Blower Table Airflow Calculator

Concepts behind this calculation

Estimate airflow for one or more blower speed taps from measured total external static pressure and the matching equipment manufacturer's airflow table.

A blower table connects external static pressure and airflow for a particular equipment configuration and speed setting. This calculator reads an exact supplied point or estimates locally between the adjacent pressure points for each tap. The interpolation fraction describes how far the measured pressure lies between those points; it applies to that interval rather than creating a general fan curve.

The table and field measurement must share the equipment model, operating mode and external-pressure boundary. Filter installation, coil condition, voltage and accessories can matter through the source footnotes. Each supplied tap can have its own pressure range, and a measurement outside supported data cannot be resolved by extending the last line. A table estimate remains different from directly measured airflow.

How to use this calculator

1. Complete Equipment, blower table and operating-condition reference, including the mapping from numeric tap IDs to the source speed labels.
2. Establish Equipment and table basis and enter Measured total external static pressure from the matching tap boundary.
3. Enter Blower speed-tap static-pressure and airflow points for each desired setting. Inspect every reported bracket and obtain additional data for unsupported pressures.

Calculation method and applicability

At an exact table pressure P, use its listed airflow Q. Between adjacent table points (P₁,Q₁) and (P₂,Q₂), estimate Q(P) = Q₁ + (P−P₁)/(P₂−P₁) × (Q₂−Q₁). No extrapolation.

P = measured TESP (in. w.g.); Q = estimated airflow (CFM). Subscripts 1 and 2 are the adjacent pressure points for the same identified blower tap.

Input definitions and units

Equipment, blower table and operating-condition reference

Identify the exact unit/model, document and page/revision, tap-ID mapping, airflow mode, filter/coil condition and table pressure boundary. Use only the table rows matching the current installation conditions.

Equipment and table basis

Confirm the supplied pressure/airflow points come from the exact equipment configuration and the measured TESP uses the manufacturer's matching operating boundary. Choices: Not established; Model, tap, filter/coil condition and pressure boundary matched.

Measured total external static pressure (in. w.g.)

Enter measured TESP for the same operating condition as the manufacturer table. This calculator does not measure TESP or correct an incompatible pressure-tap boundary.

Blower speed-tap static-pressure and airflow points (tap ID, external static pressure in. w.g., airflow CFM)

Enter 2–20 points per tap, up to four taps. Each row has an integer tap ID 1–4, nonnegative external static pressure and positive airflow. Map the numeric tap IDs to the source table's actual speed labels in the reference note. Each tap can have its own pressure points. Use exact lookups or interpolation within the supplied range only; no extrapolation.

How to interpret the result

Read each estimated CFM with its exact or bracketing pressure points and tap-ID mapping. The estimate is only as applicable as the table and measured boundary; it is neither an operating-point solution nor a direct airflow verification.

Worked examples

Assumptions and limits

• Requires source table points for the exact unit, blower setting and pressure/airflow basis. The reference note and confirmation do not authenticate user-entered data.
• Linear interpolation between adjacent table values is a local estimate, not a universal OEM interpolation rule. The measured TESP must lie within the supplied pressure range for every tap; the tool never extrapolates.
• Filter, coil wet/dry condition, accessories, voltage, airflow mode and pressure taps must match the table footnotes and measured field setup. A mismatch can invalidate the estimate.
• The result is not direct airflow measurement, a fan/system curve intersection, a recommended speed tap, a CFM-per-ton approval, a diagnosis or code/safety certification. No universal airflow range or default blower table is provided.

Sources

• Lennox 011Q3-105 furnace blower performance table, printed p. 6bManufacturer PDF returned HTTP 200 and was rendered directly on 2026-11-15. The 011Q3-105 table lists external static pressure 0.30/0.40 in. w.g. and High/Med-High/Med-Low/Low airflow 1495/1450, 1250/1225, 940/925 and 760/755 CFM; its note says CFM was measured external to the furnace with the air filter in place. This is a historical model-specific numerical fixture, not a default or current product recommendation. The PDF is a scan without extractable text.
• ENERGY STAR, HERS Points for HVAC Design and Installation (2026), ANSI/RESNET/ICC 310 airflow methodsDirect HTTP 200 PDF fetch and text inspection on 2026-11-15. Slide 26 identifies the OEM static-pressure-table method: measure supply/return external static, identify the fan-speed setting and use the blower table's TESP/speed row to determine airflow. The presentation says tables can be difficult for raters to obtain; this calculator therefore accepts user-supplied equipment data and does not provide a generic lookup. It is method guidance, not a code-compliance claim.
• Free HVAC Calculators: Blower Fan Table Airflow Calculator (Speed Taps)HTTP 200; calculator example was directly run with TESP 0.25 in. w.c., static columns .1/.3/.5/.7/.9 and three supplied speed rows. It displayed 1398/1248/1098 CFM; independent interpolation gives 1397.5/1247.5/1097.5 CFM before the peer's integer rounding. The peer's optional CFM/ton rule is not adopted.