Air admittance valves continue to stir up debate.

Air admittance valves (AAVs) are the most controversial devices introduced into plumbing in the past century (maybe even the last millennium). Plumbers either hate them or love them. There seems to be no middle ground. Those who hate air admittance valves flood me, my editor and our publisher with e-mail, letters and nasty-grams. I guess if you hate them, you really hate them.

So why mention air admittance valves and risk the possibility of being cursed, yelled and screamed at? The plumbing engineers issued a position statement supporting air admittance valves. The American Society of Plumbing Engineers published it Oct. 30, 1999, but that hasn't put an end to the rumors and debate about AAVs.

Rampant Rumors

For those of you still in the dark about air admittance valves, let me review what is and what is not an air admittance valve. If the valve has a spring in it, it is not an air admittance valve. These devices are typically called cheater vents. They are only recognized for manufactured housing for use on one fixture.

An air admittance valve is a gravity-operated valve that opens when there is negative pressure inside the drainage system and closes when the pressure differential balances. They do not leak sewer gas when they are sitting there doing nothing.

The long and short of it is that the ASPE position statement said the valves work. I know, a lot of you are saying, "We already knew the valves work, what's the big deal?" It all started a few years ago. Someone passed a rumor that ASPE was preparing a statement opposed to air admittance valves. For the haters of AAVs, this was major news. They could proclaim that the engineers agreed with their position.

What made matters worse is that a draft of a statement opposed to air admittance valves surfaced that had the appearance of being a document from ASPE. The problem was that it wasn't from ASPE. Of course, with today's technology, it is easy for anyone to scan ASPE's logo and apply it to a draft statement. ASPE was embarrassed, to say the least, and did everything possible to clear its good name.

But the rumor took on a life of its own. Before the ASPE had issued a statement of any kind on AAVs, those against air admittance valves began declaring that "ASPE has not come out in support of air admittance valves." The implication was clear - it was their way of saying, "If the plumbing engineers are not in support of air admittance valves, they must be against air admittance valves." From ASPE's perspective, at that time it had never issued a statement either for or against air admittance valves.

ASPE debated long and hard whether to issue a statement regarding air admittance valves. There are engineers who are members of ASPE and are haters of air admittance valves. Thus, it was extremely difficult for ASPE to take a position. If you read the position statement issued by ASPE, you can see the compromising that was necessary to get the statement published.

The haters of air admittance valves will love the vague language used by ASPE. I expect to hear it twisted around that ASPE has concerns with air admittance valves and further installation should cease until the concerns are addressed. However, that is not what is stated. ASPE has concerns about the design and installation of every plumbing system. They want all systems installed correctly.

The ASPE wants to make sure that plumbing contractors use air admittance valves in accordance with the limitation specified in the plumbing codes and by the manufacturers. If the installation is correct and the valves properly installed, you will not have a problem.

Pros & Cons

To comply with code, the valves must meet ANSI/ASSE 1051. Some valves, I've been told, say they meet ASSE 1051; however, they do not. To ensure that the valve complies with the standard, they are also listed to NSF 14.

The biggest argument used against air admittance valves is that they don't relieve high pressure in the drainage and vent system. That is correct: The valves stay closed if the pressure inside the drainage piping is above atmospheric pressure. Because of this fact, every plumbing code requires a minimum of one vent to open to the outdoors when using air admittance valves. Yes, that is good enough.

Furthermore, I would never classify the pressure inside a drainage pipe as high pressure. The pressure of 1 inch of a water column translates to 0.036 psi. I don't know about you, but that pressure looks awfully low to me.

If you are wondering about the limitations of use, check the International Plumbing Code, the International Residential Code or the manufacturer's installation requirements. They are all very clear as to the proper application of air admittance valves.

As to why there has been a proliferation in the use of air admittance valves, there are two reasons. The valves are convenient, and they are cheap to install. Why spend $100 to pipe a vent out through the roof when you can terminate the vent to a $15 air admittance valve?

If you think our objective in the plumbing business is to make the cost of installations more expensive, you're in the wrong business. Our objective is to keep costs down while keeping the total project cost the same. In other words, increase the profit margin. I never heard of increasing your costs to increase your profit margin. That leads to bankruptcy.

If you haven't used air admittance valves and your competitor is, I guarantee you, your competitor is making more money than you are. You might want to try them.