What is the Ideal Temperature Range for Induced Draft Gas Furnace Flue?
The ideal flue temperature for an induced draft gas furnace is typically between 300°F to 400°F (149°C to 204°C) when the furnace is operating at its rated output. This temperature range ensures that the flue gases do not condense within the flue, which can lead to corrosion and other issues.
| Measurement | Typical Range |
|---|---|
| Flue Gas Temperature | 300°F to 400°F (149°C to 204°C) |
| Measurement Location | Within 24 inches of the induced draft fan |
The flue temperature can vary based on factors such as the type, condition, length, and size of the flue, as well as the flue draft. However, for a properly tuned 80% efficient furnace, the flue temperature should be within the recommended range.
What Factors Affect Flue Levels in Gas Furnaces?
Several factors can influence the flue levels in gas furnaces, including:
- Venting System:
- The type and condition of the venting system, including the size and material of the flue, can significantly affect the flue gas temperature.
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A larger flue can cause the gases to cool too much, leading to condensation issues.
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Altitude:
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High-altitude installations may require special kits to ensure proper operation and to maintain the correct flue gas temperature.
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Combustion Air Supply:
- Sufficient combustion air supply is crucial to maintain the correct flue gas temperature and to prevent issues like low flue temperatures.
Can Gas Furnaces and Oil-Fired Appliances Share the Same Flue?
It is generally not recommended to share a flue between a gas furnace and an oil-fired appliance due to compatibility issues and safety concerns.
Compatibility Issues
- Gas furnaces, especially those with induced draft, create a negative pressure that can interfere with the operation of oil-fired appliances, which typically rely on natural draft.
Safety Concerns
- Sharing a flue can lead to improper venting, which can result in carbon monoxide buildup and other safety hazards.
- Local codes often prohibit such configurations to ensure safe operation.
Necessary Modifications
- It is advisable to use separate vents for gas furnaces and oil-fired appliances to avoid compatibility and safety issues.
- Always check with local authorities to ensure compliance with regional regulations, as some areas may have specific requirements or prohibitions regarding shared venting systems.
What Regulations and Compliance Requirements Apply to Gas Furnace Flue Levels?
Local Codes and Compliance
- In the USA, the National Fuel Gas Code (NFPA 54/ANSI Z223.1) provides guidelines for gas appliance venting.
- Local jurisdictions may have additional or more stringent requirements, so it’s essential to check with local authorities.
- In Canada, the relevant standards include CAN/CSA B149.1 and CAN/CSA B142.2, which provide similar guidelines for gas appliance venting.
Technical Specifications and Measurements
- Normal draft pressure for gas furnaces is typically between -.01 to -.02 inches of water column, measured at the breach before the draft hood.
- Flue gas temperature is typically measured within 24 inches of the induced draft fan to ensure compliance with manufacturer specifications.
By understanding the ideal flue temperature range, the factors that affect flue levels, and the relevant regulations and compliance requirements, you can ensure the safe and efficient operation of your gas furnace.
