Pipe Heat Loss Calculator
How much heat an insulated pipe loses per foot — and how much the insulation saves. Radial conduction through the insulation plus the outer surface film, from the pipe and ambient temperatures.
What a Hot Pipe Costs You
Every foot of hot pipe bleeds heat to the room, and over a long run that is real money and real temperature drop. Insulation slows it dramatically — often cutting the loss by 80 to 90 percent — but how much depends on the material, the thickness and the temperature difference. This calculator turns those into watts lost per foot.
The heat flows outward through the insulation by conduction, then leaves the outer surface by convection. The two resistances add in series. The logarithm is the giveaway that this is radial flow — heat spreads through ever-larger cylindrical shells, unlike the straight-line flow through a flat wall.
Thickness and Diminishing Returns
The first inch of insulation does the most; each additional inch adds less, because the log term grows slowly. Doubling thickness does not halve the loss. A lower conductivity k helps across the board — foam and mineral wool beat perlite — and there is a point where more insulation is no longer worth the cost.
Frequently Asked Questions
What surface temperature do I enter?
The pipe outer wall temperature, which for a well-conducting metal pipe is very close to the fluid temperature inside. The calculator treats that as the inner boundary.
Why does the bare-pipe number look so high?
With no insulation, only the thin surface air film resists the heat, so a bare hot pipe sheds heat fast. That is the figure the insulation is saving you against.
What outer film coefficient is used?
A typical still-air value of about 10 W/m2K. Wind raises it (more loss); a reflective, low-emissivity jacket lowers the radiant part. Use a measured value for precise work.
Related calculators
- R-Value Calculator — the flat-wall cousin of this calculation.
- Heat Transfer Calculator — conduction and convection in general.
- Sensible Heat Calculator — the energy to heat the fluid in the first place.
- Engineering Unit Converter — power and energy units.