As you might have noticed if you have been in or near the outdoors over the last few days, it is very hot. The negative consequences of this are all around us: sweltering, ill-willed subway stops, undershirts as overshirts, flip-flops rampant. Because you have probably been busy splitting your time between sweating, panting in front of an air conditioner, and turning your long pants into cutoffs — and because it is freaking hot out — it's likely that you haven't spent much time thinking about Number Four and Number Six heating oil, the sludgy, oil-esque byproducts that fire a surprising number of boilers at some surprisingly luxurious apartment buildings in Manhattan, primarily the Upper East and Upper West Sides (and those of less-luxe buildings in the Bronx). But while Number Six heating oil is not to blame for the fact that it currently feels like the surface of Mercury outdoors — at least not in an abstracted, it-contributes-to-global-warming sense — it is nice to know that, when it finally cools down enough that we can all start thinking about this subject again without getting sweaty, many Manhattan boilers that formerly burned Number Six will be using a notably less toxic fuel. So, yeah: let's all think about heat a little bit, shall we? Does that sound nice?

Well, let's do it anyway. To a certain extent, this is not a new trend. Back in April of last year, we wrote about the trend towards natural gas heat — which is cheaper, and also has the added edge on old No. 6 of not being a neurotoxin — in Manhattan, and a suite of green building laws from later that summer mandated a timetable for the transition away from Number Six. And while those dates are still a ways off — 10,000 buildings will drop Number 6 by 2015, and both Number Four and Number Six will be banned by 2030 in favor of natural gas or the exponentially cleaner Number Two heating oil — many buildings are doing what New Jersey Governor Chris Christie (for one) declined to do. That would be taking advantage of lower-than-low labor costs and tax breaks — and exercising some basic economic common sense — to make some big capital improvements.

"Since buildings will be required to use either No. 2 oil or natural gas by 2030, many building owners are contemplating making the larger change now to avoid two separate conversions. Natural gas currently costs about 30 percent less than fuel oil," Vivian Toy writes in the New York Times. "City officials say that the soot pollution created by the 10,000 buildings that use No. 6 oil exceeds the amount created by all the cars and trucks in the city. At a seminar given by the Real Estate Board of New York earlier this month, a representative from the mayor's office said that while converting to natural gas can be expensive, switching from No. 6 to No. 4 oil could cost a building as little as $7,000. But contractors and consultants in the audience challenged that figure, saying it represented a best-case scenario — a building whose equipment needed only minimal upgrading." Which is kind of corny of the mayor's office, honestly. But the examples that Toy finds are heartening, even if they're notably m0re expensive. "The switch from No. 6 oil to natural gas cost [Greenwich Village condo] The Brevoort $225,000," Toy reports. "It involved replacing the burner on the boiler, removing two 20,000-gallon oil tanks, and installing equipment to draw gas from the available Consolidated Edison pipeline. The board expects to save as much as $70,000 a year in fuel costs." Which means a big return on (an admittedly massive) investment sometime around when the city-mandated phase-out becomes law, and huge savings going forward. From a breathing person's perspective, a New York City free of Number Six heating oil is obviously a better New York City. But the increasing recognition that natural gas is both cleaner and cheaper — that is, both a better decision from a sustainability perspective and an economic one — is the sort of green building news that turns frowns upside down over here at gbNYC. At least until it's time to go outside again.