I've included a link below to EPA's "A Citizen's Guide to Radon," which covers the subject in plain language. The 4 pCi/L number is an "action level," a guideline: it doesn't mean that above that level you will get cancer and below it you will be safe. It's good you are investigating this, but don't freak out. Let me quote from this guide:
The average indoor radon level is estimated to be about 1.3 pCi/L, and
about 0.4 pCi/L of radon is normally found in the outside air. The U.S.
Congress has set a long-term goal that indoor radon levels be no more
than outdoor levels. While this goal is not yet technologically
achievable in all cases, most homes today can be reduced to 2 pCi/L or below.

Risk is a relative thing: it's all around us in varying degrees, but people want to think they can reduce it to zero, and that is usually not possible. Even if all you were exposed to was the existing outdoor radon level of 0.4 pCi/L, there is still a lifetime risk of 3 in a 1000 of getting lung cancer. In comparison, your lifetime risk of being killed in a car accident is about 12 in a 1000; dying from flu, 16 in a 1000; or dying from a fall, 5 in a 1000. If you are exposed to higher levels of radon, your risk will rise. If you are a smoker, the combined risk of smoking and radon exposure is really high.

It sounds like the local environmental health guy gave you basically correct info, and you are probably at low risk given how your home is constructed. While radon is present in well water, it poses a much lower risk. However, the first thing you need to do is test to see if you even have a problem. Then worry about mitigation measures if any are necessary. Above all, inform yourself, understand that none of us has zero risk from radon, and make a reasoned decision after you get results back.

A Citizen's Guide to Radon

This kind of risk is a long-term, low-level exposure type of thing. Opening the windows in winter is overkill. See what you have first before worrying that much.

toxcrusadr is right...you either don't have a problem, or you have had 12 years of radon exposure in this home and a few days more will make no difference to your risk.

All the houses in my area have basements filled with radon. When I moved in, people asked me if I had it tested (I didn't bother). Didn't a previous owner DIE in my house??? Absolutely, she did. I guess that it doesn't matter that she was 96 yrs old and had lived in the house for 55 yrs and died of natural causes... must be the radon. Relax. Unless you're going to spend all of your time in the crawl space it won't matter a bit!

chucksmom-
You're entitled to do what you want, but it's not unreasonable for the OP to have the house tested, and then make an informed decision. In your case, if you are in a house with high levels of radon in the basement, you are ignoring a potential health risk that can be mitigated for not much money. It's entirely plausible that the 96 year old woman who lived in your house previously died of something unrelated to radon: most people who live in houses with radon risks do die of something else...but that doesn't prove it's a safe situation. Like any risk, you may be lucky. But I worked in environmental health for over 30 years, and saw enough that convinced me to not ignore risks I could do something about. I have a father-in-law who smoked for more than 60 years and is still alive at 92...but it doesn't prove that it's safe for me to smoke.

I agree that there's no need to leave windows open. But I also don't think rejecting scientific information because you are suspicious of EPA will diminish your risk. There are any number of studies produced on radon by scientists and medical professionals who have no connection to EPA that draw similar conclusions on health risks posed by elevated radon levels. I'm not interested in trying to convince you of anything, though. I'm just trying to inform other readers of this forum that there are other approaches to assessing health risks than ignoring them.

For those interested, these are the summary findings from a 2009 report on radon by the World Health Organization:

-Epidemiological studies confirm that radon in homes increases the
risk of lung cancer in the general population. Other health effects of
radon have not consistently been demonstrated.

-The proportion of all lung cancers linked to radon is estimated to lie
between 3% and 14%, depending on the average radon concentration
in the country and on the method of calculation.

-Radon is the second most important cause of lung cancer after
smoking in many countries. Radon is much more likely to cause lung
cancer in people who smoke, or who have smoked in the past, than in
lifelong non-smokers. However, it is the primary cause of lung cancer
among people who have never smoked.

-There is no known threshold concentration below which radon
exposure presents no risk. Even low concentrations of radon can
result in a small increase in the risk of lung cancer.

-The majority of radon-induced lung cancers are caused by low
and moderate radon concentrations rather than by high radon
concentrations, because in general less people are exposed to high
indoor radon concentrations.

And this is from the Health Canada web site:

The only known health effect of radon is an increased chance of
developing lung cancer. Radon is the second leading cause of lung cancer
after smoking. Because it is radioactive, radon decays. As it decays,
radon produces decay products, sometimes called "radon daughters" or
"radon progeny". Radon gas and radon progeny in the air can be breathed
into the lungs where they breakdown further and emit "alpha particles".
Alpha particles release small bursts of energy which are absorbed by
nearby lung tissue. This results in lung cell death or damage. When lung
cells are damaged, they have the potential to result in cancer when
they reproduce.

Not everyone exposed to radon will develop cancer. The time
between exposure and the onset of the disease is usually many years.
Unlike smoking, occasional exposure to radon does not produce any
symptoms, such as coughing or headaches.

Your risk of developing lung cancer from radon depends on the
concentration of radon in the air you breathe and the length of time
you are exposed. If you are a smoker also exposed to elevated levels of
radon your risk of lung cancer is significantly increased.

If you have a crawl space that is venting properly you are fine. This makes your radon exposure close to what you would get in the open air. The risk is if you have a basement and radon gets in there and then the radon gets sucked into your forced air and spreads it through the house. My basement had a radon level of 9 when I moved in and I have it mitigated down to less than 2 now.

It also depends how air tight your basement is. My basement was super
drafty at the sill plate and I spray foamed that and the rim joist. I saw my radon level go up from about 1.4 to 1.8 by sealing those major drafts.

vithdude-
Glad to see a helpful post from someone who has dealt with this and understands the issues. I'm curious about how much you spent to mitigate your radon problem.

I did not know how to do it at the time, was a fairly new homeowner (didn't have the tools to do it back then either). I had a contractor come out. He brought a partner with. They did it in the winter in one day. It was approx $2000-2500 from what I remember. They ran the system inside the house from under the slab up to the roof with the radon fan in the attic. They used 3" piping (I learned you get greater suction pressure with a smaller pipe and my manometer has been 3.7 to 3.8 out of 4 since day one). Unfortunately, the only place they could hide my pipe that would conceal it was in my MBR closet. I did plenty of research on the topic before they came out so I had an idea they were doing it right and I was satisfied with their work for the most part.

I did have a problem with vibration noise where they cut the hole in the ceiling drywall and where it went through the main floor subfloor. The holes were a perfect fit so it looked good but it touched the pipe. Anything touching the pipe will make vibration noise so I made the hole a bit larger in the floor and I made the ceiling hole bigger and installed a roof flashing there in the attic and caulked the roof flashing to the top of the ceiling (having to cut the pipe, put on the flashing, then put on a coupling). The vibrations were solved with that. I also had to insulate around the radon fan in the attic because it was a more powerful unit and was louder. Another thing is that I live far north and the pipe got frozen on the roof during winter. There is a lot of condensate that comes out of that radon pipe about as much as a high efficiency furnace vent (the pipe also needs proper slope backward on any horizontal runs so water doesn't accumulate inside). I solved the freezing with the wrap on foam with adhesive on the back. I put that on the pipe in the attic and on the exposed pipe above the roof. Now I could have called the contractor about the problems I had, but it didn't bother me. I learned quite a bit by making some tweaks myself. Maybe I can just email him what I've done so he makes note of it in the future.

Hope this helps!

Thanks for all the detailed information...interesting and useful.

Thank you all for your responses. I appreciate all of them. I'm sorry I didn't respond sooner. My father died unexpectedly. He was turning 84 next week, so in that regard we knew it was not unlikely, but he developed a short illness and died the next day. My brother and sisters and I are heartbroken. Anyway, this is the first time I've had time to sit down and respond.

Okay, so we purchased a ceiling fan for our living room. It's really cute, I have to say. We are also changing our patio door (it needed an upgrade anyway) off of our kitchen to a sliding glass patio door that will have a screen for spring/summer, which will provide even more ventilation. Our Maine Coon cat will go crazy over it, I'm sure.

And finally, we're getting a simple ventilation system for our crawl space, once all of the snow finally melts.

We didn't test for the radon, because the tests at Home Depot were rated terribly. Besides, we won't know what our number has been in this house since we've been lightly ventilating the lower floor of our house with the ceiling fans and a slightly ajar window.

We are going to get a radon monitor for moving forward though. Radon is a big concern of homeowners around here, from what I've learned. We aren't getting a positive ion generator, I think the ceiling fans and crawl space ventilation system will be enough. For me, no amount of radon in my house is acceptable, even if it's under 4, so this will be a permanent change. Although leaving even one window slightly ajar when it's below zero out, is not going to happen. I found that out pretty quickly! lol I've found a balance in all this mitigation that I can live with.

Btw, my husband and I don't smoke, though my husband did smoke for about 10 years when he was 18, but he stopped before he was 30. He's 48 now. He does wonder if that bit of smoking will put him at higher risk, but none of us can change what we did in the past, only go forward with what we know now. Thanks again for responding. I enjoyed your candor.

ilovemytrees-

Do a test, rather than continuing to think about it. There are many reliable radon test kits out there, and you can get a good sense of what the number has been by just not ventilating, etc. for a couple of days first.

Take a look at the ratings for test kits on Amazon. You may want to try two different brands side-by-side to see if the results are in the same ballpark:

Radon test kits

If you want a one time test then yes test kits work but if you want to monitor it long term there is a better solution. It is more expensive but it works great (I have one). You can also reset it and it will give you a new readout in 2 days.
http://www.amazon.com/Safety-Siren-Series3-Radon-Detector/dp/B000CEAY64
Perhaps start with a one time kit and see where you are at then get the more expensive one if needed? I still think you are ok with the properly vented crawlspace. The problem is more prevalent when the living space is underground.