No. 4 Oil Isn’t as Cheap as you Think

NYC is making burning No.6 oil illegal beginning in 2015, and some property managers are switching to No.4 oil in order to satisfy minimum conversion requirements. However, burning No.4 is costly financially, and to community health.

NYC Clean Heat states that building managers should “consider system efficiencies, maintenance budgets, occupant comfort, and City and State regulations when choosing cleaner heating oils’.”

The purpose of this article is to outline the cons of burning No.4 heating oil in order to encourage building managers to transition to a cleaner heating source, such as ULS No.2 oil or natural gas.

What is No.4 oil?

No. 4 oil is a fuel source mix of 47% No.6 oil and 53% ULS No.2 oil. It operates similar to No.6 with the exception that the boiler side arm heater – which is needed to help burn the oil at 100°F in order to flow to the thank properly – is no longer needed when burning No.4.

Why No. 4 Oil Isn’t as Cheap as You Thought

As of January 2013, purchasing No. 4 oil is more expensive than No.2 oil on the Platts index, according to NYC Clean Heat. Due to a shrinking market for both No.6 and No.4, the price for No.4 is also increasing at a steady rate.  Given the fact that No.4 is a blend between No.6 and No.2, many suppliers have started phasing it out.

Although not as viscous as No.6, the density level of metals and other contaminants are still present in No. 4, and requires just as much maintenance to the boiler.  Like No.6, soot accumulates in the boiler tube sheet, causing a decrease in heat transfer, and reducing energy efficiency for the building.  The result is that “more gallons of oil are needed for the same amount of heat that a clean boiler would produce.”

Quantifying these costs, 1/8 of an inch of soot deposit on the boiler tube will reduce efficiency by 8.5% due to clogged heat transfer. Additionally, the electricity used to pre heat No.4 per burner can add a cost of $0.10 per gallon burned.

The NYC Clean Heat ‘Cleaner Heating System Workshop’ presented on December 10, 2013, outlines a possible building conversion scenario from No.6 to No. 4:


Because burning No.4 also requires an electric preheater, approximately $10,000 would need to be spent assuming 6,500 hours of use at $0.20/kWh.

Not only is burning No.4 oil detrimental to the health of tenants, but financially it is impractical for building managers in the long term. Given the approaching deadline for total conversion from No.6 oil, building managers should focus on switching to No. 2 oil with a biodiesel blend if they don’t have access to natural gas. If there is natural gas availability on their block and their internal costs are manageable buildings should consider switching to natural gas with No. 2 oil as their back up.


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