Testing for carbon monoxide

A licensed gas-fitter must perform two-stage testing for carbon monoxide gas spillage from open flued gas appliances.

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

Perform testing in the correct order to determine if the fault is with the appliance installation or caused by negative pressure when exhaust fans are operating.

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 equipment has been calibrated within the last 12 months using test gases that are NATA traceable or equivalent. The equipment supplier should be able to assist you with this requirement.

Test 1 - carbon monoxide spillage

  1. Ensure all indoor gas appliances are turned off and not operating.
  2. Carry out a safety inspection of the appliance.
  3. Turn on your detection equipment.   Take a background reading in separate locations within the building as the problem may be caused by a separate source of carbon monoxide and not the gas appliance.
  4. Light the gas and operate with the burner and fan (if fitted) on the highest setting. Place the carbon monoxide detection equipment sampling probe at all locations where leakage or spillage of combustion products can occur. This includes the:
  • draught diverter relief openings
  • heat exchanger joints
  • flue connection
  • 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, position the sampling probe next to the opening and not inside the draught diverter.

The carbon monoxide 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 carbon monoxide.

Test 2 - Negative pressure

  1. Leave the appliance operating at maximum gas consumption and shut all windows and exterior doors.  Turn on exhaust and extraction fans, one at a time.
  2. After turning on each fan, check for carbon monoxide by passing the detection equipment sampling probe over the draught diverter relief openings.
  3. If possible turn down the appliance room fan. Set the fan to the lowest setting and check for carbon monoxide again at the draught diverter relief openings.

If the carbon monoxide reading detected is above the original background level reading it  means the exhaust fans have created a negative pressure within the building 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, you are required to increase ventilation from outside the building through walls, floors or ceiling space.

Decorative effect gas log fires and space heaters can use an existing chimney to remove flue products to outside air.. Take carbon monoxide readings after 10 minutes of operation. If you are using a fabricated flue system take carbon monoxide readings after 5 minutes of operation.

Also in this case the carbon monoxide reading on the test instrument should diminish to the original background level reading at the end of the 10 minute test cycle.

Spillage discharge from central heating units located outside the building, in the roof or under floor may go unnoticed. What may be found is carbon monoxide being drawn into the building where the heat exchanger has cracked or through damaged seals within the combustion chamber.

  1. For an open flued appliance and installed indoors follow the testing procedure for open flued gas appliances first.
  2. 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 carbon monoxide for a further 10 minutes.

Note: If there is evidence of any cracks or openings within the heat exchanger of the central heater, combustion products containing carbon monoxide can be dispersed throughout the building. Carbon monoxide readings may initially only be minor. 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 carbon monoxide level exceeds the initial background level, then the appliance is leaking or spilling carbon monoxide.

Always check lower levels of room sealed gas space heaters. These appliances may incorporate a condensate drain at the base of the heat exchanger which could be an area where combustion products may discharge into the building.

This testing information was developed by Energy Safe Victoria, and reproduced with approval by Consumer Building and Occupational Services.