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The Problem


NYC Clean Heat has transitioned into the NYC Retrofit Accelerator, New York City’s new one-stop resource for energy and water efficiency. Learn more at

The Problem

Air pollution is one of New York City’s most significant public health challenges.  More than 300,000 children have been diagnosed with asthma in the City. Eliminating the use of heavy heating oil and converting all buildings to cleaner forms of energy are the highest-impact step we can take to reduce air pollution and advance OneNYC's goal of having the best air quality among all large U.S. cities.


What is Heavy Oil?

There are three grades of heating oil burned in New York City, No.’s 6, 4, and ultra-low sulfur 2 (ULS 2). The heaviest grade, No. 6 oil, resembles tar or asphalt. It is often referred to as residual oil because it literally comes from “the bottom of the barrel” of the petroleum refinement process. To maintain a liquid form, No. 6 oil must be heated to at least 110 degrees Fahrenheit.  

The use of No. 6 oil as a primary heating fuel was phased out in New York City on June 30th, 2015.  To date, the City has achieved 99.8% compliance with the regulations eliminating the use of No. 6 heating oil. The deadline for the phase out of all No. 4 heating oil is January 1st, 2030..

Containers of No. 6, No. 4, and No. 2 oil roughly 1/3 full

Pictured are vials of ULS 2, No. 4, and No 6 heating oil. Each vial was one third full and was shaken before photographing. Note that ULS 2 heating oil is dyed red

No. 6 oil and the less-viscous No. 4 oil can contain sulfur, nickel, and other impurities and can be difficult to burn cleanly and completely. During combustion, unburned fuel creates soot, some of which spews out of the chimney and the rest of which coats the boiler heat exchange surfaces – as seen in the images below.  

This soot acts like insulation and drastically reduces the efficiency of the boiler. Daily equipment cleaning is needed during periods of high use to maintain boiler operating efficiency. 


The image on the left shows sludge buildup on the burner air spinner and the combustion chamber floor. The image on the right shows soot that has been scraped out of the boiler tubes during cleaning. Photo Credit:Tom Sahagian

What are the health impacts of burning heavy oil?

Because of its high sulfur content, burning No. 4 or 6 oil releases significant quantities of fine particulate matter (PM2.5) in chimney exhaust. When PM2.5 becomes embedded in people’s lungs it can aggravate existing respiratory diseases such as asthma and cause heart attacks or other cardiovascular episodes. Emissions of the heavy metal nickel are also a major concern, as it can increase the risk of heart disease and other ailments when ingested.

The NYC Department of Health and Mental Hygiene has found that wintertime PM2.5 concentrations are, on average, 30% higher in neighborhoods where heavy oil use is prominent compared to those where it is not. Airborne nickel was also significantly elevated in these areas. Overall nickel concentrations before the Clean Heat program began were found to be nine times higher than those of any other large U.S. city.

Map showing wintertime ground-level PM2.5 concentrations—as measured by the NYC Department of Health and Mental Hygiene at 150 monitoring sites across the City – overlaid with the locations of buildings that burn No. 6 oil. Picture Credit:DOHMH

What are the health benefits of using cleaner fuels?

Eliminating the use of No. 6 heating oil in buildings and transitioning to cleaner fuels has resulted in dramatic health benefits. NYC Clean Heat has already reduced PM 2.5 emissions from buildings by over 65%, which has helped prevent hundreds of deaths and thousands of emergency room visits and hospitalizations from lung and cardiovascular diseases annually. Heating oil conversions away from no. 6 and No. 4 oil also significantly reduce greenhouse gas (GHG) emissions, the harmful emissions that contribute to global climate change.

The City has made significant progress, but there is still work to do. More than 4,000 buildings in NYC are still burning No. 4 oil and must convert to a cleaner heating fuel by 2030.

To assist these buildings, NYC Clean Heat has transitioned into the NYC Retofit Accelerator, an expanded program to help building owners and operators invest in a wide range of energy and water upgrades. The NYC Retrofit Accelerator team will continue to assist buildings with their conversions away from No. 4 heating oil to a cleaner heating fuel.

For more information about the NYC Retrofit Accelerator, visit:


DPR, Schoolyard to playground Bishop Kearney High School, Brooklyn

To get in touch with the Retrofit Accelerator's team of efficiency advisors, dial 311 or click here to contact us directly.