DS 452 sets 7 insulation classes (0-6) for the permitted heat loss. For pipes, the requirement is calculated per running metre based on the pipe's outside diameter. We go through the values of the classes, which installations fall under the standard (and which do not), and how to read a requirement in practice.
What is DS 452 — and what is it not?
DS 452 is the Danish standard for thermal insulation of technical installations. It establishes how much heat may escape (or enter) through the insulation on a pipe, a duct, a vessel or a fitting — measured as the U-value for the class's surface heat flow. The standard's full title is Thermal insulation of technical service and supply systems, and it is published by Dansk Standard.
It is easy to confuse DS 452 with other standards, so here is the brief delimitation:
| Standard | Scope | Confused with DS 452 because … |
|---|---|---|
| DS 452:2013 | Energy loss from pipes, ducts, tanks, fittings (HVAC + industry) | — |
| DS 428 | Fire insulation of ventilation ducts — resistance to fire spread | Both concern ducts, but DS 428 is fire, not energy |
| DS 418 | Calculation of the U-value of building constructions (walls, roof, floor) | Both concern heat loss, but DS 418 is the building envelope, not the installations inside |
| DS 469 | Supply and heating systems in general (defines e.g. district-heating units) | DS 452 refers to DS 469 for installation units |
| DS 439 | Water installations (cold potable water is referred here) | DS 452 shows cold potable water, but condensation details are governed by DS 439 |
| DS/EN ISO 12241 | The calculation method for heat loss from pipes and ducts | You use EN ISO 12241 to show whether the DS 452 requirement is met |
| DS/EN 1886 | Classification of the U-value of ventilation units | DS 452 refers to EN 1886 for the units' T2/T3 classification |
| DS/EN 253 | Pre-insulated district-heating pipes | DS 452 does not apply to the district-heating supply network |
DS 452 explicitly covers all parts of the installation — flat and curved surfaces, ducts, pipe systems, valves, fittings, installation units, units, fans and tanks (quoted from DS 452-3, reproduced in the BAI compendium, p. 6). The key point is that they are operated at a medium temperature between −40 °C and +650 °C — everything from cold-storage rooms to high-temperature steam pipes.
Historical development
DS 452 has existed since the 1980s, but the edition in force today is the 3rd edition from 2013:
- DS 452, 2nd edition (1999) — had only four insulation classes with permitted U-values of 0.88 / 0.66 / 0.49 / 0.25 W/(m²·K) for flat surfaces. The class was chosen on the basis of "operating parameter I" — a weighted combination of medium temperature, ambient temperature and operating time.
- DS 452-3 (2013) — entered into force on 1 December 2013 with a transitional period until 31 May 2014. As the BAI compendium writes: "from 31 May 2014 all installations must be insulated according to the new standard." The most important change was the expansion to six classes, a clear division between HVAC and industrial systems, a simple indoor/outdoor boundary at 5 °C, as well as new rules for pipe supports (whether they are insulated or not).
- Corrigendum DS 452:2013/Ret.1:2018 (dated 2018-10-02) — updates, among other things, table 6.2 (reduced insulation), table 6.4 (the requirements table) and annex tables A.1–A.3. The corrigendum also removes references to DS 1135, which has been withdrawn.
- Amendment 1 — DS 452:2013+Ret.1+Till.1:2020 (9 November 2020) — consolidates the corrigendum into one edition and adds a new annex E Space requirements for insulating pipes and ducts. Section 9.7 was changed: DS 1102 and DS 1123 no longer apply; it now refers to annex E instead [webshop.ds.dk; DIB, "Den nye DS 452 – hold dig opdateret"].
The main line: When a vocational teacher, insulator or consultant says "DS 452", the edition in force today is DS 452:2013+Ret.1+Till.1:2020. The classes and the requirements table are those of the 2018 corrigendum; the 2020 amendment added the space requirements (annex E). The Isover HVAC Handbook (9th edition, December 2022) and Rockwool build on the same classes.
The 6 classes in detail
The classes in DS 452-3 are U-value requirements for flat surfaces (W/(m²·K)). For round pipes, the compendium provides a corresponding equivalent formula per running metre of pipe, in which the pipe's outside diameter D_ep (the bare pipe, without insulation; also written p_ep) is entered. This follows from DS 452 Ret. 1:2018, Annex A, where the column is headed «Udv. rørdimension Dep» (outside pipe dimension).
| Class | U requirement, flat surface W/(m²·K) | U requirement, pipe W/(m·K) | Typical use |
|---|---|---|---|
| Klasse 0 | No insulation | No insulation | Short connecting lines in the same room as the heat source or tapping point. Connecting ducts in the rooms they serve. Exhaust-air ducts without heat recovery. |
| Klasse 1 | 1.17 | 3.3 · D_ep + 0.22 | Loosest class. Supply-air ducts on systems with mechanical cooling with a design air temperature of 15–23 °C in heated rooms. Short-term operation, small temperature difference. |
| Klasse 2 | 0.88 | 2.6 · D_ep + 0.20 | Connecting lines in rooms other than the heat source (indoors, >5 °C). Cooling pipes for offices and similar (>0 °C). Cold potable water, both with and without electric tracing. Supply-air ducts in air-heating systems >23 °C located indoors. Internal roof drains. |
| Klasse 3 | 0.66 | 2.0 · D_ep + 0.18 | Distribution lines for heating systems operating only during the heating season, ΔT ≤ 45 °C or with outdoor-air compensation. Supply-air ducts <15 °C. Exhaust-air and supply-air ducts on heat-recovery systems outdoors / in unheated rooms. |
| Klasse 4 | 0.49 | 1.5 · D_ep + 0.16 | Reference class for most distribution lines indoors (heating, hot potable water, district heating within the building). Solar-heating pipes. Cooling pipes for server rooms. Supply-air ducts in air-heating systems >23 °C located outdoors. Internal connecting pipes to heat pumps. |
| Klasse 5 | 0.35 | 1.1 · D_ep + 0.14 | Heat exchangers, hot-water tanks and water heaters indoors. Solar-heating tanks indoors. Cold-storage and freezer rooms (medium ≤ 0 °C). Hot connecting pipes to the outdoor unit of an air-to-water/air-to-air heat pump, indoors. |
| Klasse 6 | 0.22 | 0.8 · D_ep + 0.12 | Strictest class. All outdoor installations in the corresponding categories — heating pipes outside the building, hot potable water outdoors, heat exchangers and tanks outdoors, heat-pump pipes outdoors. Year-round operation with high medium temperatures. |
Why exactly those numbers? The numbers fall towards higher classes — class 6 (0.22 W/(m²·K)) permits five times less heat loss than class 1 (1.17 W/(m²·K)). The reasoning in the compendium: "It has always been the rising oil prices that formed the basis for these calculations, since the payback time on an insulated pipe had to be in proportion to the operating budget. And with the new classes you can make more targeted calculations." (BAI compendium, p. 6).
For the round pipes it can be seen that the U requirement is a linear function of the outer pipe diameter — this is due to the geometry: one m² of outer surface corresponds to an ever shorter length of the pipe, the larger the diameter. As a rule of thumb: use the flat-surface table when you think in square metres, and the pipe formula when you think in running metres.
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Sources
- Dansk Standard. DS 452:2013 — Thermal insulation of technical installations. 3rd edition 2013. Entry into force 1 December 2013, transitional period until 31 May 2014. Publisher: Dansk Standard, Göteborg Plads 1, DK-2150 Nordhavn.
- Dansk Standard. DS 452:2013/Ret.1:2018 — Corrigendum. 2018-10-02. Updates table 6.2, table 6.4 and annex A.1–A.3; removes the reference to DS 1135.
- Dansk Standard. DS 452:2013+Ret.1+Till.1:2020 — Termisk isolering af tekniske installationer. Published 9 November 2020; status "current" on webshop.ds.dk (read 1 October 2026), where DS 452:2026 is listed as a draft.
- The Continuing Education Committee for Construction/Civil Engineering & Industry (BAI). Compendium for DS 452-3. Published with support from the Ministry of Education. Vocational teacher Preben Kristensen, AMU Syd Kolding. Verified with energy consultants; quotes from DS 452-3 included with the permission of Dansk Standard.
- Isover (Saint-Gobain). HVAC Handbook, 9th edition. December 2022. Replaces the 8th edition from December 2021. Classification table pp. 24–25, dimension tables pp. 15–45, space requirements pp. 12–14.
- Lesson 1 PPTX "DS 452-3 — Classes & Heat Loss" (school material, reproduced in
materiale/.extracted/ds452-lektion1.txt). - Dansk Standard's public catalogue: ds.dk — search "DS 452".
- Molio Knowledge System: molio.dk — the construction and consulting industry's collection of technical standards and guidelines.
- Building Regulations BR18 (bygningsreglementet.dk, read 1 October 2026): § 390 (ch. 19), § 410 and § 414 (ch. 21 Water), § 421 (ch. 22 Ventilation).
- Project module
src/lib/calculations.tswith the implementation ofDS452_CLASSES,ds452MaxHeatLoss()andrecommendedThicknessForClass(). - Project module
src/lib/hvac-classes.tswith the look-up table from the Isover HVAC Handbook.