Drying heating: function heating, covering-readiness heating and their monitoring

For screeds on underfloor heating, the heating system is the most effective drying tool — if used correctly and its effect is verified. In practice, function heating and covering-readiness heating are regularly confused, protocols are filed away, and screeds that are still too moist get covered anyway. This article sorts the terms, describes the heating protocol and shows why the heating phase should be measured rather than just logged.

Function heating: a system check, not a drying proof

Function heating is the commissioning check of the underfloor heating. The system is ramped up following a defined scheme to prove tightness and even operation. A common scheme:

1. Start at the earliest after the screed’s hardening period — for cement screed (CT) usually 21 days, for calcium sulphate screed (CA/CAF) 7 days after installation (manufacturer specifications take precedence).
2. Begin with a flow temperature of ~25 °C, hold for 3 days.
3. Raise to the maximum design flow temperature, hold for another 4 days.
4. Document everything in the heating protocol (dates, flow temperatures, outdoor temperature, incidents).

Important: after function heating the screed is not ready for covering — the short heating phase expels only part of the moisture. Function heating answers “does the heating work?”, not “is the floor dry?”.

Covering-readiness heating: targeted drying

Covering-readiness heating follows on and dries the screed in a controlled way down to covering readiness. The practical procedure:

1. Step-wise heat-up of the flow temperature (commonly in steps of ~5–10 °C per day) up to the maximum design temperature.
2. Holding phase over several days to weeks — depending on screed type, thickness and climate. This is where the core moisture is expelled.
3. Do not forget ventilation: the expelled moisture must leave the building. Without consistent air exchange, room humidity rises, drying stalls, and during cool-down moisture condenses back — on windows, cold walls and in the screed itself.
4. Step-wise cool-down, then the CM test at the designated measuring points. Heated limits: CT ≤ 1.8 CM-%, CA/CAF ≤ 0.3 CM-% (details on covering readiness).
5. If the test comes out too high: extend the holding phase, test again — every repetition costs an appointment and a drill hole.

The protocol problem

The heating protocol documents target temperatures and periods — it measures nothing inside the screed. Between “protocol filled in correctly” and “screed dry” lie the usual disruptions:

• Heating phases were interrupted (site power, system fault, other trades).
• Heating happened, ventilation did not — the moisture stayed in the room.
• The screed is thicker than planned or the climate worse than assumed.
• Moisture is being resupplied from below (remoistening).

Result: the CM test after the protocol fails, the schedule tips — or worse, covering happens without a reliable measurement.

Making the heating phase measurable

With an embedded sensor in the screed, the effect of each heating step becomes directly visible: the material temperature confirms the step arrives, and the moisture curve in g/m³ shows how much water the phase actually expels. Complemented by a room climate sensor, the ventilation problem also becomes visible — if room humidity rises during the holding phase, air exchange is insufficient, and the system reports it.

Concretely, monitoring during covering-readiness heating delivers:

• Effect verification per heating step instead of flying blind until the CM test,
• Ventilation guidance based on measured room and material values,
• Condensation warning during cool-down (dew point monitoring),
• Scheduling of the CM test: testing happens when the curve reaches the threshold range — not by calendar,
• Documentation of the entire curve as a complement to the heating protocol, for acceptance and project records.

The separation remains unchanged here too: the normative proof of covering readiness is the CM test. Monitoring ensures it passes at the first appointment. [PLACEHOLDER: pilot data — heating days/test appointments saved through measurement-based control]

To make covering-readiness heating measurable in your next project: the pilot project includes material and room climate sensors with evaluation; specification templates are ready for tenders.