📊 Pressure Drop
⏱ Drop Rate
Result Breakdown
Full Calculation Table
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How to Use the Pressure Decay Test Calculator
Choose gas piping, refrigerant circuit, or duct system depending on what you pressurized and tested.
Record the pressure right after isolating the pressure source, and again at the end of the hold period, using the same gauge for both readings.
Enter how long the pressure was held and the allowable drop your procedure specifies, where 0 means no drop allowed. Optionally add the system volume for an estimated leak volume, and the temperature change during the test, end minus start.
Click Calculate Leak Rate to see the observed drop, the temperature-corrected leak-driven drop and its rate per minute, and a pass or fail against your allowable drop.
Understanding Pressure Decay Testing
A pressure decay test is one of the simplest and most widely used leak checks in HVAC work. Pressurize a sealed system with an inert gas, isolate the pressure source, and watch the gauge. If the pressure holds steady, the system is tight. If it drops, something is leaking, and the rate of drop gives a rough sense of how bad the leak is.
Gas Piping Pressure Tests
Before a gas appliance goes into service, the piping system gets pressure tested to confirm every joint is properly sealed. In Canada the governing document is CSA B149.1, which ties the required test pressure and hold time to the system's working pressure, pipe size, and length, with a passing system showing no gauge drop. Those figures change with the code edition in force, so confirm them with the authority having jurisdiction before signing off, and use the gas leak test calculator to check readings against the table values.
Refrigerant Circuit Nitrogen Testing
Before charging a refrigerant circuit, technicians pressure test it with dry nitrogen rather than refrigerant itself. This confirms brazed joints and flare connections are sealed before any refrigerant enters the system, which matters for cost, since a nitrogen leak is free to fix compared to a refrigerant leak, and for compliance. Halocarbon use and handling in Canada is regulated by the provinces and territories and, for federal works and federal or Indigenous lands, by the Federal Halocarbon Regulations, 2003, which require owners to log every installation, service, leak test, and charge. A tight nitrogen test at or above expected operating pressure, held for a meaningful duration, gives confidence the system will hold refrigerant charge once running.
Duct System Pressure Decay
While a duct blaster test actively pressurizes a duct system and measures the ongoing airflow needed to maintain pressure, a pressure decay approach instead pressurizes the duct, seals it off, and watches how quickly pressure bleeds down. This can be a useful supplementary check, especially on smaller duct sections or when a calibrated duct blaster fan isn't available for a quick spot check. A planned system's expected leakage, which the duct leakage calculator in duct design estimates, makes a useful benchmark for a pressure decay result.
Reading the Result
A small, gradual pressure drop over a long hold time often reflects a temperature change rather than a leak. For a sealed volume, gas pressure is proportional to absolute temperature, as NASA Glenn's ideal gas equation of state shows, and gauges read pressure above atmospheric, so the correction has to work from absolute pressure. This calculator adds atmospheric pressure to your starting reading, estimates the pressure change the temperature shift alone would cause, and removes it from the observed drop to find the leak-driven drop. Enter the temperature change as end minus start, so cooling is a negative number. A rapid drop that temperature cannot explain points to a more significant leak that needs to be located and repaired before returning to service.
What to Do After a Failed Test
If a system fails to hold pressure, use a leak detection solution or electronic leak detector to locate the source before attempting any repair. A smoke test can help visualize larger duct leaks, while soap bubble solution remains the standard method for pinpointing gas and refrigerant joint leaks, and the refrigerant leak finder calculator in troubleshooting covers the refrigerant side. After repair, retest from scratch rather than assuming a single fix resolved the issue.
Frequently Asked Questions
A pressure decay test pressurizes a sealed system, such as gas piping, a refrigerant circuit, or ductwork, to a set test pressure, then isolates the pressure source and monitors how much the pressure drops over a fixed time. A properly sealed system holds pressure with minimal drop, while a leaking system loses pressure more quickly.
For gas piping, CSA B149.1 sets the test pressure and hold time in a table keyed to working pressure, pipe size, and length, and a passing system shows no pressure drop over that time. Enter the allowable drop from your procedure, with 0 for no drop, and this calculator checks the temperature-corrected drop against it. Always confirm the figures for your jurisdiction before certifying a system.
A refrigerant circuit is pressure tested with nitrogen before charging to confirm brazed joints and connections are leak-free. Testing before charging avoids releasing refrigerant to atmosphere if a leak is found, which matters for both cost and the halocarbon rules that apply, which in Canada come from the provinces and territories and, on federal works and lands, the Federal Halocarbon Regulations, 2003.
Yes. Gas pressure is proportional to absolute temperature, so a system with no actual leak can still show a pressure change if ambient temperature shifts during the test, particularly on cold Canadian job sites with swings between morning and afternoon. This calculator's optional correction works in absolute pressure. Enter the temperature change as end minus start, with cooling as a negative number.
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