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Carbon monoxide testing methods for flued appliances

The sealing of buildings to achieve higher energy efficiency is impacting in particular on the presence of adventitious openings required by open flued gas appliances to operate safely.

Testing for CO gas spillage from open flued gas appliances following installation and servicing must be carried out in three tests.

Test 1: Establish baseline conditions by conducting a smoke test with the appliance and exhaust fans not in operation to establish if a negative pressure environment exists.

Test 2: Operate exhaust fans and conduct a smoke test with the appliance not in operation to establish if a negative pressure environment exists.

Test 3: Operate the appliance while operating exhaust fans and test for spillage.

Carry out these tests in the order shown otherwise you will not know whether the fault lies with negative pressure when extraction fans are operating or with the appliance installation.

Note: While carrying out spillage testing, take readings of your exposure to CO gas. Measure the CO levels where you are located. This information will allow you to calculate your average CO exposure for an eight hour period. Refer to Gas Information Sheet 44, Carbon monoxide safe working level [pdf]

Open flued indoor gas appliances testing

Test 1 – Establish baseline conditions

  1. Close external windows and doors. Ensure all open flued appliances and air extraction fans in the space being tested are not in operation.
  2. Position a suitable smoke producing device (for example, a smoke pen, smoke matches or incense stick) at the appliance draft diverter relief opening of each appliance in the space, or adjacent to appliance openings for combustion air.
  3. Observe any flow of smoke towards or away from the appliance.

Test 2 - Smoke test for a negative pressure environment

  1. Turn on all extraction fans.
  2. Close external doors and windows and open or close internal doors to achieve the greatest negative pressure effect on the flue system(s) or chimney(s) of the appliances in the space being tested.
  3. Position a suitable smoke producing device (for example, a smoke pen, smoke matches or incense stick) at the appliance draft diverter relief opening of each appliance in the space, or adjacent to appliance openings for combustion air.
  4. Observe whether smoke is being drawn away from the appliance towards the source(s) of the suction.
  5. Compare the smoke pattern with that observed during the baseline test.
    1. If the smoke pattern is different there is insufficient ventilation which will need to be rectified in accordance with AS/NZS 5601.1
    2. If the smoke pattern is the same. This indicts that the extraction fans have had no observed affect.

If smoke is drawn away from the appliance and the smoke pattern does not match the baseline condition in steps d. and e. then incrementally open an external window until smoke is no longer dawn away from the appliance.

Note:  If a window is opened during testing to overcome a negative pressure then additional ventilation, equivalent to the area of the opened window, must be provided.

The appliance must be isolated until additional permanent ventilation is provided.

  1. With the extraction fans still operating close any window opened and proceed to Test 3.

Test 3 - Spillage test - appliance and flue operation

Note: Appliances shall be checked for obvious defects and be at room temperature before proceeding. Prior to conducting this test, the appliance shall be serviced and clean.

  1. Turn on and zero or check the detection equipment in accordance with the manufacturer's instructions, then take a background reading in the room in which the appliance is situated. Record the CO reading. A background CO reading may be present due to other sources such as cookers or from the smoke test.
  2. With exhaust, fans still in operation operate all open flued appliances in space at the highest setting for 10 minutes from cold for Type 1 decorative gas flame effect fires installed in a chimney and for 5 minutes from cold for all other appliances. During this period, ensure the appliance is operating in accordance with manufacturer’s instruction including operation at nominal test point pressure.
  3. Where a space heater is installed in a chimney without a chimney liner and spillage still occurs in testing after 5 minutes operation, the appliance may be operated a further 5 minutes to see if the chimney draw establishes and spillage ceases

  4. Record the measured values of combustion products in the space under test which are now the new background levels.

Note: The CO background level may have risen due to the initial spillage from the appliance at start up.

  1. After the required time specified in step b., check for combustion product spillage from each appliance. Sample the air with combustion detection equipment at locations external to and in the vicinity of the appliance(s) where leakage or spillage of combustion products can occur eg. draft diverter relief openings, heat exchangers, fan discharge points and flue connections.
  2. 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.

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.

Measured values of combustion products at the appliance greater than the background values in step c. indicted spillage of combustion products from the appliance(s) in that space. If no CO spillage is detected then testing is completed.

  1. If however CO spillage is detected then you will need to switch off the exhaust fans and restart the appliance from a cold start.
    • If there is CO spillage after 5 minutes without a negative pressure environment then check for faults with the appliance or flue. If faults cannot be found or rectified then the appliance must be isolated and it is recommended to contact the appliance manufacturer.
    • If there is no CO spillage after 5 minutes then a negative pressure remained when conducting Test 2 and the window in Test 1 was not opened far enough. Switch on exhaust fans once again and open the window further until CO spillage ceases.

If a window is opened during testing to overcome a negative pressure then additional ventilation equivalent to the area of the open window must be provided. The appliance must be isolated until additional permanent ventilation is provided.

  1. If spillage is observed after faults with the affected appliance(s), flue system(s) have been rectified and additional ventilation provided, immediate steps shall be made to make the appliance(s) safe including disconnection if required.

Central heating units

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.

  1. If the appliance is an open flued appliance, and installed indoors, then follow the testing procedures for open flued gas appliances first.
  2. For all central heater appliances, note the background CO level. Operate the heater and place the detection equipment sampling probe in the air stream of a duct outlet (floor register or ceiling register). Monitor for CO for a further 10 minutes.

If the CO level exceeds the background level then the appliance is leaking or spilling CO and must be isolated.

If any cracks or openings within the heat exchanger of the central heater are evident, combustion products that contain CO may be dispersed throughout the building.

Note: As the heat exchanger heats up, and cracks and openings expands, more combustion products may enter the supply air stream and flow into the building.

Room sealed space heaters

  1. Check the background CO levels.
  2. Operate the appliance for 10 minutes and then check for CO at the appliance.

Always check the lower levels of room sealed gas space heaters as these appliances may incorporate a condensate drain at the base of the heat exchanger and this could be an area where combustion products may discharge into the building. The CO level should not exceed the background level.

Updated: 04 Feb 2021

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