Other factors may have to be considered such as whether the radiator is to be recessed, has a shelf above or is to be painted. Correction factor figures are available for such situations.
The most common occurrence however is for domestic heating system radiators to be connected Bottom Bottom Opposite End (BBOE). Previous estimates and practice under the BS 3528 standard estimated that between 4 & 10% of the radiators output was lost when connecting BBOE, and a further correction factor of 0.91 was recommended. Recent tests however have proved that with increased flow rates and low water content in modern systems the effect has been reduced to approximately 2%. A correction factor of 0.98 should now be applied for BBOE connections.
Correction factor application example
Heat loss for a lounge has been calculated at 2000 watts, the radiator will be connected BBOE. The system has been designed with a MWT of 76.5 C. (i.e. 82 C flow + 71 C return = 153 / 2 = 76.5 C MWT) and a room temperature of 21 C
Therefore MWT = 76.5 C minus room temperature 21 C = 55.5 C Correction factor required = 0.908 BBOE correction factor required = 0.98
2000 watts heat loss divided by 0.908 divided by 0.98 = 2247 watt Radiator output required from the brochure.
Actual radiator output calculation
To check what output a radiator would give; multiply the correction factors. For example if a 2000 watts radiator output was chosen from the brochure, then to give the actual output of the radiator.
2000 watts x 0.908 x 0.98 = 1779 watts actual radiator output (clearly too small)