Why Replacing Your Old Boiler Now Could Save You Tens of Thousands
“We’ll keep it going another five years — there’s life in it yet.” That’s something we often hear from clients with older atmospheric or pressure-jet boilers.
It seems reasonable — after all, if it’s still working, why not keep it running? But when you look at the numbers, the logic doesn’t hold up. Keeping that old boiler for “just a few more years” will likely cost you far more than replacing it now.
Old vs. New: The Real Efficiency Gap
Let’s take a common scenario: a 25-year-old 100 kW pressure-jet boiler.
Older non-condensing boilers typically operate around 70% efficiency, often less once you account for age, fouling, and part-load performance. A modern high-efficiency condensing boiler operates at 92–95%.
That difference — roughly 22% more useful heat per unit of gas — translates directly into cost savings.
For our example, we have used 4000 annual running hours. This is on the higher end for a commercial building, but not unrealistic, especially if the boiler is also providing hot water. Buildings in the hospitality or healthcare industries will often have higher run hours than this.
Annual Gas Cost Comparison
Boiler Type | Seasonal Efficiency | Annual Gas Consumption | Annual Gas Cost (at 8p/kWh)
Old 100 kW Pressure Jet | 70% | 571,429 kWh | £45,714
New Condensing Boiler | 92% | 434,783 kWh | £34,783
Annual Savings | – | – | £10,931
That’s £10,900 saved every year on gas alone. Over five years, that’s £54,655 back in your pocket.
Boiler Replacement Cost Reality
A realistic installed cost for a 100kW commercial boiler system — including flue work, plate heat exchangers, controls, and commissioning — typically costs around £200-250/kW, so we’ll use £22,500.
Given current labour and materials pressures in the HVAC industry, costs are rising at roughly 5% per year. That’s not speculation — it’s what we’re seeing across the sector. The shortage of skilled heating engineers and installers is real, and it’s driving costs steadily upwards.
So, if you wait five years:
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£22,500 × (1.05)^5 ≈ £28,700
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That’s £6,200 more just for the same job.
The 5-Year Cost Comparison
Scenario | 5-Year Fuel Cost | Boiler Replacement | Total 5-Year Cost
Replace Now | £173,915 | £22,500 | £196,415
Delay 5 Years | £228,570 | £28,700 | £257,270
Difference | – | – | £60,855
On a graph that would look like this:
If you keep your old boiler, you’ll spend around £60,000 more over the next five years — and still end up replacing it anyway.
These savings don’t account for the fact that a new modern boiler would modulate down rather than run at full capacity when it’s not needed. There are also further savings that can be made with a BMS or smart control system, with features such as weather compensation and optimisation.
Even with Finance, It Still Makes Sense
Many facility managers assume replacing now means a big capital hit. But even if you were to finance the replacement, the numbers still add up.
Let’s assume:
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Replacement cost = £22,500
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5-year loan at 6% interest
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Total finance cost ≈ £25,709
That’s still £30,000+ cheaper than the “keep it running” option. The energy savings alone more than cover the repayments — meaning the upgrade effectively pays for itself.
The Hidden Costs of Waiting
Beyond energy, old boilers bring:
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Higher servicing and repair costs
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Downtime and reliability issues
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Reduced control efficiency
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Increasing risk of non-compliance or failure
So, even ignoring inflation, the “do nothing” strategy is rarely the cheaper one.
The Bottom Line
If your commercial boiler is 20+ years old — especially a non-condensing model — the smart money says replace it now.
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Fuel savings: ~£11k/year
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Payback: ~2 years
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Avoided inflation cost: ~£6k
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Total 5-year benefit: ~£60k
Even if financed, the savings exceed the repayments. Waiting doesn’t save you money — it costs you money.
Closing Note
When a customer says, “We’ll keep it going a bit longer,” they believe they’re saving money. But as the numbers show, they’re doing the opposite.
That “extra five years” will likely be the most expensive decision they make.
Now’s the time to act — before gas prices, labour costs, and inefficiencies take a bigger bite out of your bottom line.
If you have an older boiler that’s costing you money, get in touch for a free survey today and find out what your savings could be over the next few years.
📞 01737761397
