The pH of wastewater needs to remain between 6 and 9 to protect water organisms. Condensates from a gas condensing boiler have a pH value of about 3. An optimal way to neutralize the acid condensate is to use cheap material such as dolomite. An old-style neutralization box (NB) was tested with a standard faction of dolomite. However, it did not sufficiently neutralize the condensate. Therefore, several tests were performed involving changes to the construction of the neutralization box, a finer fraction of dolomite and aerating the condensate in the neutralization box. In summary, a new NB technology with partitions, a finer fraction of dolomite and condensate aeration proved sufficient in the neutralization of the pH of the condensate in the short and long terms. It depends on what material the heat exchanger is made of in the condensing boiler. The aluminum content reduces the effectiveness of dolomite in the long run, so aerating the condensate in the NB is recommended, which leads to its more effective neutralization.