Home Gasfitters and Plumbers

Gasfitters and Plumbers

Testing for carbon monoxide spillage from gas heaters

Testing for CO gas spillage from open flued gas appliances must be carried out in two stages:

  • Test for CO spillage with only the appliance operating.
  • Test for negative pressure flue gas drawback by closing doors and windows and then turning on extraction fans in the home.

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.

Using carbon monoxide measuring equipment

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. Open flued indoor gas appliances with fabricated flue systems.

Test 1 – CO spillage

  • Ensure all indoor gas appliances are turned off and not operating.
  • Carry out a safety inspection of the appliance to be tested.
  • Turn on your detection equipment and take a background reading in separate locations within the building as the problem may be caused by a seperate source of CO and not the gas appliance.
  • Light the gas and operate with the burner and fan (if fitted) on the highest setting.
  • Place the CO detection equipment sampling probe at all locations where leakage or spillage of combustion products can occur including the draught diverter relief openings, heat exchanger joints, flue connection and the base of flue product collection hoods. Continue monitoring for leakage or spillage and in particular note, the readings taken after the appliance has been operating for 5 minutes.
  • 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.

Test 2 – Negative pressure

  • Leave the appliance operating at maximum gas consumption and shut all windows and exterior doors and then turn on exhaust and extraction fans, one at a time.
  • After turning on each fan, check for CO by passing the detection equipment sampling probe over the draught diverter relief openings.
  • If the appliance room fan can be turned down then, set the appliance room fan to the lowest setting and check for CO again at the draught diverter relief openings.
  • 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.

Decorative effect gas log fires and space heaters using an existing chimney

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.

Central heating unit

  • 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.
  • If the appliance is an open flued appliance and installed indoors then follow the testing procedure for open flued gas appliances first.
  • Continue to operate the heater and place the detection equipment sampling probe in the air stream of the nearest duct outlet (floor register or ceiling register). Monitor for CO for a further 10 minutes.
  • 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.

Room sealed space heaters

  • 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.

Australian Standards

  • 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”.


Further Resources

ESV has produced a DVD to remind gasfitters of the steps they should take when conducting safety inspections on gas heaters.

To order a copy of this DVD or for more important information for gas professionals in relation to licensing and regulations and technical information, check out ESV’s website on http://www.esv.vic.gov.au or contact ESV by email on info@esv.vic.gov.au.


This information was developed by Energy Safe Victoria.

Miss Kiss
Griffiths Goodall
Energy Safe Victoria
Origin Energy