Skip to content
ENExplore Calculators

Trap Seal Depth Calculator

Work out trap seal depth instantly with clear inputs, formula shown and shareable results.

About Trap Seal Depth Calculator

A trap seal is lost two ways. Evaporation removes a slow, steady depth each day a fixture sits unused, and a pressure swing in the drainage system displaces water by half the pressure difference in inches of water gauge, because the level drops on one leg while it rises on the other.

Formulas

Remaining seal

Remaining = installed depth - evaporation rate x days - pressure swing / 2

Time to failure

Days = (depth - pressure loss) / evaporation rate

Worked example

With the default values below, Trap Seal Depth Calculator returns Remaining seal depth of 0.600. Change any input above and every figure here is recalculated in your browser.

Inputs used

Installed trap seal depthminimum 0.5 in
2 in
Evaporation rateminimum 0.001 in/day
0.03 in/day
Days unusedminimum 1 days
30 days
System pressure fluctuationminimum 0 in.wg
1 in.wg

Results

Remaining seal depth
0.600 in
Loss to evaporation
0.900 in
Loss to pressure swing
0.500 in
Days until seal is lost
50 days

Step by step

  1. 1Values used
  2. 2Remaining seal
  3. 3Time to failure
  4. 4Remaining seal depth= 0.600 in
  5. 5Loss to evaporation= 0.900 in
  6. 6Loss to pressure swing= 0.500 in
  7. 7Days until seal is lost= 50 days

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is the Trap Seal Depth figure worked out?

Remaining = installed depth - evaporation rate x days - pressure swing / 2. A trap seal is lost two ways.

Why does a floor drain smell first?

Floor drains are rarely used, so evaporation runs unchecked. A trap primer or a sealing insert is the usual remedy.

What values do I need to enter?

This calculator takes 4 inputs: Installed trap seal depth, Evaporation rate, Days unused, System pressure fluctuation. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.

Related Calculators

Trap Seal Depth Calculator – Calculate Remaining seal depth