Valve assembly for air treatment apparatus

In an air treatment apparatus having a heat exchanging matrix disposed within a chamber for alternately giving heat up to and receiving heat from a reversing flow of air across said matrix, the improvement comprising:

• ducting disposed between said matrix and a source of intake air, said ducting defining two separate flow channels to said source, a first one of said channels being an intake channel and a second one of said channels being an exhaust channel;
• valve means disposed in each of said flow channels at the ends thereof proximate to said chamber and being biased to the closed position, the valve means in said intake channel being actuatable to the open position by air flow in said intake channel and the valve means in the exhaust channel being actuatable to the open position by air flow out of the exhaust channel.