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The share of equipment weight carried by this single spring isolator.
Rarely the total divided by the number of isolators. Plant is seldom symmetrical — a fan with its motor on one side, a chiller with its compressors at one end — so one mount carries substantially more than its neighbours. Use the manufacturer's weight distribution where there is one: an isolator loaded well under its rating is too stiff to isolate, and one loaded over it bottoms out and transmits everything.
The isolator spring's stiffness — the load required to compress it by one inch.
The rate is an input; STATIC DEFLECTION is the thing that actually decides isolation, and it is the rate and the load together that produce it. That is why two completely different springs can perform identically: a stiff one under heavy plant and a soft one under light plant reach the same deflection and the same isolation efficiency. Select for the deflection the equipment's running speed needs, then find a rate that gets there under the real load.
Static deflection under load
1.67 in
Static deflection alone doesn't confirm adequate vibration isolation — actual isolator selection should follow the full isolation-efficiency calculation comparing the equipment's disturbing frequency (from its operating speed) against the isolator's natural frequency, per ASHRAE Applications Handbook and the SMACNA Seismic Restraint Manual. Typical target deflection ranges (0.25-4 in / 6-100 mm, depending on mounting location and equipment type) are a starting point for isolator selection, not a substitute for that calculation.
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HVAC Vibration Isolation Spring Static Deflection Calculator: 1.67 in — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- Static deflection δ = Supported Weight ÷ Spring Rate (Hooke's Law), the standard way to characterize a spring isolator's deflection under load, applied in HVAC equipment isolation selection per ASHRAE Handbook — HVAC Applications (Noise and Vibration Control) and the SMACNA Seismic Restraint Manual. Typical target deflection ranges vary by application: ~0.25-0.35 in for slab-on-grade equipment, ~0.75-1 in for upper-floor mounting, up to 2 in for fans, and 1-4 in for rooftop units — actual isolator selection should follow the full isolation-efficiency calculation (disturbing frequency vs. isolator natural frequency), not deflection alone.
Inputs used
- Supported Equipment Weight
- 500 lb
- Spring Rate (lb/in)
- 300
Confidence note: Static deflection alone doesn't confirm adequate vibration isolation — actual isolator selection should follow the full isolation-efficiency calculation comparing the equipment's disturbing frequency (from its operating speed) against the isolator's natural frequency, per ASHRAE Applications Handbook and the SMACNA Seismic Restraint Manual. Typical target deflection ranges (0.25-4 in / 6-100 mm, depending on mounting location and equipment type) are a starting point for isolator selection, not a substitute for that calculation.
What this calculation does not cover
- It assumes the weight is shared equally, and it almost never is. Equipment centers of gravity sit off to one side — the motor end of a fan, the compressor end of a chiller — so the loaded mounts take far more than total weight divided by mount count. Select every mount from that average and the heavy corners compress toward coil bind while the light ones barely move, the unit sits out of level, and the isolation is worst precisely where the load is greatest.
- A spring only isolates if what it stands on is far stiffer than the spring. On a long-span floor the structure itself deflects under the same equipment load, and once that structural deflection approaches the spring's the two behave as one soft system and the isolation largely disappears. That is why upper-floor equipment gets the deeper mounts, and why the floor's deflection under the unit has to be known before the mount is picked.
- Whatever is bolted to the equipment can undo the entire mount set. A rigidly connected pipe, conduit, drain or duct carries vibration straight past the springs into the structure, and one hard-piped line will short-circuit a correctly selected isolator. Flexible connectors, and resilient hangers on the first several pipe supports away from the machine, are part of the isolation rather than accessories to it.
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This result is a specification — 1.67 in — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-09-06 · in the site-wide review of 2026-09-06 · v1.1.1
Regulatory standards & verification citations1
- Static deflection δ = Supported Weight ÷ Spring Rate (Hooke's Law), the standard way to characterize a spring isolator's deflection under load, applied in HVAC equipment isolation selection per ASHRAE Handbook — HVAC Applications (Noise and Vibration Control) and the SMACNA Seismic Restraint Manual. Typical target deflection ranges vary by application: ~0.25-0.35 in for slab-on-grade equipment, ~0.75-1 in for upper-floor mounting, up to 2 in for fans, and 1-4 in for rooftop units — actual isolator selection should follow the full isolation-efficiency calculation (disturbing frequency vs. isolator natural frequency), not deflection alone.
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