Psi To Inches Of Water Conversion
Convert pressure from PSI to inches of water column (WC), a unit used for measuring low pressures in HVAC and gas systems.
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Converting PSI to Inches of Water (inH₂O)
When measuring very low pressures, units like PSI (Pounds per Square Inch) can be too large to be practical. This is where units like "inches of water" come in. This article explains what inches of water means and how to convert it to and from PSI.
What are "Inches of Water"?
Inches of Water (inH₂O), also known as inches water column (WC), is a unit of pressure based on the pressure exerted by a column of water one inch high. It's commonly used in HVAC systems, fluid dynamics, and for measuring natural gas pressure because it's sensitive enough to measure small pressure differences.
The Conversion Factor
The conversion between PSI and inches of water depends on the temperature of the water, as temperature affects its density. The standard conversion is typically based on water at 4°C (39.2°F), where it is most dense.
1 PSI ≈ 27.7076 inches of water (inH₂O) at 4°C
For most general purposes, rounding to 27.7 is sufficient.
Conversion Formulas
- PSI to inH₂O: Multiply the PSI value by 27.7076.
inH₂O = PSI × 27.7076 - inH₂O to PSI: Divide the inH₂O value by 27.7076.
PSI = inH₂O / 27.7076
Practical Example
A natural gas line for a residential appliance might operate at a pressure of 7 inches of water. To understand this in terms of PSI:
7 inH₂O / 27.7076 ≈ 0.253 PSI
As you can see, this is a very low pressure, which demonstrates why a more sensitive unit like inches of water is necessary for such applications.
PSI to Inches of Water Conversion Chart
| PSI | Inches of Water (inH₂O) (approx.) |
|---|---|
| 0.1 | 2.77 |
| 0.25 | 6.93 |
| 0.5 | 13.85 |
| 1 | 27.71 |
| 2 | 55.42 |
| 5 | 138.54 |
Frequently Asked Questions (FAQ)
- Why is inches of water a useful unit?
- It is useful for measuring very small pressure differences that would be difficult to read in PSI. It originates from the use of manometers, which are U-shaped tubes filled with liquid (often water) to measure pressure differentials by observing the displacement of the liquid.
- Is this a gauge or absolute pressure measurement?
- Inches of water is almost always a gauge pressure, meaning it measures the pressure relative to the surrounding atmospheric pressure.
- Does the temperature of the water matter?
- Yes, strictly speaking, it does. The density of water changes with temperature. The standard conversion factor is based on water at its most dense point (4°C). For most HVAC and general applications, this standard value is used without adjustment.
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