Ventilator Sizing Calculation Table

How Many Ventilators Do I Need?

COMMERCIAL/INDUSTRIAL

Calculate the buildings M³ (Length x Width x Height)
Determine the number of air changes required for the building type (Table 1)
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

Recommended * No. of air changes per hour
Building Type	Air Changes P/Hr	Building Type	Air Changes P/Hr
Warehouses	3–5	Laundries	7–15
Factories/Workshops	3–8	Welding Workshops	12–21
Gyms/Sport halls	3–8	Animal Housing	10–50
Assembly Halls	6–12	Garages	6–12
Toilets	12–15	Cooking Factories	6–12

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

Table 2

Temperature Difference between Indoors and Outdoors (°C)
		3°C				5°C				10°C
Vent Size	Wind Speed	6m	10m	15m	20m	6m	10m	15m	20m	6m	10m	15m	20m
200mm Curved Vane	1m/s	180	230	320	380	300	340	410	460	350	580	700	810
	2m/s	260	370	500	590	550	680	760	830	590	750	920	930
	3m/s	470	720	770	880	730	830	930	1030	800	870	1060	1075
	4m/s	720	900	1060	1150	1000	1130	1250	1320	1060	1250	1280	1300
	5m/s	1080	1120	1230	1400	1100	1230	1320	1360	1180	1300	1390	1430
300mm Curved Vane	1m/s	270	340	420	490	360	430	500	550	510	720	940	1050
	2m/s	320	510	610	760	610	740	840	936	720	870	1110	1220
	3m/s	580	930	960	1080	870	990	1100	1200	1000	1090	1280	1340
	4m/s	860	1240	1290	1350	1200	1300	1480	1530	1310	1490	1580	1680
	5m/s	1310	1480	1580	1640	1450	1490	1630	1680	1520	1670	1810	1910
500mm Curved Vane	1m/s	910	1090	1090	1410	1000	1230	1450	1750	1250	1570	1990	2040
	2m/s	1390	1540	1570	1710	1430	1570	1820	2010	1630	1640	2270	2530
	3m/s	1640	2246	2080	2210	1840	2010	2250	2420	2100	2250	2710	2860
	4m/s	2570	2610	2610	2800	2450	2650	2730	2910	2620	2750	3200	3300
	5m/s	3110	3120	3130	3220	3120	3130	3370	3440	3150	3380	3410	3770
600mm Curved Vane	1m/s	1210	1450	1820	2050	1390	1820	2210	2600	1840	2340	2850	3380
	2m/s	1900	2050	2300	2600	2090	2310	2680	3059	2360	2780	3230	3690
	3m/s	2640	2880	3050	3140	2830	2990	3250	3510	3050	3380	3920	4160
	4m/s	3600	3600	3720	4120	3620	3770	3930	4160	3830	4090	4420	4740
	5m/s	4320	4450	4530	4880	4450	4580	4710	4870	4600	4860	5130	5395
700mm Straight Vane	1m/s	2136	2542	2923	3289	2491	2964	3468	3988	2905	3457	4045	4651
	2m/s	3087	3488	3907	4313	3419	3863	4327	4776	3786	4278	4791	5289
	3m/s	4695	5258	5837	6391	5153	5772	6406	7015	5656	6335	7032	7700
	4m/s	5887	6475	7123	7764	6346	6980	7679	8370	6841	7525	8277	9022
	5m/s	7600	8132	8701	9136	7969	8527	9124	9580	8356	8941	9567	10046
900mm Straight Vane	1m/s	2848	3389	3897	4385	3321	3952	4624	5318	3873	4609	5393	6202
	2m/s	4410	4983	5581	6162	4884	5519	6181	6824	5408	6111	6845	7556
	3m/s	7825	8764	9728	10652	8589	9619	10677	11692	9427	10558	11720	12833
	4m/s	9344	10278	11306	12324	10073	11080	12188	13285	10859	11944	13139	14321
	5m/s	11259	12047	12890	13535	11806	12633	13517	14193	12380	13247	14174	14883

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.

House Size (m²)	No. of Ventilators Required (200mm / 300mm)
Recommended Ventilation Guide
90–120	1–2
130–180	2–3
200–350	3–4

Frequently Asked Questions

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.

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.

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.

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.

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.

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.

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.

Calculation Table

How Many Ventilators Do I Need?

COMMERCIAL/INDUSTRIAL

Frequently Asked Questions

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

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

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

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

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

What factors should New Zealand customers consider alongside the calculator?

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

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