Special venting system and type BH venting system termination clearances



Reference number

This directive is being issued by a provincial safety manager pursuant to section 30 of the Safety Standards Act.


This directive details vent termination clearances for special venting systems or BH venting systems when not specified by the CSA B149.1 Natural Gas and Propane Installation Code (the Code) or appliance manufacturers certified installation instructions.


Special venting system: a venting system certified with the appliance and either supplied or specified by the appliance manufacturer.

BH vent: a vent complying with ULC S636 and consisting entirely of factory-made parts, each designed to be assembled with the others without requiring field fabrication, and intended for venting gas appliances.


Clause 8.10.4 of the Code requires a special venting system or a BH venting system to be installed in accordance with the terms of its listed type and the appliance and vent manufacturer’s certified installation instructions.

Manufacturers of appliances that require a special venting system or BH venting system commonly do not specify all required vent termination clearances in the certified installation instructions, including, but not limited to specifics for soffits or inside and outside corners. Generally, in these occurrences manufacturer’s instructions include a clause stating: clearance to be in accordance with local installation codes and the requirements of the gas supplier or Authority Having Jurisdiction.

In the event that manufacturers do not provide certified instructions detailing the clearance requirements for appliances installed with special venting systems or BH venting systems, the termination clearances associated with listing standards and industry practice must meet the requirements detailed below.

Ref Description Requirement
A Vertical clearance to ventilated soffit located above the terminal within a horizontal distance of 2 ft (61 cm) from the center line of the terminal 36 in (91 cm)
B Clearance to unventilated soffit 36 in (91 cm)
C Clearance to permanently closed window 12 in (30 cm)
D Clearance to outside corner 12 in (30 cm)
E Clearance to inside corner 36 in (91 cm)
Special venting termination


Vicky Kang
Provincial Safety Manager, Energy


Gas Safety Regulation
CSA B149.1 Natural Gas and Propane Installation Code