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line set length over 75ft

hi can anyone tel me what is needed if you have a 2 ton ac unit more then 75 ft away from the air handler i know if it's on a roof top you would have to make oil traps every 20 ft but but lets say i want to go 60ft under ground then 16 ft up and 20ft straight to the air handler can this be done?

i don't need to do it but id like to understand how line sets work.

and do longer line sets that are both insulated
cause the unit like 14 seer to be less efficient

also what is the maximum length of line set a unit can run efficiently without loosing seer value of the unit

thank you


  • Eugene SilbersteinEugene Silberstein Member Posts: 1,380
    Line Sets

    I am going to break your question down into a number of bite sized pieces.

    First of all, you need to check tha mnaufacturers recommendations as far as the maximum length of a line set. It is important to remember though, that the maximum line set length is the total equivalent length, not the linear length of the run. For example, a line run that has an excessive amount of bends, turns and twists, will reach the maximum "equivalent" length sooner than a refrigerant line that has very few bends. This can be equated to the "Total Equivalent Length" that we have mentioned in the past when discussing duct systems.

    As far as refrigerant traps go, it is good field practice to always trap the suction line at the outlet of the evaporator when the evaporator is located below the compressor. Typically, a trap is installed for each 15 feet of vertical run and the top of the riser is often equipped with an inverted P-trap to help keep the oil on the roof. It is also good field practice to pitch the refrigerant lines away from the inverted P-trap back to the compressor to further facilitate oil return.

    As far as running the refrigerant line underground, you do not have to trap the suctinline at the outlet of the evaporator if the line is sloped downward from the air handler to the below-ground location. For example, if the air hanlder is located in the attic and the customer wants the condensing unit located away from the house, the line from the evaporator coil to the underground chaseway needs no trap. However, when the line rises from the ground and up to the compressor, there should be a trap at the base of the line. This wil help prevent the entire underground run from becoming a refrigerant trap.

    Your final question referred to the system's SEER rating and how long of a line set will begin to affect the SEER rating of the equipment. The answer is that pretty much any line set you install will affect the SEER rating. The SEER rating is calculated in a manner that is similar to the method used by the EPA to determine MPG of a new car.

    SEER ratings are a function of EER, which in turn is a function of the Coefficient of Performance (COP)of the system. The COP is a function of the systems's net rrefrigeration effect (NRE) and the heat of compression (HOC). The NRE is the number of btu/lb that are absorbed in the evaporator and the HOC is the number of btu/lb that are picked up in the compressor and the suction line. As additional heat is picked up in the suction line, the HOC increases and the COP decreases. The COP is found be dividing the NRE by the HOC, so an increase in HOC leads to a decrease in the COP of the system.

    To make a long story short, the sinlge most importnat hing you can do to help improve system performance (aside from properly charging the system) is the locate the condensing unit as close to the air handler as possible. Also, be sure to insulate the suction line very well.
  • Dave_4Dave_4 Member Posts: 1,405

    Eugene thank you so much for this great reply i have a big interest in hvac when i walk into a building or a room the first thing i do is look for what it heated or cooled with
    i hope some day to join this trade

  • Eugene SilbersteinEugene Silberstein Member Posts: 1,380

    Where are you located?
  • Dave_4Dave_4 Member Posts: 1,405

    i am located in Connecticut
  • Eugene SilbersteinEugene Silberstein Member Posts: 1,380
    If you grab the Ferry

    If you grab the ferry to the Island of Long, feel free to pop in at the college and say hello.
  • Dave_4Dave_4 Member Posts: 1,405

    sure i go to long island sometimes is this a hvac collage whats the name of it

This discussion has been closed.


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