, prevents new limescale forming and removes existing scale throughout the hot and cold water system.
- It needs nothing from anyone once it’s fitted. No salt, no chemicals, no electricity, no servicing, and no input from the resident or maintenance team.
- It’s quick and low-disruption to install. Typically under an hour of a plumber’s time, in a single visit. Ideal to install alongside the annual boiler check.
- It lasts. Domestic units carry a 30-year warranty, so the benefit isn’t lost to short-life consumables or replacement cycles.
- It’s kinder to the environment. No brine flushed away, and no salt mined, bagged and delivered to keep it running.
- It’s proven in use. More than 3,000 Halcyan units sold in the UK alone, and many more overseas in commercial and industrial settings. UK installations range from student homes with Unite Students and hotels with Hilton, to university buildings at Imperial College London and offices for RBS.
Why does a water conditioner fit the retrofit agenda?
Awards are nice. This one matters because of who gave it. When the country’s leading retrofit contractors look at a water conditioner and say it belongs in the conversation, that’s the argument we’ve been making for ten years.
1. Retrofit has to work without relying on the resident.
The best retrofit measures do their job whether or not anyone remembers them. Halcyan is passive: once fitted, there’s nothing to top up, switch on or service. That matters most in rented and social homes. Tenants are rarely expected to run a salt softener, so most tenanted homes in hard-water areas have no scale protection at all.
2. Low disruption is not optional.
The NHDG wants installations that are fast, efficient and minimally disruptive for residents. One short plumber visit, no power supply, no drain connection and no lost cupboard is about as low-disruption as a measure gets.
3. It protects the new low-carbon kit.
Retrofit is moving homes to heat pumps and hot water cylinders. Hard water doesn’t stop because the heating source has changed. Keeping scale off the hot surfaces the water touches keeps that investment performing the way it was designed.
4. It thinks in decades, as retrofit must.
Retrofit is judged on whole-life value, not the price on the day. A 30-year warranty and no running costs fit that thinking naturally.
5. It fits the wider sustainability case.
No salt, no brine, no electricity, no consumables. Just people-friendly water that behaves more like soft water, with its healthy minerals left in.
What does Highly Commended prove — and what doesn’t it?
Being Highly Commended means a panel from the retrofit sector read our application and judged our approach worth championing. It is not a product test. The judges didn’t install units or measure energy use.
The evidence behind Halcyan sits elsewhere:
- WRAS approval (certificate 2312081), covering our range for use with UK drinking water.
- Our research partnership with Lincoln University on laboratory testing.
- Real-world case studies, including our work with Perth Housing Authority.
- Thousands of customers, hundreds of reviews, shared openly.
- The evidence pack we submitted to the judges.
Naturally, results vary depending on the water system, water flow and water type in each household but the overall impact is highly positive across all these variations.
What we don’t yet have is large-scale, independent field data from real retrofit programmes. That’s what we want to build next, and we’d welcome housing providers, local authorities and contractors who want to do it with us.
What happened next
The recognition moved us fast. Within days we’d booked a stand at Futurebuild 2026 at ExCeL London (12–14 May), where this year’s six winners took to the stage at the National Retrofit Conference: Kestrix, DiscreteHeat, Healthy Air Technology, Wrapt, IoT Solutions Group and Transform-ER. Congratulations to all of them, and to our fellow Highly Commended businesses, Greenworkx, Showerkap and Trust Electric Heating.
Retrofit only works when the measures fit together. Many of these solutions don’t just sit alongside each other — they complement and support each other, and together make a home that works better as a whole.
Frequently asked questions
Does hard water affect heat pumps and hot water cylinders?
Yes. Hard water forms scale on hot surfaces, and every heat pump system still heats water in a cylinder. Changing the heating source doesn’t change the water, so scale protection matters just as much after a heat pump retrofit as before it.
Do UK building regulations require limescale treatment?
Yes. Part L of the Building Regulations (conservation of fuel and power), through its supporting Domestic Building Services Compliance Guide, requires scale treatment for hot water systems in hard water areas (above 200 ppm).
Isn’t a boiler scale inhibitor enough?
It protects the boiler only. Bathrooms, kitchens, showers and taps are left unprotected, and many inhibitors need refills or have a short working life. Halcyan treats the whole property from one unit, with no refills and a 30-year warranty.
What is the difference between a water conditioner and a water softener?
Softening removes the minerals; conditioning changes their behaviour. A salt-based water softener strips out the calcium and magnesium, uses salt and flushes brine to drain and relies on tenants to work. A Halcyan water conditioner stops those minerals bonding together as limescale — removing the one real problem with hard water — while keeping the healthy calcium and magnesium in the water. No salt, no electricity, no wastewater.
Is Halcyan suitable for social housing and rented homes?
It’s ideal for them. Halcyan is passive and needs no input from the resident or maintenance team, no servicing and no power. It fits near the stoptap in under an hour, is WRAS approved for UK drinking water, and carries a 30-year warranty for domestic properties.
What does Halcyan do to limescale?
Halcyan prevents new limescale forming and removes existing scale throughout the hot and cold water system, treating the whole property from a single unit.
Who else was recognised in the Big Retrofit Challenge 2026?
The six winners were Kestrix, DiscreteHeat, Healthy Air Technology, Wrapt, IoT Solutions Group and Transform-ER. Greenworkx, Halcyan, Showerkap and Trust Electric Heating were Highly Commended.
A word from Samantha Mant, CEO
“Limescale has been left out of retrofit for far too long. It’s invisible, so it doesn’t make the plan — and every hot water system in a hard-water area pays for that quietly, every day. Being Highly Commended by the people who actually deliver retrofit at scale tells us we’re right to keep pushing. Now we want to prove it in the field, with partners who care about homes that work properly for decades, not just on handover day.”
Delivering retrofit, managing homes or specifying hot water systems?
To talk about effective, long-term and sustainable limescale protection for a retrofit programme, or running a field trial with us, email [email protected] or visit halcyanwater.com/commercial.
Halcyan. The Intelligent Solution.
