Feeling the Draught

Feeling the Draught

Commissioning of an appliance is a vital part of the installation process and a draught gauge is a really important item to hold in your tool kit to ensure the job is done properly. Here are some top tips on getting it right.

Flue Draught Test

The constant flow of flue gases at the correct rate of flow with the least possible variation is required for safe and efficient combustion. Insufficient flue draught will cause ignition difficulties and is likely to result in fume emission and a potential health risk. Too much draught will make control of the fire difficult and may result in overheating.  In this instance, fitting a draught stabiliser may be required. An appliance manufacturer will specify a range of flue draft conditions under which their appliance will operate.

Flue draught readings can be taken using a purpose made flue draught gauge or using any suitable pressure differential measurement device. See our examples later on in the article.

The correct place for measuring the chimney draught is close to the appliance and at least 150mm away from any draught regulator. Sometimes this distance may also be described as two times flue diameter.

Some appliances include purpose-made flue draught test points for test equipment sampling probe insertion. If no purpose-made point exists, a suitable point will need to be provided adjacent to the appliance outlet. In some instances a draught measurement can be taken by temporarily removing a sweeping access cover and using a cone or plate with a hole in the centre to prevent secondary air entry and enable insertion of the sampling probe. A flue draught reading should be taken before the appliance is lit to identify potential problems which could result from down draught.

Procedure for Taking Flue Draught Readings

The typical procedure when using a purpose made mechanical draught gauge as shown in Fig 30 is as follows:

1.   Visually inspect the draught gauge for signs of damage and/or defect.

2.  Ignite a small amount of fuel in the appliance and leave to burn for 20 minutes.

3.   Adjust pointer to zero (before each measurement).

4.  Position the gauge on a level base or hang upright.

5.   Insert metal sampling tube into test point preventing secondary air entry.

6.  Wait approximately 30 seconds for stabilisation and then take the draught reading.

7.     Take the reading every 10 minutes until the maximum draught is reached

Please Note: Atmospheric or weather conditions may cause incorrect draught readings.


Depending upon the draught reading obtained, it may be necessary to adjust the appliance air control devices and/or the flue draught stabiliser (if fitted). Any adjustment should be made in accordance with the appliance manufacturer’s instructions and the draught should be reading retaken after each adjustment.

If acceptable draught conditions are not able to be achieved, the appliance should be taken out of service and where appropriate the HETAS unsafe situations procedure (see HUSP form below) should be followed while the fault is rectified. Refer to Appendix E in the back of this Unit for more details.

Testing & Commissioning

Unless you have to leave a warning notice, a summary successful maintenance report for your customer will add a level of professionalism and give reassurance that you are leaving the installation in a safe state. A signed and dated testing & Commissioning sheet should offer the following as relevant:

·         Confirm operation status as per manufacturers requirements.

·         Confirm or detail non-compliance with current requirements.

·         Check the CO Alarm is operational and correctly positioned.

·         To check/confirm the condition of the “hidden seals” within the appliance carry out Smoke Test I.


·         Smoke Draw Test (Smoke Test II). This should be carried out with all the doors and windows closed in the room in which the appliance is installed.

·         Confirm flue draft readings are as per manufacturers requirements.

·         Ensure end user is confident in the continued use of the appliance.

·         Complete appropriate paperwork and where necessary obtaining customer signature and leave a copy with the customer.

Draught Gauges

HETAS currently has three draught gauges available in the HETAS Shop.


HETAS have produced the Unsafe Situation Procedure Assessment Form to help installers assess whether an installation is to be deemed unsafe and lists the re-commisioning checks needed if the installation is found to be compliant.

Visit the HETAS Technical Area for further information on the HUSP.


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