First off.... Welcome. There are a few of us Fahrenheit guys here.
Using Manual, will only cause the units distribution blower to run non-stop, if the heat is high enough. What is the on/off temp set at? There is a small box, on the left side, that houses the Honeywell unit. It controls the temp at which the main blower comes on and off. I have mine set, so that on level 1 and level 2 (manual) the blower will shut off, then build heat, and come on (about 10 min off-10 min on, on Level 1).
I am heating a larger home, about 2,180 upstairs, and almost 800 downstairs (I don't have my cold air return hooked up). But I run a woodstove about 15'-20' away. This where I get away with running lower settings. Above 30* outside, I have to run my freestanding stove upstairs. Because even level 1 is to much.
Most times I run level 2 manual. And this is good to about 20* outside. After that, I run t-stat mode, with setting at level 3.
Couple questions. As noted above, what serial # is your unit? There are several things that can be done to improve the overall burn. The early models burned like chit. Period. Since the inception. There have been numerous updates to the exchanger, burn pot, control board, exhaust manifold, sail switch, and even the front door (air wash was MUCH different on the 1st version).
The firebox should be a nice grey/white color when burning properly. Forum member amc343 has one, as does Earl Beech.
Welcome to the gang.. Any questions, don't hesitate to ask... Also, any pics?? We LOVE Pics!?!
Oh and OAK it, you won't regret it. Use 3" rigid vent from HD or bLowes. It's about $25-$35 for materials. I did my Wood stove and the Endurance for $70.