You're right, Dennis. Good note. I'm going to have to set up the left
side with flapper valve closed.

Thanks.

Mark

On Dec 27, 2010, at 3:27 PM, Dennis Haynes wrote:

> The system is designed so there is always air flowing through the
> heater boxes. Even when the heat is off. That is why the flaps have
> opening on top. Without the air the sheet metal outer boxes burn up
> and the exchanger core can crack.
>
> Dennis