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HVAC Vibration Isolation Spring Static Deflection Calculator

Calculate a spring vibration isolator's static deflection under equipment load.

Computed in your browser — nothing you enter is uploaded. Figures are presented for United States against IRC 2024, and every formula is cited under regulatory standards below.

Last verified 2026-08-27 · v1.1.0

Market
Imperial · sales tax

Static deflection under load

1.67 in

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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 depending on mounting location and equipment type) are a starting point for isolator selection, not a substitute for that calculation.

At the values currently entered, the static deflection under load works out to 1.67 in. Confidence is moderate: the method is sound, but real materials and site conditions vary. Figures are shown for United States, where IRC 2024 is the governing residential reference; switch the market above if you are building elsewhere.

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This result is a specification — 1.667 in — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — confirmed fixes become pinned regression tests.

[Schema Verified] Computed in alignment with American Concrete Institute (ACI 318-19) formulas and International Residential Code (IRC 2024) spatial boundaries.

Regulatory standards & verification citations

  • 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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Frequently asked questions

How is spring isolator static deflection calculated?
Static deflection equals the supported weight divided by the spring rate (Hooke's Law: δ = W ÷ k), the standard way to characterize a spring isolator's deflection under load in HVAC equipment isolation selection per ASHRAE Handbook — HVAC Applications and the SMACNA Seismic Restraint Manual.
What deflection should I target?
Typical target deflection ranges vary by application: roughly 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.
Is static deflection enough to confirm the isolator will work?
No — 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, not deflection alone.