Tag: Condensate

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

 

 

This article was written by HVAC / Furnace technician Benoît Mongeau. Thank you Ben.


 

 

High efficiency (or 90%, or condensing) furnaces use a set of two heat exchangers in order to retrieve more heat from the combustion products than their mid-efficiency counterparts.  Because of this, they generate flue gases much colder than those of a mid-efficiency or natural draft unit.  This not only completely changes the way the furnace has to be vented (I will talk about venting specifically in a later tip) but also, and it’s what we’ll focus on, a lot of condensates is generated.  This water comes from two sources:  moisture which was already present in the combustion air, and the combustion process itself, as the hydrogen atoms from the natural gas molecules (methane, CH4) combine with oxygen to form water. Now as technicians you don’t need to know this part but if you’re a bit into chemistry, here’s the basic chemical equation:

 

CH4 + 2 O2 + heat = CO2 + 2 H2O

 

This means that in perfect combustion, for every molecule of CO2 you produce, there are also 2 water molecules produced. This adds up to a lot of water vapor.

 

In order for the furnace to work properly, that condensation needs to be drained out or else it would accumulate inside the heat exchanger, inducer and venting, impeding proper gas/combustion product flow.  Most furnaces will have at least 2 internal drains, typically one for the heat exchanger and one for the vent, usually at the inducer outlet or on the inducer housing.

 

The secondary heat exchanger outlet is sealed inside a plastic part called the collector box, which is designed to collect the condensate and drain it out.

 

All condensate drains go into a trap.  The condensate trap is absolutely mandatory for a high-efficiency gas furnace.  Since the drain taps into the exhaust system, leaving it open to the air would allow for a potential exhaust/flue gas leak in the living space, which is a big no-no.  Additionally, the inducer motor would suck air through the drain if it weren’t trapped, which could affect combustion, and would prevent proper drainage.  Keep that in mind, because if you ever add an extra drain (off a tee on the venting, for example), you will need to TRAP it, always.

 

The only downside to the trap is potential for blockage.  The trap needs to be cleaned out regularly, and that should be done every maintenance.  Rinse it out, make sure water flows through the trap properly from all its ports.  If there’s any poor flow, fill it up and blow through it a few times to get the dirt out.  Hotter water helps for stubborn blockages.  The need for regular cleaning also means that drains should be installed as much as possible in a way that allows for the trap to be easily removed.  I highly recommend using clamped flexible hoses for the drain, as close as possible to the trap.  Avoid hard-piping the whole drain, as it will be impossible to remove and clean out the trap.

 

To ensure proper drainage, here are the proper practices:

-Make sure every component that produces condensate is sloped towards the drain.  That means slope the venting down towards the furnace (typically a ¼’’ slope per foot of length, minimum), and also, slope the furnace itself!  Look in your install manual, most manufacturers will call for the furnace to be installed with a slight forward pitch to allow condensate to drain from the heat exchanger.

-Slope the drain line itself, obviously.  Avoid double trapping and vent the drain after the trap to prevent airlocks

-Avoid running the drain in an area where it could freeze.  That includes running it under the natural fresh air inlet if there is one.  

 

Finally, note that furnace condensate is acidic, and some states/provinces/countries may require the condensate to be neutralized prior to draining.

— Ben


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

In commercial HVAC you will find several different types of multi-stage evaporator coils, intertwined (like shown above), horizontal face split (one coil on top of another), and vertical (side by side).

Pay attention when staging a horizontal evaporator to ensure that stage #1 is on the bottom and stage #2 is on the top. If stage #1 is on top you risk condensate being pulled off of the coil when the water runs down the wet fins and then hits the dry second stage on the bottom.

By keeping stage #1 on the bottom the moisture adhesion will stay consistent as condensate drops no matter if one or both stages are calling.

You can also have this same effect when stage #1 fails and stage #2 keeps running on a stacked horizontal coil.

— Bryan

Condensate_Pump

One of my techs (Jim Walch) mentioned to me that another common “double trap” style issue that comes up often is techs and installers running a drain too far into a condensate pump.

When you run the system drain too deep into the pump reservoir the water level can rise high enough to cover the drain end. This can create the same type of “airlock” you get with a double trap.

When draining into a condensate pump only extend the drain tube 1″ or so into the reservoir of the pump to prevent the water from rising and covering the end. Also, make sure to wire up the overflow switch on the pump in series with your system condensate switch so that whether the pump itself fails or the system drain pan has a blockage it will shut the system off.

Simple stuff, but it can prevent thousands of dollars in damage.

— Bryan

Double_trap

Double traps are no good. End of tip. Ok, here is some detail.

Anytime your drain goes up and down more than once you have a double trap UNLESS you place an air vent between the two traps that vents ABOVE the drain inlet.

The double trap causes drainage issues because air becomes trapped between the two traps and air is lighter than water. This causes the air to want to travel up as the water flows down resulting in NO DRAINAGE.

A vent allows the air to move instead of becoming trapped. This is why you vent a drain after the first trap if there is another trap or the potential of another trap.

This is also why you vent a drain after the first trap and before a common drain if you are connecting more than one drain. It helps prevent the possibility of a double trap and thus prevents a nasty backup.

In general just pitch the drain properly, install only one trap and don’t interconnect (unless required) and you will have no problem.

That was easy!

— Bryan

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