terminate on an outside wall instead of
above the roofline?
Retrofitting an existing home with a typical
EBM fan powered mitigation system can be
expensive and/or aesthetically unpleasing
because of the PVC materials needed to
terminate the system above the roof. Many
affected homeowners do not have the funds
available to devote to these traditional
mitigation methods which cost anywhere from
$1,500 to $5,000 installed. EPA studies show
less than 15% of the homes that exceed
recommended radon levels have an active
The Radon VAC
requires no exterior PVC saving both
material and labor costs while at the same
time minimizing the effects on the home’s
appearance.Why is it
typically recommended that the fan be
outside or in the attic?
Since sealed fans were not used in original
studies, a bias for putting the fan outside
the living space was developed. From a
practical perspective fans installed in the
attic stand little chance of being inspected
for operation or serviced. Temperature
extremes in attics and in cold weather
climates also are an extremely undesirable
environment for operating a motor. Exterior
PVC is susceptible to moisture and freezing
The Radon VAC’s gasket
sealed housing keeps radon gases contained
within the fan housing prior to being
exhausted to the outdoors. Built-in schedule
40 connectors on the Radon VAC’s housing and
discharge hood eliminate the need for
adapter boots and clamps, the most likely
point of leakage. All PVC pipe connections
are designed to be sealed with schedule 40
PVC cement.What about
recirculation of the exhaust gases back into
When using a
standard fan to exhaust near the ground
level problems can develop for installations
that have restrictive soil densities and/or
extensive PVC pipe runs. At lower flow rates
the discharge velocity can drop below that
needed to fight wind loads and propel the
gases away from the home’s exterior.
Tjernlund’s adjustable Variable Aspiration
Control hood lets the installer increase
dilution and discharge velocity on lower
flow applications. This allows for the radon
to be discharged and diluted in a jet of air
regardless of soil density.
the engineered VAC hood our installation
instructions state minimum distances from
doors, windows and fresh air intakes to
avoid recirculation issues. These distances
have been used for decades to avoid
recirculation of exhaust gases from side
wall vented gas and oil fired furnaces,
boilers, water heaters and fireplaces. See
the RMS160 instructions for an illustration
with specific clearances.Is
using the Radon VAC against code?
No. The International Building Code
(IBC) and International Residential Code
(IRC) do not address Active Slab
Depressurization (i.e. Fan-Powered Systems)
as a radon mitigation technique. Some
institutions (e.g. EPA) offer guidelines and
recommendations for radon mitigation
techniques when using basic fans, but these
organizations do not regulate radon
mitigation. You should always follow local
building codes. In absence of these codes
follow the IBC and IRC.
-Radon is a colorless, odorless,
cancer-causing radioactive gas that
naturally occurs in the environment. It is
produced by the decay of uranium in the soil
and rocks below the earth’s crust where it
is released into the air and water.
-Radon is measured in pCi/L (picocuries per
liter of air), a measurement of
-The average indoor
radon level is 1.3 pCi/L while the average
outdoor radon level is about 0.4 pCi/L, but
can vary from site to site.
estimated 21,000 deaths per year, radon is
the second leading cause of lung cancer in
the United States. Only smoking causes more
-When radon decays, it
expels alpha particles. These small, heavy,
electrically charged sub-atomic particles
consist of two protons and two neutrons. If
an alpha particle attaches itself to the
chromosomes in a lung cell, it can alter the
way that cell reproduces.How
Radon enters your home
amount of radon that escapes from the soil
to enter the house depends on the season,
weather, soil porosity, soil moisture and
the suction within the house
can seep into your home from the soil
beneath it through dirt crawlspaces, cracks
in the foundation and walls, floor drains,
pipes and sump pump pits. If you get your
drinking water from a well, it can also be a
source of radon in your home.
act like large chimneys. As the air in the
house warms, it rises to the attic and exits
through cracks, openings and around the
upper floor windows. This creates a small
suction (“vacuum”) at the lowest level of
the house, pulling the radon out of the soil
and into the house.
water can transport the radon from the soil
into the house at any time when running
water (e.g., taking a shower, doing laundry,
washing dishes, etc.). The EPA says it takes
about 10,000 pCi/L of radon in water to
contribute 1.0 pCi/L of radon in air.
-If your water comes from a city supply,
there is no need to worry about radon in the
water. When radon in water is stored in a
reservoir for more than 30 days, the radon
decays away to practically nothing. Every
3.825 days half the radon disappears through
natural radioactive decay.
Testing for Radon
is the only way to know your home's radon
levels. There are no immediate symptoms that
will alert you to the presence of radon. It
typically takes years of exposure before any
-There is no safe
level of radon. The EPA recommends
mitigating radon in a home when levels are
at, or exceed, 4.0 pCi/L. In addition, the
EPA says to consider action if the level is
2.0 to 3.9 pCi/L.
-Testing should be
done in the lowest level of the home that is
are a quick and inexpensive way to measure
for radon in a home. They are typically left
in place for 3 to 7 days.
tests, often called an “alpha track,” should
be left in place for a minimum of 90 days
and up to 12 months. Long-term tests provide
results that reflect the average amount of
radon in the home during a year.
-Retesting should be done every 2-5 years or
if any major changes to the home have been
done (e.g., finishing a basement, addition,
new heating system or adding central a/c).
-Even homes in areas considered at low
risk for radon can have high radon levels.
About 15% of homes in the U.S. have radon
levels above 4.0 pCi/L.
of homes have radon, even new construction.
Do not assume that just because your
neighbor’s levels are low, that yours will
-Changes in season,
temperature, rainfall, wind and barometric
pressure can all affect the radon
goal is to make the exhaust vent a better
“vacuum” than the house is.
Soil Depressurization is where a fan is used
to exhaust radon from the home. There are 6
different types of ASD: Drain Tile
Depressurization, Sump Depressurization,
Baseboard Depressurization, Block Wall
Depressurization, Sub-slab Depressurization,
and Sub-membrane Depressurization.
-Drain Tile Depressurization is used where
drain tile is present in an application. The
mitigation system is tapped into the drain
tile tube around the perimeter of the house.
-Sump Depressurization is also used
where drain tile is present. This system is
tapped into the sealed sump pit cover to
pull radon out through the drain tile.
-Baseboard Depressurization may be
appropriate where a French drain is present.
This option is rarely used today.
-Block Wall Depressurization uses the hollow
block wall foundation. The system is piped
into the block wall to pull out radon.
-Sub-slab Depressurization is used in
90% of all radon mitigation systems. This
involves drilling a hole through the
concrete slab to pull radon out below the
is used where a dirt floor crawl space is
present. The floor is covered with thick
plastic sheeting, which is then secured and
sealed. The PVC is inserted below the
plastic to pull the radon from the dirt.
-Passive Soil Depressurization is where
no fan is present. PVC pipe is used to
create a natural chimney for radon to vent
through. PSD is commonly used in Radon
Resistant New Construction and almost never
used in existing homes.
Resistant New Construction (RRNC) is a new
building code requiring all new homes to be
built with additional steps taken to prevent
radon infiltration. The 5 main steps of RRNC
include: 4” of coarse gravel below the
foundation slab; thick plastic sheeting
above the gravel; a 3” or 4” PVC pipe run up
through conditioned space from below slab to
above roof; all openings, cracks and
crevices are sealed with polyurethane caulk
and a junction box is installed in the attic
for use with a fan.
-Seal up cracks
and openings in basement floors, foundation
walls, openings around pipes, etc. to
prevent radon infiltration. If a home has a
crawl space, install a vapor barrier over
the bare soil.