Underfloor Heating Heat Pump Control: Maximize COP with Engo ZigBee

Q: Why is underfloor heating better for the heat pump than radiators?

Heat pumps are physically designed such that their efficiency (COP) increases as the flow temperature decreases. Radiators require a flow temperature of 55–70 °C — at this temperature, an air-to-water heat pump only achieves a COP of 2.5–3.0. Underfloor heating systems operate with a flow temperature of 30–35 °C — at this temperature, the same heat pump achieves a COP of 4.0–4.8. This means that with underfloor heating, the heat pump consumes 40–50% less electricity for the same amount of heat compared to radiators.

Q: Which Engo thermostats are best suited for heat pumps?

Recommendation: EONE-230V (ZigBee, €64.09) combined with ECB62-ZB control box (€95.43) and EGATE-PRO gateway (€61.81). This system uses TPI for precise, heat pump-friendly control (±0.5 °C), stores time programs locally for reliable offline operation, and allows individual room profiles for each zone. The offline function is particularly important for heat pumps: if the internet fails, the system continues to heat according to the stored heat pump-optimized schedule.

Q: Can I set the night setback on a heat pump to 16 °C?

No — that is the most common mistake with heat pump + underfloor heating systems. With a night setback of 16 °C (instead of 20 °C), the heat pump has to make up for a 4 °C screed temperature difference in the morning. This takes 3–6 hours and forces a high flow temperature (40–50 °C) — the most inefficient mode of operation. Recommendation: a maximum 2–3 °C setback at night, start the heating program 2–3 hours before getting up. This saves more energy than a more aggressive setback.

Q: Do I have to meet GEG § 61 for individual room control with a heat pump?

Yes. GEG § 61 mandates room-by-room temperature control when replacing a heating system (e.g., installing a heat pump). Failure to implement individual room control risks denial of BAFA funding and fines. In practice, this means: one thermostat + actuator per heating circuit. Engo systems fully comply with GEG § 61.

Q: What is the TPI algorithm, and why is it more important for heat pumps than for gas?

TPI (Time Proportional & Integral) modulates the on-time of the actuators proportionally to the temperature difference — not a hard on/off, but gentle opening pulses. For gas heating, this improves comfort. For heat pumps, it is crucial for efficiency: if all actuators open abruptly and simultaneously, a hydraulic shock is created in the system — the heat pump must briefly go into high-temperature operation. TPI prevents this shock by staggered, proportional opening. The result: stable flow temperature, no heat pump cycling, maximum COP.

Q: Is ZigBee single-room control financially worthwhile for a new heat pump?

Yes. A 4-zone ZigBee system (EONE ×4 + ECB62-ZB + EGATE-PRO + actuators ×4) costs approximately €380–450. For a heat pump with an annual electricity consumption of e.g. 3,500 kWh, precise individual room control, through optimized COP operation, saves approximately 20–30% — i.e., 700–1,050 kWh × €0.30/kWh = €210–315 per year. Amortization in 1.5–2 years. Additionally, there may be requirements for BAFA funding (individual room control as mandatory proof).

Q: How do I set the heating curve of the heat pump when using Engo thermostats?

The heating curve is set directly on the heat pump—independently of the room thermostats. Recommendation: Flatten the heating curve so that at an outdoor temperature of -10 °C, a maximum flow temperature of 38–40 °C is reached, and at 5 °C outdoor temperature, approximately 28–30 °C. The Engo thermostats then regulate, room by room, which heating circuits actually demand heat at this flow temperature. Important: Hydraulic balancing at the manifold ensures that all circuits are flowed through evenly—otherwise, individual rooms will lose heating capacity when the heating curve is flattened.

Q: How does PV power improve the economic efficiency of heat pump-UFH?

A 5 kWp photovoltaic system generates 1–3 kWh of surplus electricity daily during the heating season, which would otherwise be fed into the grid. Using Tuya automation or Home Assistant, the heat pump can switch to an elevated setpoint (1–2 °C above normal) during these times and use the concrete as a thermal storage. Result: 200–400 kWh/year of self-consumption instead of grid feed-in — with savings of 25 ct/kWh vs. an 8 ct/kWh feed-in tariff: approx. €50–100/year.

Q: How do I set the heating curve of the heat pump when using ENGO thermostats?

With ENGO thermostats, the room temperature controls the actuators (individual room control). The heat pump heating curve should set the flow temperature to the minimum that supplies all rooms – typically 30-40 °C for insulated houses, 35-45 °C for older buildings. The thermostats close zones when the set temperature is reached. Guideline: If more than 2 zones are closed simultaneously, the heating curve is set too steeply.

Underfloor Heating Heat Pump Control: Maximize COP with Engo ZigBee

A heat pump and underfloor heating are the most efficient heating pair—but only with the right controls. This guide explains why a flow temperature of 30–35 °C is the key to COP 4.0+, why the TPI algorithm is indispensable for HP systems, and what most operators do wrong with night setback. Includes concrete Engo product recommendations, setup instructions, and a cost calculation for 2026.

⏱ 13 min read

COP up to 4.8 at 35°C flow temperature

Night setback max. 2–3 °C with HP

Requirements for WP-optimized FBH operation

This is what you should check before setup

→Check the heat pump's flow temperature: Can it be set to 30–35 °C? (hydraulic balancing required)
→Is individual room control available? GEG § 61 stipulates room control when replacing the heating system
→Heating manifold with actuators (NC, M30×1.5) for zone-by-zone shut-off, accessible
→Determine the number of heating circuits/rooms — recommended: 1 thermostat + 1 actuator per room
→Clarify heat pump type: air-to-water, brine-to-water, or water-to-water — all benefit from low flow temperatures

COP Table: How Flow Temperature Determines Efficiency

The COP (Coefficient of Performance) of a heat pump indicates how much thermal energy is generated per kWh of electricity consumed. The flow temperature is the decisive factor: at 55 °C (radiator level), an air-to-water heat pump typically achieves a COP of 2.5–3.0. At 35 °C (underfloor heating optimum), the COP increases to 4.2–5.0. Every Kelvin reduction in flow temperature improves the COP by approx. 2.5–3 %.

Flow Temperature & Efficiency — Concrete Figures

Flow Temperature	Application Area	COP (typical)	SCOP (Annual Performance Factor)	Recommendation
30 °C	Underfloor Heating Passive House / KfW 40	5.0 – 6.0	5.5 – 6.0	✓ Optimal
35 °C	Underfloor Heating Insulated House (WSchVO)	4.2 – 5.0	4.5 – 5.5	✓ Very Good
40 °C	Underfloor Heating Old Building without Additional Insulation	3.5 – 4.2	3.8 – 4.5	○ Good
45 °C	Low-Temp Radiators	3.0 – 3.5	3.2 – 4.0	○ Acceptable
55 °C	Standard Radiators	2.5 – 3.0	2.8 – 3.5	✗ Uneconomical

✓ Underfloor heating + heat pump at 35 °C flow temperature saves approx. 35–50 % of electricity costs compared to radiator operation at 55 °C — which corresponds to a saving of 420–600 €/year for heating costs of 1,200 €/year.

Hydraulic Balancing: Underestimated Efficiency Lever

Without hydraulic balancing, individual heating circuits are over-flowed — the heat pump increases the flow temperature for the worst circuit, all others overheat. Result: SCOP loss of up to 15 %. Solutions:

Method 1: Manual presetting of the flow valves at the manifold according to heat load calculation according to EN 12831.
Method 2: Automatic hydraulic balancing by motorised actuators with flow measurement (e.g. ELV motorised).
ENGO solution: TPI algorithm with ±0.1 °C precision in EONE thermostats approximates balancing through precise pulse width modulation — in practice typically < 5 % deviation.

The Night Setback Trap for Heat Pumps

⚠ Night setback to 16–17 °C is often counterproductive for heat pumps: Instead of saving energy, the heat pump has to heat up in the morning at maximum power (worst COP). Guideline: Night setback max. 2–3 °C below comfort temperature, heating time 60–90 min. Start underfloor heating before wake-up time. EONE time program with early preheating start is more efficient than a strong setback.

KfW 458 & BAFA: Funding 2026 for Heat Pump + Underfloor Heating Control

KfW 458 (from July 2026): Up to 80 % funding rate for heat pump installation, max. 28,000 € eligible costs — underfloor heating control is an eligible accompanying measure.
BAFA BEG EM: 15 % (20 % with iSFP) on thermostats & control boxes — can be combined with KfW 458.
PV Surplus Heating: Smart thermostats enable preheating with surplus solar power (via Tuya automation or Home Assistant) — with 5 kWp PV, approx. 200–400 kWh/year can be used additionally.

Set up WP-Optimized Control in 5 Steps

Step 1: Reduce flow temperature to 30–35 °C: The biggest single measure for heat pump efficiency is lowering the flow temperature. Every degree less improves the COP by approx. 2.5%. At a flow temperature of 35 °C instead of 45 °C, the COP increases from approx. 3.5 to approx. 4.5 — that's 28% less power consumption for the same heating output. Prerequisites: sufficient heating surface in the floor (typically 8–12 W/m² at 30 °C flow), correctly laid heating pipes (15 cm spacing) and hydraulic balancing at the manifold. Engo thermostats with TPI algorithm precisely maintain this low flow temperature without overheating individual rooms.

Step 2: Activate individual room control: Without individual room control, the heat pump heats all rooms simultaneously – rooms that are already warm (south-facing, kitchen with cooking heat) continue to heat up and force the heat pump to operate at a higher output. With Engo ZigBee thermostats in each room, actuators automatically close the warm circuits: the heat pump only supplies the truly cool rooms at a constant low flow temperature. The result: fewer cycles, better COP stability, precise room temperature (±0.5 °C).

Step 3: Adjust night setback for HP accordingly: Gas and oil heating systems allow for night setbacks of 4–6 °C because they heat up quickly. Heat pumps cannot do this: the thermal mass of the underfloor heating (screed, floor structure) takes 3–6 hours to catch up by 4 °C with a heat pump. Too large a setback forces the heat pump into high-temperature operation in the morning – precisely what destroys the COP. Recommendation for heat pumps: night setback max. 2–3 °C, start the heating phase 2–3 hours before waking up. In the Engo EGATE-PRO, these time programs are stored locally and run reliably even without an internet connection.

Step 4: Configure the TPI thermostat: All Engo thermostats (Easy-230, EONE, E25) use the TPI (Time Proportional & Integral) algorithm: Instead of simply switching the actuator on/off, TPI modulates the ON-time proportionally to the temperature difference. This means that if the room is 0.5 °C below the setpoint, the actuator only opens briefly—whereas at a 3 °C difference, it opens significantly longer. This is crucial for the heat pump: No abrupt opening of all circuits simultaneously, no pressure surge in the hydraulic system, no unnecessary cycling. TPI keeps the flow temperature stable and the heat pump in efficient continuous operation.

Step 5: Set up ZigBee system & create schedules: The EGATE-PRO Gateway connects all EONE thermostats via ZigBee 3.0 Mesh. Time programs are stored locally on the gateway — no internet needed for heating operation. For heat pump-optimized operation, the following programs are recommended: Living room 20 °C (6:00–22:00), 18 °C (22:00–6:00); Bedroom 17 °C (22:00–6:00), 19 °C (6:00–22:00); Bathroom 22 °C (6:00–8:00, 19:00–21:00), 19 °C otherwise. The Engo Smart App allows changes on the go — e.g., activating vacation mode with frost protection at 12 °C.

COP Comparison & System Data 2026

Parameter	Value
COP at 55 °C flow temperature (standard radiators)	approx. 2.5–3.0
COP at 45 °C flow temperature	approx. 3.2–3.8
COP at 35 °C Flow Temperature (Underfloor Heating Optimum)	approx. 4.0–4.8
Efficiency gain per 1 °C flow temperature reduction	approx. +2.5% COP
Ideal Living Room Temperature (HP Mode)	20 °C
Ideal Bedroom Temperature	62.6–64.4 °F
Optimal night setback for heat pump (max. value!)	2–3°C
Control accuracy Engo TPI thermostat	±0.5 °C
Engo EONE-230V ZigBee Thermostat	€64.09
Engo ECB62-ZB Control Box (8 Zones ZigBee)	€95.43
EGATE-PRO Gateway (Offline Time Programs)	€61.81
Actuator E30NC-230 (per heating circuit)	€9.50
4-Zone ZigBee Complete System	approx. €380–450
Amortization (30% heat pump efficiency gain)	a heating season

FAQ: Heat Pump + UFH Control