The Private Heat Exchanger Gallery is now online, with over 65 models of furnaces. This is a great tool to help find heat exchanger failure. A donation of $20.00 will get you access to the private Heat Exchanger Gallery.
https://hvactechgroup.com/iGallery/
You can donate by clicking the PayPal logo - Here (http://www.hvactechgroup.com/files/paypal.html)
Members who have donated, can PM the admin for access - Here (https://www.hvactechgroup.com/hvacforum/index.php?action=pm;sa=send;u=1)