Tag: drain line

It should be stated and restated that codes and code enforcement vary from location to location within the US. The IMC (International Mechanical Code) is one of the most widely utilized and referenced and the 2015 version of the IMC section 307 is what I will be referring to in this article.

Condensate Disposal 

The code as it relates to condensate disposal in the IMC is pretty vague. It says that it must be disposed of into an “approved location” and that it shouldn’t dump on walkways, streets or alleys as to “cause a nuisance”.

This leaves us a lot of wiggle room for interpretation and a lot of authority to the AHJ (authority having jurisdiction) and design professionals to establish what is and what isn’t an “approved location”. Here are a few good guidelines –

  • Don’t dump condensate in places that could cause people to slip
  • Don’t dump condensate around foundations, basements or other areas that could cause ponding, erosion and/or leakage
  • Don’t dump condensate on a roof
  • When discharging into a shared drain or sewer system ensure that it isn’t piped in such a way that waste fumes could enter the system or occupied space

Drain Sizing

IMC 307.2.2 tells us that an A/C condensate drain inside diameter should not be smaller than 3/4″ and should not be smaller than the drain pan outlet diameter. 3/4″ is sufficient for up to 20 tons according to the IMC unless the drain outlet size is larger than 3/4″.

Drain Pitch 

The IMC dictates a 1% minimum pitch of the drain which is equal to 1/8″ fall for every 12″ (foot) of horizontal run. In practice, it is safer to use 1/4″ of fall per foot to ensure proper drainage and provide some wiggle room for error.

Support

Drains can be made out of many materials but PVC is by far the most common. When a drain line is PVC the IMC dictates that it should be supported every 4′ when horizontal (while maintaining proper pitch) and every 10′ vertically.

Cleanout

IMC 307.2.5 states that the condensate assembly must be installed in such a way that the drain line can be “cleared of blockages and maintained” without cutting the drain.

Traps & Vents 

The IMC states that condensate drains should be trapped according to manufactures specs HOWEVER, wording was added in IMC 307.2.4.1 that states that ductless systems must either have a check valve or a trap in the condensate line. While most manufacturers don’t specify this on this gravity ductless drains, it is something to look out for.

Venting after the trap (like shown on the EZ Trap above) is a really good idea in most applications because it helps prevent airlock that can occur due to double traps and shared drains as well as prevent siphoning. This vent is AFTER the trap and must remain open to be effective. The vent opening should always rise above the trip level of the condensate overflow switch when it is in the primary drain line or pan or above the secondary / aux overflow port on the primary drain pan. This helps ensure that if a backup occurs that the water properly trips the switch instead of overflowing out of the vent. While venting is a common best practice it isn’t part of the IMC code.

Drain Insulation 

The IMC code doesn’t directly state that the drain line must be insulated.  Many will point to the where the ICC energy efficiency code states

N1103.3
Mechanical system piping insulation.[/b] Mechanical system piping capable of carrying fluids above 105?F (40?C) or below 55?F (13?C) shall be insulated to a minimum of R-2. but this really isn’t talking about condensate drains when read in context.

Some municipalities do require that horizontal portions of drain inside the structure be insulated to prevent condensation and this standard makes sense to me. In Florida we always insulate horizontal portions of the drain because if we didn’t we would have consistent issues with growth and water damage due to the high dew points.

Condensate Switches 

IMC 307.2.3 states that all HVAC equipment that produces condensate must have either a secondary drain line or a condensate overflow switch, a secondary drain pan with a secondary drain line or condensate switch or some combination of these installations should be used to prevent overflow if the primary drain line blocks.

This includes rooftop units, ductless units and downflow units but the code does allow for the overflow prevention switch to be placed in the primary drain pan in these cases but NOT the primary drain line according to 307.2.3.1

— Bryan

 

 


Condensate overflow prevention devices or float switches as they are often called are such simple devices that you wouldn’t think there would be much room for controversy. In my experience there are few areas of the trade where technician and installer preferences and opinions vary greatly.

Let’s start with some float switch basics

Float (condensate) switches are designed so that they will remain closed when water is going down the drain like it’s supposed to and then open when an overflow condition occurs. In order for the switch to open it must be positioned in a location that is dry normally and will reliably fill with water when a drainage issue occurs.

There are very simple switches that just clip onto the edge of primary or secondary drain pans like the Rectorseal Safe-T-Switch SS3 shown above. When the primary drain overfills it begins leaking into the secondary pan below and a pan sitch like the SS3 will open when the water levels rise. This type of switch can also be used in the primary pan so that it only trips when the water level exceeds the normal levels. In both of these cases, it is important that the switch is firmly mounted and level so that it will function as designed when the time comes.

Then there are the more typical devices like the Safe-T-Switch SS1 and SS2 that are designed to be installed to an aux drain port or sometimes even in the primary drain. When it comes to the mechanical code, there is no “nationally adopted code” but most states and localities adopt the International Mechanical Code (IMC) is the most widely adopted code in the country and it states a few things that are important to consider in addition to the general requirements stating that an overflow device is required.

307.2.3.1: “On downflow units and all other coils that do not have a secondary drain or provisions to install a secondary or auxiliary drain pan, a water-level monitoring device shall be installed inside the primary drain pan. This device shall shut off the equipment served in the event that the primary drain becomes restricted. Devices installed in the drain line shall not be permitted.

307.2.5: “Condensate drain lines shall be configured to allow the clearing of blockages and performance of maintenance without having to cut the line.”

So while this may not apply to you depending on where you live, in general, the code says –

  1. You need to have overflow protection
  2. It needs to be in a secondary pan, in an overflow drain or in the primary pan UNLESS the unit also has an aux drain line that drains outside or a secondary pan under it. 
  3. The primary drain needs to have some sort of cleanout that doesn’t require taking the drain apart

While there are cases where installing in the main drain is permitted the cases are limited and there is also the issue of buildup collecting on the float itself when it is installed in the main drain. While some technicians swear by the practice of putting the float switch in the main drain line I generally advise against it.


So in most upflow applications, we will be installing the condensate switch to the aux port on the evaporator coil. When installing the switch you want to set in such a way that you accomplish the following –

  1. The float trips (rises) before the pan overflows
  2. Have free access to the access panels and filter door
  3. Water should flow freely to the float if an overflow occurs
  4. The float is installed level so it can rise and fall freely 
  5. The switch is installed so that it cannot be easily moved into an improper position 

Many technicians swear that if the aux drain is pitched down that water will flow into the float all the time and they pull the drain perfectly level or even pitched upwards. Others swear that the switch must be mounted directly to the front of the unit. The truth is that so long as you follow the 4 rules above the float could be positioned in many different locations. It is not the orientation of the PVC connected to the aux port that holds back the water, it is the level of the aux port opening that does that. The level that the water must rise and the total depth of the primary pan varies from model to model. This means that in some cases a practice that works just fine on one brand may not on another.


Many contractors have found that installing a float switch with a flat bottom like the SS2 right on the front of some shallow coils can result in the pans overflowing before the float trips. Others have found that this same practice can result in difficulty accessing air filters. In these cases it may make sense to route the aux drain around to the side, pitch the drain down and level it out with 45s and install the switch there. Like all drains, it must be pitched slightly down for the water to reliably reach its destination, but the switch itself should still be installed level.

Once again, this practice does not result in false tripping because it is the level of the aux drain port that holds back the water, not the pitch of the drain (unless the drain is improperly pitched upward).

Finally, there is a dispute over whether to break the “R” circuit or the “Y” circuit with the switch. It is generally recognized that breaking R is a better practice to prevent short cycling unless the system has another dedicated method for condensate switch connection.

— Bryan

Scroll to top
Translate »

Daily Tech Tip

Get the (near) daily Tech Tip email right in your inbox!
Email address
Name