ARTICLE NO.149 | How Much Weight Can a Floor Spring Handle? Reading the Size Numbers
ARTICLE NO.149 | How Much Weight Can a Floor Spring Handle? Reading the Size Numbers
A Floor Spring buried beneath a grand hotel entrance may control a door weighing three hundred kilograms. Another unit, identical in appearance but installed under a lightweight office door, manages only a fraction of that mass. The difference lies in the size number stamped on the unit—a code that tells the full engineering story if you know how to read it. Understanding floor spring sizing is not merely a matter of matching numbers. It requires knowing what the size designation actually represents, how door weight relates to door width, and why selecting the wrong size creates problems that go far beyond a door that closes too fast or too slow.
What the Size Number Means
The size number on a Floor Spring is defined by the European standard EN 1154, which classifies door closers and floor springs according to their closing power. The number—typically ranging from 1 to 7—corresponds to a specific range of door mass and door width that the unit is designed to control. An EN 1154 size 3 floor spring is rated for doors up to 60 kilograms with a maximum width of 950 millimetres. A size 4 covers doors up to 80 kilograms and 1100 millimetres wide. A size 5 handles 100 kilograms and 1250 millimetres. The scale continues upward, with size 7 units rated for doors up to 160 kilograms and 1600 millimetres wide. These ratings are based on standard door configurations—single-leaf doors of average height, installed in sheltered locations with moderate wind exposure. Real-world installations often require adjustment of the size selection to account for conditions that deviate from these assumptions.
Why Door Width Matters as Much as Weight
The mass rating alone does not tell the full story of what a Floor Spring must handle. Door width is equally critical because it determines the closing moment that the spring must overcome. The closing force required is proportional to the door's moment of inertia about its pivot axis. A wider door concentrates its mass further from the pivot, increasing the rotational inertia that the floor spring must control. A 60-kilogram door that is 1100 millimetres wide demands a higher-capacity floor spring than a 60-kilogram door that is only 850 millimetres wide, even though the mass is identical. This is why the EN 1154 standard ties the size classification to both mass and width simultaneously—selecting a floor spring based on weight alone ignores the leverage effect that makes wider doors fundamentally harder to control.
The Effect of Tall Doors and Wind Loads
A Floor Spring installed in a location exposed to wind faces demands beyond what the standard size chart anticipates. Wind pressure against a door leaf creates a closing or opening force that adds to or subtracts from the spring's workload. The wind force is proportional to the door area, so a tall door—one measuring 2500 millimetres instead of the standard 2100 millimetres—presents significantly more surface to the wind. The wind moment increases with the square of the door height, meaning a door that is 20 percent taller than standard can experience wind loads 44 percent higher. Standard EN 1154 classifications assume sheltered installation conditions. For exterior doors exposed to prevailing winds, particularly in coastal or high-rise locations, the specified floor spring size should be increased by at least one EN size category above what the mass and width alone would suggest. A door that qualifies for a size 4 by weight and width may need a size 5 when wind exposure is factored in.
Consequences of Undersizing
An undersized Floor Spring fails to control the door in ways that are immediately noticeable and progressively damaging. The closing force is insufficient to overcome the door's inertia, resulting in a door that slows down and stalls before reaching the fully closed position. Users respond by pushing the door harder to ensure it latches, which accelerates wear on the mechanism. The back-check function—designed to cushion the door if opened too forcefully—activates earlier and more frequently than intended, subjecting the internal hydraulic components to pressure spikes they were not designed to endure. Over time, the seals degrade, oil leaks develop, and the closing speed becomes increasingly erratic. The door may close reliably in calm conditions but fail to latch on windy days, compromising both security and weather sealing. Undersizing also places excessive stress on the floor spring's cement box and its anchorage to the concrete substrate. The constant struggle to control a door beyond its capacity transmits shock loads into the surrounding floor structure, which can lead to loosening of the cement box and cracking of the surrounding floor finish.
Consequences of Oversizing
Selecting a Floor Spring that is too large for its door creates a different set of problems, though they are generally less destructive than those caused by undersizing. An oversized floor spring closes the door with excessive force. The door accelerates through its closing arc faster than intended, reaching the latch position with enough momentum to slam rather than close gently. This slamming generates noise, stresses the glass or timber panel, and accelerates wear on the latch and strike plate. The back-check function may not engage effectively because the door never reaches the opening speed that triggers it. Users must exert more force to open the door against the higher spring resistance, which creates accessibility issues—a door that requires more than the regulatory maximum opening force of 40 to 50 newtons for external doors may violate building code requirements. In extreme cases, an oversized floor spring makes a door feel heavy and resistant throughout its entire opening arc, discouraging use or causing people to prop the door open, defeating its purpose entirely.
Reading the Size Code on the Unit
Most Floor Spring manufacturers stamp the EN size classification directly onto the unit body or cover plate. A marking such as "EN 3" or "EN 4" indicates the standard size. Some units are adjustable across a range—marked "EN 3-5" or "EN 2-4"—meaning the closing power can be adjusted within those limits by changing the spring tension or valve settings during installation. The adjustment range is a useful feature for installers who stock a limited number of units but need to accommodate varying door specifications across a project. However, adjustable units still have limits. A floor spring marked EN 3-5 cannot safely control a door requiring size 6 capacity, regardless of how the internal adjustments are set. The adjustment is for fine-tuning within a defined window, not for extending the unit's capacity beyond its engineered range. The physical size of the unit also provides a visual clue: larger size numbers generally correspond to physically larger cement boxes, longer spindles, and heavier-duty pivot assemblies. A size 6 floor spring is visibly more substantial than a size 3, and attempting to install a small unit where a large one is required creates a mismatch that no amount of adjustment can overcome.
Special Cases: Heavy Glass and High-Traffic Doors
Certain applications push Floor Spring sizing beyond the standard EN 1154 chart. Fully frameless tempered glass doors, commonly used in retail and commercial lobbies, often exceed the standard width and weight assumptions. A typical glass door measuring 1100 by 2500 millimetres in 12-millimetre glass weighs approximately 85 kilograms—within the mass limit for size 4 but well above the height assumption. The combined effect of height, width, and wind exposure on a glass door of these dimensions demands a size 5 or even size 6 unit, particularly if the entrance faces prevailing winds. High-traffic doors in airports, hospitals, and shopping centres present an additional consideration: cycle count. A floor spring in a busy retail entrance may accumulate 200,000 cycles per year, far exceeding the duty cycle of a unit in a residential or low-traffic commercial setting. For high-cycle applications, selecting a floor spring one size larger than the mass and width calculations indicate provides additional reserve capacity that extends service life and reduces maintenance frequency. The incremental cost of the larger unit is recovered many times over through reduced downtime and longer replacement intervals.
Conclusion
The size number on a Floor Spring is not a suggestion—it is an engineering specification derived from decades of testing and field experience. Matching the size to the door requires considering not just the door's weight, but its width, its height, its exposure to wind, and the expected cycle count over its design life. Undersizing leads to doors that fail to close, hydraulic systems that degrade prematurely, and structural connections that loosen over time. Oversizing leads to doors that slam, users who struggle, and accessibility compliance failures. The correct size ensures that the door closes smoothly and latches reliably, cycle after cycle, year after year. Reading the size number correctly is the first step toward a floor spring installation that performs as intended for the full life of the building.
