Inputs
Example data table
| Room (L × W) | Ceiling | Listed spacing S | Condition | Effective spacing | Recommended detectors |
|---|---|---|---|---|---|
| 60 ft × 40 ft | 10 ft | 30 ft | Smooth | 30.00 ft | 6 |
| 80 ft × 50 ft | 14 ft | 30 ft | Beams | 20.40 ft | 12 |
| 25 m × 18 m | 4.0 m | 9.1 m | Sloped | 8.19 m | 9 |
Examples are illustrative; confirm requirements with project documents and authorities.
Formula used
1) Effective spacing
Let S be listed spacing.
RF = HeightFactor × ConditionFactor × AirFactor × CustomFactor
Seff = S × RF
2) Grid detector count
nL = ceil(L / Seff), nW = ceil(W / Seff)
GridTotal = nL × nW
Wall offset guidance: about Seff/2.
3) Area minimum check
Aroom = L × W, Adet = Seff × Seff (or custom).
AreaMin = ceil(Aroom / Adet). Recommended total is max(GridTotal, AreaMin).
How to use this calculator
- Select units and enter room length and width.
- Enter ceiling height and the detector’s listed spacing S.
- Choose ceiling condition and airflow to adjust spacing conservatively.
- Optional: use Area method for an area-per-detector minimum check.
- Click Calculate to view totals, spacing, and wall offset guidance.
- Use CSV or PDF exports for coordination and submittals.
1) Design intent and coordination value
Detector spacing affects detection time, notification performance, and system credibility during commissioning. Early layout decisions also impact conduit routing, ceiling coordination, and access for maintenance. This calculator helps teams convert room geometry and practical modifiers into a consistent planning baseline that can be discussed in coordination meetings and reflected in submittal narratives.
2) Starting from listed spacing information
Listed spacing is typically provided for standard, smooth ceiling conditions. Real construction introduces beams, slopes, soffits, ductwork, and lighting features that influence smoke travel paths. Use the listed spacing as the starting point, then apply conservative reductions when ceiling height increases or when obstructions could prevent uniform smoke spread across the sensing plane.
3) Applying reduction factors responsibly
The reduction factor in this tool combines ceiling height, ceiling condition, and airflow. Higher ceilings may increase stratification, while strong air movement can redirect smoke away from detectors. If your organization uses its own spacing adjustments, enable the custom factor to align outputs with internal criteria, and document the basis in your design notes.
4) Reading the layout outputs on plans
The calculator reports detectors along length and width using a simple grid. Treat the rows and columns as a starting pattern. Place devices near the centerlines of the grid cells and keep wall offsets around half of effective spacing to avoid low-coverage edges. After placement, adjust for architectural features, diffusers, beams, and access panels.
5) Using the area check for robustness
Some project approaches use a target area per detector for preliminary layouts. The Area method compares the grid total to an area-based minimum and recommends the higher value. This is useful when room proportions are unusual, when the grid produces very few devices, or when your standards require a minimum density. Export the results to keep assumptions transparent during review cycles.
FAQs
1) Does this replace code-required design?
No. It supports early planning. Confirm rules using project specifications, local regulations, manufacturer documentation, and the authority having jurisdiction.
2) What should I enter for listed spacing (S)?
Use the device’s published listed spacing for your application. If unavailable during early design, start with 30 ft (9.1 m) and replace it with the selected product’s value later.
3) Why does ceiling height reduce spacing?
Higher ceilings can slow smoke accumulation at the sensing level and increase stratification. A conservative height factor reduces effective spacing to reflect potentially delayed response.
4) When should I use the Area method?
Use it when your workflow specifies an area-per-detector target or when you want a second coverage check. The tool recommends whichever method yields the higher detector count.
5) How do beams or obstructions affect results?
Beams and obstructions can create pockets and directional smoke flow. The condition factor reduces effective spacing to keep early layouts conservative, especially before detailed coordination drawings are complete.
6) Can I override the reduction logic?
Yes. Enable the custom factor and enter a value from 0.30 to 1.00. It multiplies the built-in factor, aligning assumptions with internal standards or engineering judgement.
7) How should I place devices after I get the count?
Use the grid as a starting pattern. Keep wall offsets near Seff/2, then adjust for diffusers, beams, access panels, and architectural constraints before final drawings and calculations.
Verify local codes before finalizing any detector layout always.