Exhaust and supply air ventilation with heat recovery (FTX system)

The illustration shows an FTX system. No. 1. Fresh outdoor air is admitted = supply air. No. 2. The cold supply air is heated in a heat exchanger using the extracted warm room air = exhaust air. No. 3. The heated supply air is distributed in the house. No. 4.The polluted exhaust air is extracted from the kitchen and bathroom. There is often a separate duct from the kitchen fan, since greasy deposits could otherwise occur in the heat exchanger, which would give rise to the risk of fire. No. 5. The exhaust air gives up its heat to the supply air in the heat exchanger and flows out. Illustration: Bo Reinerdahl

Exhaust and supply air ventilation with heat recovery, known as an FTX system, can supply large quantities of ventilation air, and the system performs well regardless of the weather. The system is also energy efficient.

Moreover, it is simple to recover heat from the exhaust air in an FTX system. However, there is risk of sound problems and the system is sensitive to fouling, which involves a certain amount of maintenance.

How the system works

One supply air fan and one exhaust air fan ventilate the house through two duct systems. The supply air flows to bedrooms and living rooms, while the exhaust air is drawn from the kitchen, bathroom and utility room. Heat is transferred from the warm exhaust air to the cold outdoor air in the heat exchanger. The energy saving could be 50–60 % compared to a system in which heat is not recovered.

Requires maintenance

If the system is to perform as it should, it needs maintenance. Maintain and clean the ducts, registers, fans and ventilation unit at regular intervals. Change the filter regularly and check that the system performs as intended.