Union-Connection Threaded Circulation Pumps
Union-connected (threaded) circulation pumps for residential heating, underfloor heating, and solar circuits: 130 and 180 mm models, including variable frequency drive (VFD) versions.
Products (34)
- DAB Evoplus 40/180XM Variable Frequency Drive Circulation Pump, 180 mm, for 18–25,000 Boilers, 4.2 m, 7.5 m³/h – $509.46
- DAB Evoplus Lite 60/180-32 Variable Frequency Drive Circulation Pump, Union Connection, 2", 180 mm – $872.53
- DAB Evosta2 40-70 Variable-Speed Circulation Pump, 130 mm, 40,000–60,000 kcal/h Boiler, 6.9 m, 3.6 m³/h – Request a quote (out of stock)
- DAB Evosta3 40-180 Variable-Speed Circulation Pump, 180 mm, for 18,000–25,000 kcal/h Boilers, 4 m, 2.9 m³/h – $215.48
- Duca Cosmo 25-8 Variable-Speed Circulation Pump, 180 mm, 8 m – Request a quote (out of stock)
- Forza FRZ-SXR 25-6-130 Circulation Pump, 3-Speed, 130 mm – $70.00
- Grundfos ALPHA1 25-40 (180 mm) VFD Circulation Pump for 18,000–25,000 kcal/h Boilers, 4 m, 2.6 m³/h – $259.17
- Grundfos ALPHA2 25-40 (180 mm) Circulation Pump with VFD, for 18,000–25,000 kcal/h Boilers, 4 m, 2.6 m³/h – $331.32
- Grundfos ALPHA3 15-40 (130 mm) Variable Frequency Drive Circulation Pump, 18,000–25,000 kcal/h Boilers, 4 m Head, 2.6 m³/h – Request a quote (out of stock)
- Grundfos MAGNA1 25-40 (180 mm) VFD Circulation Pump for 60–80,000 Boiler, 4 m, 6.2 m³/h – $393.91
- Grundfos UPS2 25-80 Variable-Speed Circulation Pump, 180 mm, 40,000–60,000 kcal/h Boiler, 8 m, 5.6 m³/h – Request a quote (out of stock)
- Grundfos UPS 25-40 N 180 Circulation Pump, 4 m, 3 m³/h – Request a quote (out of stock)
- Kentaş AUTO 25-6/130 Variable-Speed Circulation Pump, 45 W – Request a quote
- Master EVOMAG 25/180.10 Union-End Circulation Pump, 180 mm, 12 m³/h, 10 m, 185 W, 1.1/2'' – Request a quote (out of stock)
- Micra APF 25-6-130 Variable-Speed Circulation Pump, Combi Boiler, Boiler, 6 m, 3 m³/h – Request a quote (out of stock)
- Nortek SRF 25-130 VFD Circulation Pump, Union Connection, 1-1/2'', 250mm – $180.00
- Sumak SSP 25/6-130 INV VFD Circulation Pump, 6 m, 4.8 m³/h – $189.60
- Taifu GRC 25/7-130 Variable-Speed Circulation Pump, 52 W, 130 mm – $78.02
- Taifu GRS 32/12-M Circulation Pump, 370 W, 2" – $134.10
- Welko GPA 25-8 130 mm Variable-Speed Drive Circulation Pump, 8 m, 4.9 m³/h – $79.41
- Welko GPA 25-8 IV Variable-Speed Circulation Pump, 8 m, 6.5 m³/h – $196.57
- Welko LPA 25-8 VFD Circulation Pump, 130 mm, 8 m, 4.2 m³/h – $116.62
- Welko WLK 32-12 EA Variable-Speed Circulation Pump, 180 mm, 12 m, 11 m³/h – $204.37
- Wilo ATMOS MAXO1.0 25/0,5-8 Variable-Speed Circulation Pump, 180 mm, 1 inch – $539.78
Brands: DAB · Duca · Forza · Grundfos · Kentaş · Master · Micra · Nortek · Sumak · Taifu · Welko · Wilo
What is a union-connected circulation pump?
Union-connected circulation pumps are compact circulating pumps that connect to pipework via threaded unions. They are widely used in radiator heating systems in detached houses, villas, and apartments; underfloor heating circuits; solar collector lines; solid-fuel boilers; and domestic hot water recirculation. Despite their small size, they operate quietly and consume little electricity.
Model types
- Variable frequency drive (VFD) models: Automatically adjust speed to match system demand, providing energy savings.
- Multi-speed models: Operate at several manually selectable speed settings; an economical option.
- 130 mm and 180 mm installation-length models: Selected to match the length of the existing pump in the installation.
- Bronze or stainless steel body models: Resistant to corrosion in domestic hot water lines.
The category includes models from brands such as Wilo, Grundfos, DAB, Welko, Sumak, Taifu, and Kentaş.
Selection recommendations
Codes such as "25/6" or "15-40" in product names typically indicate the connection size and maximum head for most manufacturers; some manufacturers express head in decimetres (e.g., 40 means 4 metres). Some products also state the compatible boiler capacity in kcal/h, which is a practical reference for residential installations. When replacing an existing pump, note the installation length, connection size, and electrical connection type. Do not use a pump intended for heating water on a domestic water line; pumps that will come into contact with drinking water must be specified as suitable for that purpose.
Installation and initial start-up
The arrow on the pump indicates the direction of water flow. During installation, the shaft must remain horizontal, and a ball valve should be placed on each side of the pump so the entire system does not need to be drained for replacement. On initial start-up, the system must be completely filled and bled of air. On VFD models, selecting the operating mode (constant pressure, proportional pressure, etc.) to suit the system improves efficiency.
Frequently asked questions
Which pump is suitable for underfloor heating?
Underfloor heating circuits typically consist of longer pipes, so a VFD model with sufficient head is preferred.
Does the installation need to be drained to replace the pump?
If valves are fitted on both sides of the pump, only that section needs to be isolated for replacement.
How much electricity does it consume?
The power drawn by VFD models varies with demand and is generally at low wattage levels; a range is given in the product information.
Can it be used in a solar circuit?
Only models specified as suitable for the temperatures and antifreeze-mixed water found in collector circuits should be used.
What do you recommend for larger buildings?
For central systems, you can look at flanged circulation pumps.