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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


Heating a large building can be a challenge. Though the most common clean fuels used arenatural gas and ultra-low sulfur No. 2 (ULS 2) fuel oil, there is a growing array of alternative technologies that can be used to replace or supplement traditional boiler systems. Jump ahead to: solar thermal, geothermal, combined heat and power, and biodiesel.

Solar Thermal

Solar thermal systems use solar energy to produce heat. These are different from photovoltaic systems that use solar energy to produce electricity. Solar thermal requires water or another heat transfer fluid such as glycol to be heated by direct solar radiation in collector panels, typically located on rooftops.

In NYC's large buildings, solar thermal is best suited to supplement or replace domestic hot water (DHW) systems. Utilizing solar thermal for hot water can produce benefits across the building:

  • Solar thermal DHW systems can replace or offset fossil fuels which can reduce or eliminate particulate matter (PM 2.5) and greenhouse gas (GHG) emissions from these systems.
  • Separating DHW systems from the central heating system creates more efficient space heating by allowing a building downsize the boiler and shut it down in summer months.
  • Since there are no fuel costs associated with solar DHW systems, implementing these systems can also protect a building's finances from spikes in commodity costs.
  • Federal and State incentives that are currently available can reduce the cost of installing the system by about 50 percent.
  • Buildings that are converting from No. 4 oil to ULS 2/biodiesel will benefit most from the energy cost savings and can simplify the installation by incorporating it into the conversion project.

Larger buildings with consistent hot water demand, flat open roof space, little to no roof shading, and available space in the boiler room for a storage tank, are the best candidates for solar thermal. According to CUNY’s NYC Solar Thermal study (see below), close to 60% of 5-12 floor residential buildings are suitable for solar thermal. Upper Manhattan and parts of the Bronx are some of the areas with the most solar potential.

Solar thermal is feasible for many New York City buildings and there are incentives and resources to help:

Geothermal Heat Pump Systems

Geothermal Heat Pump (GHP) systems tap into existing thermal energy that is located underground. GHP systems eliminate the need for on-site fossil fuels for heat in the winter, dramatically reduce electric cooling costs in the summer, and can be 25-40% more efficient than other conventional heating and cooling systems.

There are four predominant types of GHP systems: Direct Exchange, Open Loop, Closed Loop, and Standing Column Well.  Qualified professionals can help you assess the type best suited for your building based on its characteristics and location.

Implementing a GHP system requires significant advanced planning and a number of qualified professionals including: a well driller, a geothermal engineer, a geologist/hydrologist, a mechanical engineer, and mechanical contractors. GHP projects will also need to have permits from DEP and DEC. For those interested in investigating whether GHP may be an option for their building, there are resources available in NYC that can help:


Combined Heat and Power (CHP)/ Co-Generation

Combined Heat and Power (CHP) systems supplement or replace traditional boiler systems and are able to co-generate both electricity and thermal energy. CHP systems capture usable heat from an electric generator for use in domestic hot water or space heating, among other applications. These systems run on an external fuel source, most commonly natural gas, and a small amount of electricity, and are more energy efficient than traditional electric power generation.

CHP can reduce a building's heating fuel and electric costs. A building utilizing CHP may also less exposed to disruptions to the electric grid, which is particularly useful for hospitals, universities, or other buildings where electric power outages are particularly disruptive and costly.

In New York City, CHP is best suited for buildings that have high electric and thermal loads, including both commercial and multi-family residential buildings.

If you are considering the installation of a CHP system during a fuel conversion, there are resources available to help:



Biodiesel can be used in traditional heating systems just as any other heating oil or as a blend with heating oil. In New York, all heating oil is mandated to contain at least 2 percent biodiesel. Want more details? Check out the Biodiesel page and FAQs on Using Biodiesel for Heat.