IsoDim Help Heat Loss module


This module is used for calculating the heat loss of pipes, ducts and surfaces in technical installations.

Calculation type

You have to select one out of six categories. In pipes the media is some kind of fluid/gas, in ducts it is always air.


When calculating the external heat transfer coefficient the orientation of the pipe/duct is needed.

Calculation criteria

There's four different options:
  1. Insulation thickness: When you know the thickness of the insulation
  2. Surface temperature: When you want IsoDim to calculate the required insulation thickness to achive a certain surface temperature
  3. Heat loss: When you want IsoDim to calculate the needed insulation thickness to achive a certain heat loss
  4. EN 12828: Uses the temperature difference (media - ambient), operating hours and energy waste factor to select one of six insulation classes. The waste factor is the fraction of heat emission considered as wasted. The default value (1) means that all heat loss is considered wasted, values lower than 1 means that some of the heat loss is considered beneficial (this can be true in heated rooms). The insulation class dictates the maximum allowed heat loss and hence the necessary insulation thickness.
When selecting options 2,3 and 4 only one layer of insulation is allowed (the first option allowes up to three layers). Option 4 is only valid for pipe and surface calculations.

Facing (outside surface)

This section sets the emissivity of the outside surface of the insulated and uninsulated pipe/duct. The droplist contains typical values for different materials.


Use the outside dimension of the pipe/duct (without insulation).


Description of the conditions around and inside the pipe/duct/surface. Ambient (surrounding) nd media temperature are used in all calculations. For outdoor conditions the wind speed also has to be given. For ducts the airflow is also necessary. If annual energy use is calculated average (yearly) values should be used (if you want to calculate worst case conditions then obviously wind speed and ambient temperature have to reflect this).


It's possible to have up to three layers of insulation (the first is the layer closest to the pipe/duct/surface). For calculation criteria 2-4 insulation is restricted to one layer. Select an insulation product from the droplist. One of the standard thicknesses for the product can then be selected in droplist below or you can select and enter a user defined thickness.

Calculate energy use

Annual energy usage and CO2-emission due to heat loss will be calculated. Four parameters are needed to perform the calculations:
  1. Operating hours: If the system does not run the whole year this value should reflect this. The number of operating hours is also needed when calculating necessary insulation thickness according to EN 12828.
  2. Energy cost pr kWh: the cost of heating the media, can be a mix of electricity, oil, gas or other. The efficiency of the heater should be included in the calculation of the price (example: The heater efficiency is 80 % and the price of energy supplied to the heater is 0,15 /kWh, the effective energy price is 0,15 / 0,8 = 0,1875)
  3. CO2-emission: Emission in grams pr kWh. The efficiency of the heater should also be included in this value (see energy cost).
  4. Currency: Currency to be used for the calculations. Please note that the currency only changes the text in the calculated results, not the numbers (there's no automatic conversion between currencies).

Valves, fittings and flanges

Here it is possible to add equipment attached to the pipe that increases the total heat loss. The heat loss is calculated as extra uninsulated pipe length. The drop list contains a few pre-defined types.

Uninsulated suspensions

This is a simplified way of including the extra heat loss due to the pipe suspensions. For outdoor installations 25 % heat loss is added, for indoor installations 15 % is added.

Calculated results

Results are shown in one table, the contents change automatically as you change the input above.