Underfloor Radiant Heat Systems
Make a sketch of the floor
surface and joists through which piping will be threaded and installed.
Identify the manifold location and route to the manifold for each pipe
Measure the length of the
floor joist and multiply the joist length by two. This defines the
footage of pipe per joist cavity when floor joists are installed on 10"
through 18" centers. When floor joists are on 10" through 18" centers,
two runs of pipe are installed in each joist space. Three runs of pipe
are installed in a joist space when joists are spaced greater than 18"
Calculate the number of
joist spaces you can cover with the pipe coil length you are using. For
example, if the joist is installed on 18" centers and it is 20 feet
long, multiply 20 x 2 to get 40 feet of pipe per cavity. Assuming a 300
foot coil length, 7 joists cavities could be covered. BUT,
remember that you need to allow for the length of pipe running from the
manifold and back again. In this example and depending on the manifold
location perhaps only 6 cavities can be filled.
Pre-drill holes in the
floor joists through which pipes will run. Two 1/2" pipes require a
1-1/2" diameter hole, while four 1/2" pipes require a 2" diameter hole.
Holes should always be straight and aligned. Holes must be drilled in
the center of the floor joist and at least one foot away from the end of
the joist support point.
This process involves a
good deal of pipe threading, but it eliminates pipe kinks and reduces
stress on the pipe. Two people can work very effectively together with
this installation method - one feeding pipe while the other fastens pipe
in the joist space.
For joists installed on greater than 18" centers, three
runs of pipe are required in each joist space. The pipe handling and
installation technique is similar in concept to that described in steps
1 through 8. Create pipe slack and transfer the slack to adjacent bays
as before. Note in the following sketch however, that pipe enters the
bay at one end of the joist and exists at the opposite end in order to
accommodate three runs of pipe.
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