Heating circuit manifold heat pump: Hydraulics & KfW 458 (2026)

Manifold for Heat Pumps: Hydraulics, Temperature Spread & KfW 458 (2026)

Heat pump and underfloor heating: The perfect combination – but only if the heating circuit distributor is correctly sized and set. Differential temperature, volumetric flow, material requirements, and KfW 458 funding compactly explained.

⏱ 10 min. read

COP-optimized spread 5 K

KfW 458: up to 80% funding

Why HP + UFH is the Most Efficient Combination

Tools & Aids

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

Requirements: What your system needs to have

→Set manifold position: max. 20 m from the boiler/HP, central to all heating circuits — minimizes pipe lengths and pressure loss
→Pre-run 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 cleared for surface-mounted installation
→230V power within reach for actuators and room thermostat cables (if desired)

Manifold for heat pump: Hydraulic diagram, settings & funding

The combination of a heat pump + underfloor heating is the most efficient heating technology for new buildings and energetically renovated old buildings. The heating circuit distributor is the link between the heat pump and the surface heating system — if it is incorrectly sized or set, it significantly reduces efficiency.

35 °COptimal flow temp. HP+UFH
(vs. 55 °C for boiler)

5 KSpread flow-return
Optimal for HP efficiency

+30 %Higher COP with UFH
vs. radiator system

System diagram: Heat pump with heating circuit distributor

Hydraulic diagram HP + UFH distributor (single-family house)

Heat pumpFlow 30–45 °C
Inverter-controlled

Primary
circuit

Buffer tankopt. 50–200 L
Hydraulic separator

Secondary
circuit

Heating circuit
distributorStainless steel DN 25
Flow meter per circuit

PE-RT
Ø 16–20 mm

UFH circuits10–15 cm spacing
Screed/Dry

Buffer tank or hydraulic separator prevents heat pump cycling — saves 10–25% electricity

Requirements for the distributor in HP operation

Property	Requirement for HP	Why?
Material	Stainless steel V2A (1.4301)	HP generates slightly acidic condensate (pH 6.5–7.2) — brass corrodes
Flow temperature	30–45 °C (design)	The lower the flow temp., the higher the HP's COP (each K saves ~2.5%)
Set spread	5 K (not 10 K!)	HP optimal with small spread: 5 K instead of 10 K → higher volume flow → better HP efficiency
Pipe spacing	10–12 cm	More heating surface → lower flow temp. possible
Flow meter setting	Higher volume flow needed	5 K spread = double volume flow vs. 10 K → open flow meter accordingly
Hydraulic balancing	Mandatory — GModG § 60	Without balancing: HP runs inefficiently, KfW 458 funding is forfeited
Buffer tank/separator	Recommended (50–200 L)	Prevents HP cycling, extends lifespan

Optimally adjust distributor for HP

Set spread to 5 K

HP flow e.g. 35 °C → return should measure 30 °C. Open flow meter per circuit until return temperature rises (more flow = smaller spread).

Volume flow according to heating load

Formula: V̇ = Q / (c × ρ × 5 K). Example: 600 W room → 103 l/h target flow. Adjust flow meter accordingly.

Adjust heating curve

Set HP heating curve (flow temperature depending on outside temperature) flat: gradient 0.5–0.8. The better insulated the building, the flatter.

KfW 458: Secure funding

Hydraulic balancing is mandatory for KfW-458 proof. Perform yourself with a flow meter distributor, keep the log — no specialist company necessary.

KfW 458 (from July 2026): Funding for HP + UFH system

Basic funding: 30% of eligible costs (max. €30,000 cost basis)
Climate speed bonus: +20% for replacing an oil/gas heating system before 2030
Income bonus: +30% for households with annual income under €40,000
Combination possible: up to 80% total funding rate achievable
Application via KfW Federal Funding, BAFA supplementary application for remaining costs

Heat pump + UFH distributor: What applies to DACH

In Germany, heat pumps will be de facto mandatory for new builds from 2026 (GModG requirements for EE share). In Austria, § 19 OIB-RL 6 applies, and in Switzerland, BAFU supports through cantonal programs. The heating circuit distributor as a central component of the low-temperature system must be dimensioned according to EN 1264-4 in all DACH countries.

→Step 1: Fit distribution box into wall recess, align horizontally, and secure with anchors
→Step 2: Screw ball valves (flow top / return bottom) to manifold with PTFE tape
→Step 3: Insert distributor into the box, snap retaining clips into place
→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 all circuits 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 slow 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.

Frequent questions about underfloor heating manifold installation

The installation of the manifold itself (mechanical installation) is permitted as a craft without the need for a master craftsman's license. The connection to the heating system (boiler side) should be carried out by a heating engineer if there is no specialized knowledge — especially for heat pumps. You can document the pressure test yourself. GEG § 60 (Hydraulic balancing) does not require a specialized company, but must be documented.

Experienced DIYers 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 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 for circuit 1. 2. Slowly open the ball valve, fill the circuit until water exits the air vent without bubbles. 3. Close the air vent. 4. Open the next circuit, repeat. 5. With 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 screw connection, re-wrap the sealing tape (12+ layers), tighten again. UFH pipes themselves: Leaks due to kinking or crushing usually occur during installation, not at the connection.

Upon initial start-up: max. 25 °C supply temperature for 3 days (avoid screed burn-in 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 large a setback costs more energy than it saves, as the heating-up time becomes too long.

Labeling is not mandatory, but highly recommended — you'll be glad you did, at the latest when performing hydraulic balancing or troubleshooting. Standard: Metal tags or adhesive 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 with the manifold plan in the building services folder.

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