Posted by & filed under Chimney Sweeping tips, General, Technical.

The subject of the Sweep safe Technical update is type one and type two smoke testing.
The two tests serve very different purposes and must not be confused with each other.
Although you will find this guide very useful it does not supersede the process set out in building regulations section j and we highly recommend you take the time to study the document.

A type one test is a sealed test designed to check for unacceptable leakage where as a type two test is designed to check for draught and adequate smoke evacuation. It is this type two test or variations of that we perform at the end of every sweep and document on the certificate.

Let’s first look at what is required to perform the tests. We are using:

  • White smoke pellets with a 60 second burn time producing 24m3 of smoke each.
  • A lighter
  • Binoculars
  • A method to pre heat the flu
  • A metal vessel or cup to hold the pellets
  • Gloves
  • For a sealed type one smoke test we additionally require a way to safely access the pot or terminal
  • A sealing sponge or bladder to seal the terminal
  • A board or similar method to seal the appliance or opening
  • A second person
  • A pale of water for that worst case scenario

Type two smoke test

Firstly we close all door and window in the room of the appliance, we also close any closable air vents.
If there are extractor fans we turn them on full power and wait several minutes to make worst case scenario conditions
Next we preheat the flue for 10 Minutes.

After the flue is heated an up draught is formed, place one smoke pellet in the burning area inside the cup and ignite it at arm’s length wearing a glove.

We close the door of the appliance if it is designed to be used with the door closed.
Initially we check around the appliance to check for spillage or a weak or slow up draught, if the draught is weak or slow. Next open an external window to see if the smokes velocity increases. If it does this demonstrates that the ventilation is inadequate.
Next proceed outside to a pre-determined position and view the pot and chimney stack using our binoculars and check for the complete evacuation of the smoke.

The smoke must issue from only one chimney pot or terminal, the same pot or terminal as the sweeping brush was associated with.

Binoculars are essential for smoke testing

If smoke is seen from more than one pot or smoke is seen leaking from the stack, rafters or anywhere else then this is a fail as it shows leakage. In essences we are checking to see that all of the smoke goes in one end and out the other without deviation. Any accessible parts of the chimney should be visually inspected.

A failed smoke test would trigger a warning notice and do not use label being issued in most instances.

It can be difficult to see white smoke on a cloudy day.


  • We would not recommend using coloured smoke pellets as they can stain.
  • Longer chimneys may require the use of two or more pellets at a time in order to see the smoke from the ground.
  • Plan the route to the predetermined viewing point before lighting the pellet.
  • Get ready to open some windows in case the test fails or there is an inversion or down draught.
  • Check that there is an up draught with a joss stick or smoke pen prior to lighting a full 24m3 pellet

Type one testing

Firstly it is imperative that you have adequate working at heights training, equipment and have a safe working platform in order to access the terminal. You also require a second person for safety and for igniting the pellets below.
Most importantly you will be giving safety advice when performing this test and as such require professional indemnity insurance to protect yourself and your business.

We close all door and window in the room of the appliance
Preheat the flue for 10 Minutes.
Place two smoke pellets in the burning area inside the cup or flame proof container and ignite it at arm’s length wearing a glove. We advise adding one smoke pellet per additional floor of the property.
We allow to smoke to rise to the chimney terminal and then, before it escapes seal it using a bung, sponge or taped bag.

Quickly we must also seal up the aperture or appliance opening locking the smoke inside.
As the smoke is hot it continually expands and tries to escape. We must check the entire length of the chimney system and check for leakage for a minimum of five minutes.

Any leakage inside if the dwelling would constitute an immediate fail and trigger advice to repair or reline given and a warning notice raised.
If there is very minor leakage to outside via the stack it is difficult to judge a pass or a fail without significant experience, however it is usually best practice to air in the side of caution and if smoke is clearly visible leaking then the diagnoses would be a fail.


  • Immediately after the test when we open the appliance to the room or remove the board of the smoke sinks back into the room this may indicate missed leakage as the Flue cannot hold a vacuum.
  • If we remove the lower seal and smoke begins to rise this can indicate a leak higher up bearing in mind the top is still sealed so there should be no up draught
  • We must judge that the same amount of smoke that enters the chimney also exits it following the test
  • If immediately following the test upon opening the appliance doors or board the smoke begins to rise while the chimney is still capped this too would indicate a missed leak.
  • Use a Walkie talkie or mobile phone to stay in contact between the terminal person and appliance person
  • Prepare how you will seal the aperture below and ready yourself for when you light the pellets.
  • Prepare the route throughout the premises and possibly adjacent premises.
  • Practice before performing paid work.
  • Only work at heights if you are suitably qualified, insured and can do so safely from a secure platform or secured access.