Dehumidifier Surprises

December 06, 2016
Winter 2016
This online-only article is a supplement to the Winter 2016 print edition of Home Energy Magazine.
Click here to read more articles about HVAC

Construction projects are always full of surprises. Recently I experienced this first hand when I renovated my home, dubbed Green on Gift because of its location on Gift Avenue in Atlanta, Georgia. Some surprises are simply that—discoveries of something you didn’t know. They’re not necessarily good or bad, just unexpected. For example, I had no idea I was so opinionated about whether shoe molding should be painted or stained (painted, definitely). Others, like learning your home is structural masonry with no conventional wall framing, have ripple effects on nearly all aspects of the renovation.

In my renovation, I decided to install a dehumidifier in my newly enclosed crawl space to maintain a reasonable relative humidity level in this area, particularly since the HVAC system was located in the conditioned attic. I was surprised to learn that there is little consensus on the best, let alone legal, way to install a dehumidifier in a conditioned crawl space. I had what I thought was a reasonably simple question: Where can I terminate the condensate line? And in my research I identified several options, some of them conflicting with others.

As a green-building consultant, I’m constantly reviewing with contractors the proper way to install insulation, flash windows, seal ductwork, and implement other construction details. I like to remind people that there are instructions out there, but few people take the time to read them. Thus, my first step was to RTFM—read the friendly manual. It turns out that dehumidifier installation manuals tend to be rather vague on where exactly the condensate line should terminate. The various manufacturers I looked at would make it clear that the condensate line should be run with a constant downward slope, and that you should “adhere to local codes regarding draining of the condensate pan.” So far I know to respect gravity or use a pump and follow local laws. The next step was to dig into building codes.

Building codes don’t explicitly address dehumidifiers. A dehumidifier is considered a cooling coil and is addressed in the same way as a central air conditioner. This makes sense when you consider that a dehumidifier is basically an air conditioner. Condensate systems are covered in the International Plumbing Code (IPC), the International Mechanical Code (IMC), and the International Residential Code (IRC). All three codes are mostly in agreement, and my analysis here will focus on the IPC.

Section 314 of the 2009 IPC covers condensate collection and disposal. The section defines proper slope, requirements for drainpipe materials and sizes, and conditions requiring a secondary drain system (i.e., drain pan) and trap. There is surprisingly little guidance on where to dispose of the condensate. Condensate “shall be conveyed from the drain pan outlet to an approved place of disposal . . . Condensate shall not discharge into a street, alley or other areas so as to cause a nuisance” (314.2.1).

Now I know what materials to use for piping and whether or not a drain pan is required, but it’s still very ambiguous what an “approved place of disposal” is. This proved to be the hardest question to answer. Numerous people told me that dehumidifier condensate is basically dishwasher waste from the code standpoint and requires an indirect connection with backflow prevention to the drainage system. After much searching, I believe this is based on Section 608.1 of the IPC, which requires the following:

A potable water supply system shall be designed, installed, and maintained in such a manner so as to prevent contamination from nonpotable liquids, solids or gases being introduced into the potable water supply through cross-connections or any other piping connections to the system.

This is further reinforced in Section 801.2 of the IPC, which requires the following:

All devices, appurtenances, appliances and apparatus intended to serve some special function, such as sterilization, distillation, processing, cooling or storage of ice or foods, and that discharge to the drainage system, shall be provided with protection against backflow, flooding, fouling, contamination and stoppage of the drain.”

There appears to be a general consensus that evaporative cooler or A/C condensate drains should not be connected directly to soil, waste, or vent pipes. Instead, indirect waste connections to the drainage system, like those commonly found at a clothes washer drain, are permitted. This is also similar to requirements that dishwashers not be directly connected to the drainage system. Dishwashers must use an approved air gap device or drain line with a high loop. The idea is that if the sewer line becomes clogged and waste is backing up, you don’t want to contaminate the dishwasher. Installing an air gap device lets the waste spill over into the surrounding area before it makes its way into the dishwasher (or into the clothes washer).

To further complicate matters, some local municipalities forbid connecting condensate lines to the sewer, since they don’t want to pay the cost of processing this wastewater. In these municipalities, the condensate must be discharged to the ground outside the house. Luckily, I can find no such provision in the code for Atlanta.

Ultimately, I found three commonly used methods of removing dehumidifier condensate. You can install a hard connection to the sewer line; you can install a run line to the outdoors; or you can install a run line to a sump pump. The first option does not appear to meet code and was ruled out. The second option is also problematic. The grade of the lot slopes toward the front of the house and toward the rear of the house. While we plan to level the lot later, when we improve the landscaping, we did not want to contribute to the site drainage issues by dumping condensate outside the foundation wall. And we ruled out the third option because it was too expensive.

After much deliberation, we opted to try something new. We’re using the Ultra-Aire 70H dehumidifier. The unit removes up to 70 pints per day, is Energy Star rated, and includes a high-efficiency filter (MERV 11). We suspended the unit from the crawl space floor joists with a condensate pump that directs the water into the laundry room above the crawl space and ultimately down the drain for the clothes washer. 

The system has an air gap because we’re using the open clothes washer drain. While this approach may be unconventional, it has been running for about a year without any problems.

This is the second of three articles on this project that will be featured in Home Energy. The first article, "Spreading the Green-Building Gospel" can be found here. This series will close with a discussion on condensing clothes dryers and a review of the Bosch model we installed. To learn more, you can go to the project blog at, and watch the GreenShortz videos on YouTube.

Abe Kruger is coprincipal of SK Collaborative, which helps homeowners, contractors, architects, manufacturers, and nonprofit agencies create better buildings and products. Kruger is an authority on single- and multifamily green- building consulting and certification and on industry education and training.

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