In EN 12845, frost protection is not in Clause 7 but in Clause 11, which covers the type of installation. Clause 7 is headed "Hydraulic design criteria" and consists of 7.1, 7.2 and 7.3; there is no subclause 7.4 or 7.5. Frost protection is in 11.1.2, dry installations in 11.2, alternate installations in 11.3, pre-action in 11.4 and subsidiary extensions in 11.5. Source: TS EN 12845+A2:2026, Clause 11, EN p.66-69.
The decision point: wet or dry
| Installation type | Condition of use | Clause | Page |
|---|---|---|---|
| Wet pipe | Locations where there is no possibility of frost damage to the installation and where the ambient temperature will not exceed 95 °C. The cases covered by 11.1.2 are the exception. In grid and loop systems only wet installations are used | 11.1.1 | EN p.66 |
| Dry pipe | Only where there is a possibility of frost damage or where the temperature exceeds 70 °C, for example in drying ovens | 11.2.1 | EN p.67 |
| Alternate | In the winter months the downstream side of the alarm valve is filled with compressed air or inert gas and the upstream side with water; at other times of the year it operates as a wet installation | 11.3.1 | EN p.68 |
| Subsidiary dry or alternate extension | As a dry or alternate extension to a wet installation in small areas with possible frost damage in an otherwise adequately heated building; as a dry extension to a wet or alternate installation in cold stores and in high temperature ovens or furnaces | 11.5.1 | EN p.69 |
In every case the supply pipe and the control valve set are maintained at a minimum of 4 °C (Clause 8.1.3, EN p.42). The corresponding values for the pump compartment are 4 °C for electric sets and 10 °C for diesel sets (Clause 10.3.3, EN p.58).
Clause 11.1.2: protection against freezing
Clause 11.1.2.1 (EN p.66) lists three methods: parts of an installation that may be exposed to freezing may be protected by antifreeze solution, by electrical trace heating, or by subsidiary dry pipe or alternate extensions (see 11.5).
Protection by antifreeze solution (11.1.2.2, EN p.66)
- The number of sprinklers in any section of pipework protected by antifreeze solution does not exceed 20.
- Where more than two antifreeze sections are controlled by one control valve set, the total number of sprinklers in the antifreeze sections does not exceed 100.
- The freezing point of the antifreeze solution is below the expected minimum temperature of the location.
- The specific gravity of the prepared solution is checked with a suitable hydrometer.
- Systems relying on antifreeze solution are provided with backflow prevention devices to prevent contamination of the water.
The standard gives no volume limit in litres for an antifreeze section; it gives no glycol type or concentration/temperature table; and it does not state at what interval the concentration is to be measured. The only means of checking mentioned is the measurement of specific gravity with a hydrometer. Clause 20.3.4 (EN p.122), which governs the annual routine, does not include antifreeze concentration.
Protection by electrical trace heating (11.1.2.3, EN p.66-67)
| Requirement | Value or provision |
|---|---|
| Monitoring | Failure of the power supply and failure of a heating element or sensor are monitored (see Annex I) |
| Insulation class | The pipe is provided with Euroclass A1 or A2 insulation or its equivalent in existing national classifications |
| Redundancy | Duplicate heating elements are provided over unheated pipework; both elements shall be capable of maintaining the pipework at a minimum of 4 °C |
| Circuit separation | Each trace heating circuit is monitored and switched electrically by separate circuits |
| Tape routing | The tape does not cross over other trace heating tapes; it is fixed on the side opposite the face carrying the sprinkler heads; it terminates within 25 mm of the pipe ends |
| Insulation thickness | All pipework with trace heating is covered with Euroclass A1 or A2 insulation material at least 25 mm thick with a waterproof covering; all ends are sealed to prevent the ingress of water |
| Tape rating | Maximum 10 W/m |
Annex I, Table I.1 (EN p.155) classifies the row "trace heating circuits, Clause 11.1.2.3" as a type B (technical) alarm.
Clause 20.2.2.6 (EN p.120) requires, in the weekly routine, that heating systems preventing freezing in the sprinkler system be checked for correct operation.
Dry pipe installations: Clause 11.2
Dry pipe installations are normally filled with compressed air or inert gas downstream of the dry alarm valve and with pressurized water upstream of it. A permanent supply of air or inert gas is installed to maintain the pressure in the pipework. The installation is pressurized so as to fall within the pressure range recommended by the alarm valve supplier (Clause 11.2.1, EN p.67). The standard gives no pressure range in bar.
Table 18: Maximum water delivery time, dry and alternate installations (EN p.67)
| LH | OH and HH |
|---|---|
| 90 s | 60 s |
Clause 11.2.2: the maximum time between the opening of a single sprinkler and the discharge of water does not exceed the value in Table 18. The test is carried out using the remote test valve specified in 15.5.2. The same clause states that it is strongly recommended that dry and alternate installations not be used in HHS applications; the delay in water reaching the first sprinklers to operate can seriously impair the effectiveness of the system.
Note to the clause: experience has shown that, with an accelerator, volumes not exceeding 4 m³ for LH or OH and 3 m³ for HH occupancies are expected to satisfy the requirement of 11.2.2.
The same Table 18 limit also applies to alternate installations (Clause 11.3.2, EN p.68).
Limits on installation size
Table 17: Maximum protected area in wet and pre-action installations (Clause 11.1.3, EN p.67)
| Hazard class | Maximum protected area per control valve set (m²) |
|---|---|
| LH | 10 000 |
| OH (including LH sprinklers within it) | 12 000, except as permitted in Annex D and Annex F |
| HH (including OH and LH sprinklers within it) | 9 000 |
Clause 11.4.3 (EN p.69): the number of sprinklers controlled by one pre-action alarm valve does not exceed that shown in Table 17 (the number of sprinkler heads in the given area).
Clause 11.5.2 (EN p.69): the number of sprinklers in any subsidiary extension does not exceed 100. Where more than two subsidiary extensions are controlled by one control valve set, the total number of sprinklers in the subsidiary extensions does not exceed 250.
Pre-action installations: Clause 11.4
The standard defines two types; the term "double interlock" does not appear in the text of EN 12845.
| Type | Definition | Clause |
|---|---|---|
| Type A | An otherwise normal dry pipe installation in which the control valve set is tripped by an automatic fire detection system and not by the operation of the sprinklers. The air or inert gas pressure in the installation is monitored at all times (see Annex I). At least one quick opening manually operated valve is installed at a suitable location so that the pre-action valve can be tripped in an emergency. In the event of a failure of the fire detection system, the installation operates as an ordinary dry pipe system | 11.4.1.2 |
| Type B | An otherwise normal dry pipe installation in which the control valve set is tripped either by an automatic fire detection system or by the operation of the sprinklers. Independently of the response of the detectors, a pressure drop in the pipework opens the alarm valve | 11.4.1.3 |
Clause 11.4.1.4 (EN p.68-69): where a sprinkler system contains more than one pre-action installation, a risk assessment is carried out to determine whether simultaneous operation of more than one pre-action installation can occur. Where simultaneous filling can occur, the following apply:
- a) the volume of the stored water supplies is increased by the volume of the total pre-action installations;
- b) the time between the tripping of multiple pre-action installations and the discharge of water from any remote test valve in those installations does not exceed 60 seconds.
Clause 11.4.2 (EN p.69): the detection system is installed in all rooms and compartments protected by the pre-action sprinkler system and conforms to the relevant parts of EN 54 or, in their absence, to suitable specifications valid at the place of use of the sprinkler system.
Clause 16.2.3 (EN p.111): in dry and pre-action systems, each installation is provided with a low air/gas pressure alarm giving visual and audible warning in accordance with Annex I.
Pipe and sprinkler details on the dry side
- Clause 17.1.8 (EN p.112): in dry, alternate and pre-action installations, range pipes have a fall of at least 0.4 % towards the distribution pipe and distribution pipes a fall of at least 0.2 % towards a suitable drain valve. These values are percentages, not degrees. The note states that in cold climates where severe freezing conditions are possible it may be necessary to apply a fall in wet systems as well and to increase the fall in dry systems.
- Clause 17.1.2 (EN p.111): galvanized steel should preferably be used in dry, alternate or pre-action installations. Copper pipes may be used only in wet pipe systems for LH, OH1, OH2 and OH3, downstream of steel pipework (17.1.9, EN p.113).
- Clause 12.1.3 (EN p.70): except where dry pendent type sprinklers are used, sprinklers in dry pipe, alternate and pre-action installations are upright. An upright sprinkler is fitted with the yoke arms parallel to the pipe.
- Table 38 (Clause 14.5.1, EN p.106): in dry systems and Type A pre-action systems the Standard 'A' and Special sensitivity classes are permitted; Quick sensitivity is not permitted.
- Clause 19.1.1.1 (EN p.117): dry pipework is tested pneumatically at a pressure of at least 2.5 bar for at least 24 hours. Any leak causing a pressure loss greater than 0.15 bar in 24 hours is corrected.
- Clause 20.2.2.2 a) (EN p.119): in dry, alternate and pre-action installations the pressure in the pipework should not fall faster than 1.0 bar per week.
- Clause 20.3.3.2 (EN p.121): in the half yearly routine, the moving parts of dry alarm valves in dry pipe installations and subsidiary extensions, together with accelerators and exhausters, are exercised in accordance with the supplier's instructions. The note states that alternate installations need not be tested in this way because they are exercised twice a year by the change from wet to dry and back again.
Provisions not in the standard
- An ambient temperature band of 4 °C to 70 °C for wet installations: the standard gives the upper limit for a wet installation as 95 °C (11.1.1); the value of 70 °C is a condition of use for dry installations (11.2.1); 4 °C is for the supply pipe and the control valve set (8.1.3).
- Volume thresholds of 1 500 L or 3 000 L for dry installations: the standard mentions only 4 m³ and 3 m³ in the note to 11.2.2.
- A table of glycol concentration against freezing point.
- A volume limit in litres for antifreeze.
- The spacing at which low point drains are to be placed.
- A separate clause for frost protection testing (the water delivery time test is carried out with the remote test valve of 15.5.2 in accordance with 11.2.2; Clause 19 contains 19.1 and 19.2, there is no 19.3).
Field note: the standard's limitation of an antifreeze section to 20 sprinklers shows that the frost protection decision is an architectural decision. In large areas at risk of freezing, the only workable solution is not antifreeze but a dry or alternate installation, or heating of the space.
Frequently Asked Questions
Which methods does EN 12845 permit for frost protection?
TS EN 12845+A2:2026 Clause 11.1.2.1 (EN p.66): parts of an installation that may be exposed to freezing may be protected by antifreeze solution, by electrical trace heating, or by subsidiary dry pipe or alternate extensions (see 11.5). All three are methods accepted by the standard; trace heating appears not as a supporting method but as one of the three options listed directly, and its detailed requirements are given in 11.1.2.3.
How many sprinklers may an antifreeze section contain at most?
Clause 11.1.2.2 (EN p.66): the number of sprinklers in any section of pipework protected by antifreeze solution does not exceed 20. Where more than two antifreeze sections are controlled by one control valve set, the total number of sprinklers in the antifreeze sections does not exceed 100. The standard gives no volume limit in litres.
In what temperature range is a wet installation used?
Clause 11.1.1 (EN p.66): except for the cases covered by 11.1.2, wet pipe installations are installed only where there is no possibility of frost damage to the installation and where the ambient temperature will not exceed 95 °C. In grid and loop systems only wet pipe installations are used. Dry pipe installations, in accordance with Clause 11.2.1, are installed only where there is a possibility of frost damage or where the temperature exceeds 70 °C, for example in drying ovens. In addition, Clause 8.1.3 (EN p.42) requires the supply pipe and the control valve set to be maintained at a minimum of 4 °C.
How quickly must water reach the sprinklers in a dry installation?
Table 18 (Clause 11.2.2, EN p.67): the maximum time between the opening of a single sprinkler and the discharge of water is 90 seconds in LH and 60 seconds in OH and HH. The test is carried out using the remote test valve specified in Clause 15.5.2. The note to the same clause states that, with an accelerator, volumes not exceeding 4 m³ for LH or OH and 3 m³ for HH are expected to satisfy this requirement.
What requirements apply to trace heating?
Clause 11.1.2.3 (EN p.66-67): the trace heating system is monitored for failure of the power supply and for failure of a heating element or sensor (see Annex I). Duplicate heating elements are provided over unheated pipework; both elements shall be capable of maintaining the pipework at a minimum of 4 °C. Each trace heating circuit is monitored and switched electrically by separate circuits. The tape does not cross over other trace heating tapes, is fixed on the side opposite the face carrying the sprinkler heads, and terminates within 25 mm of the pipe ends. All pipework with trace heating is covered with Euroclass A1 or A2 insulation at least 25 mm thick with a waterproof covering. The tape has a maximum rating of 10 W/m.
References
- TS EN 12845+A2:2026 Clause 8.1.3 (EN p.42)
- TS EN 12845+A2:2026 Clause 10.3.3 (EN p.58)
- TS EN 12845+A2:2026 Clauses 11.1.1, 11.1.2.1, 11.1.2.3 (EN p.66-67)
- TS EN 12845+A2:2026 Clauses 11.1.2.2, 11.1.3, Table 17, Clauses 11.2.1, 11.2.2, Table 18 (EN p.67)
- TS EN 12845+A2:2026 Clauses 11.3.1, 11.3.2, 11.4.1.1, 11.4.1.2, 11.4.1.3, 11.4.1.4 (EN p.68-69)
- TS EN 12845+A2:2026 Clauses 11.4.2, 11.4.3, 11.5.1, 11.5.2 (EN p.69)
- TS EN 12845+A2:2026 Clause 12.1.3 (EN p.70)
- TS EN 12845+A2:2026 Clause 14.5.1, Table 38 (EN p.106)
- TS EN 12845+A2:2026 Clause 15.5.2 (EN p.109)
- TS EN 12845+A2:2026 Clauses 16.2.3, 17.1.2, 17.1.8, 17.1.9 (EN p.111-113)
- TS EN 12845+A2:2026 Clause 19.1.1.1 (EN p.117)
- TS EN 12845+A2:2026 Clauses 20.2.2.2, 20.2.2.6, 20.3.3.2 (EN p.119-121)
- TS EN 12845+A2:2026 Annex I, Table I.1 (EN p.155)
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Download MEP Calc on the App StoreTS EN 12845+A2:2026 (EN 12845:2015+A2:2026) Fixed firefighting systems — Automatic sprinkler systems — Design, installation and maintenance; TS EN 12845-2:2025 (EN 12845-2:2024) ESFR and CMSA sprinkler systems. Every figure in this article is taken from the published standard text; clause, table and page references are listed under References. General information only, not a substitute for the standard or for a design review.