Max length of A/C lines

I inspected a home last week where the suction and liquid lines are underground about 70 feet long, plus 2.5 stories high to the attic hvac units.

Is there a maximun length the lines can’t be installed.
How about height?

The issue becomes voltage drop, and wire gauge needs to be or should be up sized. Due to increased cost of larger wires over long runs, if the runs get excessive then sub-panels are typically installed … but not usually necessary in residential. When I worked in trade, we used rule of thumb that every 50 feet of run, up size one gauge. I am not 100% familiar with NEC as am in Canada, but physics remains same.

I a meant "suction and liquid lines ", sorry

I am not aware of limitations on the suction and liquid lines, have seen some pretty long runs in commercial buildings.

It is a closed system full of fluid. I wouldn’t think there would be a limitation.

So enlighten us as to what brought you to the conclusion that the lines are too long…

…because they were long?

Yes, there is a design issue with refrigerant line design, but I don’t want to go off on a subject that does not apply. Tell me what applies and I’ll let you know.

Is there refrigerant flooding?
What was the suction pressure?
Did you notice oil logging?
Frost on the suction line?
Surging of the liquid line?
Temperature of the liquid line at the evaporator coil?
Temperature of the suction line at the compressor?
What is the amp draw of the compressor at start-up?

Do you know that this is not the job of a Home Inspector?

Dang David! Your wife been mean to you again?

crotchety to say the least!

Mr. Andersen, I appreciate your thorough questions and concerns, but you did not ask me if I operated the systems, which I did not due to cold weather here in NJ.
Therefore, none of your questions apply except one, yes, I know the role of New Jersey licensed home inspector.
I did not come to a conclusion that the lines are too long, but pondered the performance of the systems. As I stated, my concern is that they are 70 feet long, plus 2.5 stories high to the attic hvac units.
Now that you mentioned “there is a design issue with refrigerant line design”, please enlighten me.
Thank you for your time and knowledge.

Ok, so knowing something about this, here is the appropriate answer to your question:

HVAC systems are charged with refrigerant capable of handling 50 foot of refrigeration line. A simple adjustment of charge may be necessary when longer.

It is critical that the refrigeration capacity be kept to a minimum. Thus the sizing of the refrigeration line x its total length should be considered concerning maximum capacity of refrigerant.

Elevation is critical when you have excessive rise (that would be more than your 2.5 stories). This is part and that when the condensing unit is located on the roof and the evaporator is down below. Return of oil cannot be achieved if the elevation is too high. Specific design of the suction line facilitates proper return of oil to the compressor. This is not the case here.

If you have excessive amounts of refrigerant in the system, you may require a solenoid valve to isolate the liquid refrigerant from flooding back down onto the compressor if you have a situation that you can identify and analyze during your home inspection.

Unless this is new construction, or you see that the compressor has been changed in the system is new, if it worked in the past that probably gena work fine in the future. If it does not, it’s not your responsibility (not just because it’s cold in New Jersey right now).

The majority of the houses that I inspect have 100 to 150 feet of refrigerant line. I analyze them all, regardless of outdoor air temperature and I cannot remember the last time I had a significant issue with the initial design.

Insufficient size return air grills and high density air filters create the majority of the problems. The same situation occurs (excessive refrigerant) but not the same reason.

I thought it was 25 ’ factory charge.
Am I incorrect ?


That is the way that they are factory charged around here.

Thank you

The last A/C / Heat pump seminar I attended (in Vancouver) the presenter said the system would see greatly reduced efficiency if the lineset was run longer than 70’

Joe Klampfer, RHI (BC Lic 47242)
Pacific Home Inspections