There's something genuinely luxurious about stepping onto a warm bathroom floor on a cold Sydney winter morning. Electric underfloor heating has gone from a high-end luxury to an affordable upgrade that's increasingly standard in bathroom and kitchen renovations across the Eastern Suburbs. And from an electrical perspective, it's one of the most straightforward installations we do — when it's planned properly.
This guide covers the electrical side of underfloor heating that most home improvement articles gloss over: circuit requirements, thermostat wiring, load calculations, compliance with Australian standards, and what it actually costs to install and run in Sydney.
How Electric Underfloor Heating Works
Electric underfloor heating is elegantly simple. Thin resistive heating elements are embedded in the floor structure — either in the tile adhesive layer, within a self-levelling screed, or directly under the floor covering. When electricity flows through the elements, they generate heat that radiates upward through the floor surface.
The system is controlled by a thermostat with a floor temperature sensor embedded in the screed or adhesive alongside the heating elements. The thermostat cycles the heating on and off to maintain a set temperature — typically 25°C–28°C at the floor surface, which feels warm underfoot without being hot.
Unlike hydronic (water-based) underfloor heating, which requires a boiler, manifold, and plumbing work, electric systems need only an electrical connection to the switchboard and a thermostat. This makes them far simpler and cheaper to install, especially in renovations where you're working with an existing floor structure.
Types of Electric Underfloor Heating Systems
Heating Mats
Pre-assembled mats with heating cable fixed to a fibreglass mesh in a serpentine pattern. You roll them out over the floor area and embed them in tile adhesive. This is the most common system for bathrooms and kitchens.
- Thickness: 3–4mm — adds virtually no floor height
- Power output: Typically 150W/sqm for tiled areas, 100W/sqm for timber or vinyl
- Best for: Rectangular rooms where the mat can be rolled out in straight runs. Most bathroom installations use mats
- Limitation: Not easily customised for irregular room shapes — you can cut the mesh (never the cable) to turn corners, but complex layouts are tricky
Loose Heating Cable
Individual heating cable on a spool that you lay manually in a serpentine pattern, typically held in place by clips or tape. Offers complete flexibility in layout and spacing.
- Best for: Irregularly shaped rooms, around toilet pedestals and vanity units, and areas where mat coverage isn't practical
- Spacing: Adjustable — closer spacing (50–75mm) for higher output, wider spacing (100–125mm) for lower output. This lets you concentrate heat where it's needed
- Installation time: Longer than mats — the cable must be laid and secured manually, which adds labour cost
Foil Heating Elements
Ultra-thin aluminium foil elements designed to be installed directly under floating floors (timber, laminate, vinyl plank) without screed or adhesive.
- Thickness: Under 1mm — no floor height increase
- Power output: 80–140W/sqm — lower than cable systems because floating floors have lower thermal tolerance
- Best for: Living rooms, bedrooms, and other areas with floating floor coverings
- Limitation: Cannot be used under tiles (tiles need the cable-in-adhesive method) and shouldn't be used in wet areas
Planning the Installation: The Electrical Requirements
Load Calculation
Before anything else, your electrician needs to calculate the total electrical load and ensure your switchboard can handle it. Here's how the numbers work:
- Small bathroom (4 sqm heated area × 150W/sqm): 600W = 2.6A at 230V
- Large bathroom (8 sqm heated area × 150W/sqm): 1,200W = 5.2A at 230V
- Kitchen (10 sqm heated area × 150W/sqm): 1,500W = 6.5A at 230V
- Living room (20 sqm heated area × 100W/sqm): 2,000W = 8.7A at 230V
- Whole-home system (60 sqm heated area): 7,500–9,000W = may require three-phase supply or multiple circuits
Note: You don't heat the entire floor area — only the exposed floor where people walk. The area under vanities, bathtubs, shower bases, toilets, and fixed cabinetry is excluded. This typically reduces the heated area to 60–80% of the total room area.
Circuit Requirements
Electric underfloor heating must be installed on a dedicated circuit from the switchboard under AS/NZS 3000. This isn't optional — it's a code requirement.
- Circuit protection: Each underfloor heating circuit must be protected by an appropriately rated circuit breaker (typically 10A or 16A) and an RCD with 30mA maximum trip current
- Cable rating: 2.5mm² TPS cable for circuits up to 20A is standard. The cable run from the switchboard to the thermostat location determines the voltage drop — for long runs, your electrician may upsize the cable
- Maximum load per circuit: A single 16A circuit can handle up to 3,680W (16A × 230V) of underfloor heating. Larger installations need multiple circuits
- Isolation: A double-pole isolating switch must be installed to allow the circuit to be completely disconnected for maintenance
Thermostat Selection and Wiring
The thermostat is the brain of the system. It controls when the heating runs, what temperature it maintains, and how efficiently it operates. Options include:
- Basic on/off thermostat: Simple temperature dial with a floor sensor. Cheapest option but no programming capability. The floor heating runs whenever the set temperature isn't met, which wastes energy if you forget to turn it off
- Programmable thermostat: Set daily schedules — 6:00 AM warm-up before you wake, off when you leave for work, back on before you get home, off at bedtime. This is the minimum recommended option and typically saves 30–40% on running costs vs. a basic thermostat
- WiFi/smart thermostat: App-controlled with learning algorithms, remote access, and energy usage tracking. You can adjust heating from your phone, set holiday modes, and receive energy reports. Brands like Warmup, Heatmiser, and Thermogroup offer excellent smart options
- Dual-sensor thermostat: Uses both a floor sensor (in the screed) and an ambient air temperature sensor. This prevents the floor from overheating while also considering the room temperature — the most accurate and efficient control method
Wiring note: The thermostat requires a power supply (active + neutral from the dedicated circuit), a switched output to the heating mat/cable, and a connection to the floor sensor probe. In wet areas like bathrooms, the thermostat must be mounted outside the bathroom or at minimum outside zones 0, 1, and 2 as defined by AS/NZS 3000.
Floor Sensor Installation
The floor sensor probe is a critical component that's often poorly installed. It's a small thermistor on a wire that sits in the screed or adhesive layer between the heating elements, measuring the actual floor temperature.
- Install in conduit: Always run the sensor wire through a conduit embedded in the floor. If the sensor fails (they do, eventually), you can pull it out and replace it without breaking up the floor
- Position correctly: The sensor must sit midway between two heating cables, not touching either one. If it touches a cable, it reads the cable temperature rather than the floor temperature, causing inaccurate control
- Seal the conduit end: Tape or silicone the end of the conduit to prevent screed or adhesive from entering and trapping the sensor wire
Installation Process: Step by Step
1. Subfloor Preparation
The subfloor must be clean, level, and free of sharp debris that could damage the heating elements. On concrete slabs, any cracks or defects should be patched. On timber subfloors, a fibre-cement sheet overlay provides a stable, level base.
2. Insulation (Highly Recommended)
Installing insulation board under the heating elements dramatically improves efficiency by directing heat upward into the room rather than downward into the slab or subfloor. A 6mm foam insulation board is typical for renovations — it reduces heat-up time by up to 50% and cuts running costs by 30–40%.
Without insulation, a significant portion of the heat energy goes into warming the concrete slab underneath — energy that's entirely wasted. On a ground-floor concrete slab, insulation is essential. On an upper floor with a living space below, it's still recommended but less critical.
3. Laying the Heating Elements
The tiler or floor installer lays the heating mats or cable according to the manufacturer's layout plan. Key rules:
- Never cut the heating cable: You can cut the mesh on a mat to change direction, but cutting the cable itself destroys the element
- Maintain minimum spacing: Cables must never touch or cross each other — this causes hot spots that can damage the floor and the cable insulation
- Keep away from walls: A 50–100mm gap from walls and fixed fixtures prevents heat buildup at edges
- Don't cover with insulation from above: Never place rugs, mats, or furniture directly on heated floor areas — this traps heat and can cause overheating. This is a critical user instruction that should be communicated to the homeowner
4. Electrical Testing (Before Tiling)
This is the most critical step and the one that separates professional installations from DIY disasters. Before any tile adhesive or screed goes over the heating elements, the electrician must perform:
- Resistance test: Measure the resistance of the heating element with a multimeter and compare to the manufacturer's specification (usually printed on the element label). A reading outside ±5% indicates damage — if it's wrong, the element must be inspected and repaired before covering
- Insulation resistance test: A 500V megger test between the heating conductor and the earth sheath checks for insulation breakdown. A reading below 1MΩ indicates damaged insulation — a potentially dangerous fault that must be found and repaired
- Continuity test: Verify end-to-end continuity of the heating element and the earth conductor
These tests must be repeated after tiling is complete to verify nothing was damaged during the tiling process. Document the results — they form part of the compliance certificate.
5. Tiling or Floor Covering
The tiler applies flexible tile adhesive over the mats, embedding them completely. Flexible adhesive is critical — standard adhesive will crack as it expands and contracts with heating cycles, eventually cracking the tiles above.
6. Final Electrical Connection
Once the floor is complete and cured, the electrician connects the cold tail leads from the heating element to the thermostat, connects the floor sensor, and commissions the system. Final testing and a compliance certificate are issued.
Important: The heating system must not be turned on for at least 14–28 days after tiling (check the adhesive manufacturer's specification). The adhesive and grout need to fully cure before thermal cycling begins. Turning it on too early can crack grout and debond tiles.
Running Costs: The Real Numbers
At Sydney's current electricity rates (approximately $0.30–$0.35 per kWh as of 2026), here's what underfloor heating actually costs to run:
- Bathroom (4 sqm heated, 600W): ~$0.20/hour → 2 hours/day = ~$0.40/day = ~$36 for a 3-month winter
- Ensuite (3 sqm heated, 450W): ~$0.15/hour → 2 hours/day = ~$0.30/day = ~$27 for a 3-month winter
- Kitchen (8 sqm heated, 1,200W): ~$0.40/hour → 3 hours/day = ~$1.20/day = ~$108 for a 3-month winter
- Living room (18 sqm heated, 1,800W): ~$0.60/hour → 4 hours/day = ~$2.40/day = ~$216 for a 3-month winter
With a programmable thermostat, costs drop further because the system cycles off once the set temperature is reached (typically running at 40–60% duty cycle rather than continuously). The numbers above assume continuous operation — real-world costs with a thermostat are 30–40% lower.
Compared to running a 2,400W portable electric heater all evening, underfloor heating in a bathroom is remarkably economical. You get targeted warmth where you need it most — your feet — rather than heating an entire room volume of air.
Best Rooms for Underfloor Heating in Sydney
Bathrooms (The Obvious Winner)
Bathrooms are where underfloor heating makes the most sense. The floor area is small (keeping costs low), you're walking barefoot (maximum comfort benefit), the room has hard tile floors (excellent heat transfer), and the heating is only needed for brief periods morning and evening.
Ensuites
Same logic as bathrooms but even smaller — often only 2–3 sqm of heated area. Cheap to install, cheap to run, and you notice the warmth every single morning.
Kitchens
If you have a tiled kitchen floor and spend time standing at the bench, underfloor heating transforms winter cooking from cold-footed misery to genuine comfort. The larger area means higher installation and running costs, but many homeowners consider it well worth it.
Living and Dining Rooms
Larger areas are viable with the right flooring and insulation. Electric underfloor heating in living areas works as supplementary heating rather than the primary heat source in Sydney's climate — it takes the edge off cold floors and reduces your reliance on ducted heating or split systems.
Laundries
An often-overlooked room. If your laundry has a tiled floor and you spend time there sorting and folding, a small heating mat makes winter laundry sessions far more pleasant.
Installation Costs (Sydney 2026)
- Heating mat supply (per sqm): $80–$140 depending on brand and wattage
- Loose cable supply (per sqm): $70–$120
- Basic thermostat (manual): $80–$150
- Programmable thermostat: $150–$300
- WiFi/smart thermostat: $250–$500
- Electrical installation (connection, circuit, thermostat): $400–$800
- Insulation board (supply + install, per sqm): $20–$40
Typical Total Costs (Materials + Electrical, Excluding Tiling)
- Small bathroom (4 sqm): $1,000–$1,800
- Large bathroom (8 sqm): $1,500–$2,500
- Kitchen (12 sqm): $2,000–$3,500
- Living room (20 sqm): $3,000–$5,000
These costs don't include tiling or floor covering, which is typically part of the broader renovation budget. The underfloor heating element itself is a modest addition to a bathroom renovation that already includes tiling labour and materials.
Frequently Asked Questions
How much does electric underfloor heating cost to run in Sydney?
Running costs depend on the area heated and usage patterns. A typical bathroom (4–6 sqm of heated area) using a 150W/sqm mat costs roughly $0.20–$0.35 per hour to run at current Sydney electricity rates (around $0.30–$0.35/kWh). Used for 2–3 hours per day during winter (morning and evening), that's about $0.50–$1.00 per day, or roughly $50–$90 for a typical Sydney winter season (June–August). A larger area like a living room (20 sqm) would cost around $1.00–$1.50 per hour. Using a programmable thermostat with a timer reduces costs significantly by only heating when needed.
Can electric underfloor heating be installed under existing floors?
It depends on the floor type. If you're tiling over existing tiles or concrete, ultra-thin heating mats (3–4mm thick) can be embedded in the tile adhesive layer with minimal floor height increase. If you have existing timber floorboards, foil heating elements can sometimes be installed between the joists from below (if there's subfloor access). However, the most common and effective approach is to install underfloor heating during a bathroom or kitchen renovation when the floor is being replaced anyway. Retrofitting under existing carpet or vinyl usually requires lifting and relaying the floor covering.
Does underfloor heating need its own circuit?
Yes, in almost all cases. Electric underfloor heating systems draw significant current and must be installed on a dedicated circuit from the switchboard, protected by an appropriately rated circuit breaker and RCD (safety switch). A typical bathroom mat (600–900W) can run on a 10A circuit, but larger installations may need a 16A or 20A circuit. AS/NZS 3000 requires that underfloor heating circuits be RCD-protected with a maximum 30mA trip current. Your electrician will assess the load and install the correct circuit protection.
Is electric underfloor heating safe in bathrooms?
Yes, when properly installed by a licensed electrician. Modern electric underfloor heating systems are specifically designed for wet areas — the heating elements are fully insulated and waterproofed. The system must be installed under a compliant waterproof membrane and connected to an RCD-protected circuit. The thermostat must be installed outside the bathroom (or at least outside wet zones) per AS/NZS 3000. With correct installation and RCD protection, electric underfloor heating in bathrooms is completely safe and has been standard practice in Australian homes for decades.
How long does underfloor heating take to warm up?
Electric underfloor heating typically takes 20–45 minutes to bring the floor surface to a comfortable temperature (around 25–28°C), depending on the floor type and insulation. Tiles heat up faster than stone, and insulated subfloors respond quicker than concrete slabs. This is why a programmable thermostat with a timer is essential — set it to start 30 minutes before you wake up or get home, and the floor will be warm when you need it. Once at temperature, the thermostat cycles the heating on and off to maintain the setpoint, using much less energy than the initial warm-up.
Warm Floors Start With the Right Sparky
If you're planning a bathroom renovation, kitchen upgrade, or just want warm floors this winter, call Randwick Electrical on 0413 707 758. We'll assess your switchboard capacity, recommend the right system for your floor type, coordinate with your tiler on timing, and handle all the electrical work from circuit installation through to final commissioning and certification.