How this pipe radiation condensate calculator works
A steam pipe keeps losing heat from its surface even when no heat is being used, and that loss makes condensate. This page gets the radiating diameter and surface area from the pipe outside diameter and the insulation thickness, multiplies the temperature difference by the surface heat transfer rate for the heat loss, then divides by the latent heat for the running condensate load. Enter the pipe weight, the metal specific heat and the warm up time and the warm up condensate is shown separately. If the warm up time is left blank or set to 0, the warm up load is skipped and only the running load is shown. Results are given in US units with metric values in parentheses.
The relations applied are area = pi x surface diameter x length, heat loss = heat transfer rate x area x temperature difference and running load = heat loss / latent heat, with the warm up load as pipe weight x specific heat x temperature rise / latent heat. The temperature rise is taken as the difference between the surface and ambient temperatures. Figures reflect October 2026 and the underlying values come from secondary sources, so checking the originals is advised.
The surface heat transfer rate, the latent heat and the metal specific heat were not confirmed from an authoritative source, so no tables are offered and all three are entered by you. The weight of insulation, flanges and valves is left out of the warm up part. Working a condensate load out from a heat load, sizing insulation thickness or surface temperature, and steam trap sizing are not covered. This calculator is for reference and does not replace design. Review by a qualified engineer is required.
Frequently asked questions
It depends on the surface finish, the air movement and the emissivity, so no figure is offered here because none was confirmed from an authoritative source. Take the value from your design data or the insulation maker data.
The running load comes from heat that keeps leaving the pipe surface, while the warm up load is the one off amount produced while cold pipe metal is brought up to operating temperature. The warm up load is packed into a short time, so its rate can be far higher.
The area grows but the surface temperature drops a long way, so the temperature difference shrinks. This page takes the surface temperature and the heat transfer rate as inputs, so the effect of insulation has to be reflected in those two values.