Originally Posted By: jrupert
This post was automatically imported from our archived forum.
The lateral run from the furnace to the chimney is based the BTUH of the furnace, the distance to the chimney, the furnace type or efficiency, the venting material type (single wall or double wall) is the furnace the only appliance venting to the same location, how many elbows in the flue run etc?all plugged in to the AGA/GAMA venting tables, etc? What I trying to say this is not a simple calculation and no rule of thumbs should be applied.
Depending on how old the furnace the venting may not meet the new GAMA table but this does not necessarily mean that it?s wrong, it may have complied with the manufactures guidelines at the time of installation
Generally 60% efficient furnaces with a venting over 10ft lateral with more then 2 elbows may be an issue, newer 80% efficient furnaces should be under 10ft
The vent connector from the furnace to the chimney should slope a minimum of ? inch per lineal foot towards the furnace
With the proper flue cap, the furnace flue particulates should not back draft down the chimney providing the house is not under a negative pressure
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