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Pipe Insulation Thickness

Minimum insulation against condensation (EN ISO 12241:2022), heat gain and loss per metre, surface temperature and the minimum thickness required by law in your country – for refrigeration, chilled water, heating and domestic water pipes.

Surroundings

Dew point indoors 16.7 °C, outdoors 28.2 °C.
Design for the most humid conditions the pipe will see, not the comfort design point: part load and night or weekend shutdown give higher humidity indoors; outdoors and in spaces vented to outdoor air design for about 90 % RH (ASHRAE Fundamentals 2021, ch. 23). A margin of 0.5–1 K covers uncertainty in the humidity.

Insulation

EN 14304 · λ 0.0330 W/(m·K) at 0 °C, 0.0370 at 40 °C · μ 7,000 · -50 °C … 105 °C
λ and μ are typical values of products to the standard shown. Use the declared values of the product you buy (λ(T) curve to EN ISO 13787) – choose "Other material" to type them.

Lines to insulate

Only the ticked lines get a thickness; the others are calculated as bare pipes and warn if they would condense. Suction lines and water pipes are ticked by default, the liquid line too for CO2 (R744), where it is often colder than the room. The heat flow limit (optional) also sizes warm pipes, e.g. to the losses your specification allows.

Legal minimum

No legal minimum: the thickness against condensation only.

Project

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Units

Pipes

One row per pipe run. Empty air and humidity fields use the surroundings; an empty thickness is calculated.

Result per pipe

Cross-section

Click (or tap) a part of the section – fluid, pipe, insulation, vapour barrier, jacket, air or the dew point line – to change it in the box below; drag the yellow handle to change the thickness. The small sections choose another pipe.
Thickness (mm)
Now 6 mm · needed against condensation 4.0 mm · legal minimum – mm · governs: Condensation · surface 18.5 °C
Material
λ 0.0342 W/(m·K) at the layer's mean temperature 12.3 °C · R′ins 1.371 m·K/W

Tip: drag the yellow handle on the insulation in or out – it snaps to the stocked thicknesses. Material, jacket and vapour barrier apply to the whole project.

Insulation to order

Show calculation

Calculation per pipe

PipePipe OD [mm]Thickness [mm]θm [°C]λ [W/(m·K)]De [mm]hcv [W/(m²·K)]hr [W/(m²·K)]R′ins [m·K/W]R′se [m·K/W]θs [°C]θd [°C]q′ [W/m]Bare pipe [W/m]sd [m]Length [m]Notes
Chilled water supply35612.30.0342474.295.241.370.71118.516.79.1319.54225
Suction line28.693.450.033346.574.545.192.330.70216.916.711.532.76315
Split AC liquid/suction15.91316.80.034741.8722.85.654.450.26728.628.25.335.59112
Heating flow33.70550.038533.76.836.2800.725516.7-41.6-39.4030Surface 55.0 °C: touch protection
Hot water circulation220600.039227.896.4401.016016.7-34.7-29.5015Surface 60.0 °C: touch protection
Cold water18615.10.0345304.435.282.361.0920.216.74.358.534210
Liquid line22.2613.70.034434.234.455.2620.95719.516.75.7511.74215
Hot gas line22.20700.0422.228.386.7600.9457016.7-47.6-40.5010

Basis of calculation

Method
Steady-state heat transfer through a cylindrical insulation layer in the manner of EN ISO 12241:2022: λ at the mean temperature of the layer, outside coefficient from natural convection (still air indoors) or wind (outdoors) plus radiation, solved by iteration on the surface temperature. Thickness against condensation: the smallest thickness with the surface at or above dew point + margin (bisection).
Equations
  • q′ = (θa − θf) / (R′ins + R′se)
  • R′ins = ln(De/Do) / (2π·λ(θm)), θm = (θf + θs)/2
  • R′se = 1 / (hse·π·De), hse = hcv + hr
  • hcv = 1,25·(ΔT/De)^0,25 (De³ΔT ≤ 10) | 1,21·ΔT^(1/3) | 8,1·10⁻³/De + 3,14·√(v/De) | 8,9·v^0,9/De^0,1
  • hr = ε·σ·(Ts⁴ − Ta⁴)/(Ts − Ta)
  • θs = θa − q′·R′se ≥ θd + Δθ
  • θd: Magnus, a = 17,62, b = 243,12 °C
  • d = D/2·[exp(λ/λref·ln((D + 2·dref)/D)) − 1]
  • sd = μ·d, Z ≈ 5·sd MPa·m²·s/g
Material data
Flexible elastomeric foam (FEF): typical values for products to EN 14304, λ(10 °C) 0.0340 W/(m·K), μ 7,000
Standards
EN ISO 12241:2022 · EN ISO 15758:2014 · EN ISO 13787 · VDI 2055-1 (2025-10) · ASTM C680-23
Notes
  • The inner heat transfer and the pipe wall are neglected: the pipe surface is at the fluid temperature (on the safe side for condensation).
  • Legal minimum thicknesses at another λ are converted with d = D/2·[exp(λ/λref·ln((D + 2dref)/D)) − 1] (RITE IT 1.2.4.2.1.2 point 8); Australia: thickness = R × λ (flat layer, on the safe side); England: interpolated between the λ 0.025 and 0.040 columns.
  • Dew point by the Magnus formula over water (Sonntag 1990). sd = μ·d; Z ≈ 5 MPa·m²·s/g per metre of sd (δair ≈ 2·10⁻¹⁰ kg/(m·s·Pa)).

Regulations and standards by country

Minimum thicknesses are taken only where the law itself has a table; elsewhere a reference.
  • Minimum thicknesses shown are taken from the cited regulation and edition, checked 2026-11-02. They are energy requirements; they do not guarantee freedom from condensation. Local rules, product approvals and the designer's calculation take precedence. Always check the current text.
  • Calculation standards: EN ISO 12241:2022 (heat transfer, surface temperature, thickness against condensation), EN ISO 15758:2014 (water vapour diffusion in cold insulation; replaces EN 14114), VDI 2055 Blatt 1 (2025-10), ASTM C680-23.
  • Fire class: check national rules (Sweden: BFS 2024:7 ch. 5 § 22, BL-s1,d0 / CL-s3,d0 / DL-s3,d0 by the class of the surrounding surfaces).
  • Old insulation may contain asbestos – do not disturb; use a certified contractor.
  • Germany, existing buildings: uninsulated, accessible heating and hot water pipes in unheated rooms must be insulated by the owner (GModG § 69 (2)).
  • Not yet checked here: GModG § 70 and the 12 kW threshold of § 65, DS 452, IE, FR, AT, NL, IT, US IECC, CA NECB, NZ, JP, CN – see the regulation's own text.

Frequently asked questions

How thick should insulation be to stop condensation on a cold pipe?

Thick enough that the outer surface stays at or above the dew point of the surrounding air. At 25 °C and 60 % relative humidity the dew point is about 16.7 °C; a 28 mm copper chilled water pipe at 6 °C in still air then needs about 4 mm of elastomeric foam with a black surface (in practice the thinnest stocked size) and about 7 mm under a bright aluminium jacket. More humidity, a colder fluid or a draught-free corner quickly needs more. The calculator finds the smallest thickness for each pipe (EN ISO 12241).

Why does a shiny jacket need more insulation?

A bright metal surface radiates very little heat (emissivity about 0.05–0.15 against 0.9 for rubber or paint), so the outside heat transfer coefficient is lower and the surface stays closer to the pipe temperature. On cold pipes that means a colder surface and more insulation to stay above the dew point.

Do cold pipes need a vapour barrier?

Yes. Water vapour diffuses from the warm air towards the cold pipe and condenses inside the insulation if the material lets it through. Closed-cell materials such as flexible elastomeric foam or cellular glass act as their own barrier; mineral wool and PIR need a sealed vapour barrier on the outside (EN ISO 15758). Spain's RITE asks for more than 50 MPa·m²·s/g, Australia's NCC J6D9 for a barrier on all cooling fluids.

Which insulation thickness is required by law?

Some countries have tables in the law: Germany (GModG Annex 8), Spain (RITE IT 1.2.4.2.1), England (Approved Document L), Australia (NCC J6D9 as R-value) and the Swiss cantons. Others, such as Sweden, Finland and Norway, have no table and count the losses in the building's energy performance. The legal tables are energy requirements: the calculator always also checks condensation and uses the larger thickness.

Assumptions: Steady state, one insulation layer, horizontal pipe in still air indoors or in wind outdoors; inner heat transfer and pipe wall neglected; λ(T) and μ are typical values – use the product's declared data. Joints, hangers, valves and fittings need the same thickness and a continuous vapour barrier on cold pipes.

Disclaimer: A design aid, not a substitute for the designer's own calculation and the manufacturer's data. Minimum thicknesses shown are taken from the cited regulation and edition, checked 2026-11-02. They are energy requirements; they do not guarantee freedom from condensation. Local rules, product approvals and the designer's calculation take precedence. Always check the current text.

New feature – please report any errors: Report a bug

Help

Enter the air around the pipes, choose the insulation material and the country rule, then list the pipes. Each pipe gets the larger of the thickness that keeps its surface above the dew point and the legal minimum, rounded up to a stocked thickness.

Pipes

  • + Add pipe adds a pipe like the last one. Each row: name, use (service), pipe system and size, fluid temperature, length and whether it runs indoors or outdoors.
  • Air temperature and relative humidity are taken from the surroundings panel; type a value in the row to use another one for that pipe.
  • Leave the thickness empty for the calculated value, or type your own: the result then shows whether it is enough.
  • Click a row (or a small cross-section under the drawing) to show that pipe in the drawing.
  • In "Lines to insulate" you tick which lines get insulation: suction lines MT and LT, the liquid line (ticked for CO2), hot gas / discharge / return lines and water pipes. A pipe of a refrigerating system gets its line in the column "Line".
  • The "?" beside each field and column explains what it is, what to fill in and what it changes. In the cross-section, click or tap a part to change it, and drag the yellow handle to change the thickness; "Dew point" shows the calculation step by step and has a small dew point calculator.

Condensation

  • Cold pipes must keep the outer surface at or above the dew point of the air. The dew point rises steeply with humidity: at 25 °C it is 14 °C at 50 % and 19 °C at 70 %.
  • A shiny jacket (aluminium, stainless) radiates little, so its surface stays colder: it needs more insulation than a black or painted surface.
  • Water vapour also diffuses into the insulation and condenses inside it. Cold pipes need a closed-cell material (elastomer, cellular glass) or a sealed vapour barrier outside open materials (mineral wool, PIR).

Legal minimum

  • The country tables are energy requirements read in the law itself. They do not guarantee freedom from condensation, which is why the larger of both thicknesses is used.
  • Germany: GModG covers heating and hot water, and chilled water or refrigerant pipes of air-conditioning and ventilation – not commercial refrigeration.
  • Other countries are shown as a reference only.

Files and print

  • Save file saves the project as a link file (.html): double-click it to open the project in the browser, or choose it with Open file. In Chrome and Edge Save file writes over the file chosen with Save as… or Open file. Copy link copies the link. Older .json files can still be opened. Autosave saves every few minutes to that file, or else in this browser.
  • Print / PDF prints the report and the cross-section on a page of its own; choose "Save as PDF" in the print dialog for a PDF.