CSA 4.3-2014 Gas-fired water heaters, volume III, storage water heaters with input ratings above 75,000 Btu per hour, circulating and instantaneous.
Flame spreader supports shall be constructed so the flame spreader cannot be supported at other than the correct distance from the burner.
Burners shall be provided with means to prevent disintegrated ceramic flame spreader material from falling into the burner port(s). They shall also be designed so disintegration of the ceramic will not cause a hazardous change in the operating characteristics of the burner.
4.7 Primary air adjustment means
Primary air adjustment means shall be designed so the flow of primary air can be controlled to provide proper flame characteristics.
Primary air adjustment means, when provided on main burners, shall be designed so as to give a yellow- tipped flame when adjusted for minimum primary air.
When air shutters are used, there shall be no openings other than the adjustable openings through which primary air may be entrained. Clearances, such as between air shutters and air mixer faces or around the orifice projection, shall be reduced to a practical minimum so as to have no appreciable effect on the flame characteristics when stopped by lint or other materials.
Means shall be provided to secure air shutters in any desired position. Such means shall be accessible for adjustment with the burner(s) in place and the water heater in operation.
Sheet-metal air shutters shall be not less than 0.0254 in (0.645 mm) thick. If less than 0.0508 in (1.29 mm)t thick, air shutters shall have the outer edge turned at 90 degrees (1.57 rad), or be otherwise properly reinforced. Air shutters shall be constructed of a corrosion-resistant material or have a corrosion-resistant finish. Cast iron air shutters shall be considered as complying with this provision.
* This corresponds to No. 22 U.S. Standard gage sheet steel with all applicable minus tolerances included. t This corresponds to No. 16 U.S. Standard gage sheet steel with all applicable minus tolerances included.
On a water heater provided with an induced draft or power burner, the appliance design shall be such as to prevent gas flow to the main burner(s) in the event the blower providing the draft becomes inoperative.
A properly applied centrifugal or sail switch, or equivalent device, meets the intent of this provision. If a centrifugal switch is used, the blower shall be secured to the shaft on which the centrifugal switch is located by means of: keying, two set screws with at least one on a flatted shaft, a locking type set screw on a flatted shaft, or the equivalent.CSA 4.3 pdf download.