plenum runs plenum runs. plenum run usually located in the attic or basement. run in any location...
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Plenum RunUsually located in the attic or basement.Run in any location accessible for attachment of supply tubing.More economical to run where it shortens length of 2 or more supply runs.Insure layout will allow recommend balancing.copyright Mestek, Inc. 2004
Considerations:Want to keep runs as close as possible to 10 feet in length. full 40 cfm and 2000 btu per outlet makes it much easier to balance..Generally less $$$ to run supply plenum extra distance than run long 2 runs.Want to premake the 2 runs downstairs where its nice and cool!!!!
Square Duct Board
Spiral Round DuctProper insulation and vapor barrier criticalSpacepak plenum take-offs for metal roundSupport properly
Using TeesInstall tee minimum of 24 after air handler.No outlets between fan & tee.No more than 60% of capacity on one leg24NO MORE THAN60% of CAPACITYON ONE SIDE
Branch Tees 70/3030% OFMAXIMUMCAPACITY
Ideal 50/50 Split
Think 2 SystemsSYSTEM ONESYSTEM TWO
In order to lay out the plenum run you have to know where the outlets are going to be. You want to lay out the plenum so that at least most of the runs are an equal distance away from it (ideally within 8 12). Some guys like to use a complete rectangle around the perimeter (thats fine too). Im not sure that Ive every seen a plenum layout that didnt work as long as it was sealed properly and followed these rules. You want to make sure you run enough plenum so that you dont bunch up all the take-offs in one place. Putting too many in one spot will kill the air flow on all of them. It will also weaken the plenum material.Run the plenum where you can keep most of the runs to a reasonable length about 10-15. Run outlets wide open when sound is not an issue (kitchen, hallways, bathrooms). Never exceed 35 CFM/ outlet where noise may be an issue (TV room, Bedrooms). Supply tubing is about $3/ft. and the plenum is about $8.50/ft. so it makes sense to run plenum if you can reduce the length of 3 outlets. Not to mention youll get better performance. I prefer to put the SA tubes and faceplates together, cut the outlet holes stuffing the SA tubes up into the attic, then in the attic lay my tape measure where the plenum will go and sketch that leg of the plenum run on a piece of paper, then install the plenum take-offs onto the plenum outside of in the garage where it is cooler. Then up in the attic you assemble the plenum and then measure the length of each run. It is a good idea to mark them so you know which is which if you ever have to come back and balance or trouble shoot.
Spacepak offers 8 x 8 square ductboard plenum and accessories. Its 1 thick R- 4.3 and comes in a box of 6 4 lengths. The accessories also come in boxes of 4. (except the end caps that come in a box of 10) This stuff is very easy to work with you can cut it on site very easily, the Spacepak quick connect system works very well with it, its light, easy to support The important thing is to use the right tape when sealing the joints. The tape must be labeled UL- 181 and the glue on the tape must be rated for the most extreme temperature the space will see where it is installed.
Some contractors swear by metal round. Metal round works well with Spacepak but we dont offer it. A couple important points about using metal round: It needs to be properly insulated in the field. If there is a leak In the vapor barrier in unconditioned space condensation WILL occur on the outside of the pipe (leading to wet ceiling and mold possibilities). You want to order the take-off fittings for metal round (they have a different shape and gasket). It is heavier than duct board and may require more or heavier hangers.
In general we want to have 24 of straight pipe before any fitting (90) or Tee) Here we have a bull head tee (in red). You see the 2 of straight duct between it and the unit (and no take-offs on this piece). After the bull head tee try to balance the number of outlets connected to each branch (50-50 is ideal, 60 40% is acceptable). This is a branch tee. For branch tees, connect only 30% of the total outlets to the branch portion of the plenum.Again a 50/ 50 split is ideal but 60/40 is acceptable. No outlets installed in the first 2 of plenum ever. This is also where you will take your static pressure reading.Depending on where the unit is located and where the runs are you may end up with this arrangement.Or this arrangement.When using the 5 ton unit it is advisable to use a bull head tee to knock down some of the velocity. These systems need to have some pressure drop.You can treat each side of the H as a separate system.