Why do I only get 4 hour burn times?

[laynes69]

The temperatures would be much higher if there wasn't a secondary heat exchanger on the unit. It extracts alot of heat before leaving the furnace. Forgot to add also your furnace doesn't have preheated secondary air? The extra combustion burns alot hotter. Our old woodfurnace I needed a flue temp of probably 600 to burn it cleanly. Not this one.

 

[vwboomer]

I should add that my furnace is just a plain jane HB1300.

 

[RHiller]

If you have a Grainger close, you can get a manometer for about $40.