Commissioning Guidance Smoke, Spillage & Flue Draught Testing

The following guidance will form a Technical Note which will be published by HETAS early in 2020. All of the HETAS Technical Notes and Bulletins can be accessed in the Technical Area of the website (login required).

Commissioning

Commissioning of solid fuel burning appliances is a critical final stage of any installation, servicing or maintenance works, and intended to evidence that the appliance and flue works in a safe manner at the time the commissioning takes place. One of the most important parts of the commissioning procedure for any engineer installing a solid fuel burning appliance is to ensure that the flue is operating effectively to safely disperse the products of combustion into the atmosphere via the terminal.  It also identifies performance and operation of the appliance, and whether it is operating within any set efficiency parameters – important for responsible burning and use.

For example, insufficient draught in the flue will result in ignition difficulties and potential spillage of the appliance once in operation, whereas too much draught may result in overheating of the appliance.

It is important that these tests are documented as a record of the performance characteristics on the day of the test, as these values can change over time.  It is also necessary to ‘hand-over’ the appliance to the consumer ensuring they are fully aware of the lighting, operating and maintenance procedures.

Guidance

This document sets out guidance for the relevant spillage, smoke and flue draught checking procedures as part of commissioning and recommissioning phase, either post installation or after remedial repairs/maintenance of batch fed solid fuel and biomass heating appliances.

In the first instance, appliance manufacturer installation instructions should be consulted, as some manufacturers prescribe their own commissioning procedures and records specific to the appliance, and may be a requirement for things such as the appliance warranty. In the absence of any manufacturer specific commissioning procedure, installers can use this technical note as a guide to appropriately commission solid fuel burning appliances.

It is imperative that during solid fuel appliance operation for all of the products of combustion produced to be safely discharged up the chimney and dispersed into the atmosphere, and not spill back into the room in which the appliance is installed.

Procedure

The HETAS Commissioning Testing Procedure consists of three specific tests;

  1. Smoke Draw Test (Smoke Test II)with the appliance doors shut, under initial start-up conditions using smoke pellets
  2. Flue Draught Test and Flue Draught interference test (FDIT) – with a fire established and doors closed, measure the flue draught within the flue or as directed by the manufacturers.  FDIT – If any mechanical extraction is present within the room (or property) operate the extractor and ensure there is no drop-in flue draught.
  3. Spillage Test (Refuel) with the appliance doors open, under refuel conditions using a smoke match/pen

Pre-Commissioning Checks

All solid fuel burning appliances require an adequate supply of air to ensure that efficient combustion of the fuel can occur and the chimney can function correctly in compliance with UK Building Regulations J1 detailed on page 9 of Approved Document J. It is important to undertake the following pre-commissioning checks before verification of the installation through spillage and flue draught testing

  • Ensure the flue ways are inspected for any signs of damage and swept clean of debris that may restrict the evacuation of combustion products
  • Assess the air permeability of the property, including any recent renovation works to increase energy efficiency (i.e. cavity wall insulation, increased loft insulation etc.)
  • A copy of appropriate information is available in verifying the recorded flue draught against the recommended draft specified by the manufacturer

Step 1 – Smoke Draw Test (Smoke Test II) – Initial Light Up

It is important to ensure that after the installation phase, all appliance and chimney seals are sound and that the chimney/flue effectively disperses smoke from the appliance chamber to the outside atmosphere through the terminal.

To confirm this a smoke draw test should be carried out, with the appliance doors shut, under initial start-up conditions using an appropriately sized smoke pellet. Generally, a pellet that generates 24m3 of smoke over 60 seconds will allow enough time for an assessment to be made outside the property of smoke leaving the terminal.

Further guidance is also available within Appendix E of Approved Document J.

Equipment Needed

  1. Firelighters or blow lamp
  2. Smoke Pellet (24m3/60sec)
  3. Flue Draught Gauge

Procedure

  1. Close all external doors and windows, internal doors to the room the appliance is located in and ensure all openable ventilators are closed and any devices that extract air from the dwelling are off.
  2. Before lighting, a flue draught reading should be taken to identify any potential problems resulting from down draught. Once taken, preheat the flue by lighting a small fire using either suitable firelighters, or a blow lamp heating the flue for around 10 minutes.
  3. Light a Smoke Pellet (24m3/60sec) , place into the middle of the appliance chamber and shut the appliance door and air controls. Check any seals around the door are airtight, then open the air-controls and set these to their maximum open position.
  4. Initially, check that all of the smoke enters the flue in an upward motion and none comes back into the room through any part of the stove, connecting flue pipe or air supply duct.
  5. Go outside and observe whether the smoke is evacuating from the intended flue, and ensure smoke it not dispersing from any adjacent chimneys or brickwork.

Results

The result of the flue tests should show the smoke produced from the smoke pellet/pen being effectively drawn into the chimney and out to atmosphere. Failure of smoke draw test can be due to a number of reasons;

  1. The flue isn’t warm enough for an effective draw. Heat the flue (as described in step 2) for an additional 10 minutes and repeat the test.
  2. Opening a window in increments and observe whether the smoke is drawn up the flue faster. If this solves the issue, additional ventilation is required in-line with the new measured amount of air being drawn through the window from outside

If the smoke test fails after any of the suggestion above, further investigation is required to correct the issues. Once completing any remedials, a full re-test following steps 1-5 above should be undertaken to ensure sufficient operation of the appliance.


Step 2 – Flue Draught Testing

A flue draught reading should be taken once the appliance has been lit, as well as taken during operation with any mechanical extract systems, tumble dryers and/or other open combustion appliances running on full (see flue draught interference section).

Equipment Required

A purpose made flue draught gauge or suitable pressure differential measurement device can be used to measure and record flue draught. The equipment should achieve an appropriate degree of accuracy, for in-field operation the order being within 10% of the value. Consult the gauge manufacturer instructions for further details, or visit the HETAS shop at for a range of suitable draught gauge equipment for purchase.

Procedure

A visual inspection of the device for defect should be done and ensuring the device has been appropriately calibrated if using an analyser or equivalent. Consult the equipment manufacturer instructions for more details on whether and how to calibrate the equipment.

  1. Ensure all doors and windows to the room and are closed, and all ventilation fans are switched off.
  2. Light a small fire in the appliance chamber and allow for the optimum operating temperature to be reached.
  3. The flue draught reading should be recorded and checked that it is in the parameters specified by the appliance manufacturer.

Measurement Location

The draught reading should be taken from a suitable position to give the appropriate value recommended by the manufacturer. This can be taken either in the connecting flue pipe or the appliance itself if the manufacturer provides an appropriate test point. Where no purpose-made test point is available, a measurement can be taken by temporarily removing a sweeping access cover and using a cone or plate with a pre-drilled hole to enable the sampling probe to be inserted.

In extenuating circumstances, the appliance manufacturer may allow for a 4mm diameter probe to be used within the firebox of the appliance through the rope seal, but this will prohibit a different result and will need confirmation from the manufacturer of the measurements achieved.

Measurement Recorded

The manufacturer of the appliance will have appropriately tested and verified the product’s operation under a suitable flue draught conditions, typically at 12 Pascal’s however in some instances this may be higher. It is important when taking a measurement and recording the results, that the value is in the range specified as acceptable by the appliance manufacturer and within technical literature. Both manufacturer requirement and the result of the draught test should be recorded on the appropriate commissioning form, with one being left with the customer and one retained by the installer for record purposes. In instances where the manufacturer required value cannot be obtained, specialist advice from the manufacturer should be sought

Measurement Result & Remedials

There may be cases where an installer carries out a flue draught test and does not achieve a reading within the tolerances confirmed and specified by the appliance manufacturer. If at any stage during commissioning the flue draught reading take differs from the draught parameters specified by the manufacturer, action should be taken to locate the cause of the discrepancy or query with the manufacturer and the installation rectified before proceeding with further testing.

Note – Try opening a window in gradual stages to see if the additional air into the room has an effect on the flue draught reading. If the draw begins to increase then further permanent ventilation may be required into the room the appliance is installed

What reading should I achieve?

The manufacturer of the appliance will have appropriately tested and verified the product’s operation under a suitable flue draught conditions, typically at 12 Pascal’s however in some instances this may be higher. It is important when taking a measurement and recording the results, that the value is in the range specified as acceptable by the appliance manufacturer and within technical literature. Both manufacturer requirement and the result of the draught test should be recorded on the appropriate commissioning form, with one being left with the customer and one retained by the installer for record purposes. In instances where the manufacturer required value cannot be obtained, specialist advice from the manufacturer should be sought


Step 3 – Flue Draught Interference Test

ADJ stipulates that the installation of a solid fuel appliance in a room with an extraction system should be avoided. However modern homes may contain forms of mechanical ventilation (i.e. Bathroom extract fans, cooker hoods, tumble dryers etc.) either in the room in which the appliance is installed or in another room of the property.

The extraction test is a means to verify that the manufacturers required flue draught during operation is met under the relevant conditions. In certain circumstances spillage can still occur and so it is important to carry out the prescribed smoke spillage tests detailed in this document also. 

Equipment Required

See Step 1 – Flue Draught Testing

  1. Continuing on from the flue draught test with the appliance alight, open any internal doors interconnecting the room in which the appliance is installed to rooms where extraction fans are present within the property
  2. Turn on all extract fans within the property to the maximum speed setting allowed
  3. Run the extract systems for ten minutes, and then, record the flue draught reading. The reading should ideally be the same as when the extractors were turned off however it is likely that there may be a small dip in the recorded draught. This is allowable provided the draught does not fall below the minimum specifications of the stove manufacturer.
  4. Once the tests confirm satisfactory operation, remove the test device and seal any apertures in the flue way if required and record the results.

Measurement Recorded

The manufacturer of the appliance will have appropriately tested and verified the product’s operation under a suitable flue draught conditions, typically at 12 Pascal’s however in some instances this may be higher. It is important when taking a measurement and recording the results, that the value is in the range specified as acceptable by the appliance manufacturer and within technical literature. Both manufacturer requirement and the result of the draught test should be recorded on the appropriate commissioning form, with one being left with the customer and one retained by the installer for record purposes. In instances where the manufacturer required value cannot be obtained, specialist advice from the manufacturer should be sought

Measurement Result & Remedials

Note: If at any stage during commissioning the flue draught reading taken differs from the draught parameters specified by the manufacturer, action should be taken to locate the cause of the discrepancy and the installation rectified before proceeding with further testing.

The SIA are currently incentivising manufacturer members to provide appropriate flue draught test point on the appliance under future development and production, which will allow for an accurate draught to be measured and coincide with the recommended values given within manufacturer instructions.


Step 4 – Spillage Testing – Refuelling Conditions

It is imperative that during closed solid fuel appliance operation, all of the products of combustion produced to be safely discharged up the chimney and dispersed into the atmosphere, and not spill back into the room in which the appliance is installed. This is important in modes of operation when the door is both closed and opened when refuelling the appliance, and spillage checks should be undertaken in both these scenarios, under cold and hot testing commissioning conditions.

Smoke Draw Test – with the appliance doors shut, under initial start-up conditions using a smoke pellet

Spillage Refuel Test – with the appliance doors open, under refuel conditions using smoke pen

The below gives some of the general guidance to allow installers to undertake the appropriate spillage tests upon commissioning of a solid fuel appliance. Ensure that all necessary commissioning checks have been completed beforehand, and that the installation is in compliance with appropriate standards and guidance.

Equipment Needed

  1. Kindling or electric heater
  2. Small Seasoned Logs
  3. Smoke Pellets (5m3/30sec)
  4. Smoke match/pen
  5. Torch (optional)

Procedure

With the initial chimney draw verified as adequate, light a fire in the appliance using the recommended number of firelighters/kindling/small logs and manufacturer’s recommended air control position and allow the appliance to reach its normal operating temperature. At the end of the banking period and before refuelling;

  1. Close all external doors and windows, ensure all openable ventilators are closed.
  2. Open the appliance door and with a smoke match/pen (15 sec burn time) pass over the top and side edge of the opening of the combustion chamber, observe and record if the smoke/combustion products are drawn into the chimney or spill back into the room. Once the smoke is extinguished, close the appliance door
  3. Repeat this test with all extraction fans running and internal doors open connecting the room the appliance is installed in to the extraction device(s) (see extraction test above) and record the results

Measurement Recorded

The result of the flue tests should show the smoke produced from the smoke pellet/pen being effectively drawn into the chimney and out to atmosphere.

Measurement Results & Remedials

If the results of the tests show that products of combustion enter back into the room, suitable remedial action will need to be taken to ensure the occupants are not exposed to continuing incidents of spillage. Remedial action may include incorporating additional ventilation. A quick and simple way to check for this is to gradually open an available window in the room in which the appliance is installed and observing whether the spillage stops.

If this cures the problem the it will be necessary to fit an additional amount of permanent ventilation. If the smoke continues to fail to be drawn through the appliance, it is worth carrying out an inspection of the baffle arrangement and connecting pipe/flue for any signs of significant blockage. Further assessment of the installation may be required.



Commissioning records are available via the HETAS Shop.

The HETAS Technical Helpline is on hand to discuss your technical enquiries. Contact 01684 278194 .


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