When it comes to checking for cracked heat exchangers we have to start with the bad news first! Unfortunately at the moment there is no perfect technique that will allow you to find every single crack you may have in a heat exchanger.
But there are many techniques that have developed over time that can help. In this article we will take a look at some of the suggested techniques to help you check for cracks in your heat exchangers.
Using your eyes to visually find a crack is probably the best and most accurate way to currently check. But, this is also one of the most difficult and time consuming processes.
A smoke bomb test is another popular suggestion and works by placing a smoke generator in the heat exchanger. By doing so you can then visually check the outside of the heat exchanger to see if any smoke passes through any cracks.
The salt test comes next and consists of spraying a salt solution in the combustion chamber. You are then advised to drill a hole in the supply ducting and hold a torch over the section where the air blows out to see if the colour changes. If the salt has come into contact with the flame the flame will change colour.
In our opinion the next suggestion is slightly easier than the last. With the blower in operation, wintergreen oil can be sprayed in the combustion chamber. To inspect for cracks you can then place yourself at the supply registers and see is the smell is still present.
Up next is one of our favourite suggestions the pressure test. The pressure test requires all of the openings in the heat exchanger to be sealed, with the blower energised a pressure sensor should be inserted into the heat exchanger. This will then check if a crack or hole allows air to blow into the heat exchanger.
A bit more on the complicated side is the tracer gas test. Like the pressure test, all openings in the heat exchanger need to be sealed. A methane tracer gas should then be inserted into the heat exchanger. You can then use a gas leak detector to look for areas where the gas is found to be escaping.
However we do need to stress that most of the above suggestions make lots of fatal assumptions and as we already stated there is no known test that works.
The first assumption we can see is to do with the temperature of the heat exchanger. The assumption is that the crack will be open when the metal from the heat exchanger is at room temperature. Many cracks will only open when the metal is hot.
Secondly there is the assumption that a leak is going to be from the flame side to the distribution side. Yes, this is the case if the vent system is not drafting and the blower is switched off but if the blower is on there is little to no chance that smoke or gasses etc will pass through a crack. When the blower energises it is likely to produce a lot of pressure outside the heat exchanger so there is a good chance that the air will be blown fire side not distribution side.
Then, there is the question of how we suspect there is a crack in the first place. Does the technician have the time, experience or is there a reason behind the assumption? There are many more assumptions that we could list but if anyone tells you a way to test for cracks that works 100 percent of the time, take it from us, they’re wrong!
