What to know
What actually happens
The registers get temporarily sealed and a calibrated fan is connected to the duct system, usually at the air handler or a return. The fan brings the ducts to a set pressure and measures the airflow needed to hold them there.
A sealed system needs almost nothing. A leaky one needs a lot. The reading is that airflow at a standard test pressure — which makes one house comparable with itself over time, but not directly with another house. A large duct system can leak more air than a small one and still be in better shape, so comparisons between homes use a normalised figure, against conditioned floor area or system airflow, rather than the raw number.
What the number tells you
How much your system leaks overall, expressed against the size of the house or the system. It is a total, which is its strength and its limitation.
It tells you that you are losing air. It does not tell you where from — that still takes somebody looking, or a smoke or pressure-pan check to narrow it down.
When it is worth paying for
- Before committing to sealing work, so there is a before figure to compare against.
- At handover on new construction, where it may be required anyway.
- When two contractors have given you different opinions and you want something that is not an opinion.
- Where a system underperforms and the visible ductwork looks fine.
When it probably is not
If you can already see the problem. A run hanging disconnected in a crawl space does not need quantifying; it needs reconnecting.
And if nothing is going to be done with the result, a number on a page changes nothing. Test when the answer will drive a decision.
What to ask whoever tests it
- What pressure was used, so the figure can be compared with anything else.
- Whether the reading covers the whole system or one section.
- What the result means for a house of this size and age.
- What they would do next, and whether they would be the ones doing it.
That last question is worth asking plainly. A test carried out by whoever also sells the remedy is not necessarily wrong, but you should know it going in.
Where we fit
We are duct cleaners, and cleaning does not fix leakage. What we can do is look at the accessible ductwork and tell you honestly what condition the connections are in.
If what you have is a leakage problem rather than an accumulation problem, you should hear that from us before you spend anything on cleaning.