Installing Thin-Layer Underfloor Heating: A 5-Step Guide

Q: NP12, NP14, or NP16 – which version for my old building?

Rule of thumb: the door gap is decisive. NP12 + 5 mm screed = 18 mm total height – fits under most old building doors (standard gap 20–25 mm). NP14 = 20 mm, NP16 = 22 mm. Larger foil = more thermal mass = slightly more even heat. If space is tight, always choose NP12. Beforehand, test the doors by propping them up with a 20 mm thick board.

Q: What is the maximum length a heating circuit can be?

For 12 mm PE-RT pipe, a maximum of 70 running meters. For 14 mm up to ~90 m, for 16 mm up to ~100 m – depends on pressure loss. Rule of thumb for room size: 1 heating circuit per 15–20 m² (with 10 cm spacing). Always keep multiple heating circuits of the same length (± 10 m) so that the manifold can balance evenly.

Q: Can I install thin-set systems over old tiles?

Yes – if the tiles are completely secure. Test: tap with a rubber mallet, hollow sound = adhesion lost → patch these tiles beforehand or re-bond them. Then degrease the surface (brake cleaner or soapy water), and let it dry. The self-adhesive underside of the dimpled sheet will then adhere reliably.

Q: When can I first operate the underfloor heating?

At the earliest 28 days after screed installation. Then start the heating protocol: Day 1–3 flow temperature at 25 °C, daily +5 °C until operating temperature is reached. Only then lay the floor covering. Warning: Heating too early will cause Planogel Rheo to crack. This protocol is mandatory for the warranty.

Q: Which flooring is suitable after installation?

All common floor coverings are possible: tiles & natural stone (best heat transfer), vinyl/LVT, laminate, floating parquet. Carpet: total resistance ≤ 0.15 m²K/W. Solid wood planks glued directly: only after consultation with MC Therm (observe wood moisture, laying direction). PVC glued directly works very well.

Q: Do doors need to be shortened when retrofitting?

With NP12 (18 mm total height) usually not – standard door undercut is 20–25 mm. With NP16 (22 mm) or an additional insulation board, it might be tight. Check doors beforehand: place a 20 mm board underneath as a test and open the door. Plan stairs and door thresholds early.

Q: Can I install parquet flooring over underfloor heating?

Engineered wood flooring (2-layer): yes – if approved for underfloor heating, glued directly to the screed. Suitable wood types: oak, walnut, bamboo. Not suitable: beech, cherry (too much shrinkage). Solid wood planks: only after manufacturer approval. Vinyl/LVT is the easiest and safest choice.

Q: Does a thin-film system work with my existing gas heating?

Yes – provided the gas heating system is designed as a condensing boiler (flow temperature adjustable to 35–45 °C). Older high-temperature boilers require a mixing group or hydraulic balancing. For a heat pump, a thin-layer system is immediately optimal – no conversion necessary.

Q: How do I avoid air bubbles when pouring with Planogel Rheo?

Pour Planogel Rheo evenly over the surface and immediately spread it with a long squeegee. Then roll a spike roller (deaeration roller) crisscross and lengthwise over the entire surface – this pushes out trapped air around the pipes. Work carefully, especially at corners, pipe bends, and distributor connections. Air pockets are the most common error: They form voids and permanently reduce heat transfer.

Q: When can I switch on the heating for the first time after screeding?

Start heating no earlier than 48 hours after pouring – this is the minimum curing time for Planogel Rheo. Then start the heating protocol: Day 1–3, limit flow temperature to 25 °C, increasing daily by 5–10 °C until operating temperature is reached. Premature heating creates vapor pressure in the still-soft screed → bubbles, cracks, hollow spots. Adhering to the protocol is mandatory for the manufacturer's warranty.

Thin-Layer System Installation Instructions: Installing Underfloor Heating in an Old Building

The complete installation instructions for the thin-layer system: Check the subfloor, lay the self-adhesive dimpled sheet, clip in the heating pipe, pressure test, pour Planogel Rheo. Total build-up from 18 mm. Still in the planning phase or unsure which variant is suitable? → First, read our planning guide for costs, variants & subfloor requirements.

⏱ 8 min. read

DIY Assembly Instructions

Old Buildings & Renovation

What do I need? Materials, tools & substrate requirements

Required materials

→Dimpled membrane – NP12 (13 mm), NP14 (15 mm) or NP16 (17 mm)
→PE-RT heating pipe Ø 12, 14 or 16 mm suitable for the foil variant
→Kerakoll Planogel Rheo self-levelling compound (min. 5 mm cover)
→Reinforced perimeter insulation strip, self-adhesive, min. 50 mm high
→Heating circuit manifold + pressure gauge for pressure test (4 bar)
→2 m straightedge, moisture meter (wood max. 15%), spiked roller, mixing pump

Substrate requirements

→Load-bearing substrate: Cement screed, tiles (no hollow sound) or wood
→Flatness ≤ 3 mm over 2 m – if more, apply leveling compound first
→Dry and clean: no oil, no loose dust, no wet spots
→Heating system with ≤ 45 °C flow temperature – optimal for heat pump (35–40 °C)
→Door undercut to be measured in advance: NP12 → min. 23 mm, NP14 → min. 25 mm, NP16 → min. 27 mm
→Hydraulic balancing: legally mandated since October 1, 2024 (GEG §60a) for every new heating system – Procedure B mandatory for heat pumps

Which version fits? NP12, NP14, or NP16

Your choice depends on your door undercuts – this is the decisive factor. Beforehand, measure the distance between the bottom edge of the door and the existing floor. NP12 results in the slimmest construction: 13 mm film + 5 mm screed = 18 mm total. This means most old building doors will fit without needing to be shortened. NP14 (20 mm) and NP16 (22 mm) offer slightly more thermal storage mass. For old buildings with a tight budget and limited room height, NP12 is the first choice. Set the position of the heating circuit distributor: plan for a wall niche or a flush-mounted box – the distributor requires approx. 30 cm × 60 cm.

Underfloor Heating in Old Buildings: 5 Steps to a Finished Heating System

Check & prepare the substrate: Lay down a 2 m straightedge – deviation > 3 mm? Then apply leveling compound (e.g., Kerakoll Levelite) and let it cure for 24 h. Tap tiles: Hollow sound = risk of cracks in screed → fill. Measure wood moisture (max. 15 %). Vacuum, degrease subfloor. Duration approx. 30–60 min.

Install edge insulation strips all around: Adhere reinforced edge insulation strips to every wall, pillar, and door frame – without gaps. The reinforcement holds back the screed and prevents sound bridges. Only trim the top of the strips after the screed has fully cured. Warning: Without edge insulation strips, the screed can crack! Duration approx. 20 min.

Laying self-adhesive studded sheeting: Peel off the protective film, starting from a corner or from the manifold. Interlock the sheets laterally over the snap fasteners – they will audibly click into place. No adhesive necessary: the dimpled sheet adheres to screed, tiles, and wood. Butt the sheets together, do not overlap. Mark the pipe run with chalk. Duration approx. 45 min/20 m².

Install heating pipe & pressure test: Clip PE-RT pipe by hand into the studs – no tools required. Spiral shape: more even, edge area remains cooler. Meander: easier to install. Max. 70 m per heating circuit (12 mm pipe). Connect pipe ends to manifold. Pressure test: 4 bar cold pressure, hold for 24 h, photograph result. Heating runs continuously during the entire screed installation! Duration approx. 60–90 min/heating circuit.

Pour and cure Planogel Rheo: Mixing pump recommended for consistent viscosity. Apply compound quickly - at least 5 mm above the pipe crown. Roll with a spiked roller crosswise + lengthwise: air bubbles escape, surface becomes smooth. Self-leveling - no smoothing necessary. Drying time: walkable (light traffic) after 24 h, ready for flooring after 7 days. Attention: No heating in the first 28 days! Duration approx. 1–2 h/20 m².

Caution – Screed only by a professional

The pouring of Planogel Rheo screed should only be carried out by a qualified specialist company. Errors in the mixing ratio, covering thickness or processing temperature can lead to cracks, voids and system damage – and will invalidate the warranty. Laying dimpled sheeting and heating pipes: DIY possible. Applying screed: hire a professional.

Checklist: Before casting, check

✓ Pressure test passed (4–6 bar, 24 h, protocol photographed) · ✓ Edge insulation strips completely glued · ✓ All pipe ends connected to the manifold · ✓ Substrate moisture < 2% · ✓ Room temperature 5–30 °C · ✓ No open joints or penetrations · ✓ Film completely glued without bubbles. Only start grouting when all points are fulfilled.

Frequently Asked Questions about Thin-Film System Installation