Pressure Tests

The Truth About: Pressure Testing Radiant Panel Heating Systems

Unfortunately, the hydronics industry lacks a standardized testing procedure. These tests are routinely performed by individual Contractors many of whom are not qualified, experienced, or properly licensed to perform this work. This results in invalid test results and homes being sold with leaking systems. A discussion follows on how we can remedy this problem.

The UNIFORM MECHANICAL CODE defines the requirements for testing radiant panel heat. SECTION 1208.1 HYDROSTATIC TEST states, "Approved piping or tubing installed as a portion of a radiant panel system that will be embedded in the walls, floors or ceilings of a building it is designed to heat shall be tested for leaks by the hydrostatic test method by applying at least 100 PSI of water pressure or one and one-half times the operating pressure, whichever is greater". It should be noted, the code requires a hydrostatic (water and not air) test with a minimum test pressure of 100 PSI. These requirements are very specific and apply to all radiant panel systems.

Since the normal operating pressure of an Eichler radiant heat system is 10-25 PSI, one and one-half times this would be 15-37.5 PSI. This is less than 100 PSI so the proper code testing pressure for the system is a minimum of 100 PSI.

There are no exceptions to these requirements
for the materials used in the distribution system.
The tubing could be copper, steel, plastic,
polybutylene, polyethylene, or rubber.

These requirements apply to the distribution tubing only and not the boiler safety and support equipment. Another code, the NATIONAL BOILER CODE, applies to the boiler and its equipment. We agree any copper, plastic, polybutylene, polyethylene, or rubber tubing can be safely tested to 100 PSI regardless of its age. The only exception learned through many years of field examination and experience is any steel tube system should not be tested at this pressure. We will explain the reasons for this later.

The NATIONAL BOILER CODE defines the minimum and maximum requirements for testing the boiler and support equipment. This code applies to the boiler equipment of the radiant panel system. All boiler manufactures support this code and certify their boiler per these procedures. There are no exceptions whether the boiler is installed in residential or commercial property. These equipment codes apply in both instances. Because a hydronic radiant panel system uses a low pressure boiler as the heating source, the concealed radiant panel is defined as being part of the "support equipment". The code states, "the minimum system testing pressure is a pressure equal to 1.5 times the psi rating of the pressure relief valve; the maximum test pressure is a pressure equal to 90% of the boiler test pressure as set by the manufacturer".

WHAT DOES ALL THIS MEAN? As an example, the A.O. Smith HW series boiler commonly found in many Eichler and custom homes is pressure tested to 160 PSI by the manufacturer. This means a proper pressure test of the radiant panel tube with this boiler installed would be a minimum of 45 PSI (if the boiler has a 30 PSI pressure relief valve) and a maximum of 144 PSI (as defined by the manufacturers rating).

As another example, the Teledyne Laars JVC series boiler has a maximum manufacturer's test pressure of only 30 PSI. The pressure relief valve commonly installed is 30 PSI. This means the minimum and maximum test pressure would be 45 PSI (as defined by the pressure relief valve). The test pressure and working pressure of a boiler can be different. The manufacturer's test pressure is always as a minimum at least 1.5 times the working pressure of the boiler. These pressures are easily identified and stamped on any boiler sold for installation in California. This code disregards the type of radiant panel tubing embedded in the concrete.


Before we can answer this question, we must consider whether any testing can cause damage to the radiant panel. For the Hydronic Contractor, license C-4, the type of tubing in the radiant panel should define the test procedure and pressure regardless of the system age. The burst pressure of the type "L" copper used in the radiant panel exceeds 1,000 PSI.
Therefore, a pressure test of 100 PSI or less certainly will not cause a copper tube to burst. Experience indicates a properly administered pressure test of 45-100 PSI meets the requirements of both codes and will significantly, when monitored for 45 minutes, detect any radiant panel leaks. The closer the test pressure to 100 PSI, the better the test will indicate any leaks.

Test pressures of less than 45 PSI will not in many cases detect small leaks within the radiant panel. The only purpose of the hydronic pressure test is to determine if there are any leaks, large or small, in the radiant panel. The concern of causing a leak because of pressure testing is irrelevant. Since the leaks in any copper tube system are the result of slab stress which may split the tube, a test performed by the procedures to follow will not cause a tube to burst. It is only logical to conclude a tube was leaking prior to the test if the results indicate there is a leak(s) in the panel system.


Forty years of experience in working on the Eichler and custom hydronic home has taught us leaks in steel tube radiant panels are caused by electrolysis. This occurs resulting from the improper installation of the tubing in the concrete and steel materials which oxidize, corrode and rust. Electrolysis is the chemical degradation of the tube catalyzed by one of the following conditions:
  • electrical grounding of the house outlets
  • television and telephone cables into the radiant panel
  • the introduction of new water into the system from leaks
  • poor installation procedures, such as leaving the tubing on the grade rather than raising it into the concrete
  • the contact of exposed tubing with contaminated soils

These conditions will result in the formation of acids which cannot be flushed from the system and eventually corrode through the tube. At the time of the concrete pour, the plastic coating on the ARMCO STEEL tubing designed specifically for the Eichler Home could be inadvertently chipped off by shovel edges of inexperienced workers moving the concrete. If the steel tube was not raised to a proper level within the concrete and left to lay on the grade, which was a common practice, corrosion and rusting of the steel tube would occur at the chipped point. Because of the nature of steel tube Eichler homes, it is extremely important only experienced and qualified personnel perform the pressure test.

Over-pressurization of any steel radiant panel which has been subjected to the above conditions may cause the tubing to leak. Many steel systems which have not been subjected to attack from outside environmental factors are leak free. Any steel tube radiant panel should be hydrostatically tested for two hours at the operating pressure noted on the system gauge or 10 PSI.

The simple facts are most Eichler homes with steel tubing will not pass a code approved test because testing them at the pressures defined by the code could cause severe damage to the tubing. The difference between the copper and steel tube Eichler and custom home is like night and day.

ANDERSON RADIANT HEATING recommends the following test procedures for a proper and valid test of any radiant panel system:
  1. The system shall be at ambient temperature for a minimum of 24 hours. This requires the gas supply to be turned off to the boiler for 24 hours prior to performing the test.
  2. The air expansion tank shall be isolated or removed from the system prior to the test.
  3. The pressure relief valve will be isolated or removed from the system prior to the test. It is not sufficient to plug or cap this valve. It must be removed from the test side of the system. Cap or plug the point of removal.
  4. Do not flush the panel system prior to the test. Test copper tube systems at 45-100 PSI for 45 minutes. Test steel tube systems for two hours at the pressure noted on the system gauge or 10 PSI.
  5. Testing may be accomplished with the boiler installed in the system if the above conditions are met. The best test of the radiant panel is to isolate the tubing from the boiler. This is not always practical. Either test method is acceptable. When testing the radiant panel and boiler together, the test will be accomplished IAW the NATIONAL BOILER CODE. When testing the radiant panel only, the test will be performed IAW the UNIFORM MECHANICAL CODE.
  6. The test must be performed by the hydrostatic method. This means to use water only to pressure the radiant panel. The introduction of any gas, i.e. helium, nitrogen and oxygen to pressurize the system is totally unacceptable, improper and will result in invalid test results.
  7. Verification of the system pressure prior to, during and after the test is extremely important to all concerned parties. Ensure a separate and distinct pressure gauge with minimum degradations of 1 PSI or less is used for the test. Under no circumstances should the system gauge be used or substituted for the test instrument.
  8. If a drop in the pressure is noted, repressurize the system with water only and perform the test a minimum of three times. This will verify the test results by ensuring they have not been affected by air compression, temperature changes in ambient conditions, or boiler cool down.

These procedures are designed to guide the Hydronic Contractor when testing radiant panel systems. The Owner of a radiant heated home can often be fooled into believing the heating system is operating properly even if leaks are present. Remember, 90% of all radiant panel leaks never surface into the home, nor provide a "wet spot" at the point of leak. The leakage is generally directed downward and into the grade below the concrete. Only through proper maintenance and system monitoring can the homeowner ensure safe, efficient and reliable operation of the hydronic system.


It seems whenever two different companies become involved in the pressure test and inspection of the Eichler and custom home, the testing results can differ dramatically.


Confusion results from different philosophies, non-standardized testing procedures, and the inexperience of Hydronic Contractors. ANDERSON RADIANT HEATING, with over 45 years experience in the hydronics field, feels the only proper testing method is following the guidelines set forth by the UNIFORM MECHANICAL CODE, NATIONAL BOILER CODE, common sense, and our suggested procedures.

You should challenge any Hydronic Contractor(s) to present in written form any testing procedure they will use. If they don't, simply disqualify them from inspecting and testing your system.

There are too many homes being sold containing radiant panel leaks because an improper testing procedure failed to identify the leaking condition. Until each Hydronic Contractor agrees to standardize all testing procedures, an unnecessary burden is placed on the buyer to pay for a repair of the radiant panel when improper testing has shown the system to be leak-free and in good operational condition. To elevate our reputation to a level we deserve, ANDERSON RADIANT HEATING hopes other Hydronic Contractors will follow our recommendation and standardize their testing procedures.

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Campbell, CA  95008
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