Tuesday, June 23, 2015

Venting a Bosch Therm 520PN or 520HN into an Existing Chimney

The Bosch Therm 520PN and Bosch Therm 520HN are both naturally drafting gas tankless water heaters and must be vented to the outside using a minimum of a 5" diameter galvanized type B gas vent.  6" diameter type B gas vent is required for all installations over 2,000 ft above sea level.  Under no circumstances should the vent pipe be reduced in size.  There must be a minimum of a 12" rise off the top of the heater before any 45's or 90 degree elbows.  If there is to be a horizontal section before going into the chimney then try and keep it as short as possible.  The maximum horizontal run allowed is half of the total vertical vent height.  45's, 90 degree elbows and any horizontal length is not to be considered in the total gas vent height.

The Chimney the Bosch tankless water heater is venting into must be the only thing going into the chimney.  The galvanized type B gas vent must run all the way up the chimney to an approved rain cap.  The minimum vertical vent height is 6 ft and any horizontal vent connectors or elbows are not to be considered in the total gas vent height.  All gas vent sections of pipe must be screwed together with sheet metal screws and properly supported.  The masonry chimney may have to be tile or metal lined before the insertion of the gas vent pipe.  Consult local codes for proper lining of chimney.  You may not vent any other fuel burning appliances into any free space remaining in the chimney.  Please see the illustration below for venting into the chimney and always follow the instructions listed in the installation manual for the heater.
A = Minimum of 6 ft. rise
1.  Listed approved Rain Cap
2.  Horizontal vent connection rising 1/4" per ft.
3.  Establish a 12" rise before any elbows

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