Department of Justice
Testing for CO gas spillage from open flued gas appliances must be carried out in two stages:
Carry out these tests in the correct order otherwise you will not know if the fault is with the appliance installation or is caused by negative pressure when exhaust fans are operating.
The higher energy efficiency ratings for new houses are compromising the need for fixed ventilation required by open flued gas appliances to operate safely.
A carbon monoxide reading will more than likely be evident when the flue is cold. It may take some minutes for the flue to draw properly.
Ensure that your equipment has been calibrated within the last 12 months using test gases that are NATA traceable or equivalent. The supplier of your equipment should be able to assist you with this requirement.
Note: When sampling at the draught diverter opening, please ensure that the sampling probe is positioned adjacent to the opening and not inside the draught diverter.
The CO reading on the test instrument should diminish to the original background level reading at the end of the 5 minute test cycle. If not, then the appliance is leaking or spilling CO.
If the CO reading detected is above the original background level reading it will mean a negative pressure within the building has been created by the exhaust fans and flue products are being drawn back down the flue and dispersed into the building.
To prevent negative pressure developing from the operating of exhaust and extraction fans, increased ventilation from outside the building through walls, floors or ceiling space is required.
In the case of decorative effect gas log fires and space heaters, which use an existing chimney to convey the flue products to outside air, rather than a fabricated flue system, CO readings should be taken after 10 minutes of operation (instead of the 5 minutes for fabricated flue systems).
Also in this case the CO reading on the test instrument should diminish to the original background level reading at the end of the 10 minute test cycle.
Discharge of spillage from central heating units located outside the building, in the roof or under floor may in many cases go unnoticed. What may be found is CO being drawn into the building where the heat exchanger has cracked or seals within the combustion chamber have been damaged.
Note: If any cracks or openings within the heat exchanger of the central heater are evident, combustion products that contain CO can be dispersed throughout the building. If CO readings are evident, and they may only be minor initially, please note as the heat exchanger heats up and cracks and openings expand, more combustion product can enter the supply air stream and flow into the building. If the CO level exceeds the initial background level, then the appliance is leaking or spilling CO.
Always check lower levels of room sealed gas space heaters as these appliances may incorporate a condensate drain at the base of the heat exchanged and this could be an area where combustion products may discharge into the building.
AS4553 Gas space heating appliances, states:
"There shall be no leakage or spillage of combustion products from an open flued appliance, its flue system, or draught diverter, 5 minutes after ignition when the appliance is operated at nominal gas consumption".
This information was developed by Energy Safe Victoria, and reproduced with approval by WorkSafe.