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1) Layout

This manual will deal with the two most common pipe layouts:

  1. Serpentine
  2. Spiral Counter Flow.

a) Serpentine

Serpentine layout

Figure 5

The most common is the serpentine pipe layout. In FIG.5, this pattern involves running the feed line from the manifold or header into a room (or zone), supplying the highest heat loss area first (exterior wall). Then a series of back and forth loops at the appropriate spacing will return back to themanifold.


b) Spiral Counter Flow

The spiral counter flow layout (FIG.6), is somewhat more difficult to install, but provides more flexibility in obtaining equal loop lengths. The pattern first starts along the exterior walls, the same as aserpentine, then spirals into the centre of the room on double spacing (24"), then spirals back out between the incoming spirals resulting in a 12" spacing.

Spiral Counter Flow

Figure 6

RFH pipe spacing is usually 12" and should never be exceeded. One foot of pipe per sq. ft. of floor area is the general rule. A closer spacing of 6" to 8" may also be required in areas such as bathrooms where floor areas are covered by tubs, vanities, etc. Closer spacing, usually 6", should be used in front of exterior doors, large windows, or any high heat loss area. Floor coverings with an R-value of 1 should have an 8 or 9 inch spacing. Floor coverings
with an R-value of 2 should have a 4" spacing.Joist cavity installations also require a minimum 8 inch spacing and even less depending on floor coverings.

2) Pipe Lengths

In addition to spacing, the performance of any RFH zone will depend upon the loop lengths. There are many formulas for calculating all sorts of pertinent data, but they result in fairly consistent averages in 99% of utility and residential applications.

RFH pipe is classified in two I.D (inside diameter) sizes, 1/2"(12 mm) and 5/8"(16 mm).Feed pipe is available in 3/4"(20 mm), 1"(25 mm) and 1 1/4" (32 mm). 1/2" I.D. pipe should NOT exceed a 300' loop length, and where higher Btu's per sq.ft. are required, this should be reduced to a 250' loop length. Note that maximum loop lengths should only be used in basements or centre loops in larger zones.


RFH pipe of 5/8" I.D. should not exceed a 400'loop length. Larger or smaller pipe, even though it is on the market, is not recommended for most applications. Smaller pipe has inadequate volume and larger pipe has poor heat transfer characteristics.

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