Craft Quantities
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By trade

Heating and ventilation calculators

Heating and ventilation is sized against what a building loses, gains and has to change, and every figure downstream depends on that first number being honest. Oversizing is the industry's habit and its most expensive one: equipment that is too large short-cycles, dehumidifies badly and costs more to buy and to run.

  • 62Calculators
  • 4Parts of the site

How heating and ventilation is measured

Kilowatts or BTU per hour for loads, litres per second or cubic feet per minute for air, and millimetres or inches of duct chosen against a friction rate rather than a velocity alone. Equipment is then selected against the load at design conditions, not against the floor area.

Where heating and ventilation sits on this site62 across 4
62

Electrical1

Plumbing & HVAC23

Insulation & Efficiency4

Materials & Quantities34

What gets left off a heating and ventilation order

  • Duct fittings, which carry most of a system's resistance — a bend is worth many metres of straight duct.
  • The distinction between sensible and latent load, which is what decides whether a room is cool and clammy or cool and comfortable.
  • Leakage. An unsealed duct system can lose a large share of what the fan moves, and the loss is usually outside the heated space.
  • Commissioning and balancing, without which the design airflow is a drawing rather than a fact.

Job takeoffs4

Where HVAC engineers meet the rest of the job: each runs one of these calculators, with every other trade in the same job beside it.

Comparisons21

Two ways of doing the same work, weighed against each other.

Planners1

Work this trade out from a space rather than from a job.