HVAC loads

Room HVAC load estimator

Enter basic room geometry, comfort setpoints, and envelope assumptions to estimate design-day heating and cooling loads.

The calculator mirrors the clean, simple layout of our price normaliser so you can focus on the essentials—no auto-recompute, just adjust values and hit Calculate.

Results

Design-day loads

Cooling and heating estimates remain on screen after each calculation.

Cooling load
5.18 kW
ΔT 17.6°C
Heating load
2.13 kW
ΔT 16.1°C
Natural ventilation ratio 5.8%

Meets the NCC 5% operable glazing guideline.

Enter geometry and envelope values, press Calculate, and review the loads above. Numbers stay visible until you recalc.

Design references

Dry-bulb lookup

Using MELBOURNE AIRPORT (2000-2021(Hrly)) dataset pulled from the West-Edge HVAC table.

City Cooling DB (°C) Heating DB (°C) Source site
melbourne 41.6 3.9 MELBOURNE AIRPORT
sydney 37.3 7.8 SYDNEY AIRPORT AMO
brisbane 32.4 9.8 BRISBANE AIRPORT
perth 40.9 5.7 PERTH AIRPORT
adelaide 40.9 4.8 ADELAIDE AIRPORT
hobart 34.0 2.2 HOBART AIRPORT
darwin 36.0 17.2 DARWIN AIRPORT
other 38.8 -3.2 TUGGERANONG

Calculation notes

What the model assumes

  • Indoor setpoints fixed at 20°C heating / 24°C cooling (NCC typical).
  • Internal and solar gains always included (occupants + plug loads + solar).
  • Window % input disables absolute area; defaults to 5% operable glazing (NCC natural vent credit).
  • Floors are exposed by default for single-storey jobs; untick if fully internal.

Climate dataset

Default climate → MELBOURNE AIRPORT (2000-2021(Hrly))

Database dry-bulb references pulled directly from the Bureau workbook.

Worst-case cooling DB

January = 41.6°C

Maximum monthly critical 3pm dry-bulb across the entire year.

Worst-case heating DB

Winter dry-bulb = 3.9°C

Winter dry-bulb (or lowest critical month) representing the coldest scenario.

ΔT for cooling

ΔT₍cool₎ = 41.6°C − 24.0°C = 17.6°C

Design outdoor temperature minus indoor cooling setpoint.

ΔT for heating

ΔT₍heat₎ = 20.0°C − 3.9°C = 16.1°C

Indoor heating setpoint minus winter dry-bulb baseline.

Envelope conduction

Q = Σ (Uᵢ × Aᵢ × ΔT)

Each surface uses its U-value (1/R_total), exposed area, and respective ΔT.

Configurator

Adjust climate, geometry, and gains.

Location & comfort

Start typing a postcode or suburb; selecting a match will set the NCC zone and nearest climate station.

NCC 2022 climate zone

Based on Default climate (NCC postcode dataset) the climate zone is Zone 6. Update the location to change the zone automatically.

Geometry & envelope

Wall insulation R-label R3.0
Roof / ceiling insulation R-label R6.0
Floor insulation R-label R3.2

NCC zone 6 defaults shown (Wall R3.0, Roof R6.0, Floor R3.2).

Windows & ventilation

Glazing area is auto-calculated from the % entry and wall area. NCC minimum 5% operable glazing assumed by default.

Internal & solar gains

Detailed breakdown

Where the kW come from

Cooling contributors

  • Walls / façade 204 W
  • Roof / ceiling 93 W
  • Floor / slab edge 86 W
  • Windows conduction 413 W
  • Solar gains 1537 W
  • Infiltration + ventilation 1996 W
  • Internal gains 850 W

Heating contributors

  • Walls / façade 186 W
  • Roof / ceiling 85 W
  • Floor / slab edge 78 W
  • Windows conduction 378 W
  • Infiltration + ventilation 1826 W
  • Internal gain credit -425 W

Envelope summary

  • wall · R3.0 R_total ≈ 3.5 · U ≈ 0.29
  • roof · R6.0 R_total ≈ 6.6 · U ≈ 0.15
  • floor · R3.2 R_total ≈ 3.6 · U ≈ 0.28
Calculation trace (compact)

Climate dataset

Default climate → MELBOURNE AIRPORT (2000-2021(Hrly))

Database dry-bulb references pulled directly from the Bureau workbook.

Worst-case cooling DB

January = 41.6°C

Maximum monthly critical 3pm dry-bulb across the entire year.

Worst-case heating DB

Winter dry-bulb = 3.9°C

Winter dry-bulb (or lowest critical month) representing the coldest scenario.

ΔT for cooling

ΔT₍cool₎ = 41.6°C − 24.0°C = 17.6°C

Design outdoor temperature minus indoor cooling setpoint.

ΔT for heating

ΔT₍heat₎ = 20.0°C − 3.9°C = 16.1°C

Indoor heating setpoint minus winter dry-bulb baseline.

Envelope conduction

Q = Σ (Uᵢ × Aᵢ × ΔT)

Each surface uses its U-value (1/R_total), exposed area, and respective ΔT.

  • ΔT_cool = 41.6°C - 24.0°C = 17.6°C
  • ΔT_heat = 20.0°C - 3.9°C = 16.1°C
  • Q_wall_cool = U_wall(0.29) × wall_area(40.5 m²) × ΔT_cool(17.6) = 204 W
  • Q_roof_cool = U_roof(0.15) × roof_area(35.0 m²) × ΔT_cool(17.6) = 93 W
  • Q_floor_cool = U_floor(0.28) × floor_area(35.0) × 0.5 × ΔT_cool = 86 W
  • Q_windows_cool = U_window(5.80) × window_area(4.0) × ΔT_cool(17.6) = 413 W
  • Q_solar = SHGC(0.72) × area(4.0) × I_solar(620) × shading(0.85) = 1,537 W
  • Q_vent_cool = ρcp(1200) × Ṽ(0.095 m³/s) × ΔT_cool(17.6) = 1,996 W
  • Q_internal = people(150) + equipment(525) + lighting(175) = 850 W
  • Cooling load = sum components = 5,179 W (5.18 kW)
  • Heating load = sum components = 2,129 W (2.13 kW)