One of the culprits:<p>&gt; air-conditioning units (which are basically unrestricted openings to the street)<p>Window air conditioning units are virtually unknown in a large part of the warm weather world.  We use &quot;split systems,&quot; where only a couple thin pipes and some wires connect the outdoors with the indoors.  NYC&#x27;s fascination with inefficient window units is really quite strange.  I suppose landlords enjoy not having to pay for installation and maintenance of permanent units.