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Tube Pressure Drop
Correction Factors
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Pex-Aluminum-Pex
3/8" ID - multiply pressure drop by 1.3
1/2" ID - multiply pressure drop by 1.1
5/8" ID - multiply pressure drop by 0.7
3/4" ID - multiply pressure drop by 0.5

Copper
3/8" ID - multiply pressure drop by 0.5
1/2" ID - multiply pressure drop by 0.8
5/8" ID - multiply pressure drop by 0.8
3/4" ID - multiply pressure drop by 0.7

Reinforced Rubber
3/8" ID - no correction needed
1/2" ID - no correction needed
5/8" ID - no correction needed
3/4" ID - no correction needed

INDEX

Copyrights

Getting Started
Heat Load
.....heat loss basics
Floor Output
Floor Covering
Floor Surface Temp.
Average Water Temp.
Supply Water Temp.
Tube Selection and Size
Tube Spacing
Total Tube Required
Tube Circuit Length
Number of Circuits
Actual Circuit Length
Flow Per Tube
Pressure Drop
Summarize Circuits

System Flow
System Pressure Drop


 

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USE THE RadPad© and 'WORKSHEET' to complete the system sizing.

8. Tube Selection and Size
Because PEX (cross linked polyethylene) tubing is the most widely used floor heat tubing, the RadPad© is designed around PEX. It can, however, be used with other products such as PEX-Aluminum-PEX, Polybutylene, copper and even rubber if proper correction factors are applied.
 (Please note: for accurate flows and pressure drops, consult the tubing manufacturerʼs specifications)

[Correction Factors Table]

Select a tube size, based on your application, from the scrollable TUBE SELECTION CHART.

SCROLL DOWN CHART TO FIND YOUR APPLICATION

TUBE SELECTION CHART
Nominal ID: tube sizes are stated in the approximate inside diameter of the tube
Typical Use 3/8" 1/2" 5/8" 3/4"
residential yes yes maybe no
light commercial maybe yes yes yes
commercial/industrial no maybe yes yes
thin gypsum on wood yes yes maybe no
light concrete on wood yes yes maybe no
concrete slab maybe yes yes yes
large concrete slab no no maybe yes
prefab floor panels yes yes maybe no
joist space yes yes maybe no
close tube spacing yes yes no no
wide tube spacing no maybe yes yes

yes = recommended     maybe = use caution    no = not recommended

Tip:
Small diameter tube -

Con: shorter circuits, closer spacing, more tube required
Pro: more even surface temperatures and heat distribution

Large diameter tube -

Con: can produce uneven surface temperatures, difficult to manage and bend
Pro: longer circuits, wider spacing, less tube required

Tip:
Generally, the further beneath the surface the tube is placed in concrete, gypsum or a mud bed, the larger the tube can be but heat takes longer to respond.

9. Tube Spacing
Select tube spacing from the suggestion table below.
Use the closer spacing on hard surfaced areas or areas with a Floor Output greater than 20 btus/sq ft/hr.
Use the wider spacing on areas with insulative floor coverings like carpet and pad.

example: 1/2" tubing at 9" spacing under carpet

tube suggestions

size

3/8"
1/2"
5/8"
3/4"

gpm

0.3
0.6
0.9
1.2

length

200'
300'
400'
500'

spacing

6" - 9"
9" - 12"
12" - 16"
12" - 16"

 

 

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