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Helpful? -1

Exhaust-Only Ventilation Systems and Radon

Do exhaust-only ventilation systems increase the risk of radon entry?

Posted on Feb 28 2014 by Martin Holladay, GBA Advisor

Articles on mechanical ventilation commonly warn builders that exhaust-only ventilationMechanical ventilation system in which one or more fans are used to exhaust air from a house and make-up air is supplied passively. Exhaust-only ventilation creates slight depressurization of the home; its impact on vented gas appliances should be considered. systems can pull radonColorless, odorless, short-lived radioactive gas that can seep into homes and result in lung cancer risk. Radon and its decay products emit cancer-causing alpha, beta, and gamma particles. into a house through foundation cracks. The warning makes intuitive sense: after all, an exhaust-only ventilation system works by depressurizing a house with respect to the outdoors, and it seems obvious that depressurizationSituation that occurs within a house when the indoor air pressure is lower than that outdoors. Exhaust fans, including bath and kitchen fans, or a clothes dryer can cause depressurization, and it may in turn cause back drafting as well as increased levels of radon within the home. could pull soil gases into a basement.

One thing I’ve learned over the years, however, is that just because an idea is intuitively obvious, doesn’t mean it’s true. Throughout history, many observers have speculated; far fewer have actually made measurements.

Defining an exhaust-only ventilation system

An exhaust-only ventilation system depends on one or more exhaust fans (usually bathroom exhaust fans) that either operate continuously or intermittently. This type of ventilation system is usually set up to ventilate a house at the rate recommended by ASHRAE 62.2A standard for residential mechanical ventilation systems established by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers. Among other requirements, the standard requires a home to have a mechanical ventilation system capable of ventilating at a rate of 1 cfm for every 100 square feet of occupiable space plus 7.5 cfm per occupant. — somewhere in the range of 50 to 100 cfm for most homes.

The air that is removed from a home by an exhaust fan is replaced by outdoor air entering the home through random cracks in the building envelopeExterior components of a house that provide protection from colder (and warmer) outdoor temperatures and precipitation; includes the house foundation, framed exterior walls, roof or ceiling, and insulation, and air sealing materials..

Examples of warnings

It isn’t hard to find authors who warn that exhaust-only ventilation systems can be dangerous. Here are some examples from the Web:

  • From Green Builder magazine (September 2009): “Because exhaust-only ventilation pulls air through the building envelope, this approach can bring contaminants from the garage, dust from attics, pesticides from the outdoors, mold spores, and even radon into the house.”
  • From NSERDA’s “Homeowner’s Guide to Ventilation”: “Exhaust-only ventilation is a good choice for homes that do not have existing ductwork to distribute heated or cooled air. However, if there is radon in the soil around the house, this method can increase indoor radon levels.”
  • From Chapter 9 of the Alaska Residential Building Manual: “Exhaust-only ventilation systems, because they depressurize the house, may increase the amount of radon that enters the living space.”
  • From a GBA blog by Alex Wilson: “A disadvantage [of exhaust-only ventilation] is that the negative pressure can pull in radon and other soil gases that we don’t want in houses.”
  • From an online article called “How to Green Your Home”: “Improper balancing or use of exhaust-only ventilation, without fresh-air make-up, can depressurize the house and draw in radon and other soil gases from outside.”

A radon primer

Radon is a naturally occurring radioactive gas that is present in some soils. It can enter a house through cracks in the building’s foundation.

Indoor radon levels can be tested; if long-term testing shows radon levels above 4 picocuries per liter, it’s a good idea to install a radon mitigation system. (For more information, see All About Radon.)

Most experts explain that radon gas is drawn into a house by the stack effectAlso referred to as the chimney effect, this is one of three primary forces that drives air leakage in buildings. When warm air is in a column (such as a building), its buoyancy pulls colder air in low in buildings as the buoyant air exerts pressure to escape out the top. The pressure of stack effect is proportional to the height of the column of air and the temperature difference between the air in the column and ambient air. Stack effect is much stronger in cold climates during the heating season than in hot climates during the cooling season.. The stack effectAlso referred to as the chimney effect, this is one of three primary forces that drives air leakage in buildings. When warm air is in a column (such as a building), its buoyancy pulls colder air in low in buildings as the buoyant air exerts pressure to escape out the top. The pressure of stack effect is proportional to the height of the column of air and the temperature difference between the air in the column and ambient air. Stack effect is much stronger in cold climates during the heating season than in hot climates during the cooling season. is a function of delta T — the difference between the indoor and outdoor temperature — so the effect is strongest during the winter. Indoor air escapes through ceiling cracks; as a result, the lower sections of a home become depressurized, and soil gases are pulled into the house.

Authors who warn about possible dangers from exhaust-only ventilation systems assume that, since exhaust fans depressurize a house, the fans probably increase the radon risk.

Are there any studies out there?

It turns out that a few researchers have measured radon levels in homes with exhaust-only ventilation systems. The most relevant research paper that I have found is a 2002 paper authored by two Alaskan researchers, Richard Seifert and Jack Schmid: “Exhaust Ventilation and Radon Induction in a Subarctic Climate.”

The researchers gathered data at eight Alaskan homes over a three-year period from 1998 to 2000. The range in airtightness for the eight homes was from 2.39 to 8.75 ach50. One of the homes, called the Goldstream house, had an exhaust-only ventilation system. The exhaust system depressurized the home to -7 Pascals, which is a significant level of depressurization.

To find out how the home’s exhaust ventilation system affected indoor radon levels, the researchers turned off the ventilation fan for five days. The researchers wrote, “Clearly the radon level goes up steadily, nearly doubling in the five days it is turned off. Although counterintuitive, it nonetheless appears that radon induction is reduced by the ventilation fan. One hypothesis is that … the net effect of the exhaust ventilation may also be dilution of the radon.”

The data refute intuitive assumptions

Intrigued by these researchers’ findings, I contacted Max Sherman, a senior scientist and ventilation expert at Lawrence Berkeley National Laboratory. Responding by e-mail, Sherman wrote, “I did do a modeling study some years ago: “Simplified Modeling for Infiltration and Radon Entry.” This study and the data you found [from the paper by Seifert and Schmid] refute the ‘common sense’ notion that radon will increase with exhaust ventilation. Usually radon concentrations go down with ventilation.

“The physics is not complicated. If you take a given house and add an exhaust fan, you will decrease the internal pressure. This will cause an increase in infiltration and it will also likely increase radon entry. So you get more entry but also more dilution. While one can construct pathological cases where radon concentrations could increase, it will almost always decrease as a result of this. It may not decrease as fast as other pollutants, but the concentration will decrease. All data I have seen bears this out, in general.

“To me this is not an interesting case. The interesting case is what happens when one tightens the envelope and adds exhaust ventilation as one might do with weatherization or other building retrofits. Here the outcome space is much richer because it depends on the starting conditions, whether the tightening changes the radon entry paths, etc.

“Scientifically the question is rich, but from a practical standpoint maybe one should not tighten and add exhaust ventilation when radon is a serious issue. Tightening and adding supply ventilation, for example, is essentially a built-in radon mitigation system because you are reducing radon entry while providing ventilation. We know there are other practical issues with supply ventilation depending on climate, but those may be worth tackling when radon is a consideration.”

Anecdotal evidence tends to support Sherman’s generalizations. One such anecdote was recounted to me by Dick Kornbluth, a radon mitigation contractor in Syracuse, New York. “I visited a retired engineer who had a house with a really high radon level,” Kornbluth told me. “He decided to do his own radon mitigation system. He installed ductwork in the basement that he connected to a fan blowing out through the band sill. The fan was depressurizing the basement — that was his system. I thought that would have raised his radon levels, but it lowered them. It turns out that he was was diluting the basement air, either with air from upstairs or with outdoor air entering the basement through cracks near the sill.”

How many Pascals of depressurization are created by the average exhaust fan?

The Alaskan researchers (Seifert and Schmid) reported that the exhaust ventilation system at the Goldstream house depressurized the house to -7 Pascals. This level of depressurization is higher than levels measured by other reseachers.

Relevant data were reported by Andy Shapiro, David Cawley, and Jeremy King, in a 2000 paper titled “A Field Study of Exhaust Only Ventilation System Performance In Residential New Construction in Vermont.” The researchers studied 43 homes with exhaust-only ventilation systems; the homes had an average airtightness of 4.45 ach50.

The Vermont researchers reported, “The pressures induced by fans in these tests, averaging in the range of -1 Pa, were low relative to pressures induced on a house by natural forces including wind and temperature driven stack effect. As a comparison, calculations of natural infiltration often use a seasonal average of 4 Pascals as the magnitude of these forces. These forces are about 4 times greater than the pressure effects created by the EOV [exhaust-only ventilation systems].”

Radon entry is all about the stack effect

The main driver of radon entry into a home is the stack effect, which is why radon concentrations tend to be higher in winter than in summer. (Another reason: occupants are more likely to open windows during the summer.)

In many homes, the stack effect has more of a depressurizing effect than the typical exhaust fan. Moreover, even when the depressurizing effect of a fan is strong, some of the air pulled into the house is fresh outdoor air that enters from above-grade cracks rather than soil gas entering through below-grade cracks. According to the best available data, the net effect of operating an exhaust-only ventilation system is, in most cases, a reduction rather than an increase in indoor radon levels.

That said, exceptions to this generalization undoubtedly exist. Our knowledge about the effects of exhaust-only ventilation systems on indoor radon levels would benefit from more research.

The bottom line: if you are worried about radon, perform a test. “If you want to install a continuous exhaust-only ventilation system, I would just say, monitor the radon levels,” Kornbluth said. “Radon may go up, or it may not go up. And I would also say, ‘Don’t do short-term testing.’ The problem with short-term testing is you might see a short-term spike and think you are going to die. Install an Alpha Track test kit for 6 months and don’t worry about it.”

Finally, if you are sealing a home's air leakage paths as part of a weatherization job, it's important to seal below-grade cracks as well as above-grade cracks. Recommended measures include caulking cracks in the slab; caulking penetrations through the slab; caulking the crack at the slab perimeter; and installing an airtight sump lid if the basement has a sump.

Martin Holladay’s previous blog: “What’s the Definition of an ‘R-20 Wall’?”

Click here to follow Martin Holladay on Twitter.


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1.
Fri, 02/28/2014 - 11:13

Edited Fri, 02/28/2014 - 11:18.

Kind of a one sided, smoke and mirrors issue ...
by flitch plate

Helpful? -2

If EOV's depressurise houses enough to suck in naturally occurring radon (Rn), so do H/ERV's. Simply balancing an H/ERV's in-flow and out-flow does not ensure nor create a zero delta between inside and outdoor house pressure (nor from one end of the house or from one story to the other). This issue is really a bit disingenuous, since H/ERV's only balance their own in and out flow, they do not balance the net house pressures.

It is even more disingenuous when this question is being asked about EOV's and ignored about the more powerful and ubiquitous heating, cooling, fresh air systems that do pose a risk to occupants from Rn exposure.

I agree with Martins final conclusion but the folks raising the red flags on this issue are neither considering the dynamics of all mechanical ventilation systems nor understating the environmental fate and human exposure dynamics of radiogenic materials

Most seem to think H/ERV systems somehow create the perfect controlled and regulated atmosphere. As Martin repeats like a mantra, the unintended leaks in almost all buildings render unnecessary, passive air inlets for natural balancing of EOV systems. These unintended leaks also compromise the claim to perfectly controlled interior atmospheres when the alleged "balanced ventilation" solution is used. As the Vermont study indicates: natural and structural pressure differentials over-match the EOV. They would also then over-match the H/ERV.

In general, one would prefer to land on the controlled as oppose to serendipitous side (i.e. willy-nilly make up air pathways vs planned properlly situated fresh air intake paths). Passive vents allow for pressure balancing throughout the envelope of both the EOV and the H/ERV's system – the H/ERV's do not respond to the multiple interior and exterior, vertical and dynamic pressure differentials throughout and surrounding the envelope. That is, if your concerned about negative pressures pulling in radioactive gasses and particulate. In fact, the very tight envelope, H/ERV ventilated system is likely to be out of balance with natural and structural forces more often than the EOV (whether depending on passive vents or fugitive ex/infiltration). That actually makes the H/ERV more dangerous for Rn entrainment than the EOV. That is what the Vermont study really tells us.

Naturally occurring Rn is naturally occurring, and a daughter product of the uranium (U)
decay chain. Instead of measuring for Rn after a house is built, the U and Rn levels in
the site soils should be pre-determined, so that mitigation and radiation protection are
inherent to the siting, basement design and ventilation strategy. If U is elevated, then Rn
and a lot of other radionuclides will also be elevated.

Rn is the only daughter of uranium that occurs in the form of a gas. That gas is heavier
than air. If anything is to be a concern, relatively, it is room to room and multi story
ducting (including basement vents, supplies and returns) of H/ERV's, forced air heating
and air conditioning systems. They have a much wider possibility of creating conditions
and variables for entraining and launching kinetically the heavier-than-air, radiogenic
gas through the house.

A gas is made up of particulate; it has mass and radioactive materials are
not dormant, they also emit particles into the atmosphere even when in a stable
environment. The daughter product of decaying Rn (polonium) will also be entrained
and distributed by the ventilation system. The more active the air, the more disturbance
of the source, the more the particulate/gas is inhaled.


2.
Fri, 02/28/2014 - 11:14

Radon
by gavin Healy

Helpful? 0

I have been testing with a continuous radon monitor for 8 months in my house to learn more about a variety of strategies for mitigating radon. The house is tight .58 ACH50. I have learned a lot by watching the radon levels under a variety of ventilation strategies. The levels go to 40 picocuries per liter without mitigation. The sub slab depressurization system easily reduces levels to an average of less than 1. The HRV on it's own doesn't reduce levels adequately. Exhaust only depressurization effects are evident with a 50 CFM Panasonic, and become very evident with 125 CFM of exhaust from the kitchen hood. (don't worry I am well aware of make up air as method to reduce this) I would like to re-afirm the need for additional study on this issue. If we start to focus on air tightness in new construction what is the threshold of tightness and or depressurization that should be considered for the topic. Those of us who have started to make tight homes get that it's pretty easy to get a new home to 1ACH50 and we often get existing homes to less than 3ACH50. Do our past investigations that study leakier homes indicate what we should do with tighter homes? Long term testing as Dick suggest provides a greater level of comfort for discerning the magnitude of the problem in an individual house. But if we want to learn about what the thresholds are more continuous testing is needed. I think that this threshold question is relevant to more that just radon. I would like to see further study on the impacts building tightness on range hood capture efficiency. Maybe in the future we will have a time dependent recommendation for acceptable depressurization levels. Is a laundry dryer (with exterior exhaust) in a tight house running for an hour acceptable. I am sure that we could all argue about things in the middle, but for those of you who have been testing depressurization levels in tight houses (less than 2ACH50) what insights do you have?


3.
Fri, 02/28/2014 - 11:35

Edited Fri, 03/21/2014 - 11:16.

Response to Flitch Plate
by Martin Holladay, GBA Advisor

Helpful? 0

Flitch,
The last time you used the pages of GBA to express the opinion that HRV and ERV systems aren't "balanced," you were preaching to the converted -- in the sense that anyone who takes a "house as a system" approach knows that you can't adjust one element of a building without potentially affecting other systems.

Building scientists (and most of the authors who write articles for GBA) understand that no house is airtight; all homes have infiltration and exfiltration; the entire point of conducting a blower-door test is to measure the rate of air leakage; and that forced air systems, exhaust fans, clothes dryers, and holes in the wall all interact and all affect whether the indoor air at any given location in a house is at a positive or negative pressure with respect to the outdoors.

We get that.

Still, it's useful to have a word to describe ventilation systems that simultaneously remove stale air from some rooms and supply fresh air to others. The conventional description for these systems (to distinguish them from exhaust-only or supply-only systems) is "balanced." I think it's a useful descriptor.

Although you don't like it, we're still going to use it here at GBA. The use of the term "balanced ventilation system" does not represent fraud, scamming, or a misunderstanding of pressure dynamics or building science. It is a standard term in the industry to describe a type of ventilation system.


4.
Fri, 02/28/2014 - 11:45

Edited Fri, 02/28/2014 - 12:01.

Response to Gavin Healy
by Martin Holladay, GBA Advisor

Helpful? 0

Gavin,
Thanks for your thoughtful comments. I agree that further research is always welcome. I look forward to more research, as well as more reports from GBA readers about their own measurements.

There have been several studies trying to see whether there is a correlation between the airtightness of homes and radon levels, as well as several studies to see whether radon levels go up or down after weatherization work is performed.

To the best of my knowledge, this is what researchers have found:

1. There is no correlation between airtightness and radon levels. A tight home can have high or low levels of radon. A leaky home can have high or low levels of radon. The only way to know the levels of radon in your home is to conduct a radon test.

2. Weatherization work has no consistent affect on radon levels. Tightening a house sometimes raises radon levels, and sometimes lowers radon levels. The only way to know the levels of radon in your home is to conduct a radon test.

Building science principles can help us make sense of these findings. Radon enters a home through foundation cracks, and the most important driving force for radon entry is the stack effect. Sealing cracks in the foundation tends to lower the rate at which radon can enter a house. Reducing the stack effect tends to lower the rate at which radon enters a house. Infiltration through above-grade cracks tends to dilute indoor radon levels. Ventilation systems that pull more fresh air into a house from above-grade cracks or vents tend to dilute indoor radon levels. Exhaust ventilation systems can increase the rate at which radon enters a home while simultaneously pulling in fresh outdoor air to dilute indoor radon levels. All of these factors interact.


5.
Fri, 02/28/2014 - 14:29

H/ERV's are more likely to entrain radionuclides than EOV
by flitch plate

Helpful? 1

Interesting that you ignore the most important point: H/ERV's are more likely to entrain radionuclides than EOV's. That is, if you're concerned about negative pressures pulling and redistributing radioactive gasses and particulate.

In the very tight-envelope, H/ERV ventilated system, there is likely to be more air disturbance than the EOV in an equally as tight a system (whether depending on passive vents or fugitive ex/infiltration to equalize pressures).

Rn is the only daughter of uranium that occurs in the form of a gas. That gas is heavier than air. Room to room and multi story ducting (including basement vents, supplies and returns) has a much wider possibility of creating conditions and variables for entraining and launching kinetically, the heavier-than-air, radiogenic gas through the house.

The more active the air, the more disturbance of the source, the more the particulate/gas is put into the human breathing zone. Inhalation being the primary pathway for biological assault by Rn.


6.
Fri, 02/28/2014 - 14:31

Interesting
by Gavin Farrell

Helpful? -1

Fascinating article Martin. So to me it seems the off-gassing from soils of radon may have nothing (or very little) to do with air pressure difference between the house and the outdoors or between the attic and the basement, and alot more to do with the barrier between the house interior space and the soil. The soil may just have a natural concentration and off-gas it at a certain rate regardless of the relatively small pressure differences above. It is not as if exhaust-only vents are sucking air directly out of the soil under the basement and bringing the deadly gas with it, the new air is making its way into the house from the outdoors somehow.

So, a highly sealed house with an open soil basement would be the worst case. Testing concentration levels between an exhaust only system versus a system that supplies some fresh air would be the way to determine what is going on. My armchair scientist hypothesis is that either system would be equally effective if they are exhausting the same air volume (so long as the house allows enough infiltration for the exhaust only system to function properly).


7.
Fri, 02/28/2014 - 14:59

Edited Fri, 03/21/2014 - 11:16.

Second response to Flitch Plate
by Martin Holladay, GBA Advisor

Helpful? 0

Flitch,
One of the points I tried to make in my article is that speculation is less interesting than data.

If you can refer to a study that supports your hypothesis that homes with HRVs are more likely to have high radon levels than homes with exhaust-only ventilation systems, please provide a link or a reference so I can read the data.

Absent such a paper, or some type of data to support your hypothesis, I'm skeptical.


8.
Fri, 02/28/2014 - 15:21

Response to Gavin Farrell
by Martin Holladay, GBA Advisor

Helpful? -1

Gavin,
You wrote, "So to me it seems the off-gassing from soils of radon may have nothing (or very little) to do with air pressure difference between the house and the outdoors or between the attic and the basement, and a lot more to do with the barrier between the house interior space and the soil. The soil may just have a natural concentration and off-gas it at a certain rate regardless of the relatively small pressure differences above."

A. You may be overstating the case somewhat. There are many factors at work; as "house as a system" seminars have taught us, all of the factors interact. If the basement is depressurized -- for whatever reason -- then more soil gas will be pulled through the existing cracks. Basement slabs with wide cracks obviously allow soil gases to enter the home at a faster rate than basement slabs with few cracks. And homes with lots of fresh air to dilute the radon are likely to have lower radon levels, all other factors being equal, than homes without any ventilation or with little above-grade infiltration.


9.
Fri, 02/28/2014 - 16:43

Simple is key
by aj builder, Upstate NY Zone 6a

Helpful? -2

Anyone who worries about radon. should simply install underslab radon mitigation. No further testing, and forget everything this blog is which is basically making a simple problem-solution into an unknown unending to be brought up again monster.

Simple is key. If radon, then underslab mitigation, not "lets debate 8 million unrelated cause and effects till the internet bandwidth is gone."

Speaking of proof... prove that my statement is wrong.


10.
Fri, 02/28/2014 - 16:52

Radon kills?
by aj builder, Upstate NY Zone 6a

Helpful? 0

OK, so a home has high radon and four living there. All four die of lung cancer I would assume since radon kills.

I have searched the internet for a news story or study showing that a house full of non smoking non mine workers have died and at the autopsy radon was found in the lung tissues.

Eggs used to be bad, now milk is of late thought to be totally not needed in a diet. Eggs are good now sort of.

Show me facts that show me a person directly linked to dieing from radon. One person. I have watched people die of lung disease that smoked like chimneys... I believe. Show me some radon facts that are not "studies." Tissue samples, dead folks and follow up checks of their homes finding high radon levels.

I need easy logical bullets, bullet holes, and dead folks stories.


11.
Fri, 02/28/2014 - 16:54

Edited Fri, 02/28/2014 - 16:59.

Response to AJ's comment, "Simple is key"
by Martin Holladay, GBA Advisor

Helpful? 0

AJ,
As I wrote in my earlier article, All About Radon, builders of new homes should include a passive radon mitigation system in all new homes, and, if long-term testing shows that the house has radon levels over 4 picocuries per liter, the passive system should be turned into an active system by adding a fan.

So my advice in that article is similar to yours. (You wrote, "Anyone who worries about radon should simply install underslab radon mitigation.")

The article on this page provides advice to owners of existing homes. Moreover, it provides a useful perspective to builders of new homes who wonder whether exhaust ventilation systems are dangerous.

Of course, AJ, you are free to "forget everything in this blog" if you want to.


12.
Fri, 02/28/2014 - 20:11

Selling
by aj builder, Upstate NY Zone 6a

Helpful? -1

Martin, you are selling words.

I am a person driven by logic and simplicity. Done.


13.
Fri, 02/28/2014 - 22:44

Edited Fri, 02/28/2014 - 22:47.

when in doubt, insult the post, ignore the logic
by flitch plate

Helpful? 0

Can one only have an opinion if one has a study behind it? You're not listening, only trying to be right.

Entrainment of radioactive particulate and Radon (Rn) gas is a function of (1) humidity and electrostatic charging which makes airborne radionuclides move and concentrate, (2) the kinetics of the radiation itself (Rn emits A, B and G particles as it decays), (3) and mechanical forces like air disturbances.

Tell me why stack effect and natural pressure features (i.e. strong winds, prevailing winds, negative downwind, positive upwind, humidity and temperature) over-match EOV’s but not H/ERV’s? (Rhetorical question … no need to answer)

Leaky envelopes ex/infiltrate fugitive unconditioned air. Why is that not an issue with H/ERV’s but it is with EOV solutions? (Rhetorical question … no need to answer)

The Vermont study indicates the negative pressure of an EOV system is not sufficient to entrain and distribute Rn.

Rn already flows inwards due to negative air pressure in basements. The issue really is (1) do relative increases in negative pressure bring in more Rn and (2) does ventilation makes the Rn more bioavailable.

The oft repeated advantage to H/ERV’s systems is their better distribution of fresh air and better purging of stale air, wider area and multiple room and levels distribution, more effective air-exchange.

Air handlers and H/ERV’s are operating in basements; pulling fugitive outside air through basement walls, spaces along sills; etc. This is particularly true with forced air heating … often with connected fresh air make up and H/ERV’s.

H/ERV’s are set for “balanced” supply and return volumes, so how can the convert the natural negative pressures in basements to a positive condition, relative to the outdoor and above the
NPP? How can H/ERV’s create a positive pressure condition on the lateral regions, back slope and leeward of a building with steady prevailing winds and or solar driven ground level airflow? (Please answer this).

So why would there be a default assumption that EOV ventilation is a threat to health due to Rn entrainment? Whereas “balanced ventilation” H/ERV’s are not even considered implicated when they also share negative pressure basements, differential negative pressure zones throughout the envelope, leaky envelopes, and natural dynamic pressure changing forces?

Distributed “balanced ventilation” H/ERV’s disturbs more air and therefore entrains more particulate (i.e. Radon and Radon daughters) than EOV’s. That has to be true or all this sites repeated advocacy of H/ERV’s has faulty logic. Disturbed air entrains particulate and entrained particulate is bioavailable (i.e can be inhaled).

More interesting would be to measure the electrostatic charging of the air that passes air handlers, fans and hardware – whether H/ ERV’s, furnaces or bath and kitchen EOV fans.


14.
Sat, 03/01/2014 - 00:15

Response to aj and fitch
by Donald Endsley

Helpful? 0

Aj, tissue samples would likely not show what you are looking for, as the half life of radon is short enough at 3.8 days that it will not show long term exposure. The studies and medical consensus are the best evidence you are likely to get. The risk is 1.5% (iirc, from nursing school) chance of getting lung cancer for a non smoker living with elevated radon levels.

Fitch, I fail to see how an h/erv would be worse than eov. They are both moving a similar amount of air through the structure, both diluting a similar amount. A h/erv also is not disturbing the source of the gas, so I fail to see how increasing air movement in the house will lead to long term exposure increases.


15.
Sat, 03/01/2014 - 06:45

Edited Fri, 03/21/2014 - 11:17.

Response to Flitch Plate
by Martin Holladay, GBA Advisor

Helpful? -1

Flitch,
Q. "Tell me why stack effect and natural pressure features (i.e. strong winds, prevailing winds, negative downwind, positive upwind, humidity and temperature) over-match EOV’s but not H/ERV’s?"

A. Both the stack effect and an exhaust fan can depressurize certain areas of a house with respect to the outdoors. It's also possible for an unbalanced HVAC system to depressurize certain areas of a house. Conceivable, a badly installed HRV could also contribute to depressurization, but I have never heard of such a case, nor have I read a research report describing an HRV system that contributes significantly to depressurization. Since the commissioning process for an HRV tries to balance the supply airflow with the exhaust airflow, the main depressurizing appliances in a house with an HRV are likely to be the range hood fan, the clothes dryer, and (if it exists) an unbalanced forced-air heating system.

Q. "Leaky envelopes ex/infiltrate fugitive unconditioned air. Why is that not an issue with H/ERV’s but it is with EOV solutions?"

A. Leaky envelopes contribute to the stack effect in both types of houses, as I explained in my first answer. The stack effect tends to depressurize the lower sections of a house with respect to the outdoors. An exhaust-only ventilation system additionally contributes to depressurization, on the order of about -1 Pascal to perhaps -7 Pascals. Most HRVs do not contribute to depressurization.

Q. "How can H/ERV’s create a positive pressure condition on the lateral regions, back slope and leeward of a building with steady prevailing winds and or solar driven ground level airflow?"

A. At no point have I claimed that they could. To the extent that a house has infiltration due to wind, the infiltration will dilute any radon in the house. Infiltration tends to lower radon levels, whether the infiltration occurs in a house with an HRV or in a house with an exhaust-only ventilation system. If, in addition to having a leaky envelope that allows for a lot of wind-driven infiltration, a house also has an HRV, both of these sources of outdoor air -- the infiltration air and the fresh air introduced by the HRV -- will tend to lower indoor radon levels.

Q. "Why would there be a default assumption that EOV ventilation is a threat to health due to Rn entrainment?"

A. I never asserted that exhaust-only ventilation is a threat to health. In fact, my article supplies evidence that it is not. I quote from some sources (articles on the web) that imply that exhaust-only ventilation may increase indoor radon levels. I don't know the reasoning behind those statements, although I provide some speculations on the issue in my article. Then I go on to refute the assertion that exhaust-only ventilation may be a threat to health.

Q. "Why aren't 'balanced ventilation' H/ERV’s even considered implicated when they also share negative pressure basements, differential negative pressure zones throughout the envelope, leaky envelopes, and natural dynamic pressure changing forces?"

A. The factors you describe -- negative pressure basements, differential negative pressure zones throughout the envelope, leaky envelopes, and natural dynamic pressure changing forces -- are present in all houses to some degree. Since the factors are present whether or not the house has an HRV, I don't see why there is any reason to assert that HRVs are "implicated." (Implicated in what?) Researchers have not found any correlation between the leakiness of a home's envelope the home's indoor radon levels.


16.
Sat, 03/01/2014 - 09:10

Radon kills
by John Crocker

Helpful? -1

AJ Builder,

Based on large scale studies, radon exposure clearly does kill plenty of people via lung cancer, just many years after their exposure....so there is no easy-to-see smoking gun or cancer cluster.

Interestingly, the same studies show that radon + smoking is much worse than either one alone. A smoker living in a high radon house has a much higher risk of getting lung cancer than a smoker who doesn't. So only looking for suspicious cases of lung cancers among non-smokers would miss an important point—Many of the folks being killed by radon are current or former smokers.


17.
Sat, 03/01/2014 - 09:20

Foundation, slab cracks
by Derek Roff

Helpful? 0

Thanks for an interesting and informative blog, Martin. You mentioned radon entering the house through cracks in the foundation several times, and through cracks in a basement slab once. I'd like to understand those mechanisms more fully. Are you making a distinction between the two, or are these terms being used as synonyms? If they are listed as distinct mechanisms, I am curious about what the research shows, regarding the magnitude of radon entering the building from under the building, that is, vertical movement of radon from below the house's footprint, vs. horizontal movement through the foundation walls/cracks from outside the footprint. Does the research offer distinctions on this point?

My understanding of the standard radon mitigation strategies is that they primarily attempt to interrupt the vertical movement of radon from below the house, within the footprint. Existence or absence of a basement wouldn't make a big difference in the area (square footage) involved in the vertical movement. Any horizontal migration of radon through the vertical walls of the foundation would seem likely to be affected by the greater area of the higher walls of a basement, compared to a slab on grade. I would expect vented and unvented crawl spaces to have different radon profiles, even when built in identical soil. Does the available research provide interesting information on these variations?


18.
Sat, 03/01/2014 - 11:03

Response to Derek Roff
by Martin Holladay, GBA Advisor

Helpful? -1

Derek,
As far as I know. radon can be a component of the soil gas that is found under a basement or crawl space slab, and it can also be a component of the soil gas that is found on the exterior side of a basement wall or a crawl space wall. If the basement wall or the crawl space wall has cracks, then radon can enter the home through those cracks, just as it can enter through slab cracks.

That's why, if a foundation wall (especially a CMU wall) is in bad shape, a radon mitigation contractor may recommend that the wall should be parged or otherwise sealed. Wall cracks can also be caulked.


19.
Wed, 03/05/2014 - 19:57

Continuous EOV can increase Rn level
by Mark Heizer

Helpful? 0

Look for an upcoming study from NEEA on this issue. They found that a 24/7 EOV system raised the Rn level by 50% over an intermittent (8-hr per day) vent system.

The logic is pretty simple for a vented crawlspace home. The constant EOV increases leakage from the crawlspace into the building (regardless of air sealing of the building). It may not be much, but every CFM of infiltration from below equals reduced CFM cross-ventilation of the crawlspace, possibly to the point of no cross ventilation. Reduce the cross ventilation and you've increased the Rn concentration level in the crawlspace. So the concentration per CFM entering the home can be dramatically higher. In their study, it seems the incoming concentration exceeds the "dilution" capacity per CFM of the EOV fan.


20.
Thu, 03/06/2014 - 05:11

Response to Mark Heizer
by Martin Holladay, GBA Advisor

Helpful? 0

Mark,
Thanks for your comments; I certainly look forward to reviewing the data in the study you describe. The house you describe sounds like the "pathological case" envisioned by Max Sherman.

There are several variables here, including (1) the type of foundation, (2) radon levels in the lowest level of the house, (3) the tightness of the floor assembly that separates the house from the vented crawl space, and (4) the tightness of the home's above-grade walls and ceiling assembly.

In order for an exhaust-only ventilation system to raise indoor levels, you need several factors to be aligned -- as they apparently were in the case you describe.

First of all, most building experts don't recommend venting crawl spaces. But we all know that vented crawl spaces exist.

Second, not all vented crawl spaces have elevated radon levels. But some do.

If these conditions exist, you would certainly want to seal leaks in your floor assembly. But in the case you describe, the floor assembly was probably leaky.

If you operate an exhaust fan in this type of house, you want most of your makeup air to come from above-grade cracks. If that's the case, the exhaust fan is likely to lower indoor radon levels. But if your house has very tight walls, a very tight ceiling, and a leaky floor assembly, you have the worst case scenario.


21.
Thu, 03/06/2014 - 11:47

Response to Martin
by Mark Heizer

Helpful? 0

"There are several variables here, including (1) the type of foundation, (2) radon levels in the lowest level of the house, (3) the tightness of the floor assembly that separates the house from the vented crawl space, and (4) the tightness of the home's above-grade walls and ceiling assembly"

First some background: in the Northwest, vented crawlspace is still the norm and still are common in existing homes in the rest of the country. The tigntness of the assembly will not matter: air gets in through every crack. You're implying home sealing will control where the air enters the home: that isn't ever going to happen and there are plenty of studies to back this up. But there is one known factor: as another commenter noted, stack effect is one of the strongest drivers of infiltration/exfiltration: If most air is leaving the home at ceiling/roof line, where is the incoming air source? The sides and floor (whether slab on grade or even unveted crawlspace). Where is that radon source? Not the roof. Even in an unvented crawlspace, the EOV will reduce the level of negative pressure between the occupied space and the crawlspace (I sure hope noone is recirculating this air if you're in radon country). This increases the odds of Rn into the home.

EOVs are worthless for providing "fresh air" where you need it (debatable 'dilution' of contaminants), contribute to uncontrolled infiltration, can exacerbate combustion air problems we're already seeing in tight homes (not the cause, just contribute to the problem), and cause unnecessary energy use. So do I really want to increase my odds of radon infiltration as well? I think it's time for Mr Sherman to show the benefits (if any) of the EOV outweigh the negatives.


22.
Thu, 03/06/2014 - 17:17

Edited Thu, 03/06/2014 - 17:21.

Response to Mark Heizer
by Martin Holladay, GBA Advisor

Helpful? 0

Mark,
You wrote, "You're implying home sealing will control where the air enters the home: that isn't ever going to happen and there are plenty of studies to back this up."

I never said that. But if you are performing air leaking work on a house with an exhaust-only ventilation system, it's clearly useful to pay attention to sealing cracks in the floor assembly (or, if the house has a basement, to sealing below-grade cracks). These efforts are a standard part of any radon mitigation job; it's not rocket science, and weatherization workers are familiar with the routine.

The worst-case scenario would be to concentrate on sealing above-grade cracks while ignoring below-grade cracks. Common sense will tell you that such a weatherization approach would be ill-advised.

Most old homes are leaky, and, try as you might, you won't be able to seal up all above-grade cracks with your weatherization efforts. I feel safe in reporting that if you install an exhaust fan in the 50 cfm to 100 cfm range, most of the makeup air in the average home is going to come from above-grade cracks, and this makeup air is likely to dilute any radon in the house. Researchers' data support that generalization.

If there is a case study of a house that doesn't fall under these general rules, I'm not surprised. But I'd like to read it in a published paper or article to know more details about the house construction.

I'll repeat my overall recommendation concerning radon: It's a good idea to test your house for radon. If your radon levels are consistently above 4 picocuries per liter, call a radon mitigation contractor.


23.
Thu, 03/06/2014 - 20:42

can't find what you don't look for
by flitch plate

Helpful? 0

Martin ... you make my point by missing it. The objective of the study is to discredit EOV, not make a credible analysis of particulate entrainment by common ventilation systems. You are a little obsessed with having to have a study when logic tells us that the more turbulence and flow, the more entertainment. That's pretty simple.

Your blogs set the politic of this site, indicated by your tendency to downplay passive and green solutions in favor of higher technology and active (energy expensive) solutions. So you do not recognize the weakness in the very study you’re critiquing. You accept the content without examining the design of the experiment and more importantly the politic of its authors. Don’t get me wrong, you’re a bright guy with good knowledge in this field. I have learned from you. But you have your blinders (as we all do). Understanding ‘group think” provides into the FHF/GBA mind set.

Back to the study: (as reported in the blog) it is inherently misleading to create the impression that only EVO house basements are negatively pressurized whereas E/HRV houses are somehow magically positively pressurized. And nowhere do the authors (based on your report) understand the basics, so their research is not only one sided (i.e EOV only) but also incorrect designed (i.e the vectors by which radon are brought into the environment and pathways of bio-uptake by humans).

This by the way is floating around the same commercial promotional spin that refers to E/HRV ventilation as “balanced”, it is not, it’s neutral.


24.
Thu, 03/06/2014 - 20:50

Edited Fri, 03/21/2014 - 11:17.

Response to Flitch Plate
by Martin Holladay, GBA Advisor

Helpful? 0

Flitch,
Your references are mysterious. You refer repeatedly to "the study." Which study? Are you talking about the study by Richard Seifert and Jack Schmid?

You wrote, "It is inherently misleading to create the impression that only EVO house basements are negatively pressurized whereas E/HRV houses are somehow magically positively pressurized." I have no idea what I wrote that you are responding to.

Due to the stack effect, almost all basements are at a negative pressure with respect to the outdoors, at least during cold weather, due to the stack effect. This fact is independent of your choice of ventilation system; it's even true if you have no ventilation system. So I never ascribed any magic to ERVs and HRVs.

You also misunderstand me if you think that the purpose of this blog is to praise and promote complicated, expensive ventilation systems that include an HRV. On the contrary; this blog can be interpreted as a defense of simple, inexpensive ventilation systems.


25.
Sat, 03/08/2014 - 09:03

Research to the rescue
by flitch plate

Helpful? 0

Research to the rescue …

Martin … this Finish study shows mechanical ventilation concentrates indoors radon and moves it largely via convection.

My point remains: Why would there be a specific accusing of EOV, while ignoring other types of mechanical ventilation, which I maintain shows a distinct bias for H/ERV, by selectively ignoring of the pressure phenomena that entrain contaminants.
It takes us full circle on the issue we disagreed upon before. When “balanced ventilation” is nothing more than equalized supply and exhaust air volumes, building pressures are not balanced. H/ERV’s could be used to approximate balanced interior pressures but are not. Therefore it is misleading not only to refer to H/ERV systems as balanced ventilation (I suggest its technology bias and marketing misinformation), it is also disingenuous to single out EOV ventilation as the cause of radon exposure when the same pressure, turbulence and convection dynamics are also present with H/ERV.
Here are quotes from study/analysis
Intro
“Elevated radon concentrations in indoor air are normally caused by the convective low of radon bearing soil air. Convective flows are created when pressure differences force the sub-foundation soil air to flow into indoor spaces through gaps, cracks and openings in the foundation.”

Conclusion
“In airtight houses balancing ventilation makes it possible to control the pressure differences. The use of mechanical exhaust ventilation (MEV) results in high pressure differences. Simple basic calculations, modeling estimates and measurements in air tight apartments and houses with passive construction show the potential for high pressure differences and for subsequent elevated indoor radon concentrations also RADPAR WP6, D13/6: Review of Low Energy Construction, Pressure conditions and Indoor Radon in Finnish in houses with balanced ventilation.”

Review of Low Energy Construction, Pressure Conditions and Indoor Radon in Finnish Residential
Buildings, HANNU ARVELA, OLLI HOLMGREN AND HEIKKI REISBACKA RADIATION AND NUCLEAR SAFETY AUTHORITY (STUK) – FINLAND, 2012
http://rpd.oxfordjournals.org/content/early/2013/11/14/rpd.nct278.abstract


26.
Sat, 03/08/2014 - 15:54

Edited Fri, 03/21/2014 - 11:18.

Response to Flitch Plate
by Martin Holladay, GBA Advisor

Helpful? 0

Flitch,
Thanks for pointing out the research paper; it's interesting. (After a little detective work, I tracked down the paper online; if other GBA readers are interested in reading it, here is a link: "Review of Low Energy Construction, Pressure Conditions and Indoor Radon in Finnish Residential Buildings.")

I haven't had a chance to read the paper in depth yet. The most interesting finding -- one that apparently contradicts U.S. studies -- is the Finnish finding that there is a correlation between tight houses and high indoor radon levels.

While it appears that the Finnish researchers found that Finnish homes with HRVs have a lower level of indoor radon than Finnish homes with exhaust-only ventilation systems, I don't think that they are asserting that exhaust-only ventilation systems actually raise indoor radon levels.

The two quotes you have chosen to share do not appear to contradict what I have written; nor do they support your apparent prejudice against HRVs. I will comment on the quotes in brackets.

“Elevated radon concentrations in indoor air are normally caused by the convective flow of radon bearing soil air [presumably, driven by the stack effect]. Convective flows are created when pressure differences force the sub-foundation soil air to flow into indoor spaces through gaps, cracks and openings in the foundation [as I have written].”

“In airtight houses balancing ventilation makes it possible to control the pressure differences. [I'm not sure what the researchers mean by this, but this quote appears to contradict your point, Flitch.] The use of mechanical exhaust ventilation (MEV) results in high pressure differences. Simple basic calculations, modeling estimates and measurements in air tight apartments and houses with passive construction show the potential for high pressure differences and for subsequent elevated indoor radon concentrations also in houses with balanced ventilation. [In other words, the stack effect occurs in all houses -- houses with exhaust-only ventilation systems as well as houses with HRVs.]"


27.
Sat, 03/08/2014 - 16:00

Edited Fri, 03/21/2014 - 11:19.

One more response to Flitch Plate
by Martin Holladay, GBA Advisor

Helpful? 0

Flitch,
I forgot to respond to one of your comments. You wrote, "It is also disingenuous to single out EOV [exhaust-only ventilation] ventilation as the cause of radon exposure when the same pressure, turbulence and convection dynamics are also present with H/ERV."

I don't know why you think that I am singling out exhaust-only ventilation systems. My article is an attempt to refute the singling out performed by other people. I provide evidence that in most cases, exhaust-only systems lower rather than raise indoor radon levels. If it is your intent to defend the performance of exhaust-only ventilation systems, then perhaps we agree.


28.
Fri, 03/21/2014 - 11:11

Independent of radon,
by Jon R

Helpful? 0

Independent of radon, pressure balance matters. For example, you don't want to be pulling warm, humid air into the walls all summer. And tight homes do need H/ERVs.


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