The flue-cured tobacco industry in the U.S. conducted a retrofit program between the 1999 and 2000 growing seasons to convert bulk curing barns from direct-fired to indirect-fired heating. This was necessary to remove the products of combustion from the curing air space and thus avoid the formation of tobacco specific nitrosamines (TSNAs) resulting from the reaction of nitrous oxides and secondary alkaloids present in the tobacco leaf. In the vast majority of cases this process was accomplished through the replacement of traditional LPG fueled ring burners with heat exchangers and a new gas burner. The result was a substantial reduction in the overall level of TSNAs present in flue-cured tobacco. Heat exchangers must be periodically tested to ensure structural integrity and continued elimination of combustion gases. Many heat exchangers have required repair and some have been repaired multiple times as units age and thus more prone to failure. The condition of some heat exchangers currently in service warrants consideration of replacement. Growers should consider the efficiency of a heat exchanger when replacement of a unit is necessary. Thought was not given to this factor during the earlier retrofit program. The thermal efficiency of heat exchanger has only recently been discussed with the availability of energy conservation cost share funding for replacement with high efficiency heat exchangers. However, a procedure for evaluating heat exchanger in place in a tobacco curing barn is needed to provide quantitative ratings of heat exchangers and allow for comparisons. A protocol for heat exchanger testing will be described and comparative data of different heat exchangers presented. (Reprinted with permission)