Measuring the floor plan and calculating the insulation area

Start by identifying the colours and symbols used on the drawing. Extract and exhaust air are normally marked in blue, while supply and inlet air are marked in red. Also note which elements are present: pressure control boxes, silencers, plant rooms, fire insulation markings and rising or falling ducts.

Read the stated dimensions (diameter or width × height) and the given scale, for example 1:100, 1:50 or 1:20. The scale is crucial for all subsequent conversions from the drawing's millimetres to real dimensions.

Measure all straight pieces from centre line to centre line — not from outside to outside. For bends, measure from the point where the two centre lines meet, i.e. the centre of the bend. For tee pieces, you can choose to measure either to the centre of the pipe or to the tee piece itself; just be consistent in your choice.

Always measure centre to centre — also in bends.

When a reducer connects two different dimensions, the length of the reducer must always be included in the larger of the two dimensions. If, for example, you start at a silencer and move towards a reducer that goes down to a smaller dimension, the whole run including the reducer is measured as the larger dimension.

Measure the desired length on the drawing with a ruler and read the value in millimetres. Multiply this value by the scale (e.g. × 100 at 1:100) to get the real measurement in millimetres. Then divide by 1,000 to convert to metres. Example: 18.5 mm on the drawing × 100 = 1,850 mm ÷ 1,000 = 1.85 m.

Measure and total all pipe runs of the same dimension separately. So collect all metres for, for example, Ø 160, then for Ø 250 and so on. This gives you the total pipe length per dimension, which is the basis for the insulation calculation.

Determine the required insulation thickness for each duct size based on the applicable duct class. Remember that the insulation thickness can vary with the size — for example, pipes up to a certain diameter may require 30 mm, while larger sizes require 40 mm.

Add twice the insulation thickness to the pipe diameter to get the insulated diameter: insulated Ø = pipe diameter + (2 × insulation thickness). Multiply the insulated diameter by pi (3.14) to get the insulated circumference in millimetres, and divide by 1,000 to get the circumference in metres. Example: (300 + 40 + 40) mm × 3.14 = 1,193.2 mm ÷ 1,000 = 1.1932 m.

Calculate the uninsulated perimeter as the sum of all four sides: (width + width + height + height). Then add 4 × the insulation thickness, because the insulation adds thickness at all four corners. Example: a 400 × 600 mm duct has an uninsulated perimeter of 2,000 mm. With 50 mm insulation: 2,000 + (4 × 50) = 2,200 mm = 2.2 m.

Multiply the insulated circumference (in metres) by the total pipe length for the size in question (in metres). The result is the insulation area in square metres for that size. Example: 1.1 m (insulated circumference) × 1.85 m (length) = 2.04 m².

If a second layer of insulation is to be applied, use the already insulated diameter as the starting point and recalculate using the same method. The insulated diameter from the first layer becomes the new 'pipe diameter', to which further insulation thickness is added.

Add up the insulation areas for all dimensions to a total number of square metres per insulation type and thickness. Add a waste allowance — typically 15 % — by multiplying the total area by 1.15. Then convert to the number of rolls or packs to be ordered.

Present all intermediate calculations clearly so that errors can easily be traced. For each size, state: pipe size, pipe length, insulation thickness, reason for the chosen thickness (duct class), insulated circumference and the calculated area. Finish with a combined materials list stating insulation type, thickness and quantity.