What is economic insulation thickness?

Economic insulation thickness is the thickness at which the sum of insulation cost and energy loss cost is at its minimum over a defined lifetime period. Below this thickness you are wasting energy. Above it you are paying more for insulation than you save in energy.

The concept is defined in EN ISO 12241, Annex B, and is a key tool for engineers optimising insulation projects — not just technically but also financially.

The factors that determine optimal thickness

Economic insulation thickness is not a fixed number — it varies with a range of parameters:

  • Energy price: Higher energy prices mean thicker insulation pays off. With current energy prices the difference between 50 mm and 80 mm insulation can amount to tens of thousands of kroner per year for a longer pipe run.
  • Operating hours: A plant running 8 760 hours/year (continuous operation) has substantially higher energy losses than one running 4 000 hours/year. More operating time means insulation pays back faster.
  • Insulation cost: Material choice and labour cost. More expensive insulation requires greater energy savings to break even.
  • Pipe size: Larger pipes have more surface area per metre — energy loss scales with diameter, and optimal thickness is generally higher for large pipes.
  • Temperature difference: Higher ΔT between medium and ambient gives more energy loss per mm of missing insulation.
  • Discount rate and lifetime: A net present value analysis over 15–25 years gives a different result than a simple payback period calculation.

Why "more insulation = better" is not always true

Many assume that applying as much insulation as possible is always sensible. But beyond a certain point the savings effect flattens out — the next millimetres deliver marginally less energy saving while the cost remains constant or increases (larger cladding, more labour, heavier system).

For a DN200 pipe at 200 °C the first 40 mm of mineral wool can reduce heat loss by 85 %. The next 40 mm reduces it by perhaps a further 8 %. The cost curve, on the other hand, rises linearly or steeper — you pay as much for the last "insignificant" reduction as for the first major one.

Example: DN200 steam line — how 20 mm extra can save 15 000 NOK/year

Let us examine a realistic scenario: a DN200 steam line (outer diameter 219.1 mm) with steam temperature 180 °C, ambient temperature 15 °C, outdoors. Operating hours 7 500 hours/year. Energy cost 0.80 NOK/kWh. Length: 200 metres.

Option A — 60 mm mineral wool:

  • Heat loss: 92 W/m → 92 × 200 = 18 400 W = 18.4 kW
  • Annual energy loss: 18.4 × 7 500 = 138 000 kWh → 110 400 NOK/year
  • Insulation cost: approx. 1 200 NOK/m × 200 = 240 000 NOK

Option B — 80 mm mineral wool:

  • Heat loss: 72 W/m → 72 × 200 = 14 400 W = 14.4 kW
  • Annual energy loss: 14.4 × 7 500 = 108 000 kWh → 86 400 NOK/year
  • Insulation cost: approx. 1 550 NOK/m × 200 = 310 000 NOK

Result: Option B costs 70 000 NOK more in investment but saves 24 000 NOK/year in energy. Payback period: 2.9 years. Over a 20-year lifetime the net saving exceeds 400 000 NOK. But 100 mm insulation would increase investment by a further 80 000 NOK and only save 8 000 NOK/year more — payback period 10 years. Therefore 80 mm is closest to the economically optimal thickness.

EN ISO 12241 Annex B — the formal method

The standard defines a systematic method for finding economic insulation thickness. Annex B describes how to set up a net present value analysis comparing annual energy costs (discounted) with the capital cost of insulation. The optimal thickness minimises the sum of these two over the chosen lifetime.

In practice this requires iteration: you calculate U-value and energy loss for each candidate thickness (e.g. 40, 50, 60, 80, 100 mm) and plot the total cost. The minimum of the curve is the economic insulation thickness.

The method accounts for discount rate, energy price estimates (with possible escalation), maintenance costs for the insulation and residual value at end of life.

How IsoCal makes it easier

IsoCal calculates economic insulation thickness automatically for all 229 materials in the database. You enter pipe dimension, temperature, energy price, operating hours and calculation period — and get optimal thickness with accompanying cost analysis. Results can be exported as a PDF report for use in project documentation or tender submissions. Try IsoCal free at isocal.aeris.no.