Heat Loss Calculations and System Design
Note: Urecon offers a complete computer assisted engineering service providing such information as: heat loss, time to freeze, fluid outlet temperature, minimum flow rates, tracing wattage required, heat gain, etc., all based on the specific requirements of each project. Basic information needed for typical heat trace design includes: project name/location; minimum ambient temperature; above and/or below ground; depth of bury if applicable; core pipe material and diameter; pipe length per circuit; insulation thickness; required maintain temperature; flow direction for sensor positioning; power point location (one or both ends, middle etc.); voltage available.
Contact Urecon for more info and help with custom design/calculations.
It is recommended that a safety factor of 10 to 25% be added to allow for such field conditions as voltage drop, under voltage condition, etc.
Heat Flow Chart Watts/ft/hr/100°F T^{(2)}
Dia.^{(1)} 
Urethane Insulation Thickness 
25 mm (1 in) 
40 m (1½ in) 
50 mm (2 in) 
63 mm (2½ in) 
75 mm (3 in) 
1 
1.8 
1.4 
1.2 
1.1 
1.0 
2 
2.9 
2.2 
1.8 
1.6 
1.4 
4 
4.9 
3.6 
2.9 
2.5 
2.2 
6 
6.9 
4.9 
3.9 
3.3 
2.9 
8 
8.9 
6.3 
4.9 
4.1 
3.6 
10 
n/a 
7.6 
5.9 
4.9 
4.2 
12 
n/a 
9.0 
6.9 
5.8 
4.9 
14 
n/a 
10.4 
7.9 
6.5 
5.6 
16 
n/a 
n/a 
8.9 
7.4 
6.2 
18 
n/a 
n/a 
9.9 
8.3 
6.9 
20 
n/a 
n/a 
10.8 
9.0 
7.6 
22 
n/a 
n/a 
11.8 
9.9 
8.3 
24 
n/a 
n/a 
12.7 
10.8 
9.0 
Heat flow in watts per lineal foot
The table is based upon the application
of the following formula:
Where:
W = Watts/ft/hr (W x 3.414 = Btu/hr)
K = Btu/ft²/hr/1°F/ft = 0.0108 for Urethane
T = temperature differential°F
D = outside diameter of insulation
d = outside diameter of pipe 
 Diameters for (D/d) taken as 3/1 for 1" pipe +1" insulation and is typical for all other combinations.
 For other than 100°F T, divide by 100 and multiply by required T.

Formula
The heat loss for an externally traced pipe may be calculated by the following formula:
Where:
W = Watts per foot of pipe
Tm = maintained temperature°F
Ta = ambient temperature°F
Ln = natural log
Di = outside diameter of insulation (in)
Dp = outside diameter of pipe (in)
Ki = K value of insulation (BTU • in / hr • ft² •°F)
Dj = outside diameter of jacket (in)
Kj = K value of jacket
(BTU • in / hr • ft² •°F)
Sf = Safety Factor
For more information on time to freeze and raw data requirements:
