Stagnant water in a drain pain isn’t just unsightly — it can lead to indoor air quality (IAQ) problems and more.

“When you have a dark environment and you’ve got a lot of water in the pan, particularly in a high-humidity area, you can develop a lot of molds and mildews,” stated Nelson McGuire, market manager for split-system air conditioning at Bryant Heating and Cooling Systems, Indianapolis, IN.

“Then you have air blowing by this stuff, so if you have somebody with allergies [or asthma], it can aggravate that.”

The buildup in the pan can also end up blocking the condensate drain, “and then you’ve got big problems” with water filling and overflowing the pan.

The amount of water generated is substantial. A coil can remove as much as 25 gal a day in high-humidity areas. The average is about 10 gal.

“When we looked at redesigning our coils,” said McGuire, “one of the things we looked at was trying to figure out a way to get rid of those problems.”

Typically, the industry has produced flat drain pans. “But it’s not very efficient in terms of getting rid of water,” he said. Quite often, the water just sits there.

So Bryant opted to go with the idea of a tilted drain pan. It’s sloped toward the drain to provide quick, full drainage. The degree of tilt is 3/8 in. over a 19-in. depth.

Go with the flow

The company says that when 2 cups of water are poured into the tilt-flow drain pan, all but one teaspoon drains out within 11 sec.

When 2 cups of water are poured into a flat drain pan, it’s about 1 min and 30 sec before the draining stops, and there is still about 1 1/2 cups of water left in the pan exposed to the airstream.

The tilted pan also includes two drains. In case the primary drain is blocked, the secondary drain is available.

A galvanized sheet underneath the reinforced polyester pan helps prevent the pan from bowing due to heat from the furnace, which also prevents leakage from the pan.

The new drain pan is used with the company’s N-coil and A-coil on all residential a/c units.

Another concern: total efficiency

“When you look at it from a national perspective,” said McGuire, “about 60% of the time, an indoor coil is replaced when an outdoor coil is replaced.” There are strong arguments for making that figure 100%.

The manufacturer asked contractors why they don’t change the indoor coil along with the outdoor unit, and they responded that they didn’t have enough information on what they should tell the customer about the need for changing an indoor coil.

McGuire asserted that you can have efficiency and capacity losses if you don’t change the indoor coil as well. “Basically, you can lose 10% in efficiency and capacity.”

Older coil designs were less efficient. They didn’t have the enhanced fins that provide more air turbulence, and they didn’t have rifled tubing, which provides more heat transfer.

Matching a new coil with an old coil actually reduces total system performance. “About three-quarters of the outdoor units that are sold are minimum SEER efficiency — 10 SEER — and if you don’t change the indoor coil, you’re really delivering 9 SEER.”

To give customers the efficiency and performance they expect, McGuire emphasized the need to replace both coils.