Construction and renovation projects treat heating as a late-stage decision more often than they should — specified once from a catalogue, installed without much thought to how differently a new-build and a renovated property actually behave thermally, and then discovered to be wrong only after completion, when fixing it is far more expensive. This piece looks at why that mismatch happens, what it costs when it isn’t caught early, and the practical fix. For developers, contractors, and property owners in London who want heating specified correctly the first time, Olia’s Plumbing & Heating is a Gas Safe registered team that works directly with construction and renovation projects across Central and West London — get in touch before the design freezes, not after the floors go down.
The Problem: One Heating Spec Doesn’t Fit Both Project Types
A new-build and a renovation arrive at the heating question from opposite directions, and treating them the same is where the money starts leaking out of a project budget.
A new-build starts with a blank slate: insulation, window performance, and layout are known from the design stage, so the heating system can be sized precisely to what the finished building will need. A renovation starts with an existing structure that already has its own thermal quirks — uneven insulation, a pipe layout from a previous decade, and a heat loss profile that’s rarely been properly calculated at all.
That difference matters for sizing. A boiler and radiator setup correctly specified for a new-build’s calculated heat loss is often wrong — usually undersized — for a renovation with the same floor area, because the renovation’s real heat loss is higher and harder to predict. Projects that use new-build assumptions on a renovation, or vice versa, routinely end up with a heating system that underperforms from the day the keys are handed over — and a snagging list that includes a problem nobody wants to pay to fix twice.
Where the Money Actually Gets Lost
A handful of mistakes show up repeatedly across both project types:
- Sizing the boiler off floor area alone, rather than a proper heat loss calculation — a shortcut that works for a rough estimate and causes real problems when it’s the only calculation done.
- Treating radiator placement as an afterthought, especially in renovations where it’s tempting to just reuse existing pipe runs rather than reconsider whether they’re right for the new layout.
- Specifying heating before the building’s fabric performance is finalised — a late change to insulation specs can quietly invalidate a heating design calculated against the original numbers.
- Underestimating a renovation’s existing heat loss, especially in older London stock with solid walls, older windows, and uninsulated floors.
- Leaving commissioning as a box-ticking exercise rather than genuine balancing and testing — a correctly specified system poorly commissioned on installation day underperforms just as badly as one that was undersized.
Every one of these is avoidable, and every one of them is cheaper to catch at the design stage than after the walls are closed up.
What Getting It Wrong Actually Costs
Beyond the technical headache, both new-build and renovation projects carry real legal and financial exposure when heating is mis-specified:
Building Regulations (Part L) set minimum energy efficiency standards for heating in both new construction and major renovations — non-compliance can hold up sign-off and completion.
Gas Safe registration is a legal requirement for any work on gas-connected heating systems. Unqualified work isn’t just a safety risk; it can block the completion certificate a project needs to close out.
EPC ratings are directly affected by heating system performance, and a poorly performing system can measurably reduce a property’s value or rentability — a cost that shows up long after the contractors have left site.
The pattern is consistent: correcting a heating specification after installation — rebalancing an undersized system, retrofitting controls, or replacing an incorrectly sized boiler — costs substantially more than getting it right before installation begins. On a typical London project, that’s the difference between a modest line item in the original budget and a five-figure remedial job once the snagging list comes back.
The Fix: Bring in a Qualified Engineer Before the Design Freezes
Every mistake above traces back to the same root cause: heating treated as a trade to slot in once everything else is decided, rather than a discipline that should shape the design from the start. The fix is correspondingly simple, even if it’s rarely followed:
- Commission a proper heat loss calculation for the actual building, not a generic estimate based on floor area.
- Involve the heating engineer at design stage, not after the walls are up.
- Re-check the specification if insulation or glazing changes during the project.
- Budget for proper commissioning and balancing, not just installation.
- Confirm Gas Safe and Building Regs documentation is in place before completion.
For developers, contractors, and homeowners managing a project in London, this is exactly the gap Olia’s Plumbing & Heating is set up to close. As a Gas Safe registered team working across Central and West London, they carry out proper heat loss surveys, specify systems correctly for new-build and renovation projects alike, and handle commissioning and compliance documentation as standard — not as an afterthought bolted onto the end of a project.
If heating hasn’t been specified yet, or a snagging list already has a heating complaint on it, the time to call is before the next phase of work starts, not after. Get in touch with Olia’s Plumbing & Heating to have the system assessed properly — it’s consistently the cheapest point in the project to get this right.
The Bottom Line
A new-build and a renovation are solving genuinely different heating problems, even when the finished properties look identical on paper — and treating them with the same off-the-shelf specification is one of the most common, most expensive, and most avoidable mistakes in UK construction.
The fix isn’t more equipment — it’s bringing in the right expertise early. For any London project where heating hasn’t been locked in yet, that’s a conversation worth having with Olia’s Plumbing & Heating before the next phase of work begins, not after the snagging list comes back.
