The question is often asked, “Do I have an air leak or a water leak in my furnace, and how can I tell them apart?” Fortunately, there is a really simple test procedure that yields very accurate results. Here’s how it works.

Fig. 2. Copper, steel, stainless steel coupons

Test Procedure

The test can be run in any style of furnace. Here we illustrate the procedure for a continuous mesh-belt furnace running a dissociated ammonia (75% hydrogen, 25% nitrogen) atmosphere. The test involves gathering clean, relatively thin cross-section samples made of steel, copper and (if available) stainless steel. Many people simply use steel shim stock and cut a small length of copper tubing and, if necessary, sand the surface so that it is bright and shiny for this test.

The furnace temperature is lowered to 1800-1850ºF (980-1010ºC) and the belt speed reduced so as to assure a dwell time in the high heat and cooling chamber of at least 20 minutes. CAUTION: Pure copper has a melting point of around 1981ºF (1083ºC), so care must be taken not to approach this temperature.

Fig. 3. Copper, steel, stainless steel coupons

Interpreting the Results

Results of the test are interpreted as follows. Steel parts will discolor (oxidize) in an atmosphere contaminated with either air or water. Copper will emerge shiny if water is present but will be discolored if air is present, usually with black spots or streaks. Stainless steel will be gray if the air or water leak is a minor one and various shades of light to dark green if the leak is more severe.

Fig. 4. Copper, steel, stainless steel coupons


Upon exiting the furnace the sample coupons can be visually examined for surface appearance (Figs. 2, 3 and 4).