Pascal to Inch of Water Converter

Accurate conversion between Pascals (Pa) and inches of water (inH₂O) for HVAC duct pressure measurements, ventilation system design, and air flow calculations.

1 Pa = 0.0040147 inH₂O | Default: 2 decimal places

Conversion Factor

1 Pascal (Pa) = 0.0040147 inH₂O | 1 inH₂O = 248.84 Pa

Pa
inH₂O

Precision: 2 Decimal Places | Formula: inH₂O = Pa × 0.0040147

Common HVAC Pressure Measurements

Pascals and Inches of Water

Understanding these essential pressure units for HVAC systems, duct design, and air flow measurements.

The Conversion Formula

Pascal to Inch of Water Conversion

1 Pascal (Pa) = 0.0040147 inches of water (inH₂O)
1 inch of water (inH₂O) = 248.84 Pascals (Pa)
inH₂O = Pa × 0.0040147
Pa = inH₂O × 248.84

Example Calculation 1:

Convert 248.84 Pascals to inches of water:

inH₂O = Pa × 0.0040147

inH₂O = 248.84 × 0.0040147

inH₂O = 1.0 (with 0 decimal places)

Example Calculation 2:

Convert 5 inches of water to Pascals:

Pa = inH₂O × 248.84

Pa = 5 × 248.84

Pa = 1244.2 (with 1 decimal place)

Note: These conversions are standard for HVAC pressure measurements at 20°C (68°F)

When to Use This Conversion:

  • HVAC system design and duct pressure calculations
  • Air flow measurement and balancing
  • Fan pressure rating conversions
  • Filter pressure drop measurements
  • Ductwork sizing and pressure loss calculations
  • Building ventilation system testing and commissioning
  • ASHRAE standard compliance verification

About the Units

Pascal (Pa)

The SI unit of pressure, defined as one newton per square meter (N/m²). It's the standard metric unit for pressure measurements in scientific and engineering applications.

Equivalents:

  • 1 Pa = 0.0040147 inH₂O
  • 1 Pa = 1 N/m²
  • 1 kPa = 1000 Pa
  • 1 bar = 100,000 Pa
  • 1 atm = 101,325 Pa
  • 1 Pa ≈ 0.000145 psi

Note: Pascals are the official SI unit for pressure measurements

Inch of Water (inH₂O)

A non-SI unit of pressure based on the pressure exerted by a column of water one inch high at 20°C. Commonly used in HVAC for measuring low pressure differences in air systems.

Equivalents:

  • 1 inH₂O = 248.84 Pa
  • 1 inH₂O = 0.03613 psi
  • 1 inH₂O = 2.4884 millibars
  • 1 inH₂O = 0.073556 inHg
  • 1000 inH₂O = 248.84 kPa
  • 1 psi = 27.68 inH₂O

Note: Also known as "inch of water gauge" (iwg) in HVAC terminology

Common HVAC Pressure Equivalents:

Pascals (Pa) inH₂O Millibars (mbar) psi Typical HVAC Use
24.88 0.1 inH₂O 0.2488 mbar 0.0036 psi Air velocity measurements
248.84 1 inH₂O 2.4884 mbar 0.0361 psi Standard duct pressure
497.68 2 inH₂O 4.9768 mbar 0.0723 psi Fan static pressure
746.52 3 inH₂O 7.4652 mbar 0.1084 psi Medium pressure systems
995.36 4 inH₂O 9.9536 mbar 0.1445 psi High pressure ducts
1244.20 5 inH₂O 12.4420 mbar 0.1807 psi Industrial ventilation

Frequently Asked Questions

Common questions about Pascals, inches of water, and HVAC pressure measurements.

One inch of water (inH₂O) is equal to 248.84 Pascals (Pa) at 20°C (68°F). This is the standard conversion used in HVAC applications for duct pressure measurements:

1 inH₂O = 248.84 Pa

1 Pa = 0.0040147 inH₂O

Inches of Water to Pascals: Pa = inH₂O × 248.84

Pascals to Inches of Water: inH₂O = Pa × 0.0040147

This conversion is essential for HVAC system design, air flow calculations, and pressure drop measurements in ductwork systems.

HVAC professionals traditionally use inches of water (inH₂O) for several practical reasons:

Advantages of inH₂O in HVAC
  • Human-scale measurements for typical duct pressures
  • Traditional unit in US HVAC industry
  • Pressure gauges calibrated in inH₂O are common
  • 1-5 inH₂O covers most residential/commercial systems
  • Easy to relate to manometer readings
Advantages of Pascals (Metric)
  • SI standard unit for pressure measurement
  • Used in international engineering standards
  • Decimal system simplifies calculations
  • Wider range for industrial applications
  • ASHRAE standards reference Pascals

This converter bridges both measurement systems, allowing HVAC professionals to work with their preferred units while maintaining accuracy and compliance with industry standards.

Temperature affects the density of water, which impacts the pressure exerted by a column of water:

  • Standard temperature: Conversions use 20°C (68°F) as the reference temperature
  • Water density variation: Water density changes by approximately 0.1% per °C near room temperature
  • Practical impact: For typical HVAC applications (15-25°C), the error is less than 0.5%
  • Precision applications: For critical measurements, temperature correction may be needed:
  • Correction factor = density at actual temp / density at 20°C
  • Field measurements: Standard conversion is sufficient for most HVAC balancing and testing

This converter uses the standard 20°C conversion factor (1 inH₂O = 248.84 Pa), which is appropriate for nearly all HVAC design and field applications.

HVAC systems operate within specific pressure ranges depending on their application:

Residential HVAC Systems
  • Typical duct static pressure: 0.5-1.5 inH₂O (124-373 Pa)
  • Return air pressure: 0.0-0.2 inH₂O (0-50 Pa)
  • Supply air pressure: 0.3-0.8 inH₂O (75-200 Pa)
  • Filter pressure drop (clean): 0.1-0.2 inH₂O (25-50 Pa)
  • Filter pressure drop (dirty): 0.5-1.0 inH₂O (124-249 Pa)
Commercial/Industrial Systems
  • Typical duct static pressure: 1-4 inH₂O (249-995 Pa)
  • High-pressure systems: 5-10 inH₂O (1244-2488 Pa)
  • Kitchen exhaust: 2-6 inH₂O (498-1493 Pa)
  • Cleanroom systems: 0.05-0.2 inH₂O (12-50 Pa)
  • Industrial ventilation: 10-20 inH₂O (2488-4977 Pa)

Understanding these pressure ranges is critical for proper system design, equipment selection, and performance verification. This converter makes it easy to work with both unit systems across all these pressure ranges.

The required accuracy for pressure conversions depends on the specific HVAC application:

  • System design: 2-3 decimal places recommended (0.001 inH₂O or 0.25 Pa precision)
  • Field measurements: 1-2 decimal places sufficient for balancing and testing
  • Equipment selection: Manufacturer specifications typically use 1 decimal place
  • Code compliance: Local building codes may specify required precision levels
  • Energy efficiency: Higher precision (3+ decimals) for energy modeling and optimization
  • Typical industry practice: Rounding to 2 decimal places for most applications

This converter defaults to 2 decimal places (industry standard) but allows adjustment from 0 to 4 decimal places to accommodate all HVAC application requirements, from quick field measurements to precise engineering calculations.

Conversion Table: Pascals to Inches of Water

Common HVAC pressure measurements for duct design and air flow calculations.

Pascals (Pa) inH₂O Millibars (mbar) psi Common HVAC Uses
24.88 Pa 0.1 inH₂O 0.2488 mbar 0.0036 psi Air velocity, minor pressure differences
124.42 Pa 0.5 inH₂O 1.2442 mbar 0.0181 psi Residential duct pressure
248.84 Pa 1.0 inH₂O 2.4884 mbar 0.0361 psi Standard commercial duct pressure
497.68 Pa 2.0 inH₂O 4.9768 mbar 0.0723 psi Fan static pressure rating
746.52 Pa 3.0 inH₂O 7.4652 mbar 0.1084 psi Medium pressure systems
995.36 Pa 4.0 inH₂O 9.9536 mbar 0.1445 psi High pressure ductwork
1244.20 Pa 5.0 inH₂O 12.4420 mbar 0.1807 psi Industrial ventilation systems
2488.40 Pa 10.0 inH₂O 24.8840 mbar 0.3613 psi High-pressure industrial systems
4976.80 Pa 20.0 inH₂O 49.7680 mbar 0.7226 psi Specialized industrial applications

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