Freeze Protection Valve: Function, and Working Principle

A freeze protection valve, also known as an anti-freeze valve, reduces the risk of flow blockage caused by freezing. With thermostatic technology, the valve reacts automatically to low water temperatures and prevents ice formation inside the pipe. For those who want to understand what this device is, how it works, and how to choose the right solution, this article explains the key points clearly and practically.

Many users try alternative methods to avoid frozen pipes, such as temporarily shutting down the system, closing isolation valves, or relying only on heat tracing. In practice, these methods are often inconvenient and ineffective, especially during unexpected power outages or system failures. In such conditions, a freeze protection valve provides a more reliable and passive safety solution.

What Is a Freeze Protection Valve?

In simple terms, a freeze protection valve is a special valve designed to prevent water from freezing inside a piping system. When the water temperature approaches the freezing point, the valve opens automatically and releases water from the pipe, reducing the risk of ice formation and excessive internal pressure.

Freeze protection valves are widely used in household systems, HVAC installations, heat pump circulation systems, and industrial applications. Because system requirements vary, it is important to select products with suitable specifications, materials, and temperature settings.

Freezing does not only occur during extreme winter conditions. In many systems, freezing risk appears when circulation stops, such as during power failure or control malfunction. Outdoor pipes connected to heat pumps, water heaters, or exposed installations are particularly vulnerable to this type of freeze event.

How the Freeze Protection Valve Works

Closing or isolating a valve does not prevent freezing. In many cases, freezing starts inside the pipe rather than in the valve body itself. For effective protection, water must be released before ice can form.

A freeze protection valve uses a temperature-sensitive element that reacts directly to the water temperature inside the valve. When the temperature drops to a preset value, the valve opens and drains water from the pipe. When the temperature rises again, the valve closes automatically.

Open and Close Function

• When the water temperature drops to the opening point, the thermostatic element activates and the valve opens. This passive response occurs without any electrical input or manual intervention, making the valve functional even during complete power outages.
• Water is discharged from the pipe, reducing freezing risk and internal pressure. The drainage continues until the temperature rises back above the closing threshold, preventing ice from forming and accumulating inside the pipe wall.
• When the water temperature increases to the closing point, the valve closes and normal system operation resumes. The valve is designed for repeated thermal cycling over the life of the system without loss of performance or sealing integrity.

This automatic process does not require electricity and continues to function even during power outages.

Freeze Protection Valves for Different Applications

Not all freeze protection valves work in the same way. Different systems require different temperature settings and flow characteristics.

Freeze Protection Valve for Heat Pump Systems

In closed-loop heat pump circulation systems, freezing commonly occurs in outdoor piping when circulation stops unexpectedly. According to the International Energy Agency, heat pumps are increasingly deployed in cold climates where outdoor piping freeze protection is a critical design requirement. For this application, anti-freeze valves are designed to open at a relatively low temperature and drain the circulating water quickly.

A typical heat-pump anti-freeze valve opens when the water temperature drops below 3°C and closes again when the temperature rises above 4°C. These valves are designed for continuous water circulation systems and must be installed vertically with the outlet facing downward to allow proper drainage.

Key characteristics generally include:

• Brass valve body suitable for outdoor conditions. Brass provides the corrosion resistance and durability required for installation in exposed outdoor environments where the valve may be subject to weathering and temperature cycling across its full service life.
• Working pressure up to 10 bar. This pressure rating ensures the valve remains sealed and functional across the full range of normal operating pressures found in residential and commercial heat pump systems.
• Ambient temperature resistance down to -30°C. The valve material and thermostatic element are rated to remain structurally intact and thermally responsive at extreme ambient temperatures, which is essential for reliable operation in cold climates.
• High flow capacity to release water efficiently. A high KV value ensures the valve can drain the pipe volume quickly when the temperature drops, preventing ice from forming before the drainage is complete.

This operating behavior is represented by the 910078NT Anti-Freeze Valve, which is designed specifically for heat pump circulation systems. These valves must be installed vertically with the outlet facing downward to allow proper drainage.

ANTI-FREEZE VALVES 910078NT: Working Principle

Anti-freeze valves are used in closed circulation systems of heat pumps to prevent water from freezing inside the pipes and causing damage to pipes and valves. This risk commonly occurs during unexpected power outages or system failures, when water circulation stops and outdoor pipes are exposed to low ambient temperatures.

When the water temperature in the system drops below 3°C, the 910078NT Anti-Freeze Valve automatically opens and drains the circulating water from the pipes. When the water temperature rises again above 4°C, the valve closes automatically and stops drainage.

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  Freeze Protection Valve Normal Operation When Water Temperature Is Above 4°C

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  Freeze Protection Valve Automatic Drainage When Water Temperature Drops Below 3°C

ANTI-FREEZE VALVES 910078NT: Technical Characteristics

• Valve material: EN12165 CW617N / C46500
• Medium: Water
• Maximum working pressure: 10 bar
• Working temperature range: 0°C to 65°C
• Ambient temperature range: -30°C to 60°C
• Medium temperature (Opening): 3°C
• Medium temperature (Closing): 4°C
• Control accuracy: ±1°C

Dimensions (mm)

DN	A (G)	L	L1	L2	H1	H2
25	1″	52	10	10	82.5	32.5
32	1¼”	59	14	14	84.5	34
40	1½”	62	15.5	15.5	86	35.5

KV Table: ANTI-FREEZE VALVES 910078NT

DN	Thread	KV (m³/h)	Q3 (l/h)	Q0.5 (l/h)
25	G 1″	55	0.3	3
32	G 1¼”	70	0.3	3
40	G 1½”	88	0.3	3

ANTI-FREEZE VALVES 910078NT: Installation

The valve must be installed vertically, with the outlet facing downward, to allow the drained water to flow out smoothly and without obstruction. It must be installed on the pipes connecting the outdoor heat pump to the indoor unit, as these pipes are the most susceptible to freezing in the event of a power failure or system malfunction. The anti-freeze valve should be installed away from heat sources to ensure proper operation. It is recommended to install anti-freeze valves on both pipes (flow and return) to reduce the risk of outdoor pipe freezing.

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  Outlet must be installed at least 15 cm above ground level to prevent ice blockage

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  Maintain at least 10 cm clearance to ensure proper operation and drainage

Freeze Protection Valve for Sanitary and Water Heating Systems

For sanitary water, solar water heaters, and domestic heating systems, freeze protection valves often use progressive opening behavior.

In these systems:

• The valve begins opening at around 1.6°C. The progressive opening design means drainage starts gently before reaching full flow, which helps avoid sudden pressure changes in domestic water systems.
• Reaches full opening at approximately 4°C. At full opening, the valve drains at maximum flow capacity to ensure ice cannot form even if the temperature continues to drop below the initial opening point.
• Fully closes again at higher temperatures, such as 7°C. The higher closing temperature compared to the opening temperature creates a deliberate hysteresis band that prevents the valve from rapidly cycling open and closed around a narrow temperature threshold.

This operating logic is characteristic of products such as the 910026NT Freeze Protection Valve, which is suitable for sanitary water, solar water heating, and domestic heating applications. This design helps protect pipes from freezing while minimizing unnecessary water discharge in domestic applications.

910026NT Freeze Protection Valve: Working Principle

The 910026NT Freeze Protection Valve is designed to protect water pipes from freezing by automatically discharging water when the temperature drops. When the water temperature falls below 3.8°C, the thermostatic element opens the valve, allowing water to flow out of the pipe and reducing the risk of ice formation. Once the water temperature rises again to approximately 3.8°C, the valve closes automatically and normal operation resumes. This progressive response helps prevent freezing damage while avoiding unnecessary water discharge in sanitary and water heating systems.

910026NT Freeze Protection Valve: Technical Parameters

Parameter	Specification
Product Model	910026NT Freeze Protection Valve
Material	Brass
Application	Sanitary; heating and cooling systems; solar and electric water heating systems
Initial Opening Temperature	1.6°C
Full Opening Temperature	4°C
Full Closing Temperature	7°C
Working Temperature Range	-30°C to 80°C
Maximum Working Pressure	1 MPa (10 bar)
Max Flow Rate	20 L/min (at 300 kPa)
Control Accuracy	±1°C
Thread Specification	G3/8-19, G3/4-14

Technical Parameters of a Freeze Protection Valve

When selecting a freeze protection valve, technical parameters must match the system requirements. A reliable supplier should clearly provide information such as:

• Valve material (e.g., brass). Material quality directly affects durability, corrosion resistance, and long-term sealing performance, particularly in outdoor or exposed installations where the valve faces temperature extremes and weathering.
• Opening and closing temperatures. These determine when the valve activates and deactivates. Selecting the wrong temperature range can result in premature drainage at normal operating temperatures or insufficient protection during a freeze event.
• Working temperature range. The full range the valve is rated to withstand across its service life, including storage, transport, and operation in extreme ambient conditions.
• Maximum working pressure. Must match or exceed the maximum system pressure to ensure the valve remains sealed under all normal operating conditions.
• Flow capacity. A higher KV value means the valve drains faster when it opens, reducing the window in which ice can form inside the pipe.
• Control accuracy. Tighter accuracy (±1°C) means the valve activates and closes more consistently at its rated temperature, reducing unpredictability in borderline conditions.
• Thread size or nominal diameter. Must match the pipe connection size in the system to ensure a leak-free installation without adaptors that may introduce additional failure points.

Matching these parameters correctly helps ensure effective frost protection and long-term system reliability.

Important Facts About Freeze Protection Valves

Main Function

The primary function of a freeze protection valve is to prevent damage caused by frozen water inside pipes. By draining water when the temperature approaches freezing, the valve helps to:

• Prevent ice formation. Removing water from the pipe before it can freeze eliminates the primary mechanism of pipe damage, which is the volumetric expansion of water as it transitions to ice.
• Reduce internal pressure buildup. Ice formation inside a sealed pipe creates pressure that can exceed the structural limits of the pipe material. The freeze protection valve prevents this by releasing water before ice can form.
• Protect pipes, valves, and connected equipment. A single freeze event can cause cracking or failure in pipes, fittings, and downstream equipment. Consistent freeze protection across the full system extends the service life of all connected components.

Using the correct valve can significantly reduce maintenance costs, spare-part replacement, and system downtime.

Product Testing and Reliability

Freeze protection valves must be tested for:

• Temperature response accuracy. The valve must open and close at the correct temperature within the stated control accuracy. Valves that activate too late provide insufficient protection; those that activate too early cause unnecessary water discharge.
• Pressure resistance. The valve body and seals must withstand the maximum system pressure under both static and dynamic conditions without leaking or deforming.
• Sealing performance. When closed, the valve must maintain a complete seal to prevent unintended drainage during normal system operation. Sealing performance is tested across multiple thermal cycles to confirm no degradation occurs over the valve’s service life.

High-quality products use proven sealing materials and are manufactured under controlled standards. Choosing experienced suppliers helps ensure consistent quality and reliable performance.

Can Freezing Still Occur?

A freeze protection valve greatly reduces the risk of freezing, but it does not completely eliminate ice formation in every situation. In some cases, a thin layer of ice may form on the inner pipe wall. This does not necessarily affect system performance.

However, excessive ice buildup can still cause blockage and pressure increase. Proper valve selection, correct installation, and maintaining system pressure are essential to minimize this risk.

Part of the HVAC System as a Whole

Freeze protection valves do not work alone. They are part of a complete HVAC valve system that includes pumps, controls, piping, and other safety devices. Proper coordination between system components is necessary to ensure stable operation and effective freeze protection.

For this reason, selecting a supplier that understands HVAC applications and provides application-specific solutions is important. Jiaxing Legom Technology Co., Ltd. offers freeze protection valves designed for both heat pump circulation systems and sanitary water applications, along with other HVAC components.

Freeze Protection Valve: A Simple but Critical Safety Component

A freeze protection valve is a simple but critical safety component. When correctly selected and installed, it helps protect piping systems from freezing damage, reduces maintenance risks, and supports long-term system reliability. The difference between the two main valve types — the 910078NT for heat pump circulation systems and the 910026NT for sanitary and domestic heating applications — lies in their opening temperature profiles, flow capacities, and nominal sizes. Selecting the wrong type for the application can result in either inadequate protection or unnecessary water loss during normal operation.

Frequently Asked Questions

What is a freeze protection valve and how does it work?

A freeze protection valve is a thermostatic device that automatically opens and drains water from a pipe when the water temperature approaches the freezing point. Inside the valve is a temperature-sensitive element that expands as the water cools, physically opening the valve outlet so water drains away before ice can form. When the temperature rises back above the closing threshold, the element contracts and the valve seals again. The entire process is passive and requires no electricity, making the valve functional even during power outages when freeze risk is typically highest.

What is the difference between the 910078NT and the 910026NT?

The 910078NT is designed for closed-loop heat pump circulation systems. It opens at 3°C and closes at 4°C, with a high KV flow rate and larger nominal diameters (DN25, DN32, DN40) to drain the circulating water volume quickly. The 910026NT is designed for sanitary water, solar water heaters, and domestic heating systems. It uses progressive opening behavior, beginning to open at 1.6°C, reaching full opening at 4°C, and closing at 7°C. Its smaller thread sizes (G3/8 and G3/4) match the connection points typically found in residential plumbing. Choosing the wrong model for the application can result in either insufficient protection or unnecessary drainage during normal operation.

Does a freeze protection valve require electricity to operate?

No. Freeze protection valves operate entirely through the mechanical expansion and contraction of a thermostatic element in response to water temperature. No electrical power, control signal, or manual input is required. This is one of the key advantages of the thermostatic freeze protection valve over heat-trace systems, which rely on a continuous power supply to prevent freezing. The passive operation of the freeze protection valve means it continues to protect the system even during complete power outages, which are among the most common causes of freeze events in heat pump systems.

Where should a freeze protection valve be installed on a heat pump system?

For heat pump systems, anti-freeze valves should be installed on both the flow and return pipes connecting the outdoor heat pump unit to the indoor unit. These pipes are the most exposed to freezing during a power failure because circulation stops and the residual water in the outdoor section has no heat source to keep it above freezing. The valve must be installed vertically with the outlet pointing downward so that drained water exits cleanly under gravity. It should be kept away from nearby heat sources such as the heat pump casing or insulated sections that could prevent the thermostatic element from detecting the actual pipe temperature.

Can a freeze protection valve be used as the only freeze protection measure?

A freeze protection valve is an effective passive safety layer, but it works best as part of a broader freeze protection strategy rather than as the sole measure. In heat pump systems, the valve should be complemented by proper pipe insulation on all outdoor sections, correct system pressure maintenance, and a control system that can trigger an alert when circulation stops unexpectedly. In sanitary systems, combining the valve with adequate pipe insulation significantly reduces the frequency of drainage events and minimizes water waste. For very severe cold climates, consulting with the system designer about additional protection measures is recommended.

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Reviewed and updated by the LEGOM Technical Team on May 18, 2026. This article covers how freeze protection valves work, the difference between heat pump and sanitary valve types, technical parameters for the 910078NT and 910026NT models, and key selection and installation considerations, based on Legom’s experience as an HVAC valve manufacturer supplying freeze protection solutions to partners in more than 90 countries worldwide.