Blower Sizing Calculator for Construction Ventilation

Example data table

These sample values show typical temporary ventilation sizing. Replace them with your project inputs for a more accurate duty point.

Formula used

How to use this calculator

1. Select your unit system and enter room dimensions.
2. Choose ACH for general ventilation, or enter required airflow directly.
3. Enter duct length and diameter, then count common fittings.
4. Add filter and equipment losses from datasheets when available.
5. Apply a safety factor for leakage, dirty filters, and site variability.
6. Click Calculate and use the airflow and pressure to pick a blower curve.
7. Export a PDF or CSV summary for submittals, logs, or inspection records.

Professional guide to blower sizing on construction sites

Temporary ventilation supports worker comfort, removes dust and fumes, and helps control moisture during finishes. A blower is normally selected by matching two targets: required airflow and total static pressure. Airflow is driven by room volume and the intensity of the activity. Higher dust generation, welding, painting, or confined work typically needs higher exchange rates or a defined capture flow at the source. Static pressure comes from duct friction, fittings, and add-on devices such as filters, silencers, dampers, and temporary hoods. When pressure is underestimated, the installed blower can deliver far less flow than expected. When it is overestimated, the system may be noisier, more expensive, and harder to control.

This calculator estimates airflow from either ACH or a direct flow requirement, then computes duct losses using Darcy–Weisbach with a practical friction factor and simple K-values for fittings. The total static pressure is the sum of duct friction, fitting losses, and any user-entered losses, multiplied by a safety factor to account for leakage, dirty filters, minor routing changes, and real-world installation variability. Finally, blower shaft power is estimated from the airflow, pressure, and overall efficiency so you can choose an appropriate motor size and confirm generator capacity.

Worked example (with example data)

Consider a site store room measuring 8 m × 5 m × 3 m. If you target 8 ACH, the required airflow is: V = 120 m³, Q = 120 × 8 = 960 m³/h (≈ 565 CFM). Use a 20 m duct of 300 mm diameter with 4 elbows, 1 tee, and 1 transition. Add filter loss 120 Pa, equipment loss 80 Pa, safety 15%, and assume 60% efficiency.

With these inputs, you will obtain a duty point in the range of roughly 960 m³/h and a few hundred pascals of total static pressure, depending on material and velocity. Use the calculator results to select a blower curve that can deliver the flow at the computed pressure, then confirm noise limits and practical routing before ordering.

FAQs

1) Should I size by ACH or by direct airflow?

Use ACH for whole-room ventilation and general dilution. Use direct airflow when a method statement specifies CFM/m³/h, or when capture at a hood or extraction point is required.

2) What safety factor is reasonable?

A common planning range is 10–20%. Use higher values if filters clog quickly, ducts are temporary and leaky, or routing may change. Keep it lower when losses are well documented and controlled.

3) Why does duct diameter change results so much?

For the same airflow, a larger diameter reduces velocity, which reduces dynamic pressure and friction. Because friction scales strongly with velocity, small diameter changes can significantly reduce total static pressure.

4) How do filters and silencers affect blower selection?

They add static pressure that the blower must overcome. Enter their rated pressure drop at the target flow. If you omit them, the selected blower may not deliver the required airflow on site.

5) What efficiency should I use?

For quick planning, 50–65% is common for portable blower systems including drive losses. If you have manufacturer data for blower and motor, use the combined overall efficiency for better power estimates.

6) Can I use this for fume extraction?

You can estimate airflow and pressure, but fume extraction often needs capture-velocity design and specific hood geometry. Treat the result as a starting point and verify with the extraction equipment supplier.

7) Why is my calculated power low but motor size higher?

Motors are selected from standard ratings and need margin for startup, heat, and site variability. This tool rounds up and adds a service allowance so the motor is less likely to overload in real conditions.