If you've noticed your heating oil bill or delivery ticket reference "Bioheat," "B5," or "ULSD," you're seeing the gradual transition of the Northeast heating oil market away from traditional No. 2 heating oil toward cleaner-burning blended fuels. Here's what these designations mean and what they mean for your heating system.
Bioheat is a registered trademark for a blend of ultra-low sulfur heating oil (ULSD) and biodiesel. The base component — ULSD — has replaced traditional high-sulfur No. 2 heating oil across most of the Northeast over the past decade, driven by regulatory changes in Connecticut, Massachusetts, and New York. The biodiesel component is a renewable fuel derived from vegetable oils, animal fats, or recycled cooking grease.
The blend percentage is indicated by the "B" number: B5 means 5% biodiesel and 95% ULSD; B20 means 20% biodiesel; B50 means 50% biodiesel. The Connecticut mandated blend is currently B5, with a statutory pathway toward higher blend requirements in coming years. Massachusetts has similar legislation moving in the same direction.
| Blend | Biodiesel % | Notes |
|---|---|---|
| B2 | 2% | Common transitional blend; minimal impact on system performance |
| B5 | 5% | Current CT mandate; fully compatible with all standard oil heating equipment |
| B10 | 10% | Increasingly common; compatible with most modern systems |
| B20 | 20% | Requires confirmation of equipment compatibility; most post-2010 systems handle it fine |
| B50 | 50% | Long-term regulatory target in some NE states; requires modern equipment and storage conditions |
| B100 | 100% | Pure biodiesel; not used for residential heating in current market |
Cold flow: Biodiesel has a higher cloud point than petroleum-based fuel — meaning it begins to gel at higher temperatures than conventional heating oil. For outdoor tanks in extreme cold, high-blend bioheat (B20 and above) can be a concern. B5 blends are well within acceptable cold-flow performance for Northeast winters. Dealers supplying higher biodiesel blends to outdoor tanks typically add cold-flow improver additives during winter months.
Microbial susceptibility: Biodiesel's organic composition makes it somewhat more susceptible to microbial growth (diesel bug) than conventional ULSD. This is a minor consideration at B5 blends but becomes more significant at higher percentages. Annual preventive treatment with an antimicrobial additive like BIOBOR JF is a good practice regardless of blend.
Rubber compatibility: High-percentage biodiesel blends (B20+) can degrade some older rubber fuel line components and gaskets. In practice, this primarily affects pre-1990s equipment. If you have a very old oil system, confirm rubber component compatibility before receiving high-blend fuel.
Connecticut law requires that heating oil sold in the state meet minimum Bioheat content standards, with a graduated schedule calling for increasing biodiesel content over time. The intent is to reduce greenhouse gas emissions from the residential heating sector — one of the harder-to-decarbonize segments of the energy economy — while providing a market for domestically produced biodiesel.
For homeowners, this means the fuel you're already receiving from any licensed Connecticut dealer is already a Bioheat blend. The practical transition happened at the dealer and distributor level; you didn't need to do anything differently. Future blend increases will continue through the same channel.
Biodiesel historically trades at a premium to petroleum diesel, which adds modest cost to the fuel blend. The premium varies based on biodiesel commodity prices and the blend percentage. At B5 blends, the price impact is typically 1–3 cents per gallon — negligible in the context of overall oil price volatility. At higher blend percentages, the premium increases proportionally.
All Connecticut dealers supply compliant Bioheat blends. Let them compete on price for your next delivery.
Get Quotes Now →Related: What Is Bioheat? The Biodiesel Blend in Your Heating Oil · Bioheat vs. Standard No. 2 Heating Oil: What's the Difference?