Passive Systems: A Double-Edged Sword

What is a passive radon system? Basically, it’s a radon mitigation system without the fan. Passive and active systems are exactly the same except one has a fan and one doesn’t. The beauty of a passive system is that, if installed correctly, a fan can be easily attached making it an active system if needed.

Passive systems are supposed to be a positive for everybody, including the homeowner, realtors and the installer. The most attractive aspect of passive systems is that the pipe can be completely hidden inside the framing of the home. If installed during construction, all you would see is the pipe sticking out of the roof, looking like just another sewer vent your home or business already has.

Aside from aesthetics, this type of reduction system may be easier on your wallet. Passive systems also allow for distribution of cost to be split between two parties: the builder and the seller. It certainly saves cost if the builder has his plumber run the pipe because all the seller has to come up with is the cost for a radon mitigation professional to install a fan. This should be about half of what a full radon system and instillation costs. In Nashville, new building codes require passive radon systems to be installed in every new build and add-on.

A well-designed passive system is a great thing and can theoretically make radon reduction both less expensive and less aggravating. However, a poorly designed passive system can be more aggravating than not having one at all. I’ll get into that in a minute, but let’s talk about how passive systems should work, first.

A pipe needs to first start below the slab… Ideally, before the slab is poured so the sub-slab material can be evaluated and documented. After the slab is poured, the pipe will extend upward through the stud walls, through the attic and out through the roof. An electrical outlet needs to be installed near the pipe in the attic and the pipe needs a few feet of clearance in order to install the fan. This needs to be done with minimal 90 degree bends and ideally has a straight shot all the way up. That’s about it. All pretty simple. This next detail is critical: THE PIPE MUST HAVE A NEGATIVE SLOPE all the way from the roof to the suction point in the basement or slab. If it is installed without a negative slope, water WILL collect in the pipe and become trapped. No ifs, ands or buts. It’s just a fact. This picture is a good example of a passive system I installed:

So, this all seems great to have a pipe already installed ready for me to come in and attach a fan. But, I can’t tell you how many times I get to a job, install a fan and something is wrong. Generally, one of four things happens that make it impossible for this system to be utilized.

1. There is not a slope on the pipe and water has collected.

2. There is not enough clearance in the attic for a fan to be attached.

3. The pipe below the slab doesn’t have a tee fitting on it and is stuck straight into the dirt below the gravel layer.

4. The pipe is installed in such a way that when a fan is attached the system is automatically not up to EPA codes.

Unfortunately, these are so commonly found that I have to tell every single client that their passive system may not work before I ever get to the job site. I can’t guarantee the system will work because I wasn’t the one to install the piping, and I certainly can’t guarantee someone else’s work until I get my eyes on it.

Recently, A realtor called and said she needs a fan installed because this new house already has a passive system. I show up and can’t find the pipe in the attic. I finally find it and the pipe is completely snugged to the stud wall and I don’t have enough room to install the fan. Finally, I add some fittings and get it away from the wall and plug it in. I know within seconds that there is water in the pipe because it sounds like a washing machine. I had to unplug the fan, put the pipe back together and tell her a completely new radon mitigation system needs to be installed. I had to find a spot in the basement and start from scratch. The fan and the piping had to be installed externally which was the whole point of building the pipe in during construction. Understandably, she and the buyers were upset. There is no way to tell where the section of pipe in the walls that has the water in it is. Even if the water could be removed, it will just fill back up again. It’s best just to forget it was ever there and move on. This happens ALL THE TIME.

The code requiring a passive system to be installed is flawed. If a code is in place, it needs to be inspected and called out by building inspectors during construction. This isn’t happening, and it’s causes major headaches! Typically, many of the details required to ensure a passive system is in working order are lost in translation. For example, a builder hears “we need a radon vent pipe installed”. He knows it needs to be 3 inch and needs to start under the slab and discharge outside. The builder will tells his plumber (who more than likely has no radon experience) “I need a 3 inch pipe installed for a radon vent”, and that’s the extent of the direction the plumber gets. There are so many details that need to be considered when installing a radon system, and they get passed over on almost every home. The plumber needs to be thinking about what if a fan needs to be installed, is my slope good, do I have too many 90 degree bends to make this effective, and is this discharge point EPA compliant?

In order for a system to be guaranteed by me, it needs to be installed by me or I need to be there to consult and sign off on the work. I will gladly install a fan and test the home, but I can’t see behind walls to make sure everything is kosher.

I hope this post helps clear up some of the pitfalls of passive system design and can hopefully help those getting a passive system installed avoid these common mistakes!