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Old 03-12-2013, 01:35 PM   #1
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Primary and Secondary Air


Hi,

I get confused by exactly what constitutes primary and secondary air? My assumption is that the primary air is the air that is in the room to help combustion process and secondary air is air brought in from the outdoors? I'm probably wrong. Anyone who can explain this would be great.

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Old 03-12-2013, 03:05 PM   #2
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Primary and Secondary Air


primary/secondary air are technical terms for the air which goes into a gas burner and mainly a fan assisted power burner for larger appliances like boilers although the OLD conversion burners used both. Primary air is the main supply of air that mixes with the gas for the fire in the burners themselves. Secondary air is the air which flows around the outside of the burners and is not directly mixed with the gas in the burners. It is needed for combustion but mostly to allow draft to occur thru the furnace. This is a very simplified explanation as there is more 2 it but you would have to study fundamentals of gas or oil burning to find out.

Combustion air is the generic term for all the air needed to burn gas. ventilation air from the outdoors some people bring into their house to the return duct to get rid of excess moisture and cooking smells etc. If the furnace room is sealed airtight then we have to bring in combustion air from outside with a 4-6" hole drilled thru the wall and a pipe.

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Old 03-12-2013, 03:11 PM   #3
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Primary and Secondary Air


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Originally Posted by yuri View Post
primary/secondary air are technical terms for the air which goes into a gas burner and mainly a fan assisted power burner for larger appliances like boilers although the OLD conversion burners used both. Primary air is the main supply of air that mixes with the gas for the fire in the burners themselves. Secondary air is the air which flows around the outside of the burners and is not directly mixed with the gas in the burners. It is needed for combustion but mostly to allow draft to occur thru the furnace. This is a very simplified explanation as there is more 2 it but you would have to study fundamentals of gas or oil burning to find out.

Combustion air is the generic term for all the air needed to burn gas. ventilation air from the outdoors some people bring into their house to the return duct to get rid of excess moisture and cooking smells etc. If the furnace room is sealed airtight then we have to bring in combustion air from outside with a 4-6" hole drilled thru the wall and a pipe.
what do you mean if the furnace room is sealed airtight? You only bring in combustion air from the outside with a category 4.
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Old 03-12-2013, 03:20 PM   #4
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Primary and Secondary Air


plenty of people when they develop their basements into rec rooms drywall/sheetrock the furnace room into a box and put a solid door on the room. air cannot get in fast enough. plus most modern homes in Canada built since the year 2000 are so airtight that not enough air leaks in fast enough around doors and windows so the bldg code got changed where a combustion air pipe for any mid efficiency/80% efficient furnace was required.
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Old 03-12-2013, 04:27 PM   #5
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Primary and Secondary Air


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what do you mean if the furnace room is sealed airtight? You only bring in combustion air from the outside with a category 4.
No, you often need to bring in outside air with standard cat I, II, and III appliances.

There are also many Cat IV appliances that do not have outside air coming in for combustion.
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Old 03-12-2013, 04:58 PM   #6
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Primary and Secondary Air


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No, you often need to bring in outside air with standard cat I, II, and III appliances.

There are also many Cat IV appliances that do not have outside air coming in for combustion.
cat 1 and 2 use indoor air. Cat 3 and 4 use outside air. How do you figure different? Cat 3 and 4 are sealed and use outside air for combustion.
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Old 03-12-2013, 06:07 PM   #7
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Primary and Secondary Air


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cat 1 and 2 use indoor air. Cat 3 and 4 use outside air. How do you figure different? Cat 3 and 4 are sealed and use outside air for combustion.
Cat IV is a positive pressure flue appliance that condenses.

Cat III is a positive pressure flue appliance that is non condensing, and vents with SS flue.

Cat II is a negative pressure flue appliance that condenses.

Cat I is a negative pressure flue non condensing.

There is no spec that they get their combustion air from outside. The spec is only positive or non pressurized vent, and condensing or not.


Don't know where you get that they have to draw outside air for combustion.

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