Camus Hydronics VTech 0499 - Part 4 - Gas and Combustion Hardware; 4.1 Gas Piping and Connections; 4.2 Gas Supply Pressure

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 Concentric Venting - Kits can be ordered to provide venting
and combustion air supply through one opening. Vent/air pipe
still limited a maximum 100 equivalent feet (30.5M) in length
each.
Horizontal Concentric Vent Clearances