Dynamic Viscosity
Kinematic Viscosity
Conversion Factors
1 cSt = 1 mm²/s = 1×10⁻⁶ m²/s = 1.0764×10⁻⁵ ft²/s
ν (cSt) = μ (cP) / ρ (g/cm³) = μ (mPa·s) / ρ (kg/m³) × 1000
Re = ρ × v × D / μ = v × D / ν (turbulent if Re > 4000)
HVAC Fluid Dynamic Viscosity Reference
| Fluid | Temp (°C) | Dynamic Viscosity (cP / mPa·s) | Density (kg/m³) | Kinematic (cSt) |
|---|---|---|---|---|
| Water | 5 | 1.519 | 999.9 | 1.519 |
| Water | 20 | 1.002 | 998.2 | 1.004 |
| Water | 40 | 0.653 | 992.2 | 0.658 |
| Water | 60 | 0.467 | 983.2 | 0.475 |
| Water | 80 | 0.355 | 971.8 | 0.365 |
| Ethylene glycol 30% | -10 | 8.0 | 1050 | 7.6 |
| Ethylene glycol 30% | 20 | 2.5 | 1040 | 2.4 |
| Ethylene glycol 50% | -20 | 60 | 1075 | 55.8 |
| Ethylene glycol 50% | -10 | 25 | 1070 | 23.4 |
| Ethylene glycol 50% | 20 | 7.0 | 1060 | 6.6 |
| Propylene glycol 30% | -10 | 12 | 1030 | 11.7 |
| Propylene glycol 30% | 20 | 3.5 | 1020 | 3.4 |
| Propylene glycol 50% | -10 | 90 | 1050 | 85.7 |
| Propylene glycol 50% | 20 | 14 | 1040 | 13.5 |
| Mineral refrigerant oil (ISO 32) | 20 | 28 - 35 | 870 | 32 - 40 |
| POE refrigerant oil (ISO 32) | 20 | 28 - 35 | 980 | 29 - 36 |
| Air (at 20°C) | 20 | 0.0182 | 1.20 | 15.1 |
Values are approximate at the stated concentrations and temperatures. Glycol viscosity increases sharply at low temperatures -- always verify at minimum operating temperature for Canadian winter conditions. Use manufacturer data for exact values at your operating conditions.
Flow Regime Reference (Reynolds Number)
| Re Range | Flow Regime | Heat Transfer | HVAC Implication |
|---|---|---|---|
| Re < 2300 | Laminar | Poor (Nu ≈ 3.66) | Poor heat exchanger performance; avoid for coils and chilled water |
| 2300 - 4000 | Transitional | Variable / unstable | Undesirable operating zone; size piping to avoid |
| Re > 4000 | Turbulent | Good (Nu by Dittus-Boelter) | Target operating range for chilled water, hydronic, and glycol systems |
| Re > 10 000 | Fully turbulent | Excellent | Optimal for heat exchangers; most well-designed HVAC pipe systems |
How to Use the Viscosity Converter
Enter a dynamic viscosity value in cP (centipoise), mPa·s, Pa·s, or μPa·s in the Dynamic Viscosity section. All other dynamic units update instantly. Note that 1 cP = 1 mPa·s exactly. Use the quick presets to load common HVAC fluid values: water at 0°C or 20°C, or glycol mixes at seasonal operating temperatures for Canadian systems.
Enter a kinematic viscosity value in cSt, m²/s, mm²/s, or ft²/s in the Kinematic Viscosity section. Note that 1 cSt = 1 mm²/s exactly. Set the fluid density in the density field so the converter can cross-reference between dynamic and kinematic viscosity using the relationship: kinematic (cSt) = dynamic (cP) / density (g/cm³).
The density field defaults to 998 kg/m³ (water at 20°C). Change it to match your actual fluid: 1040 kg/m³ for 30% ethylene glycol, 1060 kg/m³ for 50% ethylene glycol. With the correct density set, entering either dynamic or kinematic viscosity automatically computes the other. Check the reference table for densities at your operating temperature.
The HVAC fluid reference table shows dynamic viscosity for water, ethylene glycol, and propylene glycol at multiple temperatures. For Canadian systems, check the viscosity at your minimum operating temperature -- not just design temperature. A 50% ethylene glycol system at -20°C has 60 cP viscosity, which is 60x more viscous than water at 20°C and may push hydronic flow into laminar regime, significantly reducing heat exchanger performance. Use the Reynolds number reference to verify turbulent flow at worst-case conditions.
Viscosity in HVAC -- Complete Guide
Viscosity determines how fluids flow through pipes and heat exchangers. In HVAC, it matters most for glycol antifreeze systems in Canadian cold climates, refrigerant oil selection for compressors, and fluid flow analysis in hydronic heating and chilled water systems. Two types of viscosity appear in HVAC work: dynamic (absolute) viscosity and kinematic viscosity.
Dynamic vs. Kinematic Viscosity
Dynamic viscosity (μ, mu) measures resistance to shear flow and is expressed in centipoise (cP) or millipascal-seconds (mPa·s) -- these are the same unit. Kinematic viscosity (ν, nu) is dynamic viscosity divided by fluid density, expressed in centistokes (cSt). Kinematic viscosity is used in the Reynolds number: Re = V x D / ν, where V is velocity (m/s), D is pipe diameter (m), and ν is kinematic viscosity (m²/s). Note that 1 cSt = 1 mm²/s = 10⁻⁶ m²/s, following the SI unit definitions set out in the NIST Guide to the SI, Appendix B. Water at 20°C: μ = 1.002 cP, ρ = 998 kg/m³, so ν = 1.002/0.998 = 1.004 cSt.
Glycol Viscosity and Canadian Hydronic Systems
Antifreeze is essential for outdoor hydronic equipment exposed to Canadian winters. Ethylene glycol is standard for most applications; propylene glycol is required where CFIA Safe Food for Canadians regulations apply (food processing, food storage facilities). Both increase viscosity significantly below 0°C. A 50% ethylene glycol mix for Prairie province systems has viscosity of 7 cP at 20°C -- 7x more viscous than water. At -20°C it reaches 60 cP. This viscosity increase requires larger pump heads, larger pipe diameters, and can push flow from turbulent into transitional or laminar regime, which the Glycol System Calculator accounts for directly. Always check the Reynolds number at your minimum operating temperature, not just the design cooling or heating temperature, when sizing pumps and piping for glycol systems.
Refrigerant Oil Viscosity
Compressor lubricants in HVAC refrigeration systems are selected based on viscosity at operating temperature. ISO viscosity grades (ISO 32, ISO 46, ISO 68) refer to the kinematic viscosity in cSt at 40°C. Mineral oils are used in older systems with HCFC refrigerants. Polyol ester (POE) oils are required with HFC refrigerants like R-410A, R-32, and R-454B because POE oil is miscible with HFCs while mineral oil is not. Oil viscosity affects compressor lubrication film thickness, refrigerant/oil mixing, and oil return from the evaporator through the suction line, with selection guidance published in the ASHRAE Handbook -- Fundamentals.
Reynolds Number and Heat Transfer
Turbulent flow (Re > 4000) provides dramatically better heat transfer than laminar flow because turbulence promotes mixing at the pipe wall boundary layer. The Dittus-Boelter correlation for turbulent flow in smooth pipes gives heat transfer coefficients 10-100x higher than laminar flow. When glycol increases viscosity and lowers the Reynolds number below 4000, heat exchanger capacity can drop significantly. The fix is to increase flow velocity (larger pump, smaller pipe) or reduce glycol concentration, a trade-off the Hydronic Pipe Sizing Calculator works through directly. For Canadian systems, balance freeze protection (higher glycol) against heat transfer penalty (higher viscosity) -- a 30% glycol mix is often the best compromise for mild-winter regions while 40-50% is required for Prairie and northern locations.
Frequently Asked Questions
Dynamic viscosity (μ) measures a fluid's resistance to shear flow in Pa·s or cP. Kinematic viscosity (ν) equals dynamic viscosity divided by density: ν = μ/ρ, expressed in m²/s or cSt. 1 cP = 1 mPa·s; 1 cSt = 1 mm²/s. For water at 20°C: μ = 1.002 cP and ν = 1.004 cSt. Dynamic viscosity is used in force and pressure-drop calculations; kinematic viscosity is used in Reynolds number calculations for flow regime and heat transfer analysis.
1 centipoise (cP) equals exactly 1 millipascal-second (mPa·s) -- they are the same unit with different names. cP is the traditional CGS unit; mPa·s is the SI equivalent. To convert to Pa·s, divide by 1000: 1 cP = 0.001 Pa·s. To get μPa·s, multiply by 1000: 1 cP = 1000 μPa·s. Water at 20°C = 1.002 cP = 1.002 mPa·s = 0.001002 Pa·s.
30% ethylene glycol (freeze protection to -15°C, common in BC and Ontario): 2.5 cP at 20°C, rising to 8 cP at -10°C. 50% ethylene glycol (freeze to -36°C, Prairie Canada): 7 cP at 20°C, rising to 25 cP at -10°C and 60 cP at -20°C. Always verify pump sizing, pipe sizing, and Reynolds number at your minimum operating temperature, not just design temperature. Cold glycol in undersized piping can shift from turbulent to laminar flow, reducing heat exchanger performance by 50% or more.
Viscosity determines the Reynolds number (Re = velocity x diameter / kinematic viscosity), which sets the flow regime. Turbulent flow (Re > 4000) gives good heat transfer; laminar flow (Re < 2300) gives poor heat transfer. Pump curves are based on water -- glycol requires correction factors for higher viscosity. A glycol system might need 15-30% more pump head than the same water system. Always check Re at minimum operating temperature, especially for 50% glycol Prairie systems where cold-weather viscosity is 25-60x higher than water at room temperature.