When a ceramic heat exchanger is used, the heat recovery can reach over 90 %. This saves about 50 % of earth gas in comparison to the metal heat exchanger. However, this construction with two reaction chambers and a constant change of direction of the gas flow requires a catalyst with high mechanical stability.
Each two minutes the flow of the waste air through the unit changes between the two chambers. A pressure equalisation tank or a third chamber is needed in order to avoid an escape of untreated air during the change procedure.