In-Slab vs Under-Tile Floor Heating: Which System Is Right for Your Home?

If you're building a new home or renovating, electric floor heating is one of the smartest comfort upgrades you can make. But choosing between in-slab and under-tile systems isn't always straightforward — the right answer depends on your project, your flooring, and your goals.

Here's a practical comparison to help you decide.

What Is In-Slab Floor Heating?

In-slab heating uses heavy-duty cables — like the ELEKTRA VCD35 — that are embedded directly into the concrete slab during construction. The cables are laid out across the slab area before the concrete is poured, turning the entire slab into a thermal mass that radiates warmth upward.

This system is designed for new builds and major renovations where the slab is being poured from scratch. It's the go-to choice for polished concrete floors, large open-plan living areas, and whole-home heating.

The VCD35 cable operates at 35 watts per metre and is designed for deep embedment in concrete. Once the slab is poured, it acts as a massive heat battery — slow to warm up, but incredibly efficient at maintaining a consistent, even temperature across the entire floor. A well-insulated slab can hold heat for hours after the system switches off.

What Is Under-Tile Floor Heating?

Under-tile heating uses thinner cables or pre-spaced heating mats — like the ELEKTRA DM20 cable or ELEKTRA undertile mats — installed on top of the existing subfloor, just beneath the tile adhesive or a thin layer of levelling compound.

This system is designed for renovations, bathrooms, kitchens, and individual rooms where you want targeted warmth without raising the floor height significantly.

The DM20 cable operates at 20 watts per metre and sits in a thin layer of screed or adhesive. Heating mats come pre-spaced on a mesh for even faster installation. Because there's less thermal mass, under-tile systems heat up quickly — typically within 20 to 30 minutes — making them perfect for rooms you use at specific times of day.

Head-to-Head Comparison

Installation

In-slab systems require coordination with your builder and concrete contractor. The cables must be laid before the pour, which means planning ahead during the construction phase. It's not something you can retrofit.

Under-tile systems can be installed by any licensed electrician during a bathroom or kitchen renovation. They go down on top of the existing slab or subfloor, directly under the tiles. Installation is faster and less disruptive.

Heat-Up Time

In-slab heating is a slow-and-steady system. Because the cables are embedded in 100mm or more of concrete, it can take several hours to bring the slab up to temperature. However, once warm, the slab holds that heat for a long time — even after the system turns off. Most homeowners run their in-slab system on a timer, heating overnight on off-peak electricity.

Under-tile heating is responsive. With less mass to heat through, you'll feel warmth underfoot in 20 to 30 minutes. This makes it ideal for bathrooms and ensuites where you want heat on demand — warm tiles when you step out of the shower, without running the system all day.

Energy Efficiency

Both systems are energy-efficient when installed correctly. In-slab systems benefit from thermal mass — the concrete stores heat and releases it slowly, reducing the number of times the system needs to cycle on. Paired with off-peak electricity rates, running costs can be surprisingly low.

Under-tile systems use less energy per session because they're heating a smaller area with less mass. However, they lose heat faster once switched off, so they may cycle more frequently if left on for extended periods.

Flooring Compatibility

In-slab heating works with almost any floor finish: polished concrete, tiles, engineered timber, vinyl, and even carpet (with appropriate underlay). Polished concrete is particularly popular because the slab itself becomes the finished floor.

Under-tile heating is primarily designed for tiled floors — bathrooms, kitchens, laundries, and entryways. It can also work under stone and some engineered timber, but tiles remain the most common and effective pairing.

Cost

In-slab heating has a lower cost per square metre for the cable itself, but the total project cost is higher because it's part of a full slab pour. It makes economic sense when you're already building or rebuilding the slab.

Under-tile heating has a slightly higher material cost per square metre, but the installation is simpler and cheaper. For a single bathroom, you can be looking at a few hundred dollars in materials plus electrician labour.

Can You Use Both in the Same Home?

Absolutely. Many of our customers use in-slab heating for the main living areas and polished concrete zones, then add under-tile mats in bathrooms and ensuites. This gives you the best of both worlds — efficient whole-home warmth plus responsive comfort in wet areas.

The Bottom Line

There's no single "better" system — it comes down to your project type, your flooring choice, and how you want to use the heating. The good news is that both ELEKTRA in-slab and under-tile systems are premium European products backed by a 20-year warranty, so whichever you choose, you're investing in long-term comfort.

Need help deciding? Contact P.A.P. Heating Solutions for a free design consultation. Send us your floor plans and we'll recommend the right system, calculate your heating loads, and provide a detailed quote — all at no cost.