Tuesday, May 11, 2010

Installing PEX Tubing Under Flooring

Click on the above link for a diagram

For Hung PEX Pipe (Slide Brackets, PEX Heat Transfer Plates or Staple Up Methods)

Installing PEX Tubing through the joists:
Drill (2) 1-1/2” holes in each joist as shown in Drawing A
Feed the PEX tubing through the hole (furthest from the sill plate) starting that particular loop in the last joist bay. PEX Tubing should be uncoiled off the top of the roll to avoid kinking.
The returning PEX Pipe goes through the holes closest to the sill plate.
Starting with the joist bay furthest from the manifold, grab the loop and twist 180°, then pull the PEX loop the length of the joist bay. Fasten the end of the loop in place or let it hang. Continue to work back toward the manifold (see drawing B).
This procedure applies for all three methods of attaching the PEX (Heat Transfer Plates, Hung Method and Staple Up). Please Note: Top of Slide Bracket (Hung Method) should be 1 5/8 inches below subfloor.
Foil Insulation is placed approximately 4 inches below the PEX tubing when done.

1 comment:

  1. There are many ways to install PEX under the floor between the floor joists. We will review three of them: heat transfer plates, hung (w/slide brackets) and clamps.

    The first is Heat transfer plates. Heat transfer plates will give the most even heat across the joist bay and provide more BTU’s per square foot. They can make a popping noise for a short while when the PEX expands. Heat transfer plates are the most expensive method.

    The second method is hung method because when the PEX expands it sags slightly up or down in the joist space causing no noise or damage. It also heats the air and in turn the air heats the floor very evenly.

    The PEX rests on the slide brackets that attach between the joists approx 1 5/8 inches down from the sub floor. The PEX is then zip tied to the slide brackets. This holds the PEX firm and in place while also allowing for the expansion. A small length of protection sleeve is used to protect the PEX where it passes through the holes drilled in the joists.

    The third method is to attach the PEX directly under floor with clamps (talon or standoff). The standoff clamps help reduce noise and friction by keeping the PEX from rubbing against the floor during expansion and contraction. We recommend attaching the clamps every 2.5 feet. This is the least expensive method and offers approximately 15 BTU per sq ft (lowest of the three methods).

    The noise and friction problem comes from the expansion and contraction of the PEX during every call for heat. PEX expands at a rate of 1.1 inches for every 10 feet of PEX for every 100-degree rise in temperature. If the PEX is held tightly it will make noise when it expands and contracts. For under the floor radiant heat applications the temperature should not exceed 150 degrees Fahrenheit with either heat transfer plates or the hung method.

    All of these methods require containment of the heated air between the joists so heated air will not be replaced with colder outside air.

    When heating within the framework of a building you need to caulk all the electrical holes, plumbing and chimney chases, around all of the band and rim joists or any other area that heated air could escape. This is easy with modern platform framing as the plywood sub floor caps off the heated air.

    For older ballooned framed houses and houses that are sheathed with boards we do not recommend radiant heating within the joist spaces. When houses that are sheathed with planking the gaps in the boards allow the heated air to travel out of the joist spaces easily. This causes a negative air pressure with in the framework and draws in cold outside air.

    All under floor radiant installations should have a reflective insulation, which helps contain the heated air. The insulation is positioned 4 inches down from the PEX and stapled against the joists.

    When the PEX is installed in a heated space the use of a secondary insulation is optional. When the PEX is over a cold space (basement) we recommend the use of fiberglass or high-density foam board below the foil.

    A most important point to remember is the heating limits you can put through the floor. The hung method can deliver up to 20 BTU’s per square foot and 25 BTU’s with heat transfer plates. If you try to deliver more heat than this (25 BTU's) you could damage the floor.

    When the heat load required for a specific area is larger than the radiant floor can provide, supplemental heat is needed.

    Supplemental heat can be from other sources such as radiators, wood stoves, or gas direct vent heaters.