How to Know If Your Radon Fan is Too Small

The radon fan connected to your home’s mitigation system piping serves a vital purpose – maintaining sufficient suction to safely vent hazardous radon gases from beneath your foundation. But problems arise when a radon fan gets installed that is too small for the home’s specifications. Undersized radon fans strain to work harder than designed, leading to premature failure and inadequate radon reduction.

Why Correct Radon Fan Sizing Matters

Radon fans rated in CFM (cubic feet per minute) air flow pull soil gases up through vent piping and exhaust them outside. Sizing a radon fan appropriately matches its rated air movement capacity to the home’s size and system design. Oversized fans waste energy and money. More critically, undersized fans cannot generate enough vacuum suction and pressure differentials for effective mitigation throughout a home.

With an undersized radon fan, hazardous gases continue infiltrating into living spaces, accumulating to dangerous levels that put your household at risk. Getting the right fan sized for your dwelling’s parameters ensures sufficient radon reduction. Consult a qualified radon mitigation contractor on proper fan selection.

Reviewing Your Home’s Original Radon System Design

Your home’s original radon mitigation contractor likely has detailed records on the fan sizing calculations they made. Request documentation on the process used to select your installed radon fan model based on your home’s specifics.

Key factors in radon fan sizing include home square footage, foundation slab surface area, number of floors, piping system design, total vent pipe length, number of elbows, pipe material (PVC vs ABS) and pipe diameter. Reviewing the original radon system design helps determine if the current fan aligns with those specifications.

Checking Sizing Charts of Fan Manufacturers

Every radon fan manufacturer provides detailed sizing guidance showing how their various models should be matched to home parameters. They factor in aspects like floor area, foundation layout, number of walls, climate, vent pipe length, diameter, elbows and material.

Compare your home’s statistics to the manufacturer’s sizing recommendations. For example, a 1500 square foot home with a unfinished basement, 3 exterior walls, 40 feet of 4” PVC vent pipe and 4 elbows should have a fan rated for around 130 CFM according to RadonAway charts. If your installed fan model falls short, resizing may be needed.

Measuring Air Velocity of the Radon Vent Pipe

One empirical way to gauge fan size adequacy is using an anemometer to measure the air velocity exiting the radon vent pipe. Compare this reading in feet per minute to the rated air flow for your fan model. Significant deviation indicates improper sizing.

For example, if your fan is rated for 100 CFM but anemometer readings show your actual air velocity translates to only 60-70 CFM, resizing to a larger fan is likely needed. Average the velocity readings across the full diameter of the pipe to account for air flow differences.

Monitoring the Static Pressure Vacuum

A U-tube manometer installed on the radon vent pipe measures the actual negative static air pressure your system maintains, in units of inches of water column (in. w.c). Compare the manometer reading to your fan’s rated vacuum capacity. For most homes, the target static vacuum pressure ranges from -1.0 to -4.0 in. w.c depending on mitigation system design.

If your measured vacuum reading falls short of your fan model’s rated capacity, insufficient air suction explains why radon levels remain elevated. Confirm your fan creates enough suction pressure for effective sub-slab depressurization.

Listening for Straining Fan Noises

The sound of a radon fan offers clues to its performance. Fans working too hard produce distinctive noises from the strain. Listen closely for rattling, grinding, squealing from the fan or vent pipe. Noise may increase as fans labor excessively to pull air against resistance.

Radon fans properly sized for normal operation emit only a low, smooth hum. Straining sounds signal problems with sizing, airflow restrictions or mounting. The fan location also impacts noise, so be sure to differentiate fan sounds from other equipment.

Checking Post-Mitigation Radon Levels

The best confirmation of adequate radon fan sizing is getting post-mitigation radon testing done soon after system activation. If follow-up short-term and long-term radon test results still show concentrations around or above 4 pCi/L, an undersized fan is likely the culprit.

Properly sized radon fans reduce home levels to well below 4 pCi/L. Undersized fans cannot maintain the needed suction and ventilation rates to drop radon adequately in all connected spaces. Use testing data to advocate for fan resizing.

Inspecting for Condensation Buildup

Another sign of insufficient fan capacity is the presence of moisture or condensation on radon vent pipes. Proper negative air pressures should vent moist air before it condenses. But an undersized fan may not adequately handle the humidity load.

Condensation forms when stale humid basement air cannot be removed fast enough. Pooling water or damp pipes indicate excess moisture in the radon vent stream that smaller fans cannot properly exhaust. Sizing up in fan capacity provides needed dehumidification.

Consult Radon Pros If Sizing Seems Inadequate

To ensure your family’s safety, get any radon fan sizing uncertainties addressed by a certified mitigation professional. Watching for issues like high post-mitigation radon levels, straining fan noise, and condensation buildup helps flag situations where radon fan upsizing may be required. Don’t let an undersized component undermine your radon protection.

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