If you've been a heating oil customer in Connecticut for a few years, you may have noticed your delivery receipts or invoices starting to say "Bioheat" rather than just "No. 2 heating oil." This isn't a different product category — bioheat is a blend of conventional petroleum heating oil with a percentage of biodiesel, a renewable fuel made from vegetable oils, animal fats, or recycled grease. Here's what the different blend levels actually mean for you.
Bioheat is designated by a B-number indicating the percentage of biodiesel in the blend:
| Blend | Biodiesel % | Petroleum % | Common Status |
|---|---|---|---|
| B2 | 2% | 98% | Widely available; minimal impact on properties |
| B5 | 5% | 95% | Standard in many CT markets; backward compatible |
| B10 | 10% | 90% | Increasingly common; some equipment notes apply |
| B20 | 20% | 80% | Growing share; higher cloud point — note for outdoor tanks |
| B50+ | 50%+ | 50%– | High-blend programs; requires modern equipment certification |
Connecticut has been a leader in bioheat adoption. The state mandated B2 minimum blends in 2018, and the CT bioheat standard has progressively increased. Most dealers in CT are currently supplying B10 or B20 as their standard product, with some offering higher blends.
For B5 and B10 blends: yes, without any modification. These blends are backward compatible with all existing oil heating equipment, storage tanks, and fuel lines. ASTM D396 — the standard heating oil specification — accommodates blends up to B5, and ASTM D6751 covers the biodiesel component. Most equipment manufacturers have approved B5 and B10 for their equipment without modification.
For B20: compatibility is broader than often claimed, but requires attention. Most modern residential oil heating equipment (post-2000 installations) is compatible with B20. Older equipment with natural rubber gaskets, seals, or hoses may have compatibility issues — biodiesel has slightly different solvent properties than petroleum diesel that can affect some elastomers over time. If your system is older (pre-1995) or uses original rubber components, ask your technician to verify compatibility before running B20.
For B50 and higher: requires equipment certified for high-blend bioheat. This is a distinct category of modern systems designed specifically to run high-blend or neat biodiesel, and is currently more common in commercial than residential settings.
Biodiesel has slightly lower energy density than petroleum No. 2 by volume:
In practical terms, you will use slightly more B20 than standard No. 2 to produce the same amount of heat — but the difference at B20 is approximately 1.4%, which at 800 gallons of annual consumption translates to about 11 extra gallons. This is small enough that most homeowners won't notice it in their annual fuel usage.
Biodiesel has a higher cloud point (the temperature at which wax crystals begin to form) than petroleum diesel. This is the main practical consideration for Northeast homeowners:
For indoor (basement) tanks, this is a non-issue — basement temperatures don't approach these levels even during the coldest Connecticut winters.
For outdoor above-ground tanks or tanks in unheated spaces, B20 cloud point may be a consideration during extended cold snaps. Ask your dealer whether their winter blend includes cold flow improver additives — most dealers who supply B20 in cold climates add these to maintain cold weather performance.
The shift toward bioheat in Connecticut is driven by state policy goals for greenhouse gas reduction. Biodiesel produces lower net lifecycle carbon emissions than petroleum diesel, and the blending increases incrementally as the state pursues its heating sector decarbonization targets. The Connecticut Clean Heat Standard and related policies are designed to gradually increase the renewable content of heating fuels sold in the state over the coming years.
For homeowners, this means the bioheat percentage in standard delivered fuel will continue to increase over time. If you're planning a new heating system or evaluating equipment replacement, confirming compatibility with higher bioheat blends (B20–B50) is a practical future-proofing consideration.
Bioheat is typically priced at or very near standard No. 2 heating oil. The biodiesel component carries a small premium on a per-unit basis, but blending costs are offset in part by the renewable fuel compliance value the biodiesel generates. In practice, you are unlikely to see a meaningful price difference between B5 and B20 at retail. Some dealers marketing "premium bioheat" at a specific high blend may charge a slight premium, but this isn't universal.
Whether your dealer supplies B5 or B20, the price difference between dealers matters more than the blend. OilOutpost gets you competing bids — same day.
Get Competing Quotes →Related: What Is Bioheat? The Biodiesel Blend in Your Heating Oil · Bioheat Heating Oil: What It Is, How It Burns, and What to Know