Diffuser Throw and Layout Calculator

Concepts behind this calculation

Compare actual diffuser products and centered room layouts at maximum and minimum occupied flow, checking directional T50, catalog NC, pressure and documented flow limits.

A centered diffuser grid divides a rectangular room into equal modules. The X and Y counts determine both per-outlet airflow and the distance each directional jet must cover. T50 is the throw to a terminal velocity of 50 FPM, compared here with source-supported directional windows. Two layouts with the same outlet count can have very different module proportions and therefore different throw margins.

Maximum occupied flow checks the high-flow condition, while minimum occupied flow can expose inadequate throw. Product performance must support both exact per-outlet points and the actual thermal and mounting conditions. The named profile keeps total-outlet and per-side flow limits distinct. Catalog NC describes one rated diffuser under its stated convention; neither a passing throw window nor a low catalog NC establishes measured comfort or room acoustics.

How to use this calculator

1. Complete Product, pattern and occupied-condition references; establish Source and operating conditions and Regular four-direction equal-flow grid applicability.
2. Choose Performance data input and enter Room length along X and Y, Actual ceiling height and Room minus supply temperature difference.
3. Enter Maximum and Minimum occupied supply airflow, Single-diffuser catalog NC ceiling and Available total-pressure loss budget per outlet.
4. Add Layout rows with X/Y counts and product profiles, plus matching Custom rows where needed. Inspect both flow states before using the coordinates or ranked layout.

Calculation method and applicability

N = Nx × Ny; per-outlet flow = total CFM/N. Module spans = roomX/Nx and roomY/Ny; directional boundary distances are half those spans. Check actual X/Y T50 against documented ratio windows plus actual-height offset at both occupied flow states. Coordinates = (index+0.5) × module span. Rank only fully supported passing layouts.

Nx/Ny = outlet counts in the two grid directions; N = total outlet count; module spans and T50 throws are feet. T50 means catalog throw to the stated 50 FPM terminal velocity, not airflow or an occupied-zone comfort guarantee.

Input definitions and units

Product, pattern and occupied-condition references

Required: actual product/neck/A 4 or custom pattern, mounting and ceiling effect, source revisions, occupied maximum/minimum flow, temperature/load applicability, T 50 and flow-cap definitions, catalog NC convention and total-pressure basis. A source reference cannot authenticate a real project or measured comfort.

Source and operating conditions established?

Named source data are for TDC square-neck A 4 horizontal supply, not TDCA, return, round neck or another pattern. Custom rows must already match actual thermal/mounting/load/ceiling conditions and any corrections. Choices: Not established — withhold comparison; Documented for this stated design screen.

Regular four-direction equal-flow grid applicable?

Confirm a rectangular unobstructed room, centered equal modules, uniform design assumptions and four horizontal discharge directions. Irregular/perimeter/high-load/obstructed spaces require a different analysis. Positive results are not measured ADPI or whole-room NC. Choices: Not established — use another layout analysis; Centered unobstructed four-direction modules.

Performance data input

Named and custom paths are methods of one selection task. Use profile 0 in candidate rows for custom data; all other profile numbers are the actual TDC square neck in inches. Missing custom rows withhold support. Choices: Named TDC square-neck A4 source points; Supplied actual performance rows or mixed candidates.

Room length along X (ft)

Coordinates originate at one room corner; X/Y grids are centered in equal rectangular modules. Room shape changes the directional throw screen.

Room length along Y (ft)

Use the actual unobstructed rectangular space, not a floor-area-only equivalent square.

Actual ceiling height (ft)

Named profiles use source ceiling rows 8/9/10/12/14/15/16/20 ft. The guide total-flow and product per-side tables cover different heights; unavailable cells stay unsupported. Named throw-window offset is height−9 ft. Custom rows carry their own documented actual-height window.

Maximum occupied supply airflow (CFM)

Actual total flow to these equal outlets. The exact per-outlet source point must exist; no nominal-neck or per-side-CFM substitution or interpolation.

Minimum occupied supply airflow (CFM)

Lowest flow expected while occupied, which may exceed a controller schedule minimum. Maximum and minimum states must both pass; equal values are allowed for a constant-flow case.

Room minus supply temperature difference (°F)

Named TDC drop guidance applies to 15–25 °F cooling. For independently documented custom data, negative values can describe heating and zero can describe neutral/isothermal supply. No automatic thermal throw correction is inferred; source applicability must match each actual state.

Single-diffuser catalog NC ceiling (NC)

Titus catalog NC assumes 10 dB room absorption and one diffuser operating. This limit compares like catalog values only; several NC ratings cannot be added or treated as measured room NC.

Available total-pressure loss budget per outlet (in. w.g.)

Compare the actual source total pressure at each flow. This is not velocity pressure, return static pressure or whole-system available static pressure.

Layout rows: ID, X count, Y count, product profile (CSV)

One to 20 unique IDs; integer X/Y counts, at most 100 outlets per layout. Profile 6/9/12/15/18/21/24/30/36/48 means that square-neck TDC A 4 source family. Profile 0 uses supplied rows. Default layouts have the same four 6 x 6 outlets in 2 x 2,1 x 4 and 4 x 1 arrangements; count alone cannot decide coverage.

Custom rows: ID, total outlet CFM, X T50, Y T50, TP, catalog NC, low ratio, high ratio, window offset, total flow cap (CSV)

Up to 40 unique ID/total-CFM points; T 50 and offset ft, pressure in. w.g., cap CFM/outlet. Allowed X throw window is lowRatio×halfModuleX+offset to highRatio×halfModuleX+offset; Y analogous. Source conditions and corrections must already be established for actual cooling/heating and height. The worked rows repeat the cooling-only TDC example and are not generic heating data. Unknown NC cannot be represented by 0. Applies to Performance data input: Supplied actual performance rows or mixed candidates.

How to interpret the result

Read each layout’s directional margins at both occupied flows, then its flow-cap, total-pressure and catalog-NC checks. Outlet-center coordinates support a preliminary layout; irregular rooms, obstructions and occupied-zone comfort require further analysis.

Worked examples

Assumptions and limits

• The automatic geometry is a centered uniform rectangular grid with equal flow and four horizontal directions. It does not solve spread, obstructions, asymmetric patterns, returns, perimeter loads, irregular rooms or actual occupied-zone velocities and temperature gradients.
• The source characteristic length for horizontal ceiling devices is the closest wall, jet-midplane or intersecting jet. Checking the documented window along both grid axes is an additional conservative directional-envelope screen, not an exact percentage-ADPI prediction for rectangular modules.
• Named Titus points are square-neck TDC A 4 horizontal nearly flush supply. Round-neck data, other patterns, TDCA controller corrections, return factors and absence of ceiling effect are separate data and are not silently transferred.
• Named preset T 50 is the third value in the 150/100/50 FPM throw triplet, not the middle 100 FPM value or per-side airflow. Exact total-outlet CFM is required; unknown and intermediate flows remain unsupported.
• The 2018 guide lists TDC total-outlet maximum flow while the product notes explicitly label per-side maximum flow. Both quantities remain separate conservative site checks, not equivalent requirements. Heights 14/16 ft lack the per-side row;15/20 ft lack the guide total row. Missing cells block complete preset selection.
• Named cooling drop guidance covers 15–25°F; the 2018 cross-pattern ratio uses a 9 ft baseline with the stated height offset and broadly described load conditions. Other thermal/ceiling conditions need actual custom source data, not automatic extrapolation.
• Catalog NC assumes 10 dB room absorption and one diffuser. It is not total room NC or a sum across outlets. Unqualified source dashes stay unsupported; no zero or presumed under-NC 10 substitute is made.
• Custom data are checked only as entered. They require source-established thermal/load/mounting/height applicability, isothermal or corrected directional throw definitions, source ratio windows and flow caps. A constructed heating scenario does not validate actual TDC heating performance.
• A chosen candidate satisfies the entered limited design conditions only. Actual ADPI, drafts, thermal comfort, room sound, ventilation effectiveness, current code and field performance are not certified. The lowest numerical outlet count is not automatically acceptable.

Sources

• Titus TDC/TDCA performance data,2017 fileF 158 square-neck A 4 total CFM, third-value T 50, NC and total-pressure rows; F 170 notes:150/100/50 FPM terminal velocities, one-outlet NC convention, nearly flush mounting and cooling per-side flow caps.
• Titus 2018 grille/diffuser engineering guidelinesADPI selection: check maximum and minimum occupied flow; Table 4 TDC cross-pattern T 50/L 1–2 at 9 ft with stated height offset; Table 5 separate total-outlet flow limits. Publication page labels and PDF physical pages differ.
• ASHRAE 2023 Applications Chapter 58: Room Air DistributionCharacteristic room length Table 5 and explicit distinction between T 50/L design selection and measured occupied-zone ADPI. Tables 6 A/6 B are not substituted for Titus product-specific historical ranges or used to invent a measured ADPI percentage.
• Titus TDC product pageActual links to model performance/dimensions and 2025 full catalog were followed. The old SectionB filename returned HTTP 200 HTML and is excluded as numerical evidence.