In-slab heating in a Geelong ensuite - cost, timing and when it actually pays off.
A cold tile floor at 5:45am on a July morning in Highton is the single most common complaint we hear from clients on a year-old bathroom. The fix is either hydronic in-slab heating, an electric wire-mat under the tiles, or a well-specified heated towel rail - and the right answer depends on whether your house is already plumbed for hydronic, which way the bathroom faces, and how the bathroom is actually used.
Two different answers to the same cold floor.
The reason an unheated tile floor reads as so cold in winter is partly radiant loss and partly conductive: tile and stone are dense, and they drag heat away from the foot. A Geelong slab-on-ground bathroom, with the slab sitting on damp ground through winter, typically reads a floor surface temperature in the 8-12°C range from June through August. Bringing that up to around 24-27°C is the comfort target. The question is how, and there is no single right answer.
Hydronic in-slab - the case for it.
Hydronic in-slab heating is a closed loop of PEX-Al-PEX tubing laid in roughly 100mm centres across the bathroom floor on a prepared substrate, screeded over with around 50mm of sand-cement screed, then tiled. The warm-water side is fed from the house boiler (gas, electric heat pump or existing hydronic system). It is slow to come up to temperature, slow to come back down, and very efficient to hold at a setpoint. If your Highton or Waurn Ponds house already runs hydronic in the living spaces, the marginal cost of extending a loop into a new bathroom is modest and the running cost is the lowest of the three options. South-facing ensuites benefit most because they lose the most heat overnight.
Electric wire-mat - the case for it.
An electric wire-mat sits in the tile adhesive immediately under the finished tile, runs off a thermostat with a floor sensor, and brings the surface from cold to warm in about 25-40 minutes. Capital cost is roughly a third of the hydronic install. Running cost is higher per hour, but if you only run it morning and evening (timer-driven), the daily total is small. For a single ensuite retrofit in a house with no existing hydronic, electric is almost always the right answer - you do not pay for the boiler tie-in, the manifold, the screed thickness, or the extra floor build-up that the hydronic loop requires.
When in-slab is the wrong call.
A small Bellarine holiday-home ensuite used 6 weekends a year. A bathroom in a heritage Newtown cottage where the floor build-up would force a step you do not have headroom for. A house with no existing hydronic system where the boiler-and-manifold install would add $4,000+ to the job before the loop itself goes in. In all three cases, electric wire-mat is the honest recommendation.
The carpentry-stage window for the rough-in.
The in-slab loop has one correct window in the bathroom program and missing it is expensive. The order is: carpenter frames and lines, plumber roughs in waste and water and pressure-tests, the slab substrate is prepared and patched, the hydronic plumber lays the loop and pressure-tests at 6 bar, the screed goes down over the loop, the screed cures, the waterproofer membranes over the cured screed, and the tiler tiles. Slip the heating decision in after the membrane and you are tearing out finished waterproofing - a $2,500-$4,500 mistake. We pin the decision at the carpentry-stage walk-through, not at fit-off.
On the same site visit we also rough in the electrical for the heated towel rail (dedicated GPO behind the wall, on its own circuit). That is covered in detail on our towel rail circuit page, and the two jobs - in-slab loop and towel rail GPO - almost always go in on the same day to save a trade visit.
Common questions about in-slab heating.
When does hydronic in-slab heating actually make sense in a Geelong bathroom?
South-facing ensuites or main bathrooms in slab-on-ground houses where the rest of the house already runs hydronic. June-August floor temps in the 8-12°C range across Highton, Waurn Ponds, Armstrong Creek and the newer Bellarine estates are the sweet spot. As a single retrofit in a house with no existing hydronic, the install cost rarely justifies it over electric wire-mat.
What does in-slab heating cost in a Geelong reno, all-in?
Hydronic retrofit including loop, manifold, thermostat and boiler tie-in typically $3,500-$6,500 supplied and installed. Electric wire-mat under-tile in the same room is roughly $900-$1,800 supplied and installed. Hydronic is cheaper to run per hour; electric is cheaper if you only run it morning and evening.
When in the build program does the in-slab loop go in?
After the carpenter frames and the plumber pressure-tests the rough-in, before the waterproofer arrives. The hydronic plumber lays the loop, pressure-tests at 6 bar, screed goes over, screed cures, membrane goes on the cured screed. Slip the heating in late and you are tearing out a finished membrane.
Does the heated towel rail share the same plumbing?
Usually no. The heated towel rail is almost always electric, on a dedicated GPO behind the wall, even in a hydronic house. We rough in the towel rail electrical at the same carpentry-stage visit as the in-slab loop so both are ready for fit-off together.
Pin the heating decision early and the budget holds.
VBA-registered builder, MBV/HIA member, fully insured, working across Geelong, the Bellarine Peninsula and the Surf Coast. We have the carpentry- stage conversation with you about heating up front, not as an afterthought at fit-off. Call us and we will tell you, on site, whether your bathroom is a hydronic candidate or a wire-mat one.