Calculation Table

How Many Ventilators Do I Need?

COMMERCIAL/INDUSTRIAL

1. Calculate the buildings M³ (Length x Width x Height)
2. Determine the number of air changes required for the building type (Table 1)
3. Next calculate the venting capacity M³/h (Table 2)

You will need to know:

• Typical area wind speed (1m/s to 5m/s).
• Temperature difference between indoors and outdoors (°C)
• Roof height

4.   Insert the information into the formula to calculate the total number of ventilator

Table 1

*Air change rate must conform to local health department’s code specific to building type.

Table 2

Formula:

  M³ x air changes (table 1)

venting capacity (Table 2)        =      No. of ventilators Required*

*If this exceeds the amount of ventilators suitable to fit the roof with the recommended spacing of 6m (no less than 5m) then recalculate using a larger size ventilator.

RESIDENTIAL

Frequently Asked Questions

How do I use the roof vent calculator/calculation table for a New Zealand building?

To use the table, calculate your building’s total volume (length x width x height) and determine the required Air Changes per Hour (ACH) for your industry. You then match your total required airflow against our Exhaust Capacity Chart to see how many Skyaxis units are needed.

How many roof vents do I need for my building size in New Zealand?

The number of vents is calculated by: (Building Volume × Required Air Changes) ÷ Vent Capacity. For a typical 90–120 m² home, 1–2 ventilators are generally required to maintain a healthy, dry environment.

Does the calculator change for residential vs commercial buildings in NZ?

Yes, the required air changes vary depending on the building’s use; for example, a standard warehouse may only need 2–5 air changes, while a hot factory may require 10 or more. Our calculator helps you adjust for these different requirements to ensure your ventilation system is fit for purpose.

What roof vent size should I choose for a typical New Zealand garage or shed?

The 300mm Skyaxis model is our standard recommendation for residential garages and sheds. It provides the ideal extraction capacity to effectively remove heat and moisture from these smaller spaces.

Can you check my ventilation sizing if I send my dimensions from anywhere in New Zealand?

Yes, we offer free sizing calculations to ensure you get the correct number of vents for your specific building. Just send us your floor area, ceiling height, and building use, and our team will provide a tailored recommendation.

What factors should New Zealand customers consider alongside the calculator?

You should consider your roof height, local wind conditions, and internal heat loads. Factors such as the “stack effect” and higher coastal wind speeds can significantly increase the actual extraction rate beyond baseline calculations.

How do I avoid under-or over-ventilating when sizing roof vents in New Zealand?

Follow our industry-specific “Air Changes per Hour” (ACH) guide and maintain a unit spacing of approximately 5–6 metres. This ensures consistent airflow across the entire building without the unnecessary cost of over-installing units.