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Minnesota Department of Labor and Industry

HVAC - Oversized furnace vent





"Over-sized" furnace vent


UMC Appendix C, Chapter 9

Submitted by:

MN B.O. Uniformity Committee

Approved by:

Thomas R. Joachim, State Building Official

Issue Date:

January 12, 2000


In the case of BTU/h input on a common vent being reduced, may a water heater, or similar appliance, remain on the common vent by itself?


Yes. The Uniform Mechanical Code Venting Tables in Appendix C, Chapter 9 address maximum Btu//h input ratings, not minimums.


GAMA and other agencies have developed their own venting tables. Some of these tables show minimum and maximum input values. If an appliance manufacturer refers to a specific venting table as part of the appliance listings and testing, then that table should apply to that appliance. Thus, if that specific table lists minimum Btu/h inputs and any remaining appliances do no meet the minimum threshold, the inspector should order corrections/remedy.

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