HVAC - Common vertical vent maximum size

Opinion

Inquiry:	05-04
Subject:	Common vertical vent maximum size
Submitted by:	Nirmal Jain, Building Code Representative
Approved by:	Thomas R. Joachim, State Building Official
Issue Date:	December 15, 2005
Question:	hat is the maximum size of a common vertical vent with two fan- assisted appliances?  What is the maximum size of a common vertical vent with two appliances, one natural draft and one fan-assisted?
Answer:	Minnesota Rule, Chapter 1346.5504.3.15: With two fan-assisted appliances or a combination of a fan-assisted & natural draft appliance, the maximum size of a common vertical vent will be no greater than four times the area of the smallest vent.
Comments:	The sizing is verified as follows: Two fan-assisted appliances: For a given common vertical vent size, the Btu/hr. input capacity of the smallest fan-assisted appliance will be within the min/max range per 2000 IFGC tables 504.2(1) and 504.2(2).    Two appliances, one natural draft and one fan-assisted: For a given common vertical vent size, the Btu/hr. input capacity of the fan-assisted appliance will be within the min/max range per 2000 IFGC tables 504.2(1) and 504.2(2).
Notes:	1.) It may be necessary to change the vent connector from single wall to double wall in order to meet the requirements of the tables. 2.) Total input of both appliances must be less than or equal to the maximum value requirements according to tables 504.3(1) and 504.3(2) under the common vent capacity sections.
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