HVAC
HVAC Load Calculator
Produce a planning load figure from the envelope and climate, as preparation for a proper Manual J rather than a substitute.
Result
This is a preliminary sizing estimate using industry rules of thumb. Actual equipment selection requires a room-by-room load calculation (ACCA Manual J) and duct design (Manual D) by a qualified professional, oversized equipment short-cycles, dehumidifies poorly and fails early. Windows are frequently the single largest load component, which is why glazing area is separated out here.
Get a Free Business AuditWhat moves the number
- Infiltration, which on an older building can rival the conduction load.
- Internal gains from people, lighting and equipment, which matter in commercial spaces.
- Orientation and glazing, since the same house rotated has a different peak load.
Where this one goes wrong
Using a whole-house figure to size individual zones. Room by room load is what sizes ducts and registers, and a system that is correct overall can still starve the rooms furthest from the air handler.
Questions
About this calculator
Is this a Manual J?
No. It gives a planning figure to sanity check a proposal. A Manual J accounts for construction assemblies, orientation, infiltration and internal gains room by room, and that is what equipment and duct design should come from.
Why do room by room loads matter?
Because the duct system distributes the capacity, and a correct total delivered unevenly still leaves rooms uncomfortable. Room loads are what size the branches and the registers.
How much does air sealing change the load?
On a leaky building, substantially. It is frequently the cheapest way to reduce the required capacity, and doing it before sizing can mean smaller equipment and a better result.
Put this calculator on your site
Free to embed. Paste this where you want it to appear. It stays up to date automatically because it loads from BDEVY.
Please keep the attribution line. It is the only thing we ask in return.
How to use this calculator
- Conditioned floor area (sq ft) (sq ft). Enter your own figure; the page starts at 2,000 sq ft.
- Ceiling height (ft) (ft). Enter your own figure; the page starts at 9 ft.
- Total window area (sq ft) (sq ft). Enter your own figure; the page starts at 260 sq ft.
- Construction and air sealing. Enter your own figure; the page starts at Average.
- Cooling climate. Enter your own figure; the page starts at Warm south.
- Heating climate. Enter your own figure; the page starts at Cool north.
The result updates as you type, so you can try a figure, see what it does to cooling load, and change it back. Nothing you enter is sent anywhere or saved.
A worked example
These are the figures the calculator opens with. Every number in the results column below is produced by the same calculation the page runs, so you can follow it through before putting your own figures in.
What goes in
| Input | Value |
|---|---|
| Conditioned floor area (sq ft) | 2,000 sq ft |
| Ceiling height (ft) | 9 ft |
| Total window area (sq ft) | 260 sq ft |
| Construction and air sealing | Average |
| Cooling climate | Warm south |
| Heating climate | Cool north |
What comes out
| Result | Value |
|---|---|
| Cooling load main result | 52,625 |
| Heating load | 102,088 |
| Cooling in tons | 4.4 |
| Load from windows | 7,800 |
Estimated 52,625 BTU/h cooling (4.4 tons) and 102,088 BTU/h heating, of which 7,800 BTU/h comes from glazing alone.
How sensitive the answer is
Holding everything else steady and changing only conditioned floor area (sq ft), this is what happens to cooling load. It is worth knowing which of your inputs the answer actually hinges on, and which barely move it.
| Conditioned floor area (sq ft) (sq ft) | Cooling load |
|---|---|
| 1,000 sq ft | 30,213 |
| 1,500 sq ft | 41,419 |
| 2,000 sq ft example above | 52,625 |
| 3,000 sq ft | 75,038 |
| 4,000 sq ft | 97,450 |
Every other input is held at the example value while this one changes, which is not how a real job behaves. Treat it as a guide to which number matters most, not as five separate quotes.
What each figure means
- Conditioned floor area (sq ft) (sq ft)
- Measured in sq ft, starting at 2,000 sq ft.
- Ceiling height (ft) (ft)
- Measured in ft, between 0 and 30, starting at 9 ft.
- Total window area (sq ft) (sq ft)
- Measured in sq ft, starting at 260 sq ft.
- Construction and air sealing
- Choose from Older, leaky, Average, Tight / modern.
- Cooling climate
- Choose from Cool north, Moderate / mid, Warm south, Hot south, Hot / humid south, Desert / extreme heat.
- Heating climate
- Choose from Hot / humid south, Warm south, Moderate / mid, Cool north, Cold north, Very cold.
What the results tell you
| Result | What it is |
|---|---|
| Cooling load | The headline result. A number. |
| Heating load | A number. |
| Cooling in tons | A decimal figure. |
| Load from windows | A number. |
Before you rely on this number
Sizing, capacity and load figures here are planning estimates. A real installation depends on the manufacturer's data for the specific equipment, the duct system it is going into, and a proper load calculation for the building. Use this to sanity-check a number or price a job, not to select equipment.
Keep going
Related calculators
AC Size Calculator
Estimate cooling capacity for a space as a cross-check on a load calculation, not as a replacement for one.
Open calculatorFurnace Size Calculator
Estimate heating input and output for a space, with the distinction between the two made explicit.
Open calculatorInsulation Calculator
Works insulation quantity, where the R-value requirement comes from the climate zone.
Open calculatorEstimating is the easy part
The jobs you never hear about cost more than the ones you mis-measure. BDEVY builds the marketing, systems and automation that bring them in.