Water. There would be no life without it, yet it sure can cause problems, too.
For example, failure to properly drain condensate from central air conditioning systems has the potential to cause property damage and can lead to standing water that can create a "bacteria playground" and affect indoor air quality. That's why it's important to ensure proper function of the condensate drain system on every service call.
Condensate Drain Options
The first and easiest option is to allow condensate to drain using gravity, from the drain pan to one of the following: main sewer drain line, floor drain, sump pit, laundry sink, window, or through the wall to the outdoors. Of course, local codes will have a say in your options here.
Gravity drains can create their share of problems and maintenance challenges, however. Long, slow moving, condensate lines, combined with dark and humid environments, can promote clogged drains and breed algae and fugal growth. Be sure to clean these drains on every visit, either by sucking them out with a Shop-vac or blowing them out with compressed air.
But what happens when gravity drainage is impossible or not feasible? The alternative to relocating the entire system near a gravity drain rests in the use of condensate removal pumps. A wide variety of condensate removal pumps are manufactured for virtually every possible installation.
When a Pump Is Required
If you encounter a system that needs a condensate pump or a pump replacement, how can you be sure that you're choosing the right pump for the job?
First, consider the condensate output of the equipment or appliance. When the system includes air conditioning alone, the rate of condensate production is based on a rough estimate that a 5-ton unit, under hot/humid conditions, can produce approximately 2.5 gal. of condensate per hour.
Next, consider the installation site. Where will the pump be mounted? What route will the discharge tubing need to follow in order to properly reach the desired discharge point? The answer to these questions will determine the lift requirement for the pump.
How high do you need to pump the condensate up to access the drain? As the vertical lift increases, the quantity of water pumped, or flow, declines to the point of maximum lift where the effective flow of water is zero. This is called the "shut-off" lift. Most pumps are typically rated to a maximum lift rating, so it's important to remember that the higher the lift required, the lower the flow of the pump.
Obviously, the pump must be rated to achieve the necessary lift, as well as handle the required flow calculated at that lift. Residential grade pumps typically lift 15 or 20 ft., while commercial grade pumps start at 20 ft. and continue on up to 60 ft. A common mistake is made by adding the horizontal run (the distance the water needs to be moved horizontally once the lift is reached) in order to specify the pump. The two measurements are not additive; in fact, most centrifugal pumps will be minimally impacted by the length of the horizontal run. (Note: this is not the case with smaller, piston or positive displacement style pumps designed for ductless mini-split applications.) A run of greater than 50 ft. will only reduce the flow of a standard pump by about 10%. This can be minimized by forming an inverted "U" trap with the discharge tubing, creating a siphon that minimizes the loss of flow. Using gravity to aid the horizontal run will also help prevent loss of flow.
Condensate pumps for residential applications can move up to 70 gal./hr. at low lifts, and about 15 gal./hr. at lifts of 13 to 14 ft. To be safe, the output flow of the pump should be at least double the input rate from the appliance. Check your equipment service manual if you're not sure about the size of the unit or the amount of condensate produced.
The last piece of information required is the line voltage. Most pumps are available in either 115 or 230V; but specialized commercial grade pumps are available in 460V.
Now that you know the basics, you can specify a pump, right? Well, yes and no. There are still a few other factors to consider.
Safety Precautions and Options
Almost every condensate pump is available with a secondary safety switch, designed to stop the flow of condensate in the event of a pump failure, clogged drain line, or loss of power to the pump. Any pump installed in an area susceptible to water damage should include a secondary safety switch.
Normal wiring of a condensate pump safety switch is connected to the thermostat circuit. The switch is wired as normally closed. In the event of a high water condition in the condensate pump, the switch opens the thermostat circuit, stops the air conditioner and the flow of condensate, preventing pump overflow. Installations in attics, utility closets, finished basements, ceiling mounts, etc. should always install a pump with a safety switch.
The proper wiring for a safety switch is as follows:
- Disconnect power to the AC/furnace and unplug condensate pump before connecting the safety switch
- Disconnect the red wire from the AC/furnace bundle coming from the thermostat
- Connect the red wire to one of the two safety switch wire leads coming off the condensate pump, using a wire nut
- Connect the second safety switch wire lead from the condensate pump to the red terminal on the AC/Furnace block. Comply with all local wiring codes.
For installations where interruption of heating or cooling is not acceptable (such as a computer room), most safety switches can be wired normally open and connected to an alarm device.
When a Standard Pump Won't Work
Once you've determined what pumps meet your requirements, you can narrow your choices by size, materials of construction, temperature rating, and price. Here are some installations that require more than a standard condensate pump:
Low level condensate drain: Some appliances, such as gas condensing furnaces, have condensate drains that exit below the inlet port of a standard sized pump. Pumps with a low-profile reservoir or bottom inlet port will solve the problem. The low-profile style pump has a shortened reservoir (about 2-in. tall) to accommodate the lower drain. Pumps with low-level inlets allow connection to a threaded fitting or barbed tubing connection.
High temperature condensate: Steam humidifiers found in many computer room air conditioning systems generate hot water condensate. High temperature pumps are available for use up to 212F. Commercial boilers also generate a steam condensation requiring a high temperature rated pump.
Ductless split systems: The growing popularity of ductless mini-splits has led to more than a few technicians scratching their heads to solve the condensate problem, particularly when the split is mounted on an interior wall. Several "mini-pumps" are available that offer a small reservoir equipped with a float/switch that connects directly to the drain pan in the air handler. The pump (a positive displacement pump vs. the typical centrifugal style condensate pump) can be mounted from six to 13 ft. above the reservoir. Condensate is drawn from the reservoir, through the pump, and out to a drain.
Due to limitations of the positive displacement design, the length of the horizontal run (the distance you need to move the water horizontally, once the lift is achieved) must be considered. Maximum horizontal run for a two ton split is about 10 to 12 ft.; however, larger pumps are available for horizontal runs up to 27 ft.
Plenum rated pumps: There is actually no agency such as UL that certifies a pump as "plenum rated." Local codes and inspectors have much to do with what is suitable for a pump installed in the plenum or ductwork. Cast aluminum reservoir pumps with flame retardant plastic components and wiring will satisfy most local codes for these installations.
You've specified the right pump, properly installed it, and it has worked brilliantly over the course of the first air conditioning season. Now what?
Particularly in locations with four seasons, the pump may not run for another six months. Algae scale and scum that has accumulated in the pump over the past few months can solidify and bind the pump impeller, creating a potential pump failure at start-up.
Ideally, the pump should be disassembled and cleaned. However, a cup of household bleach diluted with one gallon of water can be poured into the pump and cycled several times to clean the internal parts. Consult your pump's maintenance manual to be sure the materials are compatible.
Safety Switches for Gravity Drained installations
Several styles of safety switches designed to shut down the air conditioning system or furnace are available for installation in the condensate drain pan or drain line. Most are wired in the same fashion as the secondary safety switches included on the condensate pumps. The least expensive and most common is the drain-pan safety switch. The product can be attached to the secondary drain pan, and opens the thermostat circuit in the event of a drain pan or drain line clog. More recent adaptations include condensate traps equipped with safety switches, and inline switches that are easily installed in the actual drain line.
Algae and Slime Prevention
There are a number of additive products designed to retard or prevent algae growth in the drain pan or drain-line. This helps keep the condensate pump and the condensate drain line clean, and free of potential blocks. The most popular products are:
Pan strips or pan tablets are inserted directly into the drain pan, and dissolve over the course of about a month, or up to three months, depending on size and formulation. Pan strips are water activated, time-released materials that can prevent algae and slime for about six months.
In-line systems allow you to treat the drain line without requiring access to the drain pan. The tablet is easily installed in a small reservoir that connects directly to the drain line.
Liquid additives can be poured directly into the drain pan, drain line, or condensate pump. The treatments remove and resists clog creating algae and slime, and lasts about 90 days.
As you can see, ensuring proper function of the condensate drain system is an important part of your routine service calls.
It's not difficult to design and maintain a proper condensate drainage system. With a little planning and attention to detail, you can avoid not only annoying call-backs, but potential health issues and property damage as well.