> For the complete documentation index, see [llms.txt](https://docs.strata.hendersonengineers.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.strata.hendersonengineers.com/workflows/mechanical-planning/loads-and-densities.md).

# Loads and densities

Set mechanical airflow, cooling, and heating densities and review the loads they produce.

Mechanical sizing at schematic design runs on **density assumptions** — how much airflow, cooling, and heating a square foot of a given kind of space needs. Strata holds a default density per space type, applies it to each space's area, and rolls the result up the hierarchy.

> 📸 **Screenshot — Load columns in Data view** The mechanical Data view scrolled to show the Airflow Density, Airflow, Cooling Load Density, Cooling Load, Heating Load Density, and Heating Load columns, with one overridden density cell and the calculated columns visually distinct.

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## The three densities

| Field                | Unit       | Sets                                     |
| -------------------- | ---------- | ---------------------------------------- |
| Airflow Density      | CFM/ft²    | Ventilation and air-distribution airflow |
| Cooling Load Density | ft²/Ton    | Square feet served per ton of cooling    |
| Heating Load Density | BTU/h\*ft² | Heating load per square foot             |

Note the direction of Cooling Load Density: it's an area-per-ton figure, so a **lower** number means a **more** demanding space.

***

## Where the defaults come from

Cooling Load Density and Heating Load Density are set per space type in the project's **basis of design** — open **Project Settings** and find them in the Basis of Design grid. Change a value there and every space of that type picks it up.

Airflow Density defaults come from the space type itself.

There is no single project-wide load density. Densities are per space type, so a gymnasium and a classroom in the same project carry different assumptions.

***

## Overriding a default on a space

The three density fields are **editable on every space**, in the right detail panel or directly in the [Data view](/workflows/mechanical-planning/data-view.md) grid. They arrive pre-filled, which can make them look read-only — they aren't.

* **To override** — type your value over the pre-filled one. The cell is marked as overridden so you can see at a glance which spaces carry project-specific assumptions.
* **To revert** — clear the field. The space goes back to inheriting from the basis of design.

Overrides apply to that space only. They don't change the basis of design or any other space.

***

## The loads Strata produces

From those densities and each space's floor area, Strata produces two values:

| Field        | Unit | From                              |
| ------------ | ---- | --------------------------------- |
| Cooling Load | Tons | Floor area ÷ Cooling Load Density |
| Heating Load | MBH  | Floor area × Heating Load Density |

Both are calculated for spaces, zones, and sources. Zone and source values are the sum of the spaces beneath them, counted once each even when your selection overlaps. Zone and source density figures are aggregated up from their spaces the same way.

> These are density-based estimates for schematic design, not a load calculation. Strata applies a flat per-space-type density to floor area — it does not model climate, envelope, orientation, internal gains, or ventilation loads. Size equipment against a load calculation before design development.

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## Where the values appear

* **Data view** — as columns alongside Airflow, visually distinguished from the fields you edit
* **Right panel** — in the Selection Summary beneath Airflow, for whatever you have selected
* **Space pills** — on each space listed under a selected zone or source
* **Grid data export** — **File → Export → Grid Data** includes the density and load columns for spaces, zones, and sources

***

## What the loads drive

Cooling Load feeds the recommended **Nominal Size** for a source, adjusted by that source's Diversity Factor. The recommendation is a starting point — you select the size you want. See [Sources and Equipment](/workflows/mechanical-planning/sources-and-equipment.md).

Heating Load is reported for reference. It does not drive equipment selection.

***

## Related

* [Spaces](/workflows/mechanical-planning/spaces.md)
* [Sources and Equipment](/workflows/mechanical-planning/sources-and-equipment.md)
* [Mechanical Data View](/workflows/mechanical-planning/data-view.md)
* [Project Settings](/workflows/projects/project-settings.md)
* [Mechanical Equipment Schedule](/reference/exports/mechanical-equipment-schedule.md)