Minimum Pipe Insulation Thickness per. ASHRAE Table, Formula and Calculator

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Minimum Pipe Insulation Thickness per. ASHRAE Table, Formula and Calculator

Heat Transfer Knowledge and Engineering
HVAC Engineering

Minimum Pipe Insulation Thickness, in. per. ASHRAE Table, Formula and Calculator

This table defines the recommended minimum pipe insulation thickness based on the fluid design operating temperature range. The calculator located on the bottom of this webpage will determine an alternate insulation thickness outside of the stated conductivity range.

Economics can be used to (1) select the optimum insulation thickness for a specific insulation, or (2) evaluate two or more insulation materials for least cost for a given level of thermal performance. In either case, economic considerations determine the most cost-effective solution for insulating over a specific period. Life-cycle costing considers the initial cost of the insulation system plus the ongoing value of energy savings over the expected service lifetime. The economic thickness is defined as the thickness that minimizes the total life-cycle cost.

Fluid Design Operating Temp. Range, °F	Insulation Conductivity		Nominal Pipe or Tube Size, in.
Fluid Design Operating Temp. Range, °F	Conductivity, Btu·in/h·ft²·°F	Mean Rating Temp., °F	< 1	1 to < 1 - 1/2	1- 1/2 to < 4	4 to < 8	≥ 8
> 350	0.32 to 0.34	250	4.5	5.0	5.0	5.0	5.0
250 to 350	0.29 to 0.32	200	3.5	4.0	4.5	4.5	4.5
201 to 250	0.27 to 0.30	150	2.5	2.5	3.0	3.0	3.0
141 to 200	0.25 to 0.29	125	1.5	1.5	2.0	2.0	2.0
105 to 140	0.22 to 0.28	100	1.0	1.0	1.5	1.5	1.5
Cooling Systems (Chilled Water, Brine, and Refrigerant)d
40 to 60	0.22 to 0.28	75	0.5	0.5	1.0	1.0	1.0
<40	0.22 to 0.28	50	0.5	1.0	1.0	1.0	1.5

^a For insulation outside stated conductivity range, determine minimum thickness T as follows:

T = r { ( 1 + t / r )^K/k - 1 }

Where:

t = insulation thickness listed in this table for applicable fluid temperature and pipe size,
K = conductivity of alternative material at mean rating temperature indicated for applicable fluid temperature (Btu·in/h·ft²·°F);
k = upper value of conductivity range listed in this table for the applicable fluid temperature.

^b These thicknesses are based on energy efficiency considerations only. Additional insulation is sometimes required relative to safety issues/surface temperature.
^c Piping insulation is not required between control valve and coil on run-outs when control valve is located within 4 ft of coil and pipe size is 1 in. or less.
^d These thicknesses are based on energy efficiency considerations only. Issues such as water vapor permeability or surface condensation sometimes require vapor retarders or additional insulation.

Reference:

ASME Code for Pressure Piping, B31.5, Refrigeration Piping and Heat Transfer Components