There are 9 types of radon mitigation system which one can to reduce radon levels in their house. They are;
- Subslab suction
- drain-tile suction
- sump-hole suction
- block-wall suction
- submembrane suction
- active crawlspace depressurization
- Room pressurization
- Heat recovery ventilation
- Passive subslab suction
Some of them are active mitigation systems that outs radon gas with the help of a fan, while the rest are passive mitigation systems that do not require any electricity or moving parts. The first five methods listed above use a radon fan to remove the radon gas from the soil. The workings of these six methods are very similar.
The last three methods listed above uses pressure differences in the air to remove radon from the house. Room pressurization and heat recovery ventilation methods consume energy and are part of active mitigation systems.
Let me explain these different systems in detail.
SubSlab suction mitigation
Also known as Active sub-slab suction, this is the most popular radon mitigation method. This method is very effective in reducing radon levels. It can reduce radon levels by 99%.
In subslab depressurization method, a radon fan is used to suck the air out of the soil. This system depressurizes the underside of the basement or the slab-on-grade foundation preventing Radon from entering the house.
The setup of this system involves a PVC pipe, usually of 4-inch diameter, inserted through the foundation into the soil beneath. The other end of the pipe is routed to the house’s exterior and, from there, to the top of the roofline. A radon fan is installed on this pipe, on the outside of the house. The pipe can also go through the house and vent to the roof through the attic. In such cases, the radon fan is installed in the attic of the house.
The soil around the bottom end of the PVC pipe is removed, creating a pit. This pit creates a path of least resistance to collect the radon gas. The larger the surface area of the pit, the more radon gas it can collect.
When the fan starts running, it sucks the radon-filled air from the pit and vents it above the roofline. Depending on the size of the basement and the power of the fan installed, this system can reduce radon levels by 50 to 99%.
Drain tile suction mitigation system
Drain tile suction is the second type of mitigation system used in houses with high radon levels. Just like the sub-slab depressurization system, it uses a radon fan and vent pipings to remove radon from the soil. But instead of creating a suction pit for the radon through the foundation slab, the bottom of the radon pipe is connected to the drain tile system of your basement.
This method works only if your basement has an interior drain tile system. Since a drain tile system is basically a wide hole that runs alongs the walls of the basement, it collects lots of radon gas. So it makes sense to absorb the gas from drain tiles instead of making a hole in the foundation.
So, in a drain-tile suction system, a hole is drilled into the drain tile. The bottom part of the radon pipe is connected to this hole. This pipe is then run to the outside where it is connected to a radon fan. Just like in the sub-slab depressurization system, this outlet of the radon fan is connected to a vent pipe that run to the top of the roofline.
This mitigation system removes the radon collected in the drain tile. This is as effective as the sub-slab suction system, and it can reduce 50 to 99% of radon depending onthe size of the basement and the power of the fan.
Sump hole suction system
This is the third type of radon mitigation system used in various houses. This one works just like the drain tile and sub-slab suction systems. The only difference is that it colects the radon gas from a sump pit.
As you can see from the image above, the bottom part of the radon pipe is connected to a sump pit in the basement. As you know, a sump pit is used to collect water in areas where the water table is high. A sump pit and pump prevent the basement from flooding. A sump pit also acts as a collection point of radon. So if your basement has a sump pit, you can connect the radon pipe to it. The radon mitigation system will work without interfering with the working of the sump pump.
In this type of mitigation system, the sump pump has to be sealed off. Use a Silicone seal so that you can occasionally open the sump pit in case the sump pump malfunctions. This system can be implemented only if the soil is porous under the foundation and if the drain tiles form a complete loop around the basement.
PS: Radonaway has some cool, clear sump pit covers you can use.
This method is as effective as the other two systems mentioned above, with a mitigation rate of 50 to 99% depending on the system implemented and the square foot area it needs to mitigate.
Block wall depressurization system
Also known as Block wall suction system, this is another type of radon mitigation system that uses a radon fan. It is ideal for basements where the walls are made of hollow blocks. As you guessed, this system sucks air containing radon from inside the hollow blocks of the basement.
This mitigation method is ideal for homes where the radon gas enters through the walls of the basement. The block wall suction system also prevents radon from re-enteringthe house, a problem some other mitigation systems face.
In this system the suction pipe of the mitigation system, which is connected to the radon fan, is inserted into the cavity of the wall of the basement. Once the radon fan is started, it begans to suck air from the walls creating a negative pressure there. As a result, the radon gas around the walls move to this suction point, and are removed through the exhaust vents of the mitigation system.
For this system to work properly, all the openings of the walls should be sealed properly. Also, the location for the suction pipe depends on the intensity of the radon in the walls. Not all walls have equal concentration of radon. The radon pipe is installed in the wall that has the highest radon concentration.
Sub-membrane suction system
Not all houses have basements; some have crawlspaces instead. Sub-membrane suction is the ideal radon mitigation system for houses with crawl spaces or unfinished basements.
This mitigation system works by covering the floor with a polyethylene sheet aka vapor barrier, and sucking the air under this sheet with a radon fan and ducting. This system is very similar to a sub-slab pressurization system. The only difference here is that a polyethylene sheet is used to create a negative pressure zone instead of a foundation slab.
As you can see from the above video, the ground of the crawl space is completely covered with plastic sheets. All its seams are overlapped and sealed. The sheet is also sealed to the walls of the crawl space. These plastic sheets basically create an air-tight barrier in the crawl space to prevent any radon gas from entering there. You can also cover the walls of the space with this plastic sheet if you suspect that radon gas could be seeping in through the walls. The sealing of crawl space floor like this is also known as crawlspace encapsulation.
Once the ground is sealed, a radon pipe is inserted through the plastic membrane. When the radon fan is switched on, this pipe will suck the air from under the plastic sheet. You can see the plastic being pulled down to the ground, just like when you seal a vacuum storage bag.
This system is very effective in reducing the radon levels in a house. The important thing to make sure is that there are no holes in the plastic sheet. A few tiny holes can cause the system to suck air from the crawl space, thus reducing the amount of radon removed. This system can reduce up to 99% of radon gas entering a home.
Active crawlspace depressurization
Active crawlspace depressurization is a technique used to forcefully remove the air from a crawlspace using a fan. As you can guess this method is not as nearly efficient as any of the depressurization methods listed above. So, his technique is only advised in houses that have low radon levels.
You should also note that encapsulating the crawl space doesn’t make this system any more efficient. In fact, adding a vapor barrier on the crawl space floor will only make the exhaust fan draw more air from the house than from the ground below. This can cause back drafting of gases if you are not careful.
Basement pressurization with a fan
Basement pressurization is another method to mitigate radon. This system uses a fan to increase the air pressure inside a tightly sealed basement. As you know radon eneters a house because of the negative pressure inside the basement. By creating a positive pressure one can limite the amount of radon entering a house.
But this method is useful only if the radon levels in your home are already low. While this prevents radon gas from getting in through convection, it will still pass to the basement by diffusion. However, this will be a much slower process.
Basement pressurization can work in homes where the basement is sealed off from the other parts of the house. However, using a sub-slab pressurization system is far better than this in the long term. Many experts also say that adding positive pressure inside the basement can boost the growth of mold.
Heat Recovery Ventilation method
You can use a heat recovery ventilator in an air-tight basement to reduce the radon levels. A heat recovery ventilator exchanges air between the basement and the outside but with minimum energy losses. It exhausts the basement’s air and replaces it with the fresh air from the outside.
Radon reduction using this system is not as effective as a depressurization system. But this method is apt for a home with low radon levels. If the radon levels go above 12 pCi/L this system won’t be good enough to mitigate it.
Using a heat recovery ventilator can also increase the heating costs. Even though they retain most of the heat, the system is not 100% efficient, and so there will be some heat losses. The good thing is that you can use them in the summer months as well to reduce the temperature in the basement.
Passive sub-slab suction
Passive Subslab Depressurization technique is used in newly constructed homes. This is a permanent system which consists of ducting from under the slab of the basement and opens to the top of the roof. This is basically the active sub-slab depressurization system but without the radon fan. And it goes through inside the house.
This system works with the help of air pressure differences and currents. The wind blowing over the vent of its ducting creates a negative pressure that sucks out the radon gas. In addition, this vent also provides a path of least resistance for the radon to pass through.
A passive system is not as efficient as an active radon mitigation system. However, this system can reduce radon levels from 30 to 70%. Environmental Protection Agency recommends this system in all newly constructed homes.
It is impossible know the radon levels in a house untill it is constructed, none can predict this. While this passive system helps to reduce radon levels, you may still find the levels above the safe limit. The good thing about this installation is that you can make it an active system by adding a radon to it in the attic!
Which type of mitigation system is the best?
A radon mitigation system is selected based on the radon levels in your home and the installation requirements. Active sub-slab suction is the most popular mitigation system used in houses with finished basements. Submembrane suction is the best choice for crawlspaces and unfinished basements.