Build up a fan static pressure budget, component by component — total and external static.
| System Type | Typical range | Notes |
|---|---|---|
| Small residential / packaged | 0.3–0.6" | Simple filter, short duct runs |
| Commercial VAV with MERV 13 | 1.5–2.5" | Full AHU with cooling + heating coil |
| Lab / clean room AHU | 2.5–5.0" | HEPA + ERV + multiple coils |
| 100% OA DOAS unit | 1.5–3.0" | ERV + coil + high OA fraction |
| Fan coil unit (FCU) | 0.2–0.5" | Minimal duct, coil only |
Rough planning ranges, not standards. Residential, packaged and fan-coil figures are external static (what the unit’s rating table asks for); AHU, lab and DOAS figures describe the whole air path. Confirm every selection against the unit’s fan curve.
Doing this for a whole building? See this step inside a connected AIM Works project — loads, ventilation, equipment, and Design Review in one place.
Book a Demo →This static pressure budget calculator helps you build up the static pressure an air-handler fan must overcome by adding each component loss along the air path. Enter the pressure drop in inches of water column for the supply and return ducts, diffusers and grilles, cooling and heating coils, pre- and final filters, outdoor-air louvers and dampers, mixing box, and any special items such as an energy recovery wheel or HEPA filter. The tool totals them into the total static pressure (TSP), splits out the external static pressure (ESP) — the items outside the unit casing, which is what a packaged-unit vendor asks for — and groups the result by duct system, coils plus filters, and OA plus dampers.
A live budget bar tracks the total static against a 0 to 2.0 in. w.c. scale and flags whether it is moderate, elevated, or very high by rule of thumb, so you can sanity-check the fan selection. Because the component drops are series losses, the budget is a transparent line-item sum — making it easy to see which items dominate and where to trim resistance to save fan energy.
| Total static | TSP = Σ ΔPi = ΔPduct + ΔPcoils+filters + ΔPOA+dampers + ΔPERV+misc |
| External static | ESP = supply duct + diffusers + return duct + return grilles + OA louver + misc |
| Inside AHU casing | coils + filters + HEPA + OA damper + mixing box + ERV = TSP − ESP |
| Duct group | supply duct + diffusers + return duct + return grilles |
| Coils + filters | cooling coil + heating coil + pre-filter + final filter + HEPA |
| OA + dampers | OA louver + OA damper + mixing box |
Components in series along an airflow path add directly, so the total static pressure is simply the arithmetic sum of every component pressure drop. Each ΔP value comes from manufacturer data or a design allowance, normally rated at standard air (0.075 lb/ft³); at altitude, put the budget and the fan curve on the same density basis. Which items sit inside the casing depends on the unit — the split here follows a typical packaged or catalogued air handler, so move anything field-installed into Misc. The budget bar maps the total static onto a 0–2.0 in. w.c. scale and classifies it as moderate (≤ 1.5"), elevated (≤ 2.5"), or very high (> 2.5") — rules of thumb, not limits. Component ranges shown beside each input are typical submittal values, not standards.
AIM Works brings peak loads, ASHRAE 62.1 ventilation, equipment and plant sizing, compliance checks, Design Review, and engineering deliverables into one connected mechanical design workspace.
Duct and pipe distribution sizing is planned for V2 — at launch, keep using this calculator for that step.
Results are design estimates for preliminary sizing. Verify final designs against applicable codes and standards — engineering judgment and a licensed professional engineer’s review are required.