The following was printed in the TSSA Fuels Edition Fall 2010 Update, you can download it Here
The typical regulatory approach in this area is to refer to the certified installation instructions for installation details, such as the type of vent, its size and length, type of fuel and its characteristics, pressure and quantity, etc.
Among these installation details are clearances to combustible materials. Where certified installation instructions do not prescribe these minimum clearances, one needs to refer to Section 7.32 of CSA B149-05, which requires a minimum 76.2 cm (30 inches) above, 15.24 cm (6 inches) from sides and back, and 121.92 cm (48 inches) in front of a gas or propane fuelled residential range. What TSSA is finding now are very elaborate custom-designed vent hoods over gas ranges that are closer than the required 76.2 cm above the ranges. This could be due to a common misunderstanding between multiple service providers who are directly or indirectly involved surrounding the installation of a custom-designed vent hood. This could include the designer or builder of the kitchen cabinets who did not know that the range was going to be gas-fired to the person who installed the gas range relying on the designer/engineer/architect to ensure everything is up-to-code, or even the building inspector whose focus is on the structural integrity of the building envelope, not the appliances.
The reasons for maintaining clearances are very compelling while the responsibility is shared by everyone – among them, the gas technician’s responsibility and ultimate accountability to install appliances in accordance with the code requirements and certified installation instructions. This is where you come in and, if not for the regulatory requirements then for peace-of-mind and your family’s security, you may want to ask yourself whether allowing such non-code compliant installations are worth the reduced installation time or aggravation you may cause to the general contractor, kitchen builder or home owner – not to mention safety. Safety regulations are there for a reason. These are not theoretical. They are practical applications and literal prescriptive requirements of the law – and they exist, first and foremost, for your safety and all concerned.
The following is from the B149.1S1-07,
Clause 7.32.4 - Except where permitted by Clauses 4.13.2 and 7.32.5 to 7.32.7, a residential type range shall have the following minimum clearances to combustible material:
(a) above - 30" (750mm)
(b) front - 48" (1200mm)
(c) back & sides - 6" (150mm)
Clause 4.13.2 - The clearances to combustible material specified in Clause 7 shall not be reduced unless
(a) such reduced clearance is certified as safe by a nationally recognized cerification organization acceptable to the authority having jurisdiction, and so marked on the appliance nameplate; or
(b) protection is provided for the combustible material, and such protection and such reduced clearance are in accordance with Table 4.1
Clause 7.32.5 - A residential-type range certified for zero side and rear clearances may be installed with zero side clearance from combustible material, provided that there is a 1" (25mm) clearance at the back and a 28 MSG (0.3mm) sheet metal shield on the side walls spaced out a minimum of 0.25" (6mm). The shield shall extend from the rear wall to the front edge of the range and from 5" (125mm) below to 30" (750mm) above the cooking surface.
Clause 7.32.6 - A new residential-type range shall be installed in accordance with its certified clearances from combustible material as specified on the appliance rating plate.
Clause 7.32.7 - When the underside of the combustible material above a residential-type range is protected with insulating millboard at least 0.25" (6mm) thick covered with sheet metal not less than 28 MSG (0.3mm), the clearance above the range as specified in Clause 7.32.4 may be reduced to 24" (600mm).
Clause 7.32.7 is stating what Clause 4.13.2 (b) and Table 4.1 have already stated. I wonder why they don't have a seperate Clause approving a reduction of 9" or 12"?