Enter your door and environment details
Example data table
| Door use | Door size | Hinge | Sensor type | Wind | Recommended height from top | Recommended gap |
|---|---|---|---|---|---|---|
| Greenhouse | 800mm × 2000mm | Left | Standard | Medium | 250mm | 5mm |
| Garden shed | 760mm × 1800mm | Right | Wide-gap | High | 275mm | 8mm |
| Tool cabinet | 500mm × 1200mm | Left | Slim | Low | 180mm | 3mm |
Formula used
The calculator targets the stable upper corner of the latch side. It estimates a starting height using:
HeightFromTop = clamp(0.15 × DoorHeight, 150, 250).
Wind, opening direction, and obstruction clearances add small offsets. Edge offset depends on frame face width,
starting near 25mm and adjusting for narrow or wide frames.
The recommended magnetic gap is limited by the sensor rating:
Gap = min(TargetGap, 0.8 × MaxRatedGap).
This keeps normal movement from causing false alerts in garden environments.
How to use this calculator
- Measure the door width and height in your chosen units.
- Select hinge side, opening direction, and frame face width.
- Pick a sensor type that matches your expected door movement.
- Enter a desired gap; smaller is usually more reliable.
- Choose wind and humidity to receive weatherproofing guidance.
- Press Calculate placement to view results above the form.
- Download your report as CSV or PDF for installation notes.
Placement height and door dynamics
A contact sensor reads separation, so stable geometry matters. For typical garden doors between 1700–2200 mm tall, a starting height near 15% of door height places the set above kick zones while staying reachable for service. The calculator clamps this region to 150–250 mm from the top, then nudges it upward for high wind or inward-opening doors to reduce sway-driven micro-gaps.
Latch-side alignment and edge offset
Most false alarms come from torsion at the latch edge. Mounting the sensor on the latch side shortens the lever arm created by door flex. Edge offset is sized to the visible frame face: narrow trims often need 18 mm, standard faces around 25 mm, and wide faces about 30 mm. Side clearance inputs add buffer when latches, handles, or weather strips occupy the edge.
Gap management and sensor ratings
Every contact sensor has a rated maximum gap. Field reliability improves when the working gap is held below about 80% of that rating. The calculator compares your target gap to the sensor’s max and recommends the smaller value, then enforces a practical minimum. For example, a 10 mm sensor targeting 6 mm will recommend 6 mm; targeting 9 mm will recommend 8 mm.
Environment factors for garden sites
Greenhouses and sheds combine vibration, humidity, and temperature swings. High humidity prompts sealing advice, while high wind increases the risk score and suggests sturdier fixing methods. Metal frames may require spacers to avoid magnetic interference and to keep the magnet centered across the gap.
Verification, logging, and exporting
After installation, perform a slow-open test and a firm-close test, observing the panel’s open/closed status at several points. If the state changes early, reduce the gap or move the magnet closer. Save the final coordinates by exporting CSV for maintenance logs, or PDF for installer checklists and seasonal rechecks. For wireless units, note battery access and avoid irrigation spray. Recheck alignment after storms or wood swelling, and update the record with new measurements.
FAQs
1) Should the sensor go on the door or the frame?
Mount the sensor body on the frame and the magnet on the moving door. This keeps wiring stable, reduces strain, and makes alignment checks easier during seasonal maintenance.
2) What gap should I aim for in a greenhouse?
Use the smallest practical gap that still closes reliably. Staying under 80% of the sensor’s rated maximum helps prevent wind vibration and thermal expansion from triggering false alerts.
3) Does hinge side matter for placement?
Yes. The latch side moves the most during flex, so placing the contact there improves detection consistency. The calculator automatically chooses the opposite side of the hinges.
4) How do I handle metal doors or frames?
Use screws and consider a spacer to reduce magnetic interference. If alignment is hard to hold, choose a wider-gap rated sensor and keep the working gap conservative.
5) Why does wind exposure change the recommended height?
Wind can twist lightweight doors near the middle. A slightly higher mounting point near the top corner reduces oscillation, keeping the gap steadier and improving closed-state reliability.
6) When should I recheck alignment after installation?
Recheck after the first week, after major storms, and after seasonal humidity changes. Wood swelling and hardware settling can shift the magnet, so quick checks prevent nuisance alarms.