Effect of Energy Conservation Sealing Measures on Indoor Radon Concentrations
A REPORT ON
EFFECT OF ENERGY CONSERVATION HOUSE SEALING ON INDOOR
Some of the power supplier sponsored activities that are directed at energy
conservation by means of reductions in total electrical energy usage of air
conditioning systems in single family housing also have the possibility of causing
an increase in the indoor Radon gas levels in the dwelling thereby placing the
occupants a some degree of increased lung cancer health risk. It is the purpose
of this dissertation to explore and clarify the interactions that may take place
when a home undergoes modifications or improvements to weather stripping, exterior
envelope sealing or air conditioning duct sealing.
In the simplest of terms, in order for Radon to be present inside the "living
envelope" of a house or any enclosed structure three elements are necessary,
first, there must be a Radon gas source, radium a solid in constant radioactive
decay in rocks, soil or water becomes Radon gas. Second, there must be a path
for the Radon to transport along in order to reach and enter the structure.
Third, there must be a driving force to transport the Radon along the path.
If any of the factors are absent there cannot be infiltration of Radon into
a house. There may be Radon present in a building that is the result of radium
levels present in some of the building materials or interior furnishings but
this source is rare and shall not be considered as important to the purpose
of this investigation.
When the natural infiltration or exfiltration of a building in reduced, the
main goal in the weather sealing, exterior envelope sealing and duct sealing
programs sponsored and promoted by many power suppliers, the concentrations
of airborne pollutants of both internal and external origin will increase in
proportion to the reduction in ventilation rate, usually expressed in air changes
per hour, ACH. Using the example of a Page 2..... residence that had a natural
ventilation rate of .50 ACH and an indoor Radon of 3.9 pico Curies per liter
of air, pCi/l, this is just under the EPA action level of 4 pCi/l, after successful
sealing the new reduced ventilation rate may conceivably have been reduced to
.25 ACH, now the ventilation influenced Radon level would be 7.8 pCi/l well
over the EPA action level. With the successful application of the energy reduction
sealing programs having reductions in air conditioning duct losses approaching
400 cubic feet per minute CFM and window and door sealing also contributing
to the reduction in natural ventilation it is clear that any home with an existing
uncorrected indoor Radon gas problem will be made worse as a result of duct
sealing activities and thereby increase the Radon health risk to the occupants.
In addition to the increase in indoor Radon gas concentrations resulting from
reductions in ventilation rates, another possible set of conditions may act
together to further aggravate the Radon problem and add to other indoor air
pollution levels. When the air conditioning duct system in a residence is leaking
on the supply side of the air handler the house envelope will depressurize slightly,
causing an increase in the infiltration rate of the Radon and other outside
contaminates, sealing the supply side duct leaks will reduce this depressurization
of the interior and thereby help reduce the Radon levels. However, also very
common is the sealing of return side leaks, which prior to sealing, had the
effect of increasing indoor pressure levels, thus by sealing these leaks the
overall Radon intrusion rate may increase dramatically due to indoor pressure
reduction. In an average 1880 square foot Florida home it is possible to reduce
indoor radon from 14 pCi/l to below 3 pCi/l by the introduction of less than
100 CFM of outside air into the return air side of the air handler, thus sealing
a 100 CFM return side duct leak would have an opposite affect of increasing
the Radon level. Studies have shown that a 1 to 2 Pascal positive indoor air
pressure will significantly reduce indoor air pollution and the same pressure
but on the negative side will provide the necessary driving force for marked
increases in indoor contaminate levels. Conclusions
With the possible increase in indoor Radon levels from reductions in ventilation
rates added to the potential Radon entry rate growth due to the affects of air
conditioning duct sealing originated pressure relationship variations it becomes
clear that any building so modified for energy conservation should have an indoor
Radon gas level screening test upon completion of the sealing or modifications.
The occupants of any untested dwelling will be at a potential increased health
risk from Radon exposure.
EPA/400/1-91 (1991) " Building Air Quality "
Hintenlang, D. E. and Kaiss, K.A. (1992) " Periodic Atmospheric Pressure
Variation Driven Radon Entry Into Structures Built Over Low Permeability Soils"
Florida Radon Research Project.
Cummings, J.B., Tooley, J.J. and Moyer, N. (1991) "Investigation of Air
Distribution System Leakage and its Impact on Central Florida Houses",
Florida Solar Energy Center Report
Hintenlang, D. E. and Roessler, C. E. (1992) Quarterly Report " Florida
Radon Research Houses, House Dynamics and Modeling" FRRP Research Project
Cummings, J.B., Tooley, J.J. and Moyer, N. (1990) "Radon Pressure Differential
Project, Phase I", Florida Solar Energy Center Report
This report compiled by:
H. William Levy, Civil Engineer Radon Consultant EPA Approved RCP, EPA Listed
RMP Florida HRS Radon Mitigation and Measurement Certified Specialist