In the cold and moderate climates the energy demand for heating of fresh ventilation air is crucial. The mechanical ventilation systems with heat recovery are used to decrease the peak power of the heating system and to save the energy. In a case of wall-type heat recovery units there is a doubt about the possibility of mixing fresh and exhausted air in the combined intake-outtake device. In this paper experimental investigations were conducted to assess their hygienic safety. The original set-up containing test chamber and the equipment for CO₂ concentration measuring has been used. Visualization of airflows mixing with the usage of smoke is presented. The results show that the risk of the exhausted air return to the building is low. At the same time the ventilating efficiency of such systems is high. The analysis of the annual energy demand for the sample single-family and multi-family buildings has been conducted to present the possible energy benefits of usage such devices. Concluding, the wall-type heat recovery units should be considered as hygienic safe and helpful devices in achieving the standard of low energy buildings in a case of existing and refurbished ones.

在寒冷和中等气候下，加热新鲜通风空气的能源需求至关重要。具有热量回收功能的机械通风系统可用于降低加热系统的峰值功率并节省能源。在壁式热回收单元的情况下，对于在组合的进气-排气装置中混合新鲜空气和排出的空气的可能性存在疑问。在本文中，进行了实验研究以评估其卫生安全性。包含测试室和CO ₂设备的原始设置已经使用浓度测量。呈现了与烟气混合使用的气流的可视化。结果表明，排出的空气返回建筑物的风险很低。同时，这种系统的通风效率很高。已经对样本单户和多户房屋的年度能源需求进行了分析，以显示使用此类设备可能带来的能源收益。最后，在现有和翻新建筑物的情况下，壁式热回收装置应被视为达到低能耗建筑物标准的卫生安全和有用的设备。