What does L/s mean in HVAC?

L/s stands for litres per second — the volumetric airflow rate through the duct system. Each room requires a certain L/s to achieve the calculated cooling load. The total L/s determines the size of the ducted unit you need: for example, a Daikin FDYAN100 produces 285 L/s, which suits a home requiring 260–285 L/s total airflow.

Free Tool

Free HVAC Load Calculator
for Australian Homes

Q: What size ducted air conditioner do I need for a 4-bedroom house?

A typical 4-bedroom home in Sydney (climate zone 5) with a living room, kitchen, 4 bedrooms, and a study is approximately 120–140 m² of conditioned space. At 125 W/m², that gives a cooling load of 15–17.5 kW. A 14 kW ducted unit (producing around 355 L/s) would cover most configurations — add a 16 kW if your open-plan area is large or the home is well glazed.

Q: What is an NCC climate zone?

The National Construction Code (NCC) divides Australia into 8 climate zones based on temperature, humidity, and solar radiation. Zone 1 covers hot-humid regions like Darwin; Zone 5 covers temperate regions like Sydney, Perth, and Adelaide; Zone 6 covers cool-temperate Melbourne and Canberra. Your zone affects the W/m² cooling load factor used in this calculation.

Q: Is this calculation compliant with AS 4254.2?

This tool provides a rule-of-thumb sizing estimate based on W/m² load factors from AIRAH DA07. For a fully compliant design including duct velocity checks (AS 4254.2), friction rate limits (NCC J6), and fresh air requirements (AS 1668.2), use neuralduct's full design tool — it validates every element automatically.

Enter your rooms and NCC climate zone to instantly calculate your home's cooling load and find the right ducted air conditioner size — in kW and L/s. No sign-up, no cost, no download.

How this calculator works

This tool uses the W/m² load factor method recommended in AIRAH DA07 for preliminary residential sizing. Each room's floor area is multiplied by a climate-zone-specific cooling load factor (W/m²) to give a sensible heat load. Dividing the total wattage by 45 W per L/s gives the required airflow, and the tool then matches the smallest ducted unit whose rated airflow meets or exceeds your total.

This approach is accurate for standard residential homes with typical insulation and glazing. For homes with high glazing ratios, concrete slab construction, or unusual orientations, use neuralduct's full design tool which lets you adjust load factors room by room.

NCC Climate Zone load factors

The W/m² figures are rule-of-thumb values calibrated to Australian residential conditions — they account for solar gain, internal loads, and typical ventilation rates for each climate type.

Zone	Description	Key cities	W/m²
1	Hot Humid	Darwin, Cairns, Broome	160
2	Warm Humid	Brisbane, Townsville, Gold Coast	145
3	Hot Dry	Alice Springs, Broken Hill, Kalgoorlie	145
4	Mixed Dry	Mildura, Griffith, Dubbo	130
5	Mild Temperate	Sydney, Perth, Adelaide, Canberra	125
6	Cool Temperate	Melbourne, Hobart, Ballarat	110
7	Cool	Canberra, Armidale, Cooma	100
8	Sub-Alpine	Perisher, Thredbo, Falls Creek	95

From cooling load to duct design

Once you know the total L/s, the next step is to size the ductwork. AS 4254.2 sets velocity limits for each duct diameter — for example, Flex 300mm duct is limited to 140 L/s. Sizing ducts correctly ensures quiet operation, low friction losses (NCC J6 requires ≤ 1.0 Pa/m on the index run), and even airflow to each room.

neuralduct's full design tool does all of this automatically: auto-sizes every duct, validates velocities in real time, checks the friction rate on every segment, and flags any AS 1668.2 fresh air shortfalls — so you can hand over a compliant design in minutes instead of hours.

Climate zone landing pages

Use the pre-filled calculators below for your city:

Zone 1 — Darwin

Hot Humid · 160 W/m²

Zone 2 — Brisbane

Warm Humid · 145 W/m²

Zone 3 — Alice Springs

Hot Dry · 145 W/m²

Zone 4 — Inland Arid

Mixed Dry · 130 W/m²

Zone 5 — Sydney / Perth

Temperate · 125 W/m²

Zone 6 — Melbourne

Cool Temperate · 110 W/m²

Frequently asked questions

What size ducted air conditioner do I need for a 4-bedroom house?

A typical 4-bedroom home in Sydney (zone 5) with a living room, kitchen, 4 bedrooms, and a study covers around 120–140 m². At 125 W/m², that's a cooling load of 15–17.5 kW. A 14 kW ducted unit handles most configurations — step up to 16 kW if you have large open-plan areas or high glazing.

What is an NCC climate zone?

The National Construction Code divides Australia into 8 zones based on temperature, humidity, and solar radiation. Zone 1 (Darwin) is the hottest and most humid; Zone 8 (alpine regions) is the coolest. Your zone directly affects how large a system you need — a home in Darwin needs almost double the cooling capacity of the same-sized home in Melbourne.

What does L/s mean and why does it matter?

L/s (litres per second) is the volumetric airflow rate. Each room needs a certain L/s to remove its heat load. The total L/s determines the minimum size of ducted unit required — the unit must be rated at or above the total to avoid running at maximum capacity continuously. L/s also drives duct sizing: AS 4254.2 sets maximum L/s per duct diameter to limit noise and friction.

Is this calculation compliant with AS 4254.2?

This tool gives a reliable preliminary sizing estimate using the W/m² load factor method (AIRAH DA07). For a fully compliant design — including duct velocity checks (AS 4254.2), friction rate limits (NCC J6 ≤ 1.0 Pa/m), and fresh air requirements (AS 1668.2 ≥ 10% of supply) — use neuralduct's full design tool. It validates every element automatically and flags violations in real time.

Should I include bathrooms and laundry rooms?

Generally no — bathrooms and laundries are excluded from ducted systems in residential design. They use exhaust fans (AS 1668.2) rather than supply air. Only include rooms that will receive conditioned supply air in your calculation.