Non-mixing pump sets for heat pumps: how they connect, flow rates and which to choose

Our guide to underfloor heating with a heat pump explains why heat pumps and floors work well together and why you rarely need a blending valve. This guide picks up from there. It covers what a non-mixing set does, how it connects to the heat pump, how to check flow rates and pump head, PWM control, and which set to buy.

What is a non-mixing pump set?

A non-mixing pump set is the pump and pipework block that sits between the heat pump primary pipes and the manifold. It takes the heat pump's flow and return and drives water round the floor loops. Unlike a blending pack, it has no thermostatic valve, so the floor gets the heat pump's flow temperature directly.

The MaxHeatUFH sets:

• bolt straight onto the manifold flow and return bars
• take the primary flow and return from the side or bottom
• can be fitted left- or right-hand, to suit where the pipes arrive
• are rated to 10 bar and take a standard 130mm pump with 1½in unions

The pre-assembled Grundfos version is also called a heat pump circulation pack.

When should I use a non-mixing set instead of a blending pack?

Use a non-mixing set when nothing in the system can send water to the manifold hotter than the floor allows. The Danfoss underfloor heating handbook gives a maximum supply temperature of 55°C for cement and calcium sulphate screeds and 50°C for gypsum based floors.

Most heat pumps heat the hot water cylinder through a diverter valve, so the hotter water for the cylinder doesn't go to the floor. Even so, set the maximum space heating flow temperature in the heat pump controller to your floor's limit. With a non-mixing set, that setting is the floor's only protection.

How does a non-mixing set connect to a heat pump?

It connects to the heat pump's heating flow and return, either directly or through some form of hydraulic separation, and the right answer depends on the heat pump. Most heat pumps have their own internal pump. Adding a second pump on the manifold means two pumps on one circuit, and they need to work together.

The common layouts are:

• Direct. The heat pump pump and the manifold pump share one circuit. Simple, but the two pumps affect each other's flow, so it only works where the heat pump maker allows it.
• Buffer tank. The heat pump heats a buffer and the manifold pump draws from it. Adds water volume, which some heat pumps need.
• Low loss header or closely spaced tees. Separates the two pump circuits with very little pressure drop between them, so each pump can be sized for its own side.

Heat pump manuals set the rules. For example, one maker's cylinder unit manual shows two positions for a second pump, says to install a buffer tank if the system water volume is too low, and sets a default minimum primary flow of 5.0 L/min before the unit shows a flow error. Separation can lower the temperature reaching the floor if flows don't match, so follow the manual for your model and your designer's layout.

Do I need a manifold pump at all with a heat pump?

Not always. Some designs run the loops from the heat pump's own pump with no pump on the manifold, which avoids two pumps fighting. This only works when the heat pump pump has enough spare head for the longest loop plus the manifold and pipework, and the maker allows it.

A pump on the manifold is the safer choice when:

• the manifold is a long way from the heat pump
• there are many loops, or long ones near the 100m limit for 16mm pipe
• there is a buffer, low loss header or second manifold
• the heat pump maker's pump curve shows too little spare head at the flow you need

If you go without a manifold pump, the manifold still needs actuators and flow meters. Our auto-balancing manifold keeps each loop at its preset flow as zones open and close.

How do I work out the flow rate for a heat pump floor?

Divide the heat output by the temperature drop: flow in litres per minute = kW × 14.35 ÷ ΔT, where ΔT is the flow minus return temperature in °C. This comes from the heat carried by water, about 4.18kJ per kg per °C.

Worked example: a 6kW floor with 8 loops, designed at ΔT 5°C, needs 17.2 L/min in total, or about 2.2 L/min per loop. That sits well inside the 0 to 4 L/min flow meters on our auto-balancing manifold. If the heat pump needs a higher minimum flow than the floor gives with some zones closed, keep enough loops open or follow the maker's advice on a bypass or buffer.

What pump head do I need?

For most single manifolds a 6m pump is enough, and a 7.5m pump suits larger floors or long loops. The Danfoss handbook says the pressure loss of a heating circuit should not exceed 250 mbar, because the pump must also cover the manifold, valves and pipework.

One metre of head is about 98 mbar, so 250 mbar is about 2.5m. A 6m pump has room for the loop plus the rest of the system at domestic flow rates. Pick 7.5m if the manifold is far from the heat pump, if loops are close to 100m, or if the design flow per loop is high. Our guide to choosing a UFH pump compares the pumps and their settings.

Should the heat pump control the pump speed by PWM?

If the heat pump has a PWM output and the maker recommends it, yes. PWM lets the heat pump speed the floor pump up or down to hold the flow and temperature drop it wants.

• Grundfos UPM3 Flex. Takes a PWM speed signal through its signal connector. Grundfos lists this pump for the heating side of heat pumps. Its data booklet says the heating profile runs at full speed below a 10% signal and varies speed between 10% and 84%.
• Bastion. Add the Bastion PWM signal cable (£9) to use speed control.
• Wilo 6m. Runs on its own settings, with no PWM connection listed.

If the heat pump has no PWM output, any of the pumps will run on its own setting. Never connect a PWM signal to a pump unless the heat pump manual describes that connection.

Which non-mixing set should I buy?

Choose by control, then by head. All of these bolt to the manifold and are pre-assembled except the no-pump version.

Prices October 2026. The no-pump set suits jobs where the heat pump maker names a specific pump.

How do I fit a non-mixing pump set?

1. Mount the manifold and decide which side the primaries will arrive from. Fit the set left- or right-hand to suit.
2. Bolt the set to the manifold flow and return bars with the supplied seals.
3. Fit isolating valves on the primary flow and return, so you can work on the pump without draining the system.
4. Connect the heat pump flow to the set's flow side and the return to the return side, from the side or bottom.
5. Have an electrician wire the pump to the wiring centre's pump output, and the PWM lead to the heat pump if used.
6. Fill, vent and pressure test the loops, then set the pump mode and balance each loop to its design flow.
7. Check the heat pump reaches its minimum flow with the fewest zones open, and set its maximum heating flow temperature.

Products for this job

• UFH Non-Mixing Pump Set with Grundfos UPM3 Flex (pre-assembled)
• UFH Non-Mixing Pump Set with Bastion 6m pump
• UFH Non-Mixing Pump Set with Bastion 7.5m pump
• UFH Non-Mixing Pump Set (no pump)
• Auto-Balancing Stainless Steel UFH Manifold
• Bastion Replacement Pump Cables (power or PWM)
• All heat pump connection products

Frequently asked questions

What is the difference between a mixing and non-mixing UFH pump set?

A mixing set has a blending valve that lowers hot water to floor temperature. A non-mixing set has no valve and sends the heat source's own temperature to the floor, which suits heat pumps. See mixing and blending valves explained.

Can I use a non-mixing pump set with a boiler?

Only if the boiler can never send water hotter than the floor allows. Most boilers run hotter for radiators or a cylinder, so use a blending valve pack with a boiler.

Do I need a low loss header with a heat pump and underfloor heating?

Sometimes. It depends on the heat pump, the water volume and whether there is a second pump. Some makers want a buffer or separation, others prefer a direct connection. Follow the heat pump installation manual.

Is a heat pump circulation pack the same as a non-mixing pump set?

Yes. Both names describe a manifold-mounted pump set with no blending valve for low temperature heat sources.

Which way round does a non-mixing pump set fit?

Ours can be fitted left- or right-hand and take the primary pipes from the side or bottom, so you can fit them to suit where the pipes arrive.

Can I fit my own pump to a non-mixing set?

Yes. The no-pump set takes any 130mm pump with 1½in unions, such as the Grundfos UPM3 Flex, Bastion or Wilo pumps we sell.

Sources: Danfoss underfloor heating handbook, Mitsubishi Electric Ecodan cylinder unit installation manual, Grundfos UPM3 data booklet, Worcester Bosch TB 0137: hydraulic separation via closely spaced tees