Heat, cooling, condensation, fire

In everyday speech we talk about "insulating a pipe". But on a typical Danish installation the same pipe often has to solve several tasks at once, and each task has its own logic:

• A district-heating riser in the escape route of a multi-storey dwelling must both retain the heat (heat insulation, class 6) and delay a fire for 60 minutes (fire insulation, EI 60).
• A cooling pipe in a server room must keep heat out (cooling insulation) and at the same time must not sweat into the server cabinet below (condensation insulation — which here is a variant of the cooling insulation, not a separate task).
• A ventilation duct in a nursing home must be thermally insulated where it runs through cold rooms (heat/condensation), and fire-insulated where it crosses fire compartments (fire).

Inside a warehouse there are four purposes that typically use the same material — mineral wool is the answer 70 % of the time. But the requirements are not the same, the dimensioning is not the same, and the mistakes you can make are very different. That is why the trade distinguishes them: heat insulation, cooling insulation, condensation insulation and fire insulation are four different disciplines that often share the physical material but not the logic.

The Isover HVAC Handbook (9th edition, December 2022, page 11) states it directly:

HVAC installations must be insulated against energy loss in accordance with DS 452:2013… NOTE! Some installation parts must in addition be condensation-insulated, fire-insulated or insulated against high surface temperature.

Energy insulation is the starting point — all the other types come on top. That is the reading you must keep in the back of your mind on a building site: when a duct already has class 3 insulation on it, that does not mean it is finished. If it is to cross a fire wall, fire insulation is still missing. If cooling water runs inside it, a vapour barrier is still missing.

Purpose: Reduce energy loss from a pipe or duct where the medium is warmer than the surroundings. Secondarily: keep the surface temperature below a safe level for touch (typically below 50 °C where people can come into contact with it), and prevent corrosion on the pipe's outer side.

Operating temperature: From about +30 °C up to 650 °C — from a distribution pipe in a dwelling, through district heating, hot domestic water, steam and all the way up to flue-gas ducts at a power plant. The AMU compendium Grundlæggende isolering (Preben Kristensen, AMU Syd, September 2025) frames it as "where the heat must stay inside the pipe".

Standard materials:

• Mineral wool (glass wool or stone wool) as pipe section, lamella mat, wired mat or slab. Covers practically the entire temperature range. Glass wool up to about 180 °C, stone wool up to 250 °C as standard and all the way to 640 °C (ProRox WM 950) with specialty products [mineraluld-former.md].
• PIR/PUR pipe sections where space is tight. PIR has a better λ at the same thickness, but only tolerates about 110–140 °C — so it is typically used on district-heating pipes in cast-in pre-insulated systems and on hot domestic water where space is cramped.
• Cellular glass (Foamglas) where critical process pipes require a 100 % vapour-tight, fire-safe, durable material — typically industry, offshore, steam lines at power plants.

Outer cladding: Card+canvas internally for neat work, PVC film (Isogeno, Isotop) for indoor tasks (does not tolerate UV), metal cladding of aluminium, galvanised steel or stainless steel for outdoor and exposed indoor environments. The BAI industry agreement governs the safety allowance and overlaps on the metal cladding (typically 50 mm longitudinal, 30 mm circumferential).

Requirement: The energy class follows DS 452:2013 and is determined by installation type × medium temperature × location (inside/outside the heated building envelope). The Isover HVAC handbook's tables cover practically all HVAC cases — for industry, refer to IsoDim. Typically you end up in class 3–4 for ordinary distribution pipes, class 5–6 for district-heating mains and outdoors. The standard is measured in W/(m²·K) of outer surface, not W/m — so longer pipes with larger diameter may have a larger absolute heat loss at the same class [ds-452.md].

Vapour barrier: no. Vapour diffuses out from the hot pipe towards the cooler room air, and never reaches a cold surface where it can condense. That is why you do not see separate vapour barriers on district-heating or steam pipes — they are superfluous [dampspaerre.md].

Dimensioning: Use /beregnere/tykkelse on the site (or IsoDim, Rockassist, Paroc Calculus). Enter medium temperature, ambient temperature, pipe diameter, class — and get the required thickness directly. Remember that λ rises with temperature; at 200 °C the λ for mineral wool is roughly doubled compared with 10 °C. The programs account for this automatically; hand calculations must read off λ at the mean temperature between medium and surface.

Practice: Heat insulation is broadband. On an ordinary Danish building site it makes up 30–60 % of all technical-insulation tasks — it is the "starting point" that the other three are layered on top of.

Purpose: Keep heat out from a cold medium. It sounds like the mirror image of heat, and thermally it is — but there are two crucial differences that turn the practical craft logic completely around.

Operating temperature: From about −50 °C up to +15 °C. Classic areas: cooling pipes (brine, glycol, R32, R290), air-conditioning systems, freezer rooms, cryogenic installations (ammonia, LN₂ in industry and hospitals).

Standard materials:

• Elastomeric foam (Armaflex, Kaiflex KKplus s2, K-Flex ST) — the Danish standard choice on indoor cooling pipes. λ ≤ 0.033 W/(m·K) at 0 °C and — most importantly — μ ≥ 10,000, so the vapour barrier is built into the material. 13 mm elastomeric foam gives sd ≈ 130 m, which makes it an effective vapour barrier in itself [cellegummi.md].
• Cellular glass (Foamglas) for critical systems — fully vapour-tight (μ = ∞), load-bearing, tolerates −260 to +430 °C, i.e. well below the elastomeric foam's working range too. Used offshore, on cryogenic tanks and where moisture damage would be catastrophic.
• Mineral wool with alu foil + tape on large ventilation ducts where elastomeric-foam sheets become cumbersome. Requires precise execution — the foil is the entire vapour barrier, so every single hole is a weakness.

Outer cladding: Elastomeric foam is often its own outer cladding indoors — the black rubber foam tolerates ordinary handling. Outdoors it must be painted or clad within 7 days, otherwise it crumbles from UV in 1–2 years [cellegummi.md]. Metal cladding (alu, galvanised steel) is used in mechanically exposed environments.

Requirement: DS 452 class 2–4 typically, depending on whether the cooling pipe is in a heated room or not. The tables are found both in the Isover HVAC handbook (p. 26–29 for cooling pipes and cold domestic water) and from manufacturers of elastomeric foam.

Vapour barrier: ABSOLUTELY ESSENTIAL — on the warm side (outermost).

That is the point that defines cooling insulation. On a hot pipe vapour goes OUT; on a cold pipe vapour goes in. The room's warm, humid air has a higher vapour pressure than the cooled air close to the pipe's surface, and vapour diffuses from high to low pressure. It therefore travels from the outside in. Somewhere inside the insulation it reaches the dew point and condenses — first as invisible moisture, then as droplets, then as running water, then as corrosion on the pipe [dampspaerre.md].

The reversed physics means:

• The vapour barrier must sit outermost towards the room, not innermost towards the pipe (opposite to building constructions, where the vapour barrier sits towards the warm living room).
• A crack in the vapour barrier = a ruined installation within a few months. The moisture collects, λ rises to double or more, and the condensation cannot evaporate away, because the pipe is constantly colder than the surroundings.
• Mineral wool is not self-sufficient on cooling pipes. It must have alu foil and full taping of all joints, and even that system is only as good as its weakest point.

Dimensioning: Use both /beregnere/tykkelse (for the class and the energy loss) and /beregnere/dugpunkt (to ensure the surface temperature lies above the room dew point with good margin). In practice it is the dew-point requirement that often governs the thickness on indoor cooling pipes — the energy class is met at the same time [dampspaerre.md].

Common practice: On an indoor cooling pipe in an office building, elastomeric foam is standard. 13–25 mm Armaflex or Kaiflex tubes, glued with approved contact adhesive, section-glued every 2 m, all slits tightly glued. No separate vapour barrier — it is built into the material. On large ventilation ducts above Ø273 mm, lamella mat (Climcover Lamella Alu2) or sheets with alu foil and full taping are typically used.