Finds the least-cost (economic) insulation thickness for a pipe run: sweeps candidate thicknesses and picks the one with the lowest total annual cost (annualised capital + annual energy lost).
Tender-stage only. Verify final design to project spec, BS 5422 and BS EN ISO 12241.
For design guidance only. Always verify with a qualified engineer.
About this economic insulation thickness calculator
This free economic insulation thickness calculator finds the least-cost insulation thickness for a hot or chilled pipe run. It sweeps candidate thicknesses and returns the one with the lowest total annual cost, the annualised cost of the insulant plus the annual cost of the heat it lets escape. Enter the bare pipe diameter, insulation conductivity, fluid and ambient temperatures, run length, operating hours, energy price and generation efficiency, the installed insulation cost per cubic metre, and a discount rate and study period, and the calculator reports the economic thickness, the finished insulated diameter, heat loss per metre, the saving against a bare pipe, and the annual capital, energy and total costs. It is aimed at UK building-services engineers and energy assessors specifying pipe insulation at tender or feasibility stage. All figures are computed in your browser; nothing is uploaded.
How the economic thickness is calculated
The method follows the economic-thickness approach of BS 5422:2023 and the TIMSA/CINI minimum-total-cost model: the optimum is the thickness that minimises annualised capital plus annual energy cost. Heat loss per metre uses the steady-state cylindrical resistance network of BS EN ISO 12241:2022, conduction resistance Rₜ = ln(r₂/r₁)/(2πk) in series with the outer surface film Rₜ = 1/(h·2πr₂), with heat loss Q′ = ΔT/(Rₜ+Rₜ). The insulation capital is the annulus volume per metre × cost × length, annualised by the capital recovery factor CRF = i(1+i)ⁿ/((1+i)ⁿ−1), or 1/n when the rate is zero (the ASHRAE owning-and-operating-cost method). Annual energy cost is the heat lost × hours × price, divided by generation efficiency. Because both cost terms scale with run length, the optimum thickness is independent of length; only the £ figures move. This is a clearly-bounded simplification of the fuller BS 5422 method, which can add fuel-price escalation.
Frequently asked questions
What is economic insulation thickness?
It is the insulation thickness that gives the lowest whole-life cost, thin enough to keep the capital cost down, thick enough to cut the cost of wasted heat. Adding more insulation beyond this point costs more in material and labour than it saves in energy.
Does the pipe run length change the answer?
No. Both the capital and energy terms scale linearly with length, so the optimum thickness is the same for a 5 m or a 500 m run. Length only scales the annual £ figures the calculator reports, not the recommended thickness.
Can I use it for a heat pump or chilled pipe?
Yes. Enter a COP greater than 1 in the efficiency field for a heat pump, and the calculator divides heat lost by the COP to get fuel cost. For chilled lines set the fluid temperature below ambient, the ΔT and heat flow simply reverse, and the economic thickness is found the same way.