We've been called in to fix dozens of underfloor systems installed badly by others. These are the most common errors — and how to avoid them.
The most common underfloor heating mistakes are skipping the room-by-room heat-loss calculation, poor under-slab insulation, pipes laid too deep or at the wrong spacing, an undersized manifold, the wrong floor finish over high-output zones and missing commissioning records. Pipework errors can rarely be fully fixed once the slab is poured, and the network is meant to last 30+ years. AHHAC designs every underfloor system from a heat-loss calculation, across Sydney, NSW, VIC, QLD & ACT.
Reviewed by the AHHAC Technical Team — licensed plumbers & hydronic engineers, NSW Lic 262528C.How we write & review
The unfortunate truth about underfloor heating: it's easy to install badly, and very expensive to fix once the slab is poured. Mistakes made on day one can haunt the system for 30 years.
1. No heat-loss calculation. Installer guesses at pipe spacing, system runs hot or cold, can't be balanced. 2. Pipes too far from the slab surface — heat takes hours to reach the floor. 3. Insufficient insulation under the slab — heat goes down into the ground. 4. Manifold sized wrong — system can't be balanced room-by-room. 5. Wrong floor finish over high-output zones — timber cracks, vinyl warps. 6. No commissioning records — boiler is never tuned to the system.
Installer design errors get most of the attention, but just as many of the problems we are called in to diagnose happen after the pipework is laid, caused by other trades, rushed programmes or simple lack of information. These are the ones to watch for on your own project.
None of these are hard to avoid; they just need someone on the project to own them. For more on getting it right first time, see our hydronic underfloor heating page, underfloor heating in Canberra, and the underfloor heating cost guide.
Written from on-site experience by the AHHAC Technical Team.
AHHAC's in-house design and service team — licensed plumbers and hydronic engineers (Lic 262528C) who have designed and installed 2,400+ hydronic heating, cooling and hot water systems across Australia since 1998.
We design mistakes to avoid with underfloor heating from a room-by-room heat-loss calculation, install it with our own licensed plumbers to AS/NZS 3500 (plumbing) and AS/NZS 5601 (gas), commission and document it, and service it for the life of the system. Nothing is subcontracted out.
Skipping the heat-loss calculation. Without one, the installer guesses at pipe spacing — and the system can't be balanced. We refuse to quote without a heat-loss calculation, every time.
Sometimes. If the issue is commissioning, controls or balancing — yes, we can re-tune. If the pipework is wrong (too far from slab surface, wrong centres, no insulation under slab) — usually only a partial fix is possible without major demolition.
Ask for: a heat-loss calculation, named insurance, references on past installs, a fixed-fee quote (not 'cost plus'), and commissioning records at handover. If they can't provide these, walk away.
"AHHAC delivered our 22-zone underfloor system on time, on budget and to spec. The crew were tidy, the documentation was thorough, and the commissioning was textbook."
"We've worked with AHHAC for 17 years. They've installed and serviced our hot water plant across three commercial buildings — and they pick up the phone on weekends."
"Three mobs quoted us; AHHAC's design was the only one based on a proper heat-loss calculation. The system runs beautifully — the others would've been oversized and expensive."