Your test came back above 4, you’ve got a written price, and there’s a date on the calendar. Now you’re wondering what my crew and I are going to do in your basement.
The short version of how a sub-slab system goes in
A radon mitigation installation puts an active soil depressurization system in your house. A fan pulls soil gas from under the slab, pushes it through a pipe, and vents it outdoors before it can get into your air. On a straightforward basement, that’s usually a one-day job.
We cut a suction point through the floor, run PVC pipe up and out, mount the fan outside the living space, seal the openings that would let the fan pull the wrong air, and put a gauge and label on the pipe. The retest comes after the fan has run at least 24 hours. On my jobs it’s included.
The parts of the system, numbered
The drawing shows what we end up with. The numbers match the table and the steps below.
| Step | What I do | Why it matters |
|---|---|---|
| 1. Suction point | Cut a hole through the slab and dig out a small pit underneath | This is where the fan pulls soil gas from, before it reaches your air |
| 2. Pipe | Run PVC from the pit up and out of the house | Gives the soil gas a sealed path to the outside |
| 3. Fan | Mount it outside the living space | Pennsylvania’s mitigation standards keep the fan out of the basement and out of any space under a room |
| 4. Exhaust | End the pipe above the roofline and clear of openings | So the gas leaves and doesn’t drift back in through a window |
| 5. Sealing | Close the floor-wall joint, cracks, pipe openings and the sump | So the fan pulls from under the slab and not from your basement air |
| 6. Gauge and label | Mount a U-tube gauge and a label | So you can see the fan is pulling without calling anyone |
| 7. Retest | Test the house after the system has run at least 24 hours | The number is what tells you it worked |
The day starts with the plan we already agreed on
Nothing about the plan is new on install day. I diagnosed the house at the walkthrough, and your written price already names the suction point, the pipe route and the fan location. First thing, I walk that route with you before anything gets drilled.
Houses don’t always match my notes. A finished wall, a water heater that got moved or a closet that went in since I looked can all change where a pipe wants to go. It’s far easier to move a pencil mark than a hole.
Then I find the suction point and check how far it pulls
A suction point is the hole through the floor where the pipe connects. Before I commit to one, I check how far suction reaches under the slab. I drill a few small test holes away from the main spot and measure whether the pull at one location reaches the others. That’s called a pressure field test, and it’s how I know instead of guess. Some slabs sit on loose stone and carry suction a long way. Others sit on tight, packed soil and don’t.
Then I cut the hole with a core drill, with a vacuum on it to keep the dust down, and dig out some of the soil or stone under the slab to leave a pit. The pit gives the fan a larger area to pull from than a bare hole would.
The vent pipe goes in before the fan does
PVC pipe runs from the pit up through the house and out. I try to keep it out of your way: a utility room corner, a closet, a chase that’s already there. I pitch the pipe back toward the pit so any moisture that condenses inside runs back down into the ground. Water that pools in a pipe ends up in the fan, and that’s one of the quiet ways fans die early.
The route changes more than the method does. In an older house near downtown or off East Market Street, the pipe often has to work around plaster, old plumbing and a stone wall. In a poured-wall house in Spring Garden Township or the developments around Mount Zion Road, the run is usually cleaner.
The radon fan goes outside the living space
The fan can’t go in the basement, a crawl space, or anywhere under a room. Pennsylvania’s mitigation standards are specific on that. It goes outside, in an attic, or in a garage that isn’t under living space. The pipe on the fan’s exhaust side runs under pressure, so if a joint ever leaks, I want that leak outdoors or in an attic, not in a bedroom.
I use flexible couplings at the fan so it can be swapped later without cutting the pipe, and so vibration doesn’t travel into the house frame. A fan that’s hard-mounted to rigid pipe against a stud is a common cause of the hum people hear in the kitchen. If you want to know what a worn fan sounds like, I covered it in my radon fan loud noise guide.
The fan needs power nearby. We settle where it plugs in or gets wired at the walkthrough, not on install day.
The exhaust has rules about where it can end
The pipe finishes above the roofline. Pennsylvania’s standards set where the discharge can be: at least 10 feet above the ground, and at least 10 feet from any window or door that opens, unless it’s 2 feet above the top of that opening. The point is to keep the gas from re-entering through the nearest window.
This step decides how a job looks from the street. On a wide lot I have a lot of room to choose. On a tight lot with a neighbor a few feet away, like many in North York and West York, there may be one or two spots that meet the standard. I show you those at the walkthrough so there’s no surprise about which wall the pipe runs up.
Sealing comes after the pipe, not before
The fan only works the way it should if it’s pulling from under the slab. If there’s a big open path between the basement air and the pit, it pulls conditioned air out of your house instead, and the suction under the slab is weaker for it.
So I seal the floor-wall joint, the larger cracks, the openings around pipes and wiring, and any open sump. An open sump pit is often the biggest single opening in a basement, so I seal it with a lid you can still get the pump out of, and sometimes I use it as the suction point.
Sealing helps the system. It doesn’t replace it. The EPA says sealing alone hasn’t been shown to lower radon significantly or consistently, which is why I never sell it as the fix.
The gauge and the label go on last
Every system I install gets a U-tube gauge on the pipe, the small clear tube with colored liquid in it. When the fan is pulling, the liquid sits at two different levels. If both sides are level, the fan isn’t pulling. I also put on a label that shows what the gauge should read, so whoever lives in the house in 2035 can check it in ten seconds.
Before I leave, I turn the fan on, confirm the gauge shows suction, and walk you through how to read it. If it ever reads level, my fan replacement and repair page explains what to do.
Then the clock does the rest
A running fan doesn’t prove the number is down. Pennsylvania DEP says to run the follow-up test after the system has operated for at least 24 hours. I place that test myself, and the retest is included on every job, not an add-on. I explain how it works on my post-mitigation retesting page. If the number is still above 4 pCi/L, I tell you what I’m going to adjust.
What decides whether it takes one day or two
Most of the surprises come from the foundation, not the pipe.
- Rubble stone basement with a thin or patched floor: may need more than one suction point.
- Addition on its own footing: often needs separate treatment, as in some of the older farmhouses along the Susquehanna Trail corridor toward Emigsville.
- Dirt crawl space: needs a sealed membrane over the soil first.
- Finished basement: limits where the pipe can run.
I cover each of these in my guide to radon systems by foundation type. I tell you at the walkthrough if your house is one of them, with the price in writing, so nothing is added on install day.
Frequently asked questions about radon system installation
How long does a radon system installation take?
On a straightforward basement, usually a day. A house with a crawl space, an addition or a rubble stone foundation can take longer. I tell you which one yours is at the walkthrough.
Do I have to leave the house during the install?
No. Coring through the slab is loud for a short stretch, and I keep the dust down with a vacuum, but you don’t need to be out of the house.
When does the radon number drop?
The fan starts pulling as soon as it’s on. But the only way to know the number is under 4 pCi/L is a test, and DEP says to run it after the system has operated for at least 24 hours.
Will the pipe go up the front of my house?
Usually not. Most of the time I can run it up a side or back wall, or through an attached garage. The standards control where it can end, so I show you the options before anything gets drilled.
Can you finish a system that someone else started?
Yes. A capped pipe in the floor with no fan is often a system that was roughed in and never finished. I also service systems I didn’t install.
If your number’s above 4, I’ll come walk the house.
Related: Radon Mitigation · Radon Testing · Sump Pit Sealing · Fan Replacement & Repair · Post-Mitigation Retesting · Services · Service Areas
Sources
- Pennsylvania DEP, Pennsylvania Radon Mitigation Standards, Technical Guidance 294-2309-002, effective March 4, 2023
- U.S. EPA, Consumer’s Guide to Radon Reduction (EPA 402/K-10/005, 2016)