by Jon Traudt
A Systems Approach to Minimizing Indoor Levels of Radon and Other Dangerous Air Pollutants while Minimizing Heating and Air Conditioning Costs.
NOTE: The United States EPA the Association of Energy Engineers sponsored the 1992 Innovative Radon Mitigation Design Competition. The following is an updated version of the entry that won the Grand Prize.
Protection of people and buildings while conserving energy. Design, installation, and demonstration of new, useful, durable, and economically practical system to mitigate radon and other indoor air pollutants. Make it safe to seal air leaks in the shell of a building to minimize excessive air leakage and thereby minimize the amount of energy required for heating and air conditioning.
• Minimize entry of radon from the soil into tight houses by keeping indoor air pressure slightly higher than soil gas pressure.
• Reduce entry of radon from the soil into leaky houses by preventing indoor air pressure from becoming much less than soil gas pressure.
• Effectively mitigate radon even in the many existing houses that lack permeable material or soil conduit under foundation slabs.
• Be economically practical for use in both new and existing houses.
• Effectively mitigate radon without requiring complete sealing of all openings between the surrounding soil and the interior of a house.
• Provide other benefits, in addition to radon mitigation, to make the system desirable and practical even in the tens of millions of American houses that now have radon levels below 4 pCi/L.
Entry of radon gas from the soil is mitigated by keeping indoor air pressure slightly higher than soil gas pressure.
The radon mitigation system described in this entry, is commonly referred to as a VFP system because it combines Ventilation, Filtration, and indoor air Pressure control. Fresh filtered air is continuously provided at a rate selected by the homeowner. Air leaks in the house are then sealed enough that the incoming fresh air can keep indoor air pressure slightly higher than soil gas pressure.
Use of indoor air pressure to minimize entry of radon was suggested in EPA’s “Radon Reduction Techniques for Detached Houses”, Page 153, Section 6.2, EPA/625/5-87/019. It stated that “If that part of the house which is in contact with the soil can be maintained at a pressure higher than the soil gas pressure, then soil gas cannot enter the house by convection. All gas flow through floor and slab openings will be clean house air flowing out, rather than soil gas flowing in.”
More than 20 homes and a few other buildings have VFP systems in operation. Radon levels were usually reduced by 50% to 90%.
In one house the radon level dropped very little because the installer put the fresh air intake under a large porch that was constructed over bare soil. The air intake is being moved to a much better location.
Monitoring and control of indoor air pressure relative to soil gas pressure is a major innovative feature of this system, and is covered by U.S. Patents (numbers 5,003,865 and 5,131,887) for a “Pressure controlled fresh air supply ventilation system, soil gas pressure as a reference, and method of use”.
To minimize radon entry, it is necessary to keep indoor air pressure only slightly higher than soil gas pressure. High indoor air pressure is unnecessary, costly to maintain, and likely to cause serious condensation problems in the walls and attic during cold weather. To accurately maintain just a slight indoor air pressure relative to soil gas pressure, there is no reliable substitute for actually measuring indoor air pressure relative to soil gas pressure. Automatic adjustment of the fresh air supply blower enables a slight indoor air pressure to be maintained in a reasonably tight building, in spite of wind effects, stack effects, and the use of air exhaust systems.
A VFP system can be assembled using common commercially available components (air pressure meter, blower, motor speed control, ducting, filters, etc.). Use of a variable-volume mechanical ventilation system is the most effective way prevent the ventilation rate from falling below a desired level and to provide any additional fresh air whenever needed to maintain indoor air pressure.
To improve control of indoor air pressure, most of the air leaks should be sealed so that only a small flow of fresh air needs to come in to create the slight indoor air pressure needed to minimize entry of radon from the soil.
Although fresh air supply systems are commonly used in commercial buildings, they are still rare in houses. Providing the minimum amount of fresh air recommended by the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) in standard #62-1989 “Ventilation for Acceptable Indoor Air Quality”, can maintain an adequate level of oxygen while helping to dilute and flush-out many indoor air pollutants, including radon and carbon dioxide.
Sealing air leaks to prevent drafts and improve energy efficiency:
Clear siliconized acrylic latex caulking to fill the small cracks
Weatherstripping for windows and doors
Expanding foam or aluminum duct tape to seal leak holes in the floor of the attic.
Automatic flue dampers to close chimneys during the off-cycle.
Ventilation options:
Fresh air duct between exterior and the cold air return of a ducted air circulation system
Fan and filter to provide fresh clean air during the air-conditioning season.
Balanced air-supply and exhaust fans to prevent excessive indoor air pressure during the heating season.
Energy recovery ventilator
Air Pressure Sensor
An air pressure sensor can help you to prevent problems with mold, carbon-monoxide poisoning, radon, etc. by manually adjusting air supply, exhaust, and circulation systems to keep indoor air pressures are within desirable ranges
VFP systems are being used in more than 20 houses. Radon reduction typically ranged from 50% in leaky houses to more than 90% in a tight house.
Short term (3 day) tests using charcoal canisters were used to measure radon levels before and after installation of VFP systems. Radon test kits were supplied and analyzed by organizations that passed EPA proficiency tests.
The first VFP system was installed in 1988, reducing indoor radon by more than 50% even though the indoor air pressure was kept no more than 1 Pascal (0.004” water column) above soil gas pressure.
The original goal in my 1,800 square foot home in Omaha, Nebraska was to reduce radon from the initial 24 pCi/L to less than 4 pCi/L. This goal was achieved early in 1989 after tightening the house and maintaining indoor air pressure at 2 Pascals (0.008” water column) relative to soil gas pressure. The final radon level was 1.7 pCi/L, a reduction of 93%. This is similar to results achieved by EPA scientists who reported reducing indoor radon levels by more than 90% in test homes by keeping indoor air pressure up to 4 Pascals (0.015” water column) greater than the surrounding soil gas pressure. (See “Radon Reduction Techniques for Detached Houses”, Page 154, EPA/625/5-87/019).
In 1990, a VFP system mitigated radon by 65% when used in a moderately tight single family home in Sutton, Nebraska. Radon measured 8.6 pCi/L before the VFP system was installed, and 3.0 pCi/L after the VFP system was in operation for more than two days.
Using soil gas pressure as a reference appears to be necessary for accurately and consistently maintaining indoor air pressure only slightly higher than soil gas pressure.
All homes need some ventilation, even homes with radon levels no higher than outdoor radon levels. While ventilation alone is not a cost-effective method for mitigating radon from the soil, the incoming fresh air does help to dilute and flush-out the radon released indoors from water and building materials.
The incoming fresh air also helps to minimize the concentrations of many other indoor air pollutants. Some Medical Doctors believe that air pollutants commonly found in houses are strong enough to damage the human immune system and thus enable the survival and growth of lung cancer that has been initiated by radon.
The American Lung Association says that improving indoor air quality could save Americans tens of billions of dollars each year by increasing worker productivity and by reducing medical costs related to indoor air pollution
The air in a typical house usually contains many pollutants in addition to radon. The American Lung Association cites studies showing that airborne pollutants account for about 80% of the pollutants absorbed by a typical person in the USA.
Further studies indicate that a typical American spends more than 80% of each year indoors. The American Lung Association cites studies showing that the air pollution in homes is often 10 to 20 times worse than outdoor air pollution, even in smoggy cities. Polluted outdoor air is not filtered as it leaks into most homes, and then other pollutants are added from sources in the homes.
At a 1991 meeting of the American Association of Radon Scientists and Technicians (AARST), Mr. Stephen D. Page, Acting Director of the EPA Radon Division, told attendees “The EPA is placing greater emphasis on development of methods to simultaneously mitigate many common indoor air pollutants at once, rather than trying to mitigate one-pollutant-at-a-time”. Simultaneous reduction of many indoor air pollutants is practical by simultaneous application of ventilation, filtration, and indoor air pressure control.
Filtration of incoming air is optional but recommended because it helps to minimize entry of allergens, irritants, toxic particles, insects and microbes. Toxic particles tend to remain longer in the lungs, damaging lung tissue and vital elements the immune system.
Particles come from many sources and the EPA considers microscopic particles to be particularly troublesome because they can remain airborne for many miles and then flow into the deepest parts of lungs. The burning of coal releases microscopic particles that commonly contain mercury, arsenic, lead, and some radioactivity.
The American Lung Association estimates that about 60,000 Americans die prematurely each year from exposure to inhaled particles that damage their lungs.
The American Lung Association estimates that about 120,000 Americans die prematurely each year from exposure to inhaled particles that damage their cardiovascular systms.
Filtration of recirculating air helps to remove particles and microbes that either originate indoors or get carried in by people and pets.
Substantial reductions in the amount of energy required for heating and air conditioning have occurred in homes after installation of VFP systems followed by sealing leaks to minimize excessive air leakage.
After installing a VFP system, and sealing many air leaks four years ago, the heating costs in my house in Omaha have averaged about $200 per year. The minimum ventilation rate was raised to about 35% of an air change per hour. Total area of heated floor space is 1,800 square feet. All walls have 3.5” of fiberglass insulation. The natural gas furnace is rated at 90% efficiency. Omaha typically has 6,400 heating degree-days per winter.
In “The Inside Story. A Guide to Indoor Air Quality” (September 1988, EPA/400/1-88/004), the EPA reported that most American houses have uncontrolled leakage that varies wildly from one day to another, but on-the-average have 70% to 100% of an air change per hour. This “natural” air leakage averages 100% to 200% more than the 35% of an air change per hour recommended for homes by ASHRAE Standard #62-1989 “Ventilation for Acceptable Indoor Air Quality”.
In Nebraska, for each 1,000 square feet of floor space heated with natural gas, the typical savings from cutting the average ventilation rate from 70% of an air change per hour down to 35% would be $41 per winter. Potential savings are even greater, because most houses average more than 70% of an air change per hour during the winter. Air leakage due to thermal buoyancy increases as outdoor temperatures fall. Air leakage due to the wind is usually higher during the winter because wind speeds tend to be higher during the winter months.
The actual amount of fresh air needed to protect health varies according to the kinds and quantities of indoor air pollutants. ASHRAE recommends cleaning the air to protect health and to minimize the amount of fresh air needed to protect health.
Comfort has been improved by tightening the shells of homes to minimize excessive air leakage and by enabling users to bring in the fresh air they want in ways that do not produce uncomfortable drafts.
Recent research indicates that about 6% of houses in the USA may have high levels of radon. The other 94% account for about 70% of the radon inhaled in houses. If radon damage is proportional to radon dosage, even below 4 pCi/L, then it is very important to find practical methods for mitigation of radon in all houses that have radon, even in houses that average less than 4 pCi/L.
One way to inexpensively mitigate radon, and also mitigate other indoor air pollutants is to use existing air circulation equipment and a fresh-air intake, to prevent indoor air pressure from becoming less than the pressure of gasses under the lowest floors.
The original goal, in 1987, was to prevent indoor air pressure from becoming low enough to cause backdrafting “reverse flow” of chimneys. Accurate control of indoor air pressure required a steady and relevant reference pressure. Using outdoor air pressure as a reference failed because winds often caused highly variable pressure fluctuations around buildings. Success came when I drilled a hole through the basement floor and found that the soil gas pressure was very steady because it was highly shielded from the wind. Soil gas pressure is obviously useful as a reference pressure for anybody who seeks to precisely control indoor air pressure relative to soil gas pressure. Soil gas pressure under a building results when the flow of radon and other gasses from the soil is obstructed by a building. The resulting “soil gas pressure” is only slightly higher than atmospheric pressure, and thus can be used to control indoor air pressure relative to outdoor air pressure.
The incoming fresh air not only helps to prevent low indoor air pressure and block entry of radon from the soil, but also helps to flush-out radon released indoors from water and building materials.
Raising the minimum ventilation rate, to one users are comfortable with, helps to preventing dangerous concentrations of carbon dioxide and many of the other colorless, odorless, and dangerous pollutants commonly found in houses.
A minimum system consists of a fresh air supply system and a simple air pressure sensor to enable users to monitor and manually adjust indoor air pressure. The process can be automated.
Some homeowners, that had low radon levels, have installed VFP systems to gain the many benefits it provides in addition to radon mitigation. Users report having improved comfort, reduced energy costs, better smelling indoor air, less dust on furniture, fewer allergy symptoms, etc.
The incoming fresh air and prevention of low indoor air pressure enables chimneys to operate safely. This is a major advantage over subslab depressurization systems that pull air from the interior of buildings and contribute to lowering indoor air pressure, thus increasing the probability of backdrafting “reverse flow” of chimneys.
The goal in each home is usually to achieve adequate radon mitigation and to minimize energy requirements. By using soil gas pressure as a reference, the indoor air pressure can be accurately maintained at the minimum level needed to achieve the desired amount of radon mitigation.
Some existing houses are already tight. Most of the other existing houses and other buildings can be tightened enough to allow the VFP system to maintain the slight indoor air pressure needed to effectively mitigate radon.
In houses that cannot be adequately sealed from either the interior or exterior, some radon mitigation during the winter can be achieved by bringing in enough fresh air to keep indoor air pressure equal to soil gas pressure.
During construction, it is relatively easy and economical to seal air leaks with gaskets and other materials so the VFP system can very easily minimize the entry of radon and many other pollutants.
When properly applied, a VFP system can make a home cleaner, quieter, healthier, more comfortable, and less expensive to operate than typical existing homes that are primarily ventilated by wind-driven leakage of unfiltered air through many leaks that are open 24 hours a day, every day of the year.
Many houses are either too difficult, or too expensive, to adequately seal from the inside. On the other hand, sealing air leaks on the outside is often simple and economical. If a house can be only be tightly sealed from the exterior, then fresh air can be blown in through the attic and down through leaks inside the outer walls during cold weather. This helps to keep the insulation dry, pre-warm the incoming fresh air, and it can recover significant amounts of heat during the heating season. A tight outer shell can enable indoor air pressure to be kept higher than soil gas pressure to minimize entry of radon from the soil.
Of course, during warm weather, fresh air should be brought in some other way to avoid preheating it.
When a house remains leaky, it is usually impossible to maintain even 0.5 Pascal (0.002” water column) relative to the soil, without bringing in more fresh air than the occupants desire during hot or cold weather. Air leaks in the shells of some existing houses are inaccessible from the interior. The VFP system seldom achieves radon reductions exceeding 50% in leaky houses, even when the minimum ventilation rate is raised to the cubic feet per minute of fresh air as recommended in ASHRAE Standard 62.2-2004 "Ventilation and Acceptable Indoor Air Quality in Low-Rise Residential Buildings".
In schools, hospitals, offices, factories and many other buildings, the indoor air pressure is normally higher than soil gas pressure because the amount of fresh air brought in is consistently greater then the amount of stale air being removed by exhaust systems. However, a ventilation system can malfunction and fail to keep indoor air pressure higher than soil gas pressure. Regularly measuring of indoor air pressure relative to soil gas pressure can provide a timely warning when the ventilation system needs to be fixed.
Soil gas pressure is a very steady and reliable reference pressure that is useful for preventing the backdrafting (reverse flow) of “natural draft” chimneys. Backdrafting of chimneys can fill rooms with smoke and potentially lethal gasses. Backdrafting usually occurs when indoor air pressure is lower than outdoor air pressure. Soil gas pressure under a typical building is higher than outdoor air pressure, so keeping indoor air pressure higher than soil gas pressure will also keep indoor air pressure higher than outdoor air pressure. Then the smoke will flow up the chimney instead of into your face.
