Warm Air Central Heating

Grilles and Registers » Grille and Register Sizing Guidance

It is recommended that when ordering Registers, Grilles or Diffusers that you check with our sales department to ensure you have understood this guidance.

'Nominal sizes' are the dimensions of the duct opening into which a register, grille or diffuser will fit.

a) Register and Grille sizes are based on the duct that they will cover; therefore the best method of sizing is to remove the Register or Grille and to measure the duct. Measurements are normally taken in inches: width A x height B as diagram below. (Note: the measurement in inches in each case is usually an even number).

b) Should removal of the Register or Grille not be possible at the time of measuring, measure the opening / grille area of the Register or Grille. Measurements are taken width A x height B as diagram below, then add approximately 1inch to each dimension to find the nominal size of the replacement register or grille. (Note, the measurement in inches in each case is usually an even number).