This Technical Services Bulletin provides guidance specific to gas detection and gas verification that is not published in current service and operations manuals.

Many gas water heating appliances, including water heaters produced by Bradford White, are equipped with a combination gas valve that is design certified under North American standards including UL429, ANSI Z21.21/CSA 6.5, and ANSI Z21.78/CSA 6.20. The latter two, allow for gas to permeate through the combination gas control regulator diaphragm and present through an orifice to atmosphere. The release to the space in which the water heater is installed is permitted to a maximum rate of 200 cubic centimeters per hour (200 cc/hr.) under normal operation. This escape rate has been permitted since the inception of these standards. This release volume has been deemed acceptable and safe by gas industry experts, engineers, and government regulatory agencies for many years.

CSA F280 relates to determining the required capacity of Residential Space Heating and Cooling appliances and states that ventilation must be calculated based on CSA F326. CSA F326 mandates a ventilation design. Total Ventilation Capacity (TVC) Calculations ensure adequate ventilation air that enables dissipation of natural gas permeation allowable under normal valve operation.

Modern Electronic gas detection devices (Combustible gas indicators – Sniffers) are often sensitive enough to detect amounts of gas that may create nuisance findings. These instruments typically have a low range of 0 to 0.001% gas in air by volume (0 to 1000 parts per million). At this sensitive resolution of gas detection, gas in air concentrations of less than 1000 ppm would readily be detected. Concentrations of natural gas in air below 1000 ppm are not hazardous and easily dissipated by building ventilation and not notable from odour within the ambient atmosphere of the building space. The maximum leakage rate of 200 cc/hr would be detectable by gas detectors when on their sensitive (PPM) scale. However, 200 cc/hr is significantly less than the minimum required air ventilation (air replacement) rates mandated by all Canadian Building Codes and CSA F326 for both individual rooms in the house and the entire home.

Use of such gas detection devices (On the PPM Scale) may incorrectly lead the user to suspect that a safety hazard exists, even when the gas level detected is within the safe, and allowable required standards.

In the event readings are noted in the proximity of the combination valve one must determine if a safety hazard exists.