Calculating Heating Circuits: How Many Circuits Do I Need? (2026)

Calculating heating circuits: How many circuits for my underfloor heating? (2026)

How many heating circuits do I really need? This guide explains the calculation based on room size, pipe spacing, and heating load — with tables for detached houses, condominiums, and old buildings. Includes GModG § 61 requirements for individual room control.

⏱ 8 min. read

Circular Table for All Room Sizes

GModG Section 61 Individual Room Control

Basics: Why the Number of Layers Matters

Tools & Aids

→Pipe wrench or water pump pliers (for G 1" connectors)
→PTFE thread seal tape (min. 12 layers)
→Hand pressure pump for pressure testing (0–6 bar, integrated manometer)
→Bleeding key or flat-head screwdriver for bleed valves
→Spirit level (for horizontal alignment of the manifold)
→Wall plugs & screws (M6, for distribution box wall mounting)

What you need to know before calculating

→Manifold position: max. 20 m from boiler/heat pump, central to all heating circuits — minimizes pipe lengths and pressure loss
→Flow sensor in the supply pipe present or planned? (mandatory for boiler control)
→All underfloor heating pipes laid and accessible? Only install after screed installation and drying phase
→Wall niche chiselled out for flush-mounted box or wall surface exposed for surface mounting
→230V power within reach for actuators and room thermostat cables (if desired)

Calculating Circles: Tables, Formulas, and Building Types

How many heating circuits do I need for my underfloor heating? This question arises with every new build and every renovation. Too few circuits mean uneven heating; too many are unnecessary effort. The correct number of circuits depends on pipe spacing, room size, and heat load.

8–16 m²Guideline per heating circuit
(15 cm pipe spacing)

max. 120 mMaximum circuit length
PE-RT Ø 16 mm

≤ 10 %Length difference
between circuits

Number of circuits by room size: The practical table

Room size	Pipe spacing 10 cm	Pipe spacing 15 cm	Pipe spacing 20 cm
up to 10 m²	1 circuit	1 circuit	1 circuit
10–16 m²	1 circuit	1 circuit	1 circuit
16–24 m²	2 circuits	1–2 circuits	1 circuit
24–35 m² (living room)	3 circuits	2 circuits	1–2 circuits
35–50 m²	4–5 circuits	3 circuits	2 circuits
50–80 m²	6–7 circuits	4–5 circuits	3 circuits

Note: For perimeter zones (external walls, glass fronts), a narrower pipe spacing (10 cm) is recommended — this increases the number of circuits. Wet rooms (bathroom, WC) should always be planned as a separate circuit.

Calculate circuit length and number of circuits: The formulas

Step-by-step calculation

1. Pipe length per circuit:
L_pipe [m] = (Room area [m²] ÷ Pipe spacing [m]) + 2 × Supply line length [m]
2. Number of circuits:
n_circuits = ROUNDUP(L_pipe total ÷ 120)
3. Circuits per room:
n = ROUNDUP(Room area ÷ Area_per_circuit)

Rule of thumb: No circuit longer than 120 m (PE-RT Ø 16 mm) due to pressure drop. Up to 150 m possible with Ø 20 mm — but requires more pump power.

Factors influencing the number of circuits

Factor	Effect on number of circuits	Recommendation
Pipe spacing	10 cm → twice as many meters → more circuits needed	15 cm standard, 10 cm for perimeter zones
Floor structure (screed/dry)	Dry: max. 100 m recommended; Screed: up to 120 m	Check per installation system
Heat source	HP: narrower spacing for more surface area → lower flow temp.	10–15 cm for HP system
Room layout	Each room ideally its own circuit (individual room control)	GModG § 61 Individual room control
Building type	SFH: usually 5–10 circuits; Condominium: 2–5 circuits; MFH: 6–12 per floor	Heat load calculation DIN EN 12831

Manifold size recommendation for typical DACH building types

SFH 120–140 m² (new build)

Typically 7–9 circuits. Recommendation: 8-circuit manifold. 1 circuit per room (living room possibly 2), 15 cm pipe spacing, PE-RT 16 mm.

Condominium 60–80 m²

Typically 4–6 circuits. Recommendation: 4- or 6-circuit manifold. Bathroom, WC, kitchen, living room, bedroom each a separate circuit.

Old building renovation (thin-layer)

10 cm pipe spacing due to shallow build-up → more circuits. For 80 m²: 6–8 circuits. Max. 80 m pipe length per circuit for Ø 14 mm.

Heat pump (DACH)

Narrower pipe spacing (10 cm) for maximum heating surface → lower flow temperature → higher COP. Plan for more circuits.

GModG § 61 — Individual room control as mandatory for new systems

§ 61 GModG (formerly § 61 GEG): Each room must be individually controllable
Solution: One heating circuit per room + thermostat = GModG compliant
Multiple circuits in one room without separate control: GModG violation
Exception: Rooms under 6 m² can be controlled together
In Austria, ÖNORM B 8130 applies, in Switzerland SIA 382 analogously

→Step 1: Fit the distribution box into the wall niche, align horizontally, and secure with anchors
→Step 2: Screw ball valves (flow top / return bottom) to manifold with PTFE sealing tape
→Step 3: Insert distributor into the box, snap in the retaining clips
→Step 4: Connect the underfloor heating pipes (flow and return) sequentially to the manifold connections – label the circuits!
→Step 5: Slowly fill the system with water via the ball valve, bleeding each circuit individually
→Step 6: Carry out pressure test with hand pressure pump at 6 bar for 30 minutes – no pressure drop = sealed
→Step 7: Screw actuators (E30NC-230) onto all manifold outlets, lay cables to room thermostats
→Step 8: Set flowmeter to target value (0.5–2.5 l/min per circuit depending on room size) and start heating

Achtung – Fachmann empfohlen

Threaded connections without sufficient PTFE sealant tape (at least 12 layers) lead to creeping leaks — especially on G 1" threaded connections.

Achtung – Fachmann empfohlen

Pressure testing to 6 bar MUST be carried out before closing the wall niche or before plastering — subsequent repairs are costly.

Frequently Asked Questions about Underfloor Heating Manifold Installation

The installation of the manifold itself (mechanical installation) is permitted without a master craftsman's certificate. The connection to the heating system (boiler side) should be carried out by a heating engineer if you do not have the necessary expertise - especially with heat pumps. You can document the pressure test yourself. GEG § 60 (Hydraulic Balancing) does not require a specialist company, but must be documented.

Experienced DIY enthusiasts need about 2–3 hours for a 4–6 circuit manifold, including bleeding and pressure testing. Initial installation without prior knowledge: 4–5 hours. Most time-consuming step: assigning and labeling the UFH pipes to the correct circuits (30–45 min.). A professional heating engineer needs about 1.5–2 hours but usually charges for half a working day.

Filling step by step: 1. Close all circuits on the manifold except circuit 1. 2. Slowly open the ball valve, fill the circuit until water exits the vent without bubbles. 3. Close the vent. 4. Open the next circuit, repeat. 5. All circuits open: Set system pressure to 1.5–2 bar. Important: never fill quickly — trapped air leads to noise (gurgling) and uneven heating.

Pressure drop > 0.1 bar in 30 minutes means there is a leak. Procedure: Check all threaded connections on ball valves and manifold connections with leak detection spray. Most common cause: insufficiently wrapped PTFE sealing tape. Remedy: loosen the fitting, re-wrap the sealing tape (12+ layers), and tighten again. Underfloor heating pipes themselves: leaks due to kinking or crushing usually occur during installation, not at the connection.

Upon initial startup: max. 25 °C flow temperature for 3 days (avoid screed curing phase – applies only to new builds). Then gradually increase to operating temperature. Operating temperature: heat pump 30–40 °C, gas heating 45–55 °C. Night setback for underfloor heating maximum 3–4 °C – too sharp a setback costs more energy than it saves, because the heating-up time becomes too long.

Labeling is not mandatory, but highly recommended — you'll be glad you did, especially during hydraulic balancing or troubleshooting. Standard: Metal signs or tape labels on the manifold, e.g., 'LR' (living room), 'BR' (bedroom), 'B1' (bathroom ground floor). Additionally: Photograph a sketch of the circuit layout and place it along with the manifold plan in the building services folder.

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