At first I figured it was because we weren\u2019t cooking anything. But then I realized that if that were true, NO2 levels would have plummeted like that every Tuesday when we didn\u2019t use our gas stove. <\/p>\n\n\n\n

When I spent more time looking at the data, I noticed something strange. In almost every 24 hour period, our NO2 levels were the highest between about 2am and 7am. Unless my wife was sneaking out of bed for midnight snacks, something was amiss. <\/p>\n\n\n\n

I looked at the energy usage data from our Nest thermostat and discovered that those levels corresponded almost exactly with the times that our gas furnace was on. I reached out to a friend who used to work as an energy auditor and he told me that any number of things could be causing this. Our furnace could be venting improperly. Or maybe it was our water heater. Or a change in air pressure caused by the furnace could be causing the water heater <\/em>to vent improperly. <\/p>\n\n\n\n

That same week I had an energy auditor come out to our house through our utility\u2019s rebate program. When I asked them about the NO2 levels, they said they didn\u2019t have the equipment to measure it. They only focused on the stuff that kills you quickly like carbon monoxide, not the stuff that wreaks havoc on the human body slowly over the course of years. <\/p>\n\n\n\n

Shortly after the audit I sent some of the data from my tests to Josiah Kephart, an environmental epidemiologist who studies this stuff for a living. In an email he wrote, \u201cI would say you’ve got a pretty big NO2 problem. Your daily averages are mostly hovering around 25ppb, which is double the [WHO] daily guideline.\u201d Then he wrote something that really stuck with me: \u201cWhat happens ALL the time is someone actually tests indoor NO2 from gas appliances, and industry or other folks say \u2018Well your ventilation must be messed up\u2019 or in your case \u2018Oh you must have spillage from the furnace.\u2019 There are constantly folks who treat this with a hint of blaming the individual homeowner dismissing this as the exception (without evidence).”<\/p>\n\n\n\n

But he pointed out that there\u2019s a problem with this logic: \u201cI don’t care about how the cooking\/heating\/etc system is supposed<\/em> to work, I care how it really is<\/em> working in real life. And what we see when we actually test these things in real life (vs. in the lab\/factory) are high levels of indoor NO2 everywhere we look.\u201d<\/p>\n\n\n\n

In other words, it may be possible to build a home with perfectly vented gas appliances, and there may be a \u201csafe\u201d level of NO2, but in the real world \u2014 in the homes that we all actually live \u2014 this is probably the rare exception. The more likely norm is unused range hoods, furnace flues that spill chemicals into the air we breathe, and ultimately higher rates of illness. <\/p>\n\n\n\n

I began this research as a skeptic. Why? For the same reasons you may be skeptical right now. Accepting that a gas stove or any other fossil-fuel appliance makes a home less healthy isn\u2019t simply an abstract intellectual exercise. It has practical consequences like forking up the time and money to replace the thing \u2014 an option that, like so many other health improvements, isn\u2019t available to all. <\/p>\n\n\n\n

But as I\u2019ve learned more about this topic, my skepticism has faded. Every rigorous review of the research points to the same conclusion: Most homes have unsafe levels of nitrogen dioxide and that results in higher rates of respiratory illness (especially amongst children). Or to borrow a quote from John Maynard Keynes, \u201cWhen the facts change, I change my mind – what do you do?\u201d<\/p>\n\n\n\n

\u2014 <\/p>\n\n\n\n