Duct Layout

The Layout pane is where you design the duct distribution system, including routing, sizing, and component selection.

The Layout Sidebar

The sidebar has three tabs:

• Equipment — place registers, terminal units, and central units
• Routing — three sub-tabs: Ducts, Risers, and Fittings
• Pressures — read the calculated critical path for each air path

Layout opens on Equipment, with Central selected. The tab and sub-tab you pick are kept in the page address, so a reload or a shared link returns to the same one.

Placing Equipment

The Equipment tab has three sections. Terminal and Central are palettes of what the project already defines elsewhere — select an entry, then place it on the floor plan. Registers lists the registers you already placed on the current level; add more from its Place Registers button. Ducts connect the equipment you place here.

Every list that shows only the current level — Registers, Ducts, Risers, and Fittings — carries a round L1-style tag in its header (“Items below are filtered by the current level.”). Change the level in the toolbar to see the rest.

Section	Lists	Empty state
Registers	Registers on the current level, by airflow direction, then space, then register tag	No Registers — “Add a register to place it on the floor plan”
Terminal	One entry per zone	No Zones, with a Create Zone button to Building Model > Zones
Central	One entry per system	No Systems, with a Create System button to Building Model > Systems

So a terminal unit needs its zone first, and a central unit needs its system first. A zone or system with no unit on the canvas carries an extra dot in the list, and selecting it shows a Not Placed tag in place of Locate in the inspector header.

Place Registers

Place Registers opens a dialog of the project’s register types, in rows for supply, return, and exhaust, with the selected type’s data below the rows. Choose a type and click Place Registers in the dialog. The sidebar button then reads Done while you click positions on the floor plan. With no register types defined, the dialog shows No Register Types — “Register types are required to place registers”.

Duct Routing

Creating Duct Runs

Duct routing lives on the Ducts sub-tab of the sidebar’s Routing tab. It lists the ducts already drawn on the current level, each with its duct type, calculated size, and type color. Draw duct runs on the floor plan:

1. Open the Routing tab and click Draw Ducts on the Ducts sub-tab
2. Pick a duct type in the Draw Ducts dialog, then click Draw Ducts again. With exactly one duct type in the project, the button arms that type and opens no dialog
3. Click to place duct segments
4. Connect to the terminal units and registers you placed from the Equipment tab
5. Close loops where needed, then click Done to stop drawing

Duct Types

Ducts are drawn with the duct types you defined in System Types — pick one in the Draw Ducts dialog before drawing. Each duct type carries its own sizing criteria (max velocity, max pressure drop, max height, liner thickness) and a display color. Size Ducts sizes each duct against the criteria of the type it carries.

With no ducts drawn yet, the Ducts sub-tab shows No Ducts — “Draw a duct to place it on the floor plan”. With no duct types in the project at all, it shows No Duct Types — “Duct types are required to draw duct” — and a Create Duct Type button that opens Basis of Design > System Types.

There is no fixed supply/return/exhaust “duct type” to choose here. A run’s airflow direction — supply, return, or exhaust — follows the registers and equipment it connects, not the duct type.

Risers

A riser is a duct that connects the same point across floor levels. Risers live in their own Risers sub-tab, next to Ducts, in the Routing tab. The sub-tab lists the risers on the current level, each with its duct type and how many levels it spans.

1. Open the Risers sub-tab and click Place Risers, then pick a duct type in the Place Risers dialog. With exactly one duct type in the project, the button arms that type and opens no dialog
2. Click a point on the floor plan to place a riser — it spans the current level and the level above by default. Click Done to stop placing
3. Right-click the riser and drag the level range slider to extend or retract which levels it spans, up to one level beyond the range of levels already used elsewhere in the project

With no risers on the level, the sub-tab shows No Risers — “Add a riser to place it on the floor plan”. With no duct types in the project at all, it shows No Duct Types — “Duct types are required to place risers” — and a Create Duct Type button.

Click a riser to open Riser Data in the sidebar. Change its duct type, review that type’s sizing criteria (max velocity, max pressure drop, max height, liner thickness — read-only here), and, for each level-to-level segment (labeled, for example, L1 → L2 (Up)), override the duct size or review its flow rate, pressure drop, and velocity.

Routing Considerations

Plan duct routes to:

• Minimize total length
• Avoid obstructions
• Allow for insulation and access
• Fit within available plenum space

Duct Sizing

Sizing Criteria

Each duct is sized against the criteria of its duct type. HVAKR starts at a 6 in. round duct and grows it in 2 in. steps. It stops at the first size that stays within both the max velocity and the max pressure drop. Both are read at the duct’s design airflow. The sweep only grows the duct, so a result is never smaller than 6 in.

Only two of the four criteria are part of that test:

Max Velocity

Caps air velocity for noise control:

• Higher limits = smaller ducts
• Lower limits = quieter system
• Typical: 1500-2000 FPM main, 800-1200 FPM branch

Max Pressure Drop

Caps the friction rate (pressure drop per 100 ft):

• Typical: 0.08-0.10 in. wg per 100 ft
• Keeps fan power reasonable on long runs

Max Height

Caps the duct height so it fits the available plenum space. Liner thickness is included in the measure. Max Height is not part of the test above. It decides whether the result is round or rectangular:

• The duct stays round while the next round candidate fits under the cap. Leave Max Height empty and it stays round to any size.
• When the next round candidate would pass the cap, HVAKR switches to a square duct at the current height. Only the width grows after that.

Liner Thickness

Internal acoustic liner. It reduces the clear airflow area. Velocity and pressure drop are therefore calculated on the lined opening, not the outer duct size. Liner Thickness sets no criterion of its own. It makes the other criteria size a larger duct.

Running Duct Sizing

Sizing is an action you run. It does not happen while you draw:

1. Give each duct the duct type that carries the sizing criteria you want
2. Open the Automations menu in the Layout toolbar and choose Size Ducts
3. HVAKR sizes one ducted component at a time. The progress shows next to the menu item
4. It reports Sized N duct components. when it finishes

With nothing routed yet, it reports No ducted components to size — route ducts first. instead.

Sizing skips any duct whose size you set by hand. Those ducts keep the size you gave them. This is true however far that size is from the duct type’s criteria.

Some criteria cannot be satisfied. A max velocity or a max pressure drop of 0 is one example. The sweep then gives up at a very large duct and keeps the last size it tried. Read the Velocity and Pressure Drop in Duct Data back against your limits. A result above them means that no duct satisfies the criteria. It does not mean that HVAKR chose that duct.

Overriding a Duct Size

Click a duct to open Duct Data in the sidebar:

• Duct Type — reassign the duct; the four criteria of the selected type appear below it, read-only
• Shape — Round or Rectangle. Set the Diameter, or the Width and Height, to override the calculated size. A liner raises the smallest value each field accepts, to twice the liner thickness
• A preview card below the fields shows the duct cross-section, its liner, and the duct type’s color
• Refresh clears your override. The duct returns to the calculated size. It is disabled until you set an override
• Flow Rate, Pressure Drop, Velocity, and the pressure at the duct are read-only results
• Delete removes the duct

Fittings and Transitions

Fitting Types

HVAKR places fittings automatically wherever ducts meet or change size. Three fitting types are modeled:

• Elbow - A change in direction
• Transition - A size change, either an increase or a reduction
• Wye - A branch takeoff, either converging or diverging

The Fittings sub-tab of the Routing tab lists the fittings on the current level, each with its duct type. A row reads Wye when three or more ducts meet at it, and Fitting otherwise. You cannot add a row here — with no fittings on the level it reads No Fittings — “Fittings are created automatically as you route ducts”. Click a row to select that fitting and open Fitting Data.

Fitting Loss Coefficients

Each fitting adds pressure loss through a configurable loss coefficient (Cʟ). Set Cʟ (Main) for every type, plus Cʟ (Branch) for wyes, in System Types:

Fitting	Cʟ (Main)	Cʟ (Branch)
Elbow	30%	—
Reducing Transition	15%	—
Expanding Transition	30%	—
Converging Wye	5%	15%
Diverging Wye	15%	30%

• The table shows the HVAKR defaults. Edit a cell on System Types to override that coefficient for the project
• Coefficients are entered as percentages, from 0% to 100% — a Cʟ of 0.30 reads 30%
• Cʟ (Branch) applies to the two wye rows only; the other three take Cʟ (Main) alone
• The coefficient feeds each fitting’s contribution to the total pressure calculation
• A selected fitting can override the project default locally; use Edit Fitting Loss Coefficients to jump back to the project defaults

Reducing Losses

Minimize fitting losses:

• Use larger radius elbows
• Avoid abrupt transitions
• Use turning vanes where needed

Pressure Calculations

Pressure Graph

The Pressures tab lists one row per air path, each labeled with the space, zone, or system it serves and its ESP. When two paths resolve to the same name, HVAKR appends the direction — for example Zone 1 (Return). A path that serves no single space, zone, or system reads Unassigned Supply, Unassigned Return, or Unassigned Exhaust, numbered when there is more than one in the same direction. Central-unit supply paths list first, then return paths, then the rest; within each group, named paths sort by name ahead of unassigned ones. The ⓘ next to the Pressures title sums it up: “Each row shows the critical path of one piece of ducted equipment: the duct run with the highest pressure drop. ESP is the external static pressure the fan must overcome on that path. Expand a row to see the loss at each duct and fitting. The canvas highlights these paths while this tab is open.”

Click a path row to select its equipment and open an inspector titled with the path name. It plots Static Pressure falling along the path — one point per row, showing the pressure left after that row’s drop, reaching zero at the last element. Drag the inspector’s top edge to resize it; HVAKR remembers the height.

Expand a path to walk it end to end:

• Each node — central unit, terminal unit, fitting, register — shows static pressure (SP) and pressure drop (PD). A fitting reports one aggregate figure for the whole fitting, not a row per elbow, transition, or WYE inside it
• Each duct segment shows its size, SP, and PD

Click a node or duct row to select that element on the canvas; HVAKR switches to its level and centers the view on it. Export CSV downloads every path and row as a spreadsheet.

The canvas toolbar’s Toggle Critical Path button is the same view from the other side: it opens the Pressures tab and highlights every critical path on the floor plan, and clicking it again returns to Equipment.

Until the graph can be solved, the tab explains what’s missing: No duct routing (“Draw ducts on the canvas to calculate pressure paths”), or No pressure paths (“Route ducts between central and terminal units to see critical path pressures”).

Critical Path

HVAKR solves the critical path for each air path itself — the highest-pressure-drop route from the unit that roots the path to the worst register or terminal unit it feeds — and reports its total as that path’s ESP. A supply path continues through its terminal unit rather than stopping there, so its ESP covers the central-side and terminal-side drops together. Use it to:

• Size the fan against the worst-case path
• Find where the loss accumulates
• Identify the other paths that need balancing

Fan Sizing

The fan must overcome:

• Total duct pressure drop
• Terminal unit pressure drop
• Filter pressure drop
• Coil pressure drop

Reviewing the Layout in 3D

The 3D view is its own project section, not part of Layout — click 3D Viewer in the project sidebar to rotate the model, check for interferences, and verify routing and sizing. See 3D Visualization.

Best Practices

1. Route before sizing - Establish routing first
2. Use consistent duct types - Keep sizing criteria consistent within a run
3. Check velocities - Stay within acceptable ranges
4. Verify pressure drop - Within equipment capability
5. Document routing - For construction drawings