In order to characterize the condensate waste stream from experimental high efficiency heaters and a pulse combustion furnace, samples were analyzed for total solids, pH, acidity, alkalinity, nitrate, nitrite, sulfate and selected metals, and were screened for semivolatile organic priority pollutants, including phenols and polynuclear aromatic hydrocarbons. A typical condensate has a pH of approx. 4, contains quantities of nitrites (1–8 mg l−1 as N), nitrates (0.4–15 mg l−1 as N), sulfates (3–10 mg l−1) and may contain metals dissolved from the condensing surfaces of the appliance. No priority pollutant compounds were found in the condensate samples. Calcium carbonate (calcite) was used in testing the potential of a lab-scale column and a prototype treatment unit to neutralize acidity and precipitate metals in condensates from the pulse combustion furnace prior to disposal of the waste product to the residential wastewater system. Limestone neutralization effectively reduces condensate acidity and increases alkalinity and pH. The effectiveness of the test column and prototype treatment unit for precipitation and removal of high levels of metals from the condensate will require additional testing.