For example:
Home built: 1954
Observation: 1.5-inch hole in concrete, previously covered with tape, near oil furnace

• Old Condensate Drain: May have drained moisture from the furnace.
• Passive Vent or Radon Path: Unlikely for 1954 but possible if repurposed.
• Abandoned Fuel Line or Utility Conduit: May have carried old oil lines or wires.
• Test Hole for Water Table: Sometimes drilled to monitor groundwater.
• Construction Artifact: Could have been left from original building process.

Before sealing or modifying, perform the following:

• Depth Check:
  • Use a stiff wire or stick.
  • Shallow (< 6”): likely drain or utility.
  • Deep (> 12”): may connect to sub-slab soil or vent.
• Contents:
  • Dirt: leads to soil.
  • Water: possible seepage.
  • Empty: abandoned conduit.
• Odor:
  • Oil smell: possible fuel line history.
  • Earthy: sub-slab soil exposure.
  • Sewer: possible (but unlikely) drain connection.
• Edge Quality:
  • Smooth: professionally cored.
  • Rough: post-construction drilling.
• Nearby Pipes: Look for proximity to old oil, drain, or utility lines.

Based on what you find:

• Seal with hydraulic cement or expanding foam.
• Product example: *Quikrete Hydraulic Water-Stop*.
• Prevents moisture, insects, and gas entry.

• Perform radon testing first:
  • Use a short-term radon test kit (~$15–30).
• If radon normal: seal with hydraulic cement.
• If radon elevated: consult radon mitigation professional.

• Monitor after rain.
• Consider adding vapor barrier sealers after plugging.

• Verify no abandoned oil tank or active lines remain.

• Do not cover with tape again.
• Do not fill with organic materials (wood, insulation, etc.).

• Perform inspection.
• Report findings for fine-tuned recommendation.

Goal: Determine if radon is entering through a 1.5” hole near oil furnace (1954 house)

Using a radon detector inside a sealed plastic container over the hole can help identify radon entry.

• Clean area: Remove dust and debris around hole.
• Enclosure: Use a rigid plastic container or bin (e.g. food storage container or mixing bowl).
• Place detector: Set radon monitor inside container, directly over or near hole (not touching concrete).
• Seal edges: Use duct tape, painter’s tape, or putty for semi-airtight seal.
• Duration: Leave sealed for at least 24–48 hours.
• Avoid disturbance: Keep area calm with minimal air movement during test.

• This is a spot test, not a full EPA-compliant test.
• Test indicates whether this hole is an active radon entry point.
• Minimize airflow or HVAC drafts during test.
• Consider repeating test after sealing the hole to verify radon levels.

1. Stage 1: Test hole before sealing.
2. Stage 2: Seal hole (e.g. hydraulic cement), then retest same location.

If using a specific radon monitor (e.g. Airthings, Safety Siren, etc.), minor adjustments may improve accuracy. 

Device: Corentium Home Radon Detector

• Provides reliable short-term (24h), weekly, and long-term averages.
• Updates readings every hour.
• Portable and battery-powered — ideal for enclosure testing.

• Placement: Place monitor upright inside plastic container directly over hole (at least 4 inches above floor if possible).
• Enclosure: Use rigid plastic container or inverted bowl; larger is better for consistent air sampling.
• Seal edges: Use duct tape or painter’s tape to create airtight seal against concrete.
• Stabilize temperature: Try to minimize temperature swings during test.
• Duration: Leave undisturbed for at least 48 hours. Longer (3–5 days) will give more reliable data.

• Use the “short-term average” (ST) reading from display after 48 hours.
• Compare to your baseline basement radon level.

• After sealing hole, repeat identical test to confirm radon levels remain stable.
• Use same enclosure and placement for consistency.

• Avoid moving the monitor during test.
• Avoid HVAC drafts near test enclosure.
• Corentium does not need recalibration between tests.
• Battery power allows flexible placement without wires.

• Spot tests are useful diagnostic tools but not a substitute for full-home radon testing.
• If whole-house radon is above 4.0 pCi/L, consider full mitigation.

•	One-Day Average
•	Good for quick checks (e.g., after rain, testing HVAC effects).
•	Can fluctuate due to weather, barometric pressure, HVAC use, etc.
•	Do not make decisions based solely on one-day averages.
•	Seven-Day Average
•	More reliable for assessing your home’s typical radon level.
•	Use this as your main guide for decisions.

•	No action needed.
•	Retest every few years or after major home changes.

•	Retest periodically.
•	Consider:
•	Sealing cracks in foundation and basement.
•	Improving ventilation.
•	Using fans to increase air exchange.
•	Avoid prolonged closed-window conditions.
•	Proactive action is beneficial but not urgent.

•	Professional radon mitigation strongly recommended.
•	Mitigation methods:
•	Sub-slab depressurization (most common).
•	Sealing entry points.
•	Crawlspace ventilation (if applicable).
•	Typical cost: $800–$2,500 depending on house.

•	High priority.
•	Immediate mitigation recommended using methods above.

•	Selling/Buying a Home: Even borderline levels may be a concern for buyers.
•	Young Children or Respiratory Issues: Be more cautious; consider mitigation at moderate levels.

•	After mitigation, consider continuous monitoring to ensure levels remain low.

A plumber’s box is a rectangular hole in the basement concrete slab, commonly found in older homes (e.g., built in the 1950s). It allows access to sewer pipes beneath the floor. These openings can act as direct radon entry points.

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• In most cases, no, you do not need to keep the plumber’s box open.
• Modern plumbing methods usually rely on cleanouts located elsewhere.
• If your sewer system is in good condition and you have no history of backups, you likely won’t need future access to this hole.

Exceptions:

• You have no other cleanout access to the main sewer line.
• You’ve had sewer line issues in the past.

—

—

1. Clean the hole and edges.
2. Fill bottom with gravel (optional, for drainage).
3. Cover with 6 mil+ polyethylene vapor barrier.
4. Pour hydraulic cement or concrete to cap it.
5. Optionally embed a capped pipe or box for future access.

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You can temporarily reduce radon entry using this method:

1. Lay 6 mil plastic sheeting over the hole.
2. Place the wooden board on top.
3. Tape edges of the plastic to the floor with foil tape or duct tape.
4. Place a heavy object (e.g., concrete block) on the board.

Note: This is only a temporary measure. It is not airtight and should not be considered a permanent radon mitigation solution.

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• Temporary sealing helps reduce radon risk short-term.
• Permanent sealing is recommended if radon levels are high and sewer access is not needed.
• A hybrid solution with a removable access point is also possible.

Temporarily or semi-permanently seal an open plumber’s box hole in the basement floor to reduce radon entry and soil gas infiltration.

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• 6 mil (or thicker) polyethylene plastic sheeting (vapor barrier)
• Nashua 324A aluminum foil HVAC tape (UL 181A-P, 181B-FX)
• Wooden board (to cover and protect the plastic sheeting)
• Weights (e.g., concrete block or heavy object)

—

1. Clean the concrete surface around the hole:
   • Remove dust, dirt, moisture, and loose debris.
   • Allow surface to dry fully for better tape adhesion.
2. Cut plastic sheeting large enough to cover the hole and extend at least 6–12 inches beyond the hole edges onto clean concrete.

—

1. Lay the plastic sheeting flat over the plumber’s box hole.
2. Smooth out any wrinkles to ensure full contact with the floor.
3. Apply Nashua 324A tape along the edges of the plastic:
   • Press tape firmly onto both the plastic and the concrete.
   • Overlap tape strips by about 1 inch for better sealing.
   • Use a roller or your hand to press down along the full width of the tape for maximum adhesion.
4. Place the wooden board on top of the sealed plastic for extra protection.
5. Set weights on top of the board to prevent accidental shifting.

—

• This method provides a strong vapor barrier for temporary or semi-permanent use.
• Nashua 324A is suitable for this application due to its high adhesion, vapor barrier properties, and UL certification.
• This setup allows for later permanent sealing if necessary.

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If radon levels remain high:

• Seal permanently with concrete or hydraulic cement.
• Install a radon mitigation system.
• Consider embedding a removable cleanout access if future sewer access may be needed.