How to use this calculator
- Enter actual pipe OD. Use outside diameter from the pipe schedule, tube drawing or manufacturer data.
- Add insulation and temperature difference. Enter radial insulation thickness and the absolute pipe-to-ambient temperature difference.
- Set thermal data. Use insulation k-value at mean temperature and a reasonable outside film coefficient for the space.
- Review energy and surface results. Compare insulated loss, heat saved, surface temperature rise and annual cost before selecting a final insulation system.
How it works
Pipe insulation heat loss is a radial conduction problem. The calculator
uses the actual pipe outside radius r1, insulated outside
radius r2, insulation conductivity k and the
outside film coefficient h.
The insulation resistance per unit length is:
R_ins = ln(r2 / r1) / (2 x pi x k)
and the outside film resistance is:
R_out = 1 / (2 x pi x h x r2)
Heat loss per length is:
q' = dT / (R_ins + R_out)
Total heat loss is q' x L.
The bare-pipe comparison uses the same outside film coefficient at the pipe outside radius. Annual energy multiplies heat loss by operating hours and converts watts to kWh. Pair this page with pipe thermal expansion, pipe support span, pipe pressure drop and duct sizing when the same mechanical room also needs movement, support, flow or air-side checks.
Worked example
Verified against the live calculator
A 100 ft pipe run with 1.315 in OD,
1 in insulation, a 100 F temperature difference,
insulation k = 0.04 W/m-K, outside film coefficient
h = 8 W/m2-K, 4000 h/yr operation and
$0.14/kWh energy value loses about 1,392 Btu/h
insulated. The simplified bare-pipe comparison is about
4,850 Btu/h, so the screen shows roughly 71%
heat-loss reduction and about $568/yr in avoided energy.
Frequently asked questions
How do I calculate pipe insulation heat loss?
This page uses cylindrical insulation resistance, R_ins = ln(r2/r1)/(2*pi*k), plus outside film resistance, R_out = 1/(2*pi*h*r2). Heat loss per length is q/L = dT/(R_ins + R_out), then total heat loss is multiplied by pipe run length.
What is the insulation k-value?
The k-value is thermal conductivity. Lower k means better insulation. Use product data at the mean service temperature; insulation conductivity changes with material, temperature, moisture and aging.
Can this size steam or hot-water pipe insulation?
Use it as a first-pass heat-loss and savings screen only. Final steam, hot-water, chilled-water, personnel-protection and energy-code insulation thickness should come from project criteria, code, owner standards and insulation manufacturer data.
Does it handle chilled-water condensation?
No. The surface temperature rise result helps understand surface conditions, but chilled-water condensation control needs ambient humidity, vapor barrier, jacket, insulation system and dew-point checks.
Why compare with bare pipe?
The bare-pipe result gives a simple before/after reference for heat saved. It is a simplified outside-film-only comparison, so treat it as a planning estimate rather than a measured audit.
Method & assumptions
- Pipe is modeled as a straight cylinder with uniform pipe temperature and ambient temperature.
- Insulation is dry, continuous and represented by one thermal conductivity at the mean service temperature.
- Outside film coefficient is a combined screening value for convection and radiation.
- Bare-pipe comparison ignores pipe wall resistance, inside film resistance and radiation details.
- Does not model fittings, valves, supports, insulation joints, jackets, wind, moisture, damaged insulation, vapor barriers, condensation, freeze protection, personnel protection, energy-code compliance, steam-trap losses, boiler efficiency or heat-pump COP.