Written on: September 1, 2026 by Bob O'Brien
Each Winter, technicians are called to homes with one common complaint: “The burner stopped working.” While equipment failures do occur, many no-heat service calls during periods of extreme cold can be traced to fuel related issues rather than mechanical problems.
As the industry continues its transition toward lower carbon heating fuels and higher biodiesel blends, understanding how cold weather affects fuel storage and delivery has become increasingly important. Technicians who recognize the relationship between fuel characteristics, tank installation and proper maintenance can prevent many of these service calls before they occur. The time to address these problems is now, before Winter arrives and not on the first single-digit day.
Outside Tanks Demand Special Attention
Approximately 400,000 residential heating oil tanks, roughly 10 % of the market, are installed outdoors, making them especially vulnerable to cold temperatures and weather exposure.
Unlike basement tanks, outdoor tanks experience significant temperature swings, wind exposure, snow accumulation and solar heating followed by rapid nighttime cooling. These conditions increase the likelihood of fuel waxing, water condensation and fuel related service calls.
Understanding Cold Flow Properties
Several fuel characteristics determine how well heating oil performs in cold weather.
Cloud Point is the temperature at which wax crystals first begin forming in the fuel. Although the fuel may still flow, those crystals can begin plugging filters and strainers. Cloud point typically occurs 10–20°F above the pour point.
Pour Point is the lowest temperature at which fuel will continue to flow. Below this temperature, the fuel becomes waxy and eventually gels. ASTM specifies a pour point of 17°F for untreated No. 2 heating oil, although Winter additives or kerosene blending are commonly used to improve cold-weather performance.
Technicians should also recognize the importance of the Cold Filter Plugging Point (CFPP), often the first temperature at which heating systems experience operational problems because wax crystals restrict filter flow.
As temperatures fall, fuel viscosity increases stress on fuel units and filters. Additives are the foundation of a cold weather fuel program. Techs should define the problems that need addressing and choose an additive that will meet those needs. Fuel should be treated year-round; it’s too easy to get caught with untreated fuel in customers’ tanks when treating seasonally.
Biodiesel Changes the Cold Weather Equation
As biodiesel blends increase, technicians must understand that cold weather behavior changes with blend level and feedstock.
Typical cloud point ranges include:
Actual performance varies depending on the biodiesel feedstock being used.
The message is straightforward: Know the fuel being delivered to your customers and prepare outdoor systems accordingly.
Water: The Enemy
Cold weather performance is only half the story.
Ultra-Low Sulfur Heating Oil (ULSHO) and biodiesel blends interact differently with water than traditional fuels. ULSHO is slightly more hygroscopic, attracting more moisture, while biodiesel can also hold more water in solution. Eventually, that water separates from the fuel and settles in the tank, creating ideal conditions for microbial growth.
Water can enter a storage tank through condensation, loose fill caps, poor fittings or fuel deliveries. Once present, it promotes bacteria, sludge formation, corrosion and microbially influenced corrosion (MIC).
The best solution is prevention. Proper installation, annual inspection, water removal and eliminating sources of condensation remain the most effective maintenance practices. Keeping outdoor tanks full during Summer months can also reduce condensation.
Avoid Fuel Pump-overs
One common industry practice deserves reconsideration. When replacing a tank, contractors often transfer (“pump over”) the remaining fuel into the new tank. While this saves the customer money, it can also transfer sludge, water, microbial contamination and degraded fuel directly into a new installation.
Whenever practical, replacing old fuel with fresh fuel, or temporarily storing the remaining fuel until it can be properly filtered or consumed elsewhere, helps ensure the new installation begins with clean fuel.
Installation Matters
Proper tank installation becomes even more critical with outdoor systems.
NFPA 31 requires outside top-draw single wall aboveground tanks to be installed with secondary containment sized for 110% of tank capacity. It’s quite common for techs to switch bottom feed tanks with a gelling problem to top feed. This solves the immediate problem but creates a code violation and potential liability. Be careful when doing this.
Additional code requirements include:
Fuel Delivery System Improvements
Small installation changes often produce significant reliability improvements.
Single pipe systems paired with a de-aerator reduce unnecessary fuel circulation and maximize fuel warming and reduce air bubbles in the fuel. Filter placement near the appliance improves serviceability while reducing exposure to cold temperatures. Outdoor fuel lines may benefit from insulation or electric heat tracing in particularly severe climates.
Looking Ahead
NORA continues to evaluate technologies that support higher biodiesel blends in cold climates. Research has demonstrated promising results using insulated tank enclosures equipped with thermostatically controlled heating blankets, successfully maintaining fuel performance in temperatures as low as -21°F.
Additional concepts, including loop heaters, improved tank heaters and optimized piping configurations continue to expand the industry’s options for reliable cold weather operation.
The transition to renewable liquid fuels does not change the fundamentals of good fuel storage, it reinforces them.
Understanding cold flow properties, controlling water contamination, following proper installation practices and maintaining outdoor fuel systems are essential for reliable operation. As biodiesel blends increase and Winter temperatures continue to challenge equipment, technicians who apply these practices will reduce emergency service calls, improve customer satisfaction and help ensure dependable heating performance throughout the coldest months of the year. ICM
