Formulas to calculate the required power output of a radiator for a room of a specific size. Do they exist?

Arran, I came across this helpful Excel-based tool, by BRE, and while it only accomodates one emitter type per room, and is only suitable for determining emitter heat output, different emitter types can be varied throughout the dwelling, e.g. underfloor heating downstairs and radiators upstairs, etc. and there are useful look up tables for Tog and U-values or U-factors for different building elements and materials to determne the overall heat transfer. In the U.S. we use R-value which is the reciprocal of the thermal transmittance (U-factor) of a material or assembly. The U.S. construction industry preferes to use R-values, because they are additive and because bigger values mean better insulation, neither of which is true for U-factors.

Arran, I came across this helpful Excel-based tool, by BRE, and while it only accomodates one emitter type per room, and is only suitable for determining emitter heat output, different emitter types can be varied throughout the dwelling, e.g. underfloor heating downstairs and radiators upstairs, etc. and there are useful look up tables for Tog and U-values or U-factors for different building elements and materials to determne the overall heat transfer. In the U.S. we use R-value which is the reciprocal of the thermal transmittance (U-factor) of a material or assembly. The U.S. construction industry preferes to use R-values, because they are additive and because bigger values mean better insulation, neither of which is true for U-factors.