ᐅ Mill the subfloor for underfloor heating or install a new screed?

Hello everyone,

We are currently considering whether to retrofit a milled-in underfloor heating system (cost around €9,000) or to install a new screed with insulation from scratch. I know this topic has come up several times before, but unfortunately, I have never really found any detailed or conclusive posts. Often, it was mostly based on personal opinion. In our case, it is a detached house built in 1995 with a screed containing polystyrene insulation. The screed’s thickness is suitable for milling.

We could install a new screed with insulation and remove the old screed ourselves partially, for about €4,000. According to the quote, the milled underfloor heating system costs about €9,000. It would also be interesting to know the approximate cost of installing a new underfloor heating system including the manifold. Does anyone have current figures?

Besides the costs, efficiency is of course relevant too. The supplier of the milled underfloor heating argues that the milled system is much more efficient and that heat naturally rises upwards. The screed installer, on the other hand, says that the insulation with a new screed, the pipe spacing, and the efficiency are better if it’s done the “right” way.

Has anyone had experience with a milled underfloor heating system or even both methods?

Thank you very much for your help!

FCBenne04 schrieb:

We are currently considering whether to retrofit underfloor heating by milling it in.

For what area?

FCBenne04 schrieb:

(The cost is about 9,000 €)

What does that include?

FCBenne04 schrieb:

The new screed including insulation and removal of the old screed could be done partly as DIY for around 4,000 €.

That could work. But then a lot of insulation and material effort, right?

I had the underfloor heating milled into the upper floor. It cost 3000 euros for about 50m2 (three bedrooms, one bathroom, one toilet, a small hallway), including waste removal, laying of the new pipes, and installation. Everything works perfectly, just like the regular underfloor heating on the ground floor. I have a new build from a developer that did not include underfloor heating on the upper floor.

SaniererNRW123 schrieb:

What area are you referring to?

The living area for the ground floor and first floor is about 120 m² (1300 sq ft), so approximately 140-150 m² (1500-1600 sq ft) of total floor area.

SaniererNRW123 schrieb:

What does that include?

Here’s a brief summary: Grooved underfloor heating (up to 11 circuits), PE quality underfloor heating pipes 14 x 2 mm (0.55 x 0.08 inches) diffusion-tight according to DIN standards; maximum operating pressure 4 bar (58 psi) – typical pipe spacing 12.5 cm (5 inches); in bathrooms 10 cm (4 inches) at 24°C (75°F) – supply and install as finished work, including laying pipes on fittings, filling and pressure testing the system, documentation, hydraulic balancing; all work carried out in one construction phase.

SaniererNRW123 schrieb:

That could work. But that means a lot of insulation and material effort, right?

Exactly. According to the screed installer, proper insulation beneath is necessary to avoid energy loss and to save on insulating the basement ceiling. The quote states: “Thermal insulation EPS DEO WLG 035, 20 mm (0.8 inches) thick and an EPS 20-2 WLG 035 carrier board + EPS carrier board/Rolljet 20-2 WLG 035.”

Bertram100 schrieb:

I had underfloor heating milled into the upper floor. It cost 3000 euros for about 50m2 (three bedrooms, one bathroom, one toilet, and a small hallway), including disposal of the waste, laying of the new pipes, and installation. Everything works perfectly, just like the regular underfloor heating on the ground floor. I have a new build from a developer that didn’t include underfloor heating on the upper floor.

Thank you for the feedback. That sounds interesting. Of course, it’s a different situation with a new build. With the milled version, is the heat felt over a large area and not just where the heating pipes run?

FCBenne04 schrieb:

According to the screed installer, proper insulation underneath is necessary to prevent energy loss and to avoid insulating the basement ceiling. The offer states: "Thermal insulation EPS DEO WLG 035, 20 mm (0.8 inches) thick and an EPS 20-2 WLG 035 carrier board + EPS carrier board/Rolljet 20-2 WLG 035"

That is proper insulation, but it definitely does not replace insulation of the basement ceiling. It hardly gets any less insulation in terms of thickness or quality. Either use rigid PUR insulation directly (although I would also consider that thickness too thin) or simply install 8 cm (3 inches) PUR under the basement ceiling.

FCBenne04 schrieb:

I’ll summarize briefly: Milled underfloor heating (up to 11 loops), PE quality underfloor heating pipe 14 x 2 mm (0.55 x 0.08 inches) diffusion-tight according to DIN; maximum operating pressure 4 bar (58 psi) – standard pipe spacing 12.5 cm (5 inches); in the bathroom (24 °C (75 °F): 10 cm (4 inches)) – supply and installation, including laying pipes on fasteners, filling and pressure testing the lines, documentation, hydraulic balancing; work done in one construction phase

Is there a heating load calculation to confirm that the house will be heated efficiently (cost-wise) with these specifications?
For 140 m² (1507 ft²) and 12.5 cm (5 inches) spacing, about 950 meters (3117 feet) of piping will be installed (typical underfloor heating pipes are usually 16/2 mm (0.63/0.08 inches) or thicker). Then 11 loops will be sufficient.
A classic underfloor heating system with 10 cm (4 inches) spacing (more effective, as it allows lower supply temperature, which is better suited for future heat pumps) and 16/2 mm (0.63/0.08 inches) pipe will naturally provide significantly better heating performance.

I would remove the screed and look for a plumber who allows owner participation (tacking the underfloor heating pipes). You can definitely find someone via online platforms or marketplaces.
Have the heating design calculation done externally (e.g., Heckmann).