Written and maintained by CASRAI Editorial Board
Last updated
A laboratory chiller, more fully a recirculating chiller or circulating cooler, is a refrigerated unit that cools a liquid and pumps it around a closed loop to another instrument. It exists so that equipment such as a rotary evaporator or a reaction vessel can be held at a controlled temperature without running tap water through it. This page covers laboratory chillers, not the large chillers that cool buildings.
Who uses it: lab technicians, chemists and lab managers who run evaporators, reaction vessels or other sealed cooling circuits, and the buyers and facilities staff who site and maintain them.
What a laboratory chiller is
A laboratory chiller is an item of laboratory equipment that cools a sealed circulation system. BUCHI describes its F-325 Recirculating Chiller as “a closed-circuit cooler for use with evaporators”, intended for “cooling sealed circulation systems (e.g. evaporators, reaction vessels)” (BUCHI F-325 Operation Manual, sections 2.1 and 3.1, published 12.2023). Heidolph’s Hei-CHILL 400 Pro describes its intended use as “temperature control and circulation of suitable, non-flammable coolants in a closed temperature control circuit” (Hei-CHILL 400 Pro operating instructions, section 1.4).
In both manuals the chiller is a stand-alone box with a display or controller for the set temperature, connected by hoses to the instrument that needs cooling. The instrument’s heat goes into the circulating liquid, and the chiller removes it.
How a chiller works
A chiller has two circuits, and the Heidolph manual separates them clearly (section 2.2).
- The temperature-control circuit (coolant loop). A tank with a filler neck, a pump, and hose connections to the external circuit. The pump sends coolant out to the instrument and back. The Hei-CHILL measures coolant temperature with a PT 100 sensor.
- The refrigeration circuit. A sealed refrigerant circuit made of a compressor, a condenser, an expansion element and an evaporator. The compressor raises the pressure and temperature of the gaseous refrigerant. The condenser releases that heat to the ambient air, ventilated by a fan. The expansion element (a capillary tube in this model) lowers the pressure. The evaporator, a tube heat exchanger inside the coolant tank, extracts heat from the coolant as the refrigerant evaporates.
The BUCHI F-325 lists a similar set of parts: circulation pump, heat exchange container, thermostatic expansion valve, filter dryer, heat exchanger, compressor and an in-line valve (section 3.1.1). The practical point is that heat leaves the lab through the condenser, so a chiller needs air to move around it.
What it is used for
The two manuals name the same job: cooling a closed circuit. BUCHI names evaporators and reaction vessels. A chiller of this kind is the closed-loop alternative to cooling with once-through tap water, which is why it appears in sustainable lab practices. It is a separate unit from the instrument it serves; the rotary evaporator guide covers the evaporator side of that pairing.
Types and variants
The two manufacturer manuals read for this page differ in ways that matter to a user. Treat the table as a comparison of those two documented models, not as a complete catalogue of chiller types.
| Model documented | Stated use | Key difference stated in the manual |
|---|---|---|
| BUCHI F-325 recirculating chiller | Cooling sealed circulation systems such as evaporators and reaction vessels | Refrigerant R 513a (1100 g); control unit and display for set and actual cooling temperature; not to be used with flammable substances |
| Heidolph Hei-CHILL 400 Pro 115V | Temperature control and circulation of non-flammable coolants in a closed circuit | This model uses a flammable refrigerant, so the manual limits refrigerant per cubic metre of room volume |
Specifications that matter
The most useful single idea from the manuals is that cooling capacity is not one number. It depends on the temperature you set. The BUCHI F-325 data, measured at 20 °C ambient, shows it clearly (section 3.4).
| Set temperature | Cooling capacity, BUCHI F-325 |
|---|---|
| +15 °C | 2500 W |
| +10 °C | 2200 W |
| 0 °C | 1400 W |
| -10 °C | 800 W |
So a capacity figure quoted without a set temperature tells you little. Read the capacity at the temperature your process runs. The same F-325 table gives a temperature range of -10 °C to +25 °C, regulation accuracy of +/-1 °C, ambient operating range of 5 to 35 °C, a weight of 101 kg and dimensions of 1070 x 650 x 580 mm. The Hei-CHILL 400 Pro 115V states an ambient range of 5 to 31 °C, with humidity up to 80 % falling linearly to 50 % at 40 °C.
Siting, coolant and maintenance
Siting
Both manuals ask for free air around the unit, but with different distances. BUCHI asks for at least 40 cm of clearance on all sides, a firm level surface and an accessible outlet (section 5.2). Heidolph asks for at least 30 cm from the nearest object at the ventilation openings. The numbers differ by manufacturer, so use the figure in the manual for your model.
Coolant
- BUCHI warns that the wrong coolant risks damage and recommends ethylene glycol : water at 40 % : 60 % (section 5.5).
- Heidolph says to use only the manufacturer’s coolant, undiluted, not mixed with tap water. It says to check pH annually and replace the coolant if the pH is below 7, or if it is discoloured, smelly or the circuit is clogged. It also says to protect the coolant from sunlight and use hoses rated for at least 5 bar (section 3.4).
Routine maintenance
BUCHI lists checking the coolant level before each use, cleaning the ventilation slots with compressed air, and exchanging the coolant as set out in the manual (sections 7.4 to 7.6). It also says to empty the tank before transport or storage. Heidolph restricts condenser cleaning to instructed, competent personnel (section 5.1).
Safety
- BUCHI states the chiller may not be used with flammable substances or in explosive atmospheres (section 2.2).
- Direct contact with the refrigerant “can cause freeze burns and eye injuries”, so BUCHI says to wear goggles and gloves (section 2.6.2).
- For the flammable-refrigerant Heidolph model, the manual says to prevent more than 8 g of refrigerant per cubic metre of room volume. Its worked example is 100 g / 8 g per m³ = 12.5 m³ of room. This is that model’s rule, not a general one.
- BUCHI notes the refrigerant is toxic and must not enter soil or groundwater at disposal.
For related reading, see lockout-tagout for lab equipment service, and the lab safety equipment checklist for the wider picture.
Common mistakes
- Using a coolant the maker does not specify. Both manuals tie coolant choice to the model.
- Blocking the ventilation openings. The condenser rejects heat to room air, and both manuals set minimum clearances.
- Reading capacity at the wrong temperature. Capacity at +15 °C is not capacity at -10 °C.
- Using a chiller with flammable substances. BUCHI prohibits it, and Heidolph describes non-flammable coolants only.
- Skipping the pre-use level check. BUCHI lists it before each use.
Frequently asked questions
How does a chiller work?
A refrigeration circuit (compressor, condenser, expansion element, evaporator) removes heat from a liquid in a tank, and a pump circulates that cooled liquid through a closed loop to the instrument being cooled.
What is a chiller used for?
In the laboratory, cooling sealed circulation systems such as evaporators and reaction vessels, per the BUCHI manual.
Why not use tap water?
A closed-loop recirculating chiller replaces once-through tap water cooling, which is why chillers feature in sustainable lab practices.
Sources
- BUCHI, Recirculating Chiller F-325 Operation Manual, published 12.2023: manual (PDF). Read 2026-10-29.
- Heidolph, Hei-CHILL 400 Pro 115V operating instructions: manual (PDF). Read 2026-10-29.
