Here's something most Connecticut homeowners don't know: since July 1, 2025, every gallon of heating oil legally sold in the state has been at least 10% biodiesel. Your fuel changed, quietly, and if you didn't notice, that's exactly the point. This guide covers what the mandate actually requires, whether it affects your equipment (short answer: no), and what's scheduled to change next.
Bioheat is the industry name for conventional heating oil blended with biodiesel, a renewable fuel refined from vegetable oils, used cooking oil, and animal fats. Blends are named by their biodiesel percentage:
Chemically, biodiesel burns cleaner than petroleum heating oil, with lower sulfur and particulate emissions. It carries about 2% fewer BTUs per gallon at B20 levels, a difference too small for a typical household to notice on a fuel bill. For a deeper dive on the fuel itself, see our Bioheat blend guide and Bioheat vs. standard No. 2 oil.
In July 2021, Connecticut enacted Public Act 21-181 (codified at Conn. Gen. Stat. § 16a-21b), which phases renewable content into all heating oil sold in the state:
| Date | Minimum blend | Status |
|---|---|---|
| July 1, 2022 | B5 (5% biodiesel) | In effect |
| July 1, 2025 | B10 (10% biodiesel) | In effect now |
| July 1, 2030 | B15 (15% biodiesel) | Scheduled |
| July 1, 2034 | B20 (20% biodiesel) | Scheduled |
| July 1, 2035 | B50 (50% biodiesel) | Scheduled |
The statute includes a temporary-waiver mechanism if biodiesel supply falls short, but the B10 stage took effect on schedule. Connecticut is not alone: Rhode Island and New York have parallel blend requirements, which is why the whole Northeast fuel supply chain has been retooling around biodiesel.
No changes are needed for B10. This is the question homeowners ask first, and it has an unusually clean answer. The National Oilheat Research Alliance (NORA), the industry's research body, and the major burner manufacturers approve blends up to B20 for use in existing oil-fired heating systems with no modifications to tanks, pumps, or burners. B10 sits comfortably inside that envelope. Any system that burned standard heating oil burns B10.
A few practical notes your service tech would give you:
The scheduled B15 step also sits below the B20 line manufacturers already approve, so today's equipment is expected to handle 2030's fuel without modification. The industry is preparing well past that: in April 2026, ASTM International approved an update to the national heating oil specification (ASTM D396-26a) adding official grades for blends from B21 to B50. The revision passed without objection, with support from NORA, Clean Fuels Alliance America, and equipment makers including R.W. Beckett. That standard is what lets Connecticut's 2034-35 steps become practical: fuel, burners, and warranties all reference it.
Since B10 is the legal minimum for all heating oil sold in Connecticut, every registered dealer's standard No. 2 heating oil delivery is B10 or higher; compliance is enforced at the wholesale and dealer level, not something you need to test at the fill pipe. If you want confirmation:
The requirement applies to every gallon sold in the state, so no dealer has a "non-Bioheat discount" alternative; B10 is simply what Connecticut heating oil is now. Biodiesel and petroleum prices move somewhat independently (biodiesel economics depend on feedstock costs and federal credits), but at a 10% blend the effect on your delivered price is small compared to the ordinary dealer-to-dealer spread in your town. Which means the money question is the same as it's always been: which dealer near you has the best price this week?
Every dealer in Connecticut delivers B10 or better. Prices still differ by 50 cents or more per gallon in the same town. See who's competitive near you.
See CT Heating Oil Prices →Related: Bioheat Blend Guide · Bioheat & Biodiesel Basics · Bioheat vs. Standard No. 2 Oil