Vents and Venting 101

When I talk to people in the industry – plumbers, designers, and engineers – I find a lot of confusion surrounding proper venting techniques. Venting in a piping system is based on one simple principle. If you place a drinking straw in a glass of water, then place your finger over the end of the straw and remove it, the straw stays filled with water. The water in the straw cannot flow out until air is allowed in. The straw is air-locked.

In a piping system, as fluid flows through the pipe, air is pushed ahead of the fluid and air must enter the system behind the fluid. This creates pressure changes in the system with pressure ahead of the flow increasing and pressure behind the flow decreasing. In a closed system the flow would stop, as it does in the straw. In an improperly vented plumbing system the flow is restricted, pressure on downstream traps can cause sewer gasses to push through, and negative pressure on upstream traps can siphon them dry. The restricted flow can also cause stoppages.

The principles behind proper venting allow these pressure changes to be eliminated. The most basic and effective vent system would be to individually vent every fixture in the system, and some engineers use this configuration for its simplicity. But this is lazy design and adds unnecessary piping which in turn adds cost to the customer. It is not necessary to individually vent every fixture in order to create a fully functional vent system. With a little thought, vents and their related cost can be eliminated without changing the effectiveness of the system.

Two of the chief confusions I find comes from terminology used and proper application of principles. I will focus on three main concepts that represent the same basic principle and seems to create the most confusion – Wet Vents, Circuit Vents, and Loop Vents. Keep in mind our guiding principle – fluid flowing in a pipe creates pressure fluctuations. We want to limit those fluctuations and allow air to freely enter and exit the system to keep the fluids flowing.

Circuit Vents and Loop Vents are in essence the same thing. In both cases a vent is extended up from the horizontal piping between the last two fixtures on a branch in order to vent a group of fixtures. The only difference is where the vent terminates. In a Loop Vent the vent loops back to the Stack Vent. This is only possible on a stack with one branch interval or the topmost interval of a multi-interval stack. Circuit Vents terminate individually or tie into a vent stack or vent header.

Loop Venting has advantages over Circuit Venting as it creates a relief vented loop with a vent before the first fixture on the branch (the Stack Vent) and a vent before the last fixture on the branch which are then tied together providing circular air flow within the branch. We will discuss relief venting later. In the Circuit vent we are limited to a single vent to provide air to our system. Yet often that is all we need.

In a Circuit Vent, as in a Loop Vent, the horizontal branch line is vented, providing a common vent for all fixtures connected to the branch. This eliminates the need for individual vents. We are limited to eight total fixtures on the branch, and only four can be water closets unless we add another vent before the first fixture – a Relief Vent. With the relief vent, or with a Loop Vent (which provides its own relief vent) we can vent up to eight water closets. That eliminates up to seven individual vents!

We can also connect multiple circuit vented branches in series, so in essence we only need one vertical vent for every eight fixtures on the horizontal branch (Remember: only four can be water closets unless we relief vent). In applications such as gang toilets or gang showers the cost savings for the customer really add up. And we are still providing ample air flow to our system. The principle behind this technique is based on the physics of fluid flowing in the pipes. In a properly sized and graded horizontal drain line (the grade on a circuit or loop vented drain should be no more than 1:12) the fluid stays in the lower half of the pipe, leaving air in the top half. This allows the drain itself to partially act as a vent.

That brings us to the Wet Vent. A wet vent is simply a vent that is also used as a waste for another fixture – generally a lavatory or sink drain. In a bathroom group, or two adjacent bathroom groups, all of the fixtures can be vented through the lavatories as a wet vent. This configuration is very much like the Circuit or Loop Vent – the fixtures on the horizontal branch are commonly vented through the waste riser serving the lavatories – but the wet vent can be the last fixture on the branch. It is also permissible in Circuit Vents and Loop Vents to utilize a Wet Vent for any or all of the required vents or relief vents mentioned previously.

A Wet Vent can also be used to vent another fixture as a Common Vent, such as venting a floor drain with a lavatory drain. Also, one fixture above another on a stack, such as a sink connected above a washing machine or a lavatory above a water cooler, can act as a wet vent for the lower fixture. We can even stack fixtures floor-to-floor, such as hand sinks or mop basins on multiple floors connected to a single vented waste stack. There are of course restrictions to what fixture drains can serve as wet vents, and pipe sizes required, but often one vent can serve multiple fixtures and thereby lower costs and complexity of the plumbing system.

Proper venting is not that complicated when we keep the basic principle of pressure changes in mind and follow the simple sizing and maximum fixture loads spelled out (with charts!) in the NC Plumbing Code. And when in doubt, an extra vent here or there will not hurt anything. You cannot over vent, but you can waste the customer's money by adding unneeded vents. The balance we seek is adequate air flow with minimum vent piping for the most efficient design and installation.

A few points to keep in mind:

• Eight fixtures on a single branch (no more than four water closets) can be vented with a single vent located between the last two fixtures on the branch – Circuit Vent
• More than four water closets on a branch requires a relief vent before the first fixture on the branch – Circuit Vent or Loop Vent
• A Loop Vent is, in essence, a Circuit Vent tied back into the branch's relief vent (Stack Vent)
• A Wet Vent is a vent that receives discharge from another fixture
• A Wet Vent can be used to vent two complete bathroom groups
• A Wet Vent can be used as the vent and/or the relief vent on a Circuit or Loop Vented branch
• Multiple fixtures can drain into a single, properly vented stack

A few “Gotchas” in Mecklenburg County:

• Urinals on a Circuit or Loop Vented line should tie-in to the branch on the horizontal and cannot be used as a Wet Vent
• Fixtures downstream of a water closet must be individually vented (some inspectors allow floor drains on a Circuit Vent with water closets – but better to individual/common vent and be safe)
• Pumped lines, such as a washing machine drain, cannot be used as a wet vent. Some inspectors consider a dishwasher to be a pump discharge – or a pump from an icemaker or condensate line.

In closing; I would suggest a quick reading of the NC Plumbing Code, Chapter 9 – Vents. It is very clear on when and where vents should be placed. I will also suggest a quick Google Image Search of Circuit Vent. As I said at the beginning, much of the confusion seems to stem from the terminology. There is very little difference between Circuit, Loop, and Wet Vents. They are all based on the same principles.

Training the Next Generation of Plumbers

The construction industry has changed a lot over the years. I've been in the industry for thirty-five years and I've watched it evolve over that time in many ways. One of the most alarming trends is the aging of the workforce. When I was in my twenties, it seemed everyone was in their twenties. Sure we had the “old guys”. They were the foremen, the bosses, but most of the workforce was young.

Over the decades that changed as we all aged. Almost a decade ago when the insurance crisis first began, with skyrocketing premiums and ballooning heath-care costs, the company I worked for had an average age of forty-eight. The insurance companies blamed that for the rising premium costs. As the job market collapsed, forcing more young people out, that average age only increased. From boss to helper, we were all “old guys”.

The tight economy hasn't helped, and you can see the aging trend in every industry. Go to McDonald's and you may see forty and fifty year old cooks and cashiers. The jobs that were traditionally filled by high school and college students are now filled by middle aged workers trying to get by and pay their mortgage. But what does that mean for the future of the construction industry?

Construction is a difficult and physically demanding profession. It also takes years, even decades, to learn and master the skills involved to be highly productive. We have a highly skilled, highly productive workforce, but where will they be ten years down the road? Who will step into their boots and build the future? I learned much from those “old guys” when I was a young apprentice, but there are very few young people being trained today.

The current generation of young people were convinced that a college degree was their ticket to a high paying career and the American Dream, not the traditional blue-collar, middle-class dream my generation grew up with. Many struggle now to find work in their chosen fields and pay off their huge student loan debts. With the hard economy they are competing for even part-time work against people twice their age with long resumes of experience.

Over the years the construction industry has failed to entice young people into the trades. The economic decline and shrinking workforce didn't help. There wasn't a great need for new workers and seasoned workers struggled to keep the jobs they had. But as the economy rebounds the labor shortage will blossom into a major crisis. And that crisis will hit the construction and maintenance trades the hardest as companies look for young men and women to fill the boots of an aging workforce.

Over the next few weeks I will be talking to industry leaders and workers in the field about the future of the plumbing industry, and skilled trades in general, in North Carolina. We have an opportunity now to entice young people into the trades, but to do so we need strong job training programs and a commitment from the industry to hire and apprentice young people. The American Dream of my generation, and my father's generation, was built on hard work and craftsmanship. We owe it to the next generation to train them as we were trained.

I sat down last week with Shane Walden, head of maintenance at a large local facility. We discussed the aging workforce and the need to train a new generation. His people are all in their forties and fifties. One of his HVAC technicians started over in his fifties. I've known many others who were forced to do the same as the economy shrank. Our discussion focused in on what skills are needed in a changing workplace.

Shane told me that a broad skill-set and knowledge base are essential. That is sorely lacking in many training programs that teach generic fundamentals, but little or no real-world application of skills. With the ever changing industry many trade schools are behind the times or they choose the path of generic training they consider “evergreen skills”. But what new workers need is hands on experience with today's newest materials and techniques.

In times past, broad experience was gained over time on-the-job as an apprentice training under a seasoned craftsman. Years of experience on a wide range of projects offered an apprentice a diverse skill-set. But the industry today tends toward specialization. We'll talk more about that in a minute, but the unfortunate outcome of specialization is an apprentice who may be very good at one aspect of the craft yet have very limited knowledge of other aspects.

That is understandable from a business point-of-view in a highly competitive marketplace. If a company has an apprentice, or even a technician, who is highly productive running copper water pipe why would they have him doing anything else? Business is about profits and profits grow through increased productivity. Yet the craftsman gets pigeonholed into a limited skill-set. This is a place where trade schools can fill the gap with diverse training programs that offer a young apprentice hands-on experience with a wide range of skills and techniques he or she may not acquire on-the-job.

But some specialization is important for greater skill, better quality, and higher productivity. The old truism tells us that the Jack-of-all-trades is often the master of none. Shane told me that in his position as chief of maintenance he likes to cross train his plumbers in heating and air and also electrical skills. A broader skill-set is always desirable. But he still has plumbing technicians and heating and air technicians. It's good to know a little about a lot, but it's also important to know a lot about something.

Again, training programs need to follow that same diverse yet focused paradigm. Students need a broad skill-set with hands-on experience using the latest materials and techniques, but also specific knowledge in emerging areas that are in demand. I asked Shane what he sees as some of the specific skills needed in the industry today and what is likely to be needed tomorrow. Building automation and controls was his top pick. As we strive for better efficiency and conservation, greater control of systems in real-time is emerging as a highly skilled specialty.

LEED, or Leadership in Energy & Environmental Design has become a major part of building design and construction in recent decades and efficiently maintaining structures after construction can make a dramatic impact on continuing operational costs. A large part of that efficiency comes though precise system control and balancing. Though much of that work involves the HVAC and electrical trades, environmental concerns and energy efficiency is also an emerging part of the plumbing industry.

With the growth of building automation technology and energy efficient design comes the need for many skills not traditionally associated with the building trades. One of the emerging skills needed by both new and seasoned workers in the industry is basic skills and familiarity with technology. Often the older, most experienced craftsmen are the least comfortable with emerging technology – from basic use of computers to CAD (computer aided design) and BIM (building information modeling) practices.

Our industry is changing. In this new millennium plumbers will continue to learn the skills and knowledge dating back to the Roman Empire, and add to that emerging skills and knowledge which will take us into the decades ahead.