Heat Source Comparison: Heating Oil and Natural Gas

Michael Tobias
5 Minutes Read
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    Heating oil and natural gas are both fossil fuels, but they have very different properties. At room temperature, one is a viscous liquid while the other is a gas. For a given heating output, there is also a difference in the amount of natural gas or heating oil that must be burned, as well as the greenhouse gas emissions produced.

    Heating oil is normally measured in gallons, while natural gas is measured in cubic feet. Therefore, it is easier to compare their performance based on heating output - the US Environmental Protection Agency compares their emissions per million BTU (mmBTU) of heat.

    This article will focus on #2 heating oil, which is still accepted in New York City. #4 and #6 heating oil have already been phased out by legislation, in an effort to control emissions. In NYC, buildings that use fuel oil for their heating needs produce more pollution that all vehicles in the city combined.

    Comparing the Emissions of #2 Heating Oil and Natural Gas

    According to the US EPA, #2 heating oil releases 73.96 kg of CO2 per mmBtu of heat, while natural gas produces 53.06 kg of CO2 per mmBtu. In other words, #2 heating oil produces almost 40% more carbon dioxide per unit of heat, and this is even higher for the types that have been phased out by legislation, #4 and #6. Compared with heating oil, natural gas also produces reduced amounts of sulfur oxides, nitrogen oxides and soot.

    Another key greenhouse gas is methane (CH4), and replacing #2 heating oil with natural gas also reduces its emissions. The US EPA has determined that natural gas usage releases 1 g of CH4 per mmBtu, while #2 fuel oil releases 3 g of CH4 per mmBtu. Keep in mind that the global warming potential of methane is 25 times higher than that of carbon dioxide.

    Nitrous oxide (N2O) is even worse than methane, having a global warming potential 298 times higher than carbon dioxide. While #2 heating oil emits 0.60 g of N2O per mmBtu, natural gas only emits 0.10 g of N2O per mmBtu. These emissions reductions are summarized in the following table (per million Btu):


    #2 Heating Oil

    Natural Gas

    Reduction (%)

    Carbon dioxide (CO2)

    73.96 kg/mmBtu

    53.06 kg/mmBtu


    Methane (CH4)

    3.0 g/mmBtu

    1.0 g/mmBtu


    Nitrous Oxide (N2O)

    0.60 g/mmBtu

    0.10 g/mmBtu


    Even greater emissions reductions can be achieved when an old and inefficient oil boiler is replaced with a high efficiency natural gas boiler. Assume the oil boiler has an Annual Fuel Utilization Efficiency (AFUE) of 60% while the new gas boiler offers 95%. To produce one million Btu of heating output, the required input would be the following:

    • Oil boiler input = 1 mmBtu / 0.60 = 1.67 mmBtu
    • New gas boiler input = 1 mmBtu / 0.95 = 1.05 mmBtu

    Considering the emission intensity values above, this oil boiler releases around 123 kg of CO2 while the gas boiler releases 56 kg of CO2. The emissions reduction value of 28% applies when both boilers have the same efficiency, but in this case CO2 emissions are actually reduced by 54% because the new boiler is more efficient while using a less polluting fuel. Although this is a broad estimate, it provides an example of how superior boiler efficiency and conversion to natural gas work together to reduce emissions. The same effect applies for other greenhouse gases such as methane and nitrous oxide.

    However, it is important to note that natural gas is still a fossil fuel. Having the word “natural” in its name may cause the false impression that it is a renewable energy source, but this is not the case. Natural gas is simply less polluting than other fossil fuels, but has a  negative environmental impact nevertheless.

    Con Edison Incentives for Natural Gas Conversion

    Property owners in NYC who are considering a switch from heating oil to natural gas can be eligible for cash incentives from Con Edison. This reduces the cost of a fuel conversion project while keeping all the benefits, improving its financial viability. There is also a reduction in heating expenses, so it is possible to analyze the project in terms of cost and benefit. The natural gas conversion incentive from Con Edison changes depending on the type of building:


    Conversion Rebate

    Equipment Rebate

    Maximum Rebate

    Small Residential
    (1 to 4 dwellings)




    Medium Residential
    (5 to 75 dwellings)

    $300 / apartment



    Large Residential (>75 units) and Commercial




    To qualify for the incentive, the new gas-fired heating system must meet a minimum efficiency requirement. The following values apply for the small and medium residential sector:

    • Gas-fired steam heating = 82%
    • Gas-fired hydronic heating = 85%
    • Gas-fired furnace = 90%

    For large residential and commercial buildings, the minimum efficiency values to meet are the following:

    • Gas-fired steam heating = 80%
    • Gas-fired hydronic heating = 85%

    Final Recommendations

    There are many reasons to convert building heating systems from heating oil to natural gas. First of all, the US Department of Energy has determined that natural gas has a lower heating cost than fuel oil. Natural gas also has a much lower emissions intensity than #2 heating oil, and this benefit is enhanced when an aging oil boiler is replaced with a high-efficiency natural gas boiler.

    Professional guidance is strongly recommended, like with any engineering project, especially because natural gas poses a risk of fire. In addition, the combustion products must be properly exhausted, and can threaten human life if allowed to accumulate in closed spaces. Engineering services also ensure code compliance, and NYC codes are among the most demanding in the world. Upgrading from oil to natural gas is not as simple as removing one boiler or furnace and installing a new one - for example, the gas service entrance and chimney may need an upgrade.

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    Tags : Design Sustainability new york

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