Oil and Kerosene Heaters

Oil and Kerosene Heater Fundamentals

Oil and kerosene space heaters provide localized heating in areas without natural gas service or where electricity costs make resistance heating impractical. These units burn liquid petroleum fuels ranging from No. 1 fuel oil (kerosene) to No. 2 heating oil, with heat outputs from 8,000 to 75,000 BTU/hr.

Vented models exhaust combustion products through chimneys or direct-vent systems, achieving 75-85% efficiency. Portable unvented kerosene heaters operate at 98-99% fuel-to-heat efficiency but introduce combustion products and moisture into living spaces, requiring adequate ventilation and continuous monitoring.

Fuel Properties and Specifications

Kerosene (No. 1 Fuel Oil)

Physical Properties

• Density: 6.8 lb/gallon at 60°F
• Heating value: 135,000 BTU/gallon (lower heating value)
• Flash point: 100-150°F
• Pour point: -40 to -10°F
• Viscosity: 1.3-2.2 centistokes at 100°F

Combustion Characteristics Stoichiometric air-fuel ratio: 15:1 by mass

$$\text{C}{12}\text{H}{26} + 18.5\text{O}_2 \rightarrow 12\text{CO}_2 + 13\text{H}_2\text{O}$$

Actual combustion requires 25-50% excess air for complete oxidation and flame stability.

Sulfur Content Premium grade kerosene: <0.04% sulfur (400 ppm max) Standard grade: <0.3% sulfur

Low sulfur content reduces SO₂ emissions and equipment corrosion.

No. 2 Heating Oil

Physical Properties

• Density: 7.2 lb/gallon at 60°F
• Heating value: 139,000 BTU/gallon (LHV)
• Flash point: 130-180°F
• Pour point: +10 to -5°F
• Viscosity: 2.0-4.3 centistokes at 100°F

Grades and Additives

• Standard: ASTM D396 Grade No. 2
• Ultra-low sulfur: <15 ppm sulfur (required in many jurisdictions)
• Additives: Pour point depressants, biocides, stabilizers

Higher viscosity than kerosene requires preheating or atomization assistance in some burner designs.

Fuel Quality Requirements

Storage Considerations

• Above-ground tanks: Double-wall with leak detection
• Underground tanks: Cathodic protection required
• Tank capacity: 275-550 gallons typical residential
• Vent sizing: 1.25 inch minimum diameter
• Fill and vent separation: 2 feet minimum

Water Contamination Water accumulation from condensation promotes microbial growth. Weekly or monthly tank bottom sampling recommended. Water content >0.05% indicates contamination requiring fuel polishing or replacement.

Sediment and Particulates Fuel filtration critical for proper burner operation:

• Primary filter: 10-30 micron at tank outlet
• Secondary filter: 5-10 micron at burner inlet
• Replace filters annually or when pressure drop exceeds 3 psi

Vented Oil Heaters

Pot Burner Heaters

Operating Principle Fuel drips or flows into combustion pot where vaporization and burning occur. Simple, reliable design with minimal moving parts.

Burner Types

Sleeve Burner Fuel flows down center sleeve into pot. Air enters through adjustable primary air ports at pot base and secondary air ports in burner throat.

Heat output: 25,000-50,000 BTU/hr Efficiency: 65-72% Typical for floor-mounted cabinet heaters

Pot-Type Vaporizing Burner Fuel pools in cast iron pot heated by flame. Vaporized fuel mixes with combustion air above liquid surface.

Heat output: 15,000-40,000 BTU/hr Efficiency: 60-70% Used in portable vented heaters

Performance Characteristics

• Warm-up time: 3-8 minutes to full output
• Turndown ratio: None (on/off control only)
• Fuel consumption: 0.18-0.36 gallons/hour
• Stack temperature: 450-650°F

Combustion Air Adjustment Primary air controls yellow vs. blue flame appearance:

• Too little air: Long yellow flame, sooting, CO production
• Proper air: Short blue flame with slight yellow tip
• Too much air: Noisy, unstable, reduced efficiency

Secondary air dilutes products and controls stack temperature. Adjust to achieve 300-400°F rise over ambient at stack.

Gun Burner Space Heaters

Atomizing Burner Design High-pressure pump (100-140 psi) forces oil through nozzle, creating fine spray. Blower provides combustion air in proper ratio. Electric ignition (spark or interrupted pilot) initiates combustion.

Major Components

Fuel Unit (Pump)

• Type: Single-stage or two-stage gear pump
• Pressure: 100 psi typical, up to 300 psi for heavy oils
• Flow rate: 0.5-3.0 GPH at rated pressure
• Strainer: 200-mesh internal screen

Nozzle

• Spray angle: 45-90 degrees
• Flow rate: Rated in gallons per hour (GPH)
• Pattern: Solid cone, hollow cone, or semi-solid
• Material: Brass or stainless steel with sintered filter

Nozzle flow rate:

$$Q_{nozzle} = K \sqrt{\Delta P}$$

Where:

• $Q_{nozzle}$ = flow rate (GPH)
• $K$ = nozzle constant
• $\Delta P$ = pressure differential (psi)

For 100 psi and 1.0 GPH nozzle: Output 1.0 GPH ×135,000 BTU/gal = 135,000 BTU/hr

Combustion Air Blower

• Type: Centrifugal squirrel cage
• Airflow: 900-2,500 CFM depending on firing rate
• Static pressure: 0.5-2.0 inches w.c.
• Motor: 1/8 to 1/3 HP

Air-fuel ratio controlled by blower speed and air shutter position.

Ignition Transformer High-voltage output: 10,000-14,000 volts Creates spark across electrodes positioned in fuel spray cone Spark gap: 1/8 to 5/32 inch

Efficiency and Emissions

Steady-State Efficiency Gun burner vented heaters achieve 78-85% efficiency through:

• Precise fuel atomization for complete combustion
• Optimized air-fuel ratio (15-25% excess air)
• Extended heat exchanger surface area
• Lower stack temperatures (300-450°F)

Stack loss calculation:

$$\eta = 1 - \frac{K(T_s - T_a)}{%CO_2}$$

Where:

• $K$ = 0.32 for No. 2 oil
• $T_s$ = stack temperature (°F)
• $T_a$ = ambient temperature (°F)
• $%CO_2$ = percent carbon dioxide in flue gas

Target combustion parameters:

• CO₂: 11-13% (dry basis)
• O₂: 3-6%
• CO: <50 ppm (air-free)
• Smoke: <1 on Bacharach scale

Particulate Emissions Proper atomization and air mixing minimize soot:

• Clean burn: <1 Bacharach smoke number
• Acceptable: 1-3 Bacharach
• Unacceptable: >3 (indicates incomplete combustion)

Installation Requirements

Venting Systems Type L vent (listed oil-burning appliance vent) required:

• Minimum diameter: 3-6 inches depending on input
• Vertical rise: 5 feet minimum before offset
• Maximum horizontal run: 75% of vertical rise
• Draft: -0.02 to -0.04 inches w.c. over fire

Barometric damper maintains constant overfire draft despite variations in stack effect and wind conditions.

Combustion Air Confined space requirements:

• Two permanent openings
• Each: 1 square inch per 1,000 BTU/hr input (outdoor air)
• Or: 1 square inch per 5,000 BTU/hr (ventilated attic/crawl)

40,000 BTU/hr heater in confined space: 40 square inches per opening

Clearances to Combustibles

Reduced clearances possible with listed shields.

Fuel Supply

• Fuel line: 3/8 inch copper (soft or hard)
• Filter location: Before burner, accessible for service
• Shutoff valve: Readily accessible, labeled
• Line slope: 1/4 inch per foot toward burner
• Maximum lift: 8 feet (single-stage pump), 15 feet (two-stage)

Portable Kerosene Heaters

Convective Kerosene Heaters

Wick-Type Design Cylindrical or flat woven fiberglass wick draws kerosene by capillary action from reservoir to combustion zone. Air enters through bottom vents, passes through flame, and exits top grille by natural convection.

Heat Output Distribution

• Radiant: 15-25%
• Convective: 75-85%
• Room circulation driven by temperature differential

Capacity Range

• Small units: 8,000-12,000 BTU/hr (0.06-0.09 GPH)
• Medium units: 12,000-18,000 BTU/hr (0.09-0.13 GPH)
• Large units: 18,000-23,000 BTU/hr (0.13-0.17 GPH)

Wick Specifications

• Material: Woven fiberglass
• Life: 1-3 heating seasons (typical)
• Height adjustment: Controls heat output 50-100% of rated capacity
• Dry-burn cleaning: Removes carbon deposits, extends life

Wick consumption by combustion reduces height 0.5-1.5 inches per season.

Radiant Kerosene Heaters

Construction Circular wick surrounds central air tube. Combustion occurs at wick top, heating refractory or wire mesh element to 1,400-1,800°F. Hot surface emits infrared radiation.

Heat Distribution

• Radiant: 50-65%
• Convective: 35-50%
• Effective for spot heating and outdoor applications

Reflector Enhancement Polished metal reflector behind heating element directs radiation forward:

• Coverage angle: 120-180 degrees
• Intensity increase: 30-50% in primary zone
• Asymmetric patterns for wall-mounted applications

Safety Features

Tip-Over Shutoff Gravity-actuated or pendulum switch:

• Trigger angle: 15-20 degrees from vertical
• Action: Immediate fuel flow shutoff
• Reset: Manual after uprighting unit

Automatic Ignition Cutoff Flame detector (thermocouple or photocell) monitors combustion:

• If ignition fails within 45-60 seconds, fuel shuts off
• Prevents unburned fuel accumulation
• Manual reset required

Overheat Protection Bimetal thermostat monitors cabinet temperature:

• Trip point: 250-300°F
• Opens fuel circuit
• Automatic reset when temperature drops

Fuel Tank Design

• Capacity: 1.2-2.5 gallons
• Material: Polyethylene or steel with corrosion-resistant coating
• Fuel gauge: Visual or mechanical
• Child-resistant cap
• Integral siphon pump for filling

Combustion Products and Ventilation

Emissions Without Venting 23,000 BTU/hr kerosene heater operating 8 hours produces:

• CO₂: 18.5 lb (3,600 ft³)
• H₂O: 23 lb (2.8 gallons)
• O₂ consumed: 496 ft³

In 1,000 ft³ room with 0.5 ACH:

• CO₂ concentration rises to 7,200 ppm (0.72%)
• Oxygen drops to 19.2%
• Relative humidity increases 12-18%

Ventilation Requirements ANSI/NFPA standards require:

• Crack a window when operating portable kerosene heaters
• Minimum ventilation: 3 square inches per 1,000 BTU/hr
• For 20,000 BTU/hr unit: 60 square inches opening

Provides fresh air supply and dilutes combustion products to safe levels.

Fuel Quality and Odor

Odor Sources

1. Ignition/Extinction: Incomplete combustion during startup and shutdown
2. Fuel Impurities: Heavy hydrocarbons, aromatics
3. Wick Condition: Carbon buildup, degradation

Odor Reduction Strategies

• Use only 1-K kerosene (ASTM D3699)
• Replace fuel monthly if not used (prevent heavy end concentration)
• Trim and clean wick regularly
• Extinguish outdoors or with rapid air dilution
• Avoid overfilling tank (causes spillage and evaporative odors)

Fuel Testing Color test: Water-clear to pale yellow acceptable Sniff test: Mild petroleum odor; strong or pungent indicates contamination Burn test: Clean blue flame with minimal smoke

Indoor Air Quality Concerns

Carbon Monoxide Production

Properly operating oil and kerosene heaters produce minimal CO (<50 ppm in flue). Elevated CO from:

• Insufficient combustion air (oxygen depletion)
• Flame impingement on cold surfaces
• Dirty or damaged burner components
• Fuel contamination (water, sediment)
• Backdrafting (vented units)

CO Monitoring Install CO detectors:

• Within 15 feet of any fuel-burning heater
• On each floor level
• Alarm threshold: 70 ppm (ANSI/UL 2034)

Nitrogen Dioxide Formation

High-temperature combustion produces NO₂:

$$\text{N}_2 + \text{O}_2 \xrightarrow{\text{high T}} 2\text{NO} \xrightarrow{\text{+O}_2} 2\text{NO}_2$$

Formation rate increases exponentially above 2,500°F flame temperature.

Typical NO₂ emissions:

• Vented oil burners: 50-150 ppm in flue (minimal indoor exposure)
• Portable kerosene heaters: 0.1-0.5 ppm in room air

EPA and NIOSH short-term exposure limit: 1 ppm (15 min)

Sulfur Dioxide

Fuel sulfur content determines SO₂ production:

$$\text{S (in fuel)} + \text{O}_2 \rightarrow \text{SO}_2$$

For 0.2% sulfur fuel at 0.7 GPH consumption: SO₂ production = 0.0028 lb/hr = 21 ppm in 1,000 ft³ space with 0.5 ACH

Use low-sulfur fuel (<0.05%) for portable heaters to minimize SO₂ exposure.

Safety Requirements and Codes

NFPA 31 Installation Standards

Vented Heaters

• Listed and labeled for oil-burning service
• Installed per manufacturer instructions
• Clearances to combustibles maintained
• Type L venting with barometric damper
• Shutoff valve and filter in fuel line
• Electrical disconnect within sight

Portable Heaters

• Listed to ANSI Z91.1 or UL 647
• Used only in well-ventilated areas
• Never refuel while operating or hot
• Stored with fuel tank empty or outdoors
• Prohibited in sleeping rooms (many jurisdictions)

UL 647 Performance Standards

Portable kerosene heaters must demonstrate:

• CO production <100 ppm during steady operation
• Automatic shutoff on tip-over
• Tank leak test without failure
• Flame stability throughout burn cycle
• Surface temperature limits (<300°F unguarded surfaces)

Maintenance and Troubleshooting

Vented Heater Annual Service

Combustion System

1. Combustion analysis: CO₂, O₂, CO, smoke number, stack temperature
2. Nozzle replacement (annual)
3. Electrodes: Clean, gap check (1/8 inch), alignment verification
4. Pump pressure: 100 psi ±10 psi
5. Blower wheel cleaning
6. Heat exchanger inspection and cleaning

Fuel System

• Filter replacement
• Tank inspection for water and sediment
• Line leak check (soap solution)
• Shutoff valve operation verification

Control System

• Cad cell or stack relay cleaning and testing
• Safety lockout timing verification
• Thermostat calibration
• High-limit control testing

Portable Heater Maintenance

Wick Maintenance

• Dry-burn cleaning every 4-6 weeks of use
• Replace when consumption reduces height below minimum
• Signs requiring replacement: Uneven burning, persistent odor, difficulty adjusting

Tank and Fuel

• Drain old fuel at season end
• Clean tank interior annually
• Inspect siphon pump and cap
• Check for leaks before each use

Combustion Components

• Clean burner assembly
• Remove carbon deposits from heat chamber
• Inspect reflector for damage
• Test safety shutoffs (tip-over, overheat)

Common Problems and Solutions

Vented Heaters

No Ignition

• Check fuel supply and pressure
• Verify electrodes (gap, position, cracked insulators)
• Test transformer output (10,000V minimum)
• Inspect nozzle for blockage
• Confirm cad cell sees light path to flame

Sooting or Smoke

• Increase combustion air (open air shutter incrementally)
• Replace nozzle if spray pattern degraded
• Check stack draft (-0.02 to -0.04 in. w.c.)
• Clean heat exchanger of soot buildup
• Verify fuel quality (water, sediment contamination)

Short Cycling

• Oversized for load (most common cause)
• Thermostat differential too narrow
• Dirty heat exchanger reducing output
• High-limit control set too low

Portable Kerosene Heaters

Odor During Operation

• Wick needs trimming or replacement
• Fuel contamination (replace with fresh 1-K)
• Flame height too high (adjust down)
• Room ventilation inadequate

Incomplete Combustion (Yellow Flame)

• Wick height too high or too low
• Wick damaged or degraded
• Air intake blocked
• Poor fuel quality

Won’t Stay Lit

• Wick height insufficient
• Contaminated or wrong fuel type
• Automatic shutoff malfunction
• Fuel tank empty or air lock in feed system

Proper maintenance, quality fuel, and adequate ventilation ensure safe, efficient operation of oil and kerosene space heaters in residential applications.