Radon fan

A house pulls on the soil under it. EPA's Building Radon Out explains that the air pressure in a house is generally lower than in the surrounding air and soil, particularly in the basement and foundation levels, so the house acts like a vacuum, drawing air containing radon and other soil gases in through foundation cracks and other openings.

The fan reverses that pull. The same guide says the objective of a sub-slab or sub-membrane depressurization system is to create a vacuum beneath the foundation which is greater in strength than the vacuum applied to the soil by the house itself. With the space under the slab at lower pressure than the rooms above, soil gas moves toward the suction point and up the pipe instead of into the house.

Inline radon fan: why the fan sits in the pipe

An inline radon fan is installed in the vent pipe run itself. Building Radon Out says the most commonly-used fans are centrifugal fans often referred to as in-line, tubular or tube fans, and that the fan should go in a vertical run of the vent pipe, which will prevent outdoor precipitation from accumulating in the fan or fan housing. It does not blow air into the house. It pulls on the soil under the foundation and pushes that gas up and out.

The core rule is the same everywhere. EPA's Consumer's Guide says the exhaust fan must not be located in or below a livable area; for instance, it should be installed in unconditioned space. Common fan locations, it adds, include unconditioned home and garage spaces, including attics and the exterior of the home.

Why does a radon fan need to be in the attic or outside?

Because the pipe above the fan is under positive pressure. Building Radon Out says the fan and all positively pressurized portions of the vent pipe should be located outside habitable space, and that placement in a non-conditioned space prevents the accidental pumping of radon directly into a home should a leak occur in the fan housing or at the vent-pipe joints. The same guide adds that sheltering the fan in an attic or garage maximizes its efficiency and life expectancy by minimizing exposure to extreme temperatures and moisture.

Can a radon fan be installed in the basement?

No. Minnesota's mitigation page states it directly: the fan cannot be in or below a livable space. A fan in a basement, even an unfinished one, puts the pressurized side of the system under the rooms people use. The pipe can start in the basement; the fan belongs above the living space or outside.

Can my radon fan be inside the garage?

Yes, when no conditioned rooms sit above it. Nebraska's sheet describes one common layout: the pipe is routed into the garage, rises through the garage ceiling, and the fan is mounted on the pipe in the attic above the garage. Building Radon Out adds that a pipe run through the wall between house and garage needs a fire barrier around it, with a rating equal to the wall.

The discharge is the other half of the location rule. Radon leaving the pipe must not drift back in a window. EPA's Consumer's Guide says the exhaust pipes of soil suction systems must vent above the surface of the roof and 10 feet or more above the ground, and must be at least 10 feet away from windows, doors or other openings that could allow radon to reenter the home, if the exhaust pipes do not vent at least 2 feet above these openings.

Can a radon fan vent through a wall?

The pipe can leave the house through a wall; the exhaust cannot end there. Iowa's 2022 notice was written about exactly this case, systems that exit through or below the rim joist with the fan and discharge piping on the outside of the house. It says that when a horizontal run of vent stack pipe penetrates the gable end walls, the piping outside the structure shall be routed to a vertical position so the discharge point still meets the height and separation rules. Iowa's interpretation is that the discharge point must be at least 12 inches above the eave or edge of the roof on the wall the pipe is mounted on.

Searchers look for a radon fan sizing chart, or ask what CFM radon fan they need. No EPA guide publishes a chart. EPA's 1994 Radon Mitigation Standards set the rule instead: radon vent fans shall be sized to provide the pressure difference and air flow characteristics necessary to achieve the radon reduction goals established for the specific mitigation project.

EPA's builder guide gives the only published rule of thumb. Building Radon Out says the fan's size and air movement capacity should be sufficient to maintain a pressure field beneath the slab or crawlspace membrane that is lower than the ambient pressure above it, that most contractors have found 90-watt in-line fans to be adequate for most home styles, locations and sizes, and that a fan capable of moving 100 cubic feet of air per minute at one inch of water column should be sufficient for most applications. Those are 2001 figures, from a guide written for builders of new homes.

How do you size a radon fan for an existing house?

By testing how air moves under that house. EPA's Consumer's Guide says the number and location of suction pipes depends on how easily air can move in the crushed rock or soil under the slab and on the strength of the radon source, and that often only a single suction point is needed. Minnesota's ten-step process includes it: the professional may perform diagnostic testing to ensure the proper fan size and correct installation.

1. 1

   Visual inspection

   EPA says the contractor inspects the home and designs a system that considers its specific features.

2. 2

   Smoke tests

   Chemical smoke shot into holes, drains, sumps or along cracks shows the source and direction of air movement, and possible radon routes.

3. 3

   Soil communication test

   A vacuum cleaner hose in one small hole and chemical smoke in a second show how easily air moves under the foundation.

4. 4

   Choose the fan

   The fan is matched to the pressure and air flow the test showed the house needs, which is the rule EPA's 1994 standards set.

5. 5

   Check the result

   After activation, EPA's 1994 standards have the contractor measure suctions or flows in the system piping to assure the system is operating as designed.

A radon fan runs all year, so its electricity is the system's main running cost. EPA's Consumer's Guide says systems that use fans are more effective in reducing radon levels; however, they will slightly increase your electric bill. It gives no figure. Minnesota's system safety sheet, which installers there attach to every system, does.

Minnesota's estimate is for the fan alone. The sheet says it does not include additional energy costs that may occur because heated or cooled air from the building is vented to the outside by the radon mitigation system through unsealed openings to the soil. EPA's Consumer's Guide makes the same point: most types of radon reduction systems cause some loss of heated or air conditioned air, and how much your utility bills increase will depend on the climate you live in, what kind of reduction system you select, and how your home is built.

High efficiency radon fan: what actually lowers the running cost

Two things help. Sealing: EPA's Consumer's Guide says sealing cracks makes other radon reduction techniques more effective and cost-efficient and reduces the loss of conditioned air. Fan size: on Minnesota's table the running cost scales with the watts, so a fan sized to the house rather than oversized costs less every year.

A radon fan is an electrical appliance that runs unattended for years, so the standards are specific. EPA's Consumer's Guide says electrical connections of all active radon reduction systems must be installed according to local electrical codes. Minnesota adds that most installations require electrical work to power the radon fan, which requires an electrical permit.

For new homes built with a passive pipe, Building Radon Out asks for an unswitched electrical junction box in the attic or garage within 6 feet of the vent pipe, so a fan can be wired in later. The fan outlet does not require a dedicated circuit, it says, and may branch off the existing circuit for the attic light.

The suction only exists while the fan runs, and radon comes back when it stops. EPA's figures show what the fan adds: in the Consumer's Guide's table, active subslab suction typically reduces radon 50 to 99 percent, and passive subslab suction, the same pipe with no fan, 30 to 70 percent.

A radon test does not require the fan off. EPA's Home Buyer's and Seller's Guide says fans that are part of a radon-reduction system may run during the test, and its checklist says that if a radon-reduction system is in place, make sure the system is working properly and will be in operation during the entire radon test. See can I turn off my radon system.

EPA's Consumer's Guide says a warning device must be installed to alert you if an active system stops working properly, and lists examples: a liquid gauge, a sound alarm, a light indicator, and a dial, or needle display, gauge. It must be placed where it can be seen or heard easily. Minnesota requires two on every system it licenses: a u-tube manometer and an active notification monitor.

1. 1

   Find the manometer

   Nebraska says it is typically on the vent pipe in the basement, about 4 feet above the suction point: a small U-shaped tube of colored fluid connected to a hole in the pipe.

2. 2

   Read the two sides

   Pennsylvania says the fan is running if the levels of fluid on each side of the glass tube are uneven. The fan's suction pulls the fluid up one side.

3. 3

   Compare with the start-up mark

   Minnesota says the reading taken at installation is written on a sticker next to the manometer. EPA's 1994 standards require the gauge to be marked with the range that existed when the system was first activated.

4. 4

   Know what even levels mean

   If the fluid levels are even, Minnesota says, the fan stopped working or another part of the system is not working properly.

5. 5

   Check the simple causes first

   Before calling the installer, Minnesota says to make sure the monitor tubing is connected to the pipe and not kinked, and that power is being supplied to the fan.

Active notification monitors

The electronic alarm complements the gauge. Minnesota says it alerts you with a visual light and/or audible noise if the system stops working, and either measures air flow or air pressure in the pipe. Building Radon Out adds that an audible or visual alarm should be on a separate circuit, unless the indicator is integral to the fan power supply, so it activates if power to the fan is interrupted.

Condensation radon fan problems: why a radon fan leaks water

Nebraska's sheet explains the physics: soil air drawn from beneath a basement floor is laden with moisture vapor, and if the system is not installed properly this vapor will condense and pool inside the ventilation pipe, and water that pools in an unheated area will freeze at low temperatures. EPA's 1994 standards require vent pipes in a configuration that ensures that any rain water or condensation within the pipes drains downward into the ground beneath the slab. Water at the fan usually means a trap or low spot in the pipe, which is a service call for the installer.

Quietest radon fan: what reduces noise

Radon411 names no quietest model, for the same reason it names no best one. What does reduce noise is installation: flexible couplings, a secure mounting away from bedrooms, a 4-inch pipe, and few elbows. If noise matters, say so when you ask for proposals. EPA's 1994 standards require systems designed to minimize noise.

Radon fan cover

EPA's guides say nothing about decorative covers or boxes. They do say that a fan installed outside must meet local building codes for exterior use, and EPA's 1994 standards require an exterior fan to be rated for outdoor use or installed in a water tight protective housing. A cover must not block the fan's air flow, the discharge, or the manometer, so ask the installer before adding one.

Fans wear out. EPA's Consumer's Guide says fans may last for five years or more, manufacturer warranties tend not to exceed five years, and fans may then need to be repaired or replaced. EPA's FAQ on whether a system is working gives a figure: replacing a fan will cost around $200 - $350 including parts and labor. The Consumer's Guide adds that the cost varies because it is based on labor and materials, so ask qualified mitigators for estimates before work begins.

1. 1

   Notice the signal

   The manometer fluid is even, the alarm sounds, or a retest comes back higher than the last one.

2. 2

   Rule out the simple causes

   Check that the monitor tubing is connected and not kinked and that the fan has power, as Minnesota advises.

3. 3

   Call the installer or a mitigator

   EPA says that if your monitor shows that the system is not working properly, call a contractor to have it checked. Radon411 lists mitigation professionals by state.

4. 4

   Get the estimate and warranty in writing

   EPA's contract checklist asks for details of warranties on the hardware components of the system.

5. 5

   Replace with removable couplings

   EPA's 1994 standards require fans installed using removable couplings or flexible connections, to facilitate maintenance and future replacement.

6. 6

   Retest

   CDC says to always test radon levels again after you've made any of these changes.

Can I replace a radon fan myself?

It depends on your state. EPA recommends a qualified radon mitigation contractor because lowering high radon levels requires specific technical knowledge and special skills, and warns that without the proper equipment or technical knowledge, you could actually increase your radon level. Some states license the work: Building Radon Out notes that some states require that in-line fans for radon reduction be installed by a certified radon mitigation contractor. Nebraska takes the other view for owners, saying homeowners can also install a radon mitigation system in their own home if they so desire, following its practices. Check with your state radon program first.

Homes built with radon-resistant features have the pipe but no fan. EPA's Citizen's Guide says every new home should be tested after occupancy, and that if radon levels are still in excess of 4 pCi/L, the passive system should be activated by having a qualified mitigator install a vent fan. EPA's Home Buyer's and Seller's Guide adds that an alarm is installed along with the vent fan to indicate when the vent fan is not operating properly.

EPA's Building Radon Out says virtually all homes with an active system have radon levels below the 4 pCi/L action level. After a fan is added, it says, testing should be repeated with a short-term test, preferably between 24 hours and 30 days after activation. More in passive radon systems and radon-resistant new construction.

The fan is chosen with the system, by the contractor who designs it. EPA's advice for comparing proposals applies to it directly: a less expensive system may cost more to operate and maintain, and the quality of the building material will affect how long the system lasts.

Best radon fans: why there is no ranking here

Radon411 does not name a best radon fan or compare fan models. What helps instead is a set of questions that separate a well-matched fan from a guess.

• What fan do you propose for this house, and what diagnostic test did you size it from?
• Where will it go, and is that space unconditioned and not beneath living space?
• Where will the exhaust end, and how far is it from windows, doors and the neighbors' openings?
• Is the fan in a vertical run, with flexible couplings, and how is it wired?
• What warning devices will the system have, and what should the manometer read?
• What will the fan cost to run each year, and what warranty covers it?
• Who does the post-mitigation test, and when?

When a retest comes back, read it against EPA's guidance. EPA recommends fixing a home when the radon level is 4 pCi/L or higher. EPA recommends considering a fix when the level is between 2 and 4 pCi/L. The interpreter reads a result for you.