Suction points, fan pressure class, riser pipe and sealing for a sub-slab depressurization system.
Estimates are planning aids, not a professional quote. Double-check quantities and product coverage — and any local code or permit requirements — before you buy.
⚠ Never cap the top of the vent stack. A rain cap or bird screen adds back pressure the fan has to fight and can cut system performance more than any other single mistake — leave the termination open like a plumbing vent.
⚠ This sizes the mitigation hardware, not the result. Retest with a radon test kit 24–48 hours after the system is running and again a few months later — sub-slab conditions vary enough within one house that identical systems on paper can land at different post-mitigation readings.
| HVAC | $240–$324 |
| Electrical | $54–$74 |
| Concrete & Footings | $32–$44 |
| Finishing & Sealant | $9–$13 |
| Total | $336–$454 |
Excludes tools, delivery, tax and permit fees. Labor not included — this is a DIY materials estimate.
These are affiliate links: we may earn a commission if you buy through them, at no extra cost to you. It never changes what the calculator recommends — the shopping list comes from your dimensions, not from what pays.
About this calculator
A sub-slab depressurization system pulls soil gas out from under the slab before it can seep up into the house, and this calculator sizes one from your foundation instead of guessing at a fan off a shelf. Enter the slab's square footage and what's actually packed underneath it — clean gravel, sand, or compacted dirt and clay — and it works out how many suction points the slab needs and which fan pressure class can hold a vacuum through that material.
From there it sizes the PVC riser from the suction point up through the house to a termination point above the roofline, plus the crack sealing that keeps the vacuum pulling from the soil instead of leaking in through gaps in the slab. Toggle an exterior wall route if running the stack through interior closets and the attic isn't an option. This plans a new slab-on-grade or basement system — a crawlspace membrane system is a different job.
Step by step
A step-by-step walkthrough to go with your plan above. Follow the product instructions and any local code or permit requirements as you work.
Confirm elevated radon with a short-term test kit before touching anything — this calculator sizes a system, it doesn't replace the test that tells you one's needed.
Pick a spot near the center of the slab or an existing sump pit for each point the calculator calls for, spacing multiple points to cover the slab evenly.
Cut a hole through the slab with a masonry core bit and hollow out a bucket-sized cavity in the material below it so the suction point has room to pull from.
Fit the pipe boot fitting into the opening and patch around it with hydraulic cement so the pit is airtight everywhere except through the riser.
Solvent-weld the PVC riser from the pit up through the chosen route — interior closet or exterior wall — to a point at least 12 inches above the roofline.
Mount the fan in an unconditioned space like the attic or exterior wall, never inside living space, and run it to a dedicated, labeled, always-on circuit.
Caulk the sump lid, floor drains, and any visible slab cracks or the expansion joint with polyurethane sealant so the fan pulls vacuum from the soil, not through gaps.
Mount the U-tube manometer on the riser, confirm the fan is pulling vacuum at every suction point, and re-test indoor radon levels within 48 hours and again after a few months.
Equip the job
Hand-picked categories that match the shopping list above. Links open a current selection so you can compare brands and prices.
These are affiliate links: we may earn a commission if you buy through them, at no extra cost to you. It never changes what the calculator recommends — the shopping list comes from your dimensions, not from what pays.
As an Amazon Associate I earn from qualifying purchases. We may also earn from other retailer links here. This doesn’t change your price and helps keep these planners free.
Keep planning
Concrete & Masonry
Answers
It depends far more on what's under the slab than on its size. Clean, coarse gravel placed under a newer slab communicates air sideways easily and one point can hold vacuum across roughly 2,000 sq ft. Sand cuts that to around 1,500 sq ft per point, and compacted dirt or clay — including a slab poured straight over native soil with no aggregate base — barely lets air travel sideways at all, often needing a point every 800 sq ft or so to reach every corner. This calculator divides your slab area by the coverage your material supports and rounds up to a whole number of points.
The number that matters is the fan's pressure rating in inches of water column, not its CFM rating — a fan that moves a lot of air against no resistance can completely fail to hold suction through clay. Gravel-based slabs typically need only a low-pressure fan class; sand needs a mid-pressure class; clay or poorly-communicating soil needs a high-pressure class fan even though the flow rating looks similar on the box. Combining more than one suction point onto a single fan through a shared manifold also raises the pressure demand, which is why this calculator bumps the fan tier up whenever it calculates more than one point.
Most codes require the stack to terminate at least 12 inches above the roofline, at least 10 feet from any window, door or other opening on the same or an adjacent structure that's below the discharge point, and if it's within 10 feet horizontally of an opening it needs to extend at least 2 feet above that opening. Never cap it — a rain cap, bird screen, or turbine vent adds resistance the fan has to fight against and can measurably cut how much vacuum reaches the suction pit. Leave the top open exactly like a plumbing vent stack.
Yes, and it's often the cheapest option since no slab coring is required — you just need to seal the sump lid completely airtight with a gasketed cover, since any gap there leaks vacuum instead of pulling it from the soil. The catch is that a sealed sump only ever counts as one suction point. If your slab area and sub-slab material call for more than one point, the rest still have to be core-drilled elsewhere in the slab to reach full coverage.
A U-tube manometer mounted on the riser is the standard always-on indicator — the liquid column sits at a visible offset whenever the fan is pulling vacuum, and it flattens out the moment the fan fails or gets unplugged, which is otherwise completely silent and invisible. Beyond that, the only real confirmation is re-testing indoor radon levels with a short-term kit a couple of days after startup and again with a longer-term kit a few months later, since sub-slab conditions vary enough that two houses with identical hardware can land at different final readings.