I work on a lot of different brand pellet stoves. Some burn efficiently for many years while others seem to produce less heat after only 3 or 4 years. I owned a stove that started to decline and like many others, I got rid of it. Afterwards, I bought a much older pellet stove that burns like new. After fixing many stoves, I noticed a connection between the stove performance and difference in design between different heat exchangers and exhaust chambers.
There are many design differences but one difference stood out. Smaller impeller blades on combustion or exhaust blowers allow airflow to diminish as the stove ages! Over time, rust, calcium deposits, and soot clog the air passages, which reduces air flow and vacuum. Larger, deeper petals truly make a difference. My 15 year old Quadrafire stove has deep blades and works like new! I used after market blades. These fit many stoves. The deeper petals keep the pellet ash from building up under the impellers, thereby reducing draft and maintaining the stove's heating performance even when it gets a little dirty. 5" double blade impellers used in Harman stoves also fix this issue and fit a few other stoves as well.
I used the deep blades when working on an older Enviro Mini (Not Mini-A), which prevented build up. To further upgrade the stove's performance, I used a Gleason-Avery Exhaust Blower with 1.75 amps of shear power for LOW draft performance. The higher current blower keeps the burn pot clean on Heat levels 1,2 and 3 during low draft and the pellets burned completely.
Another issue with the older Enviro Mini is that it doesn't have a latch on the ash pan. When you open the door and lie a dollar bill across the gasket and close the door, you can still pull the bill out. This indicates a poor seal. A poor seal can also cause a lazy flame and contribute to poor heat performance. The ash pan is hooked in on the bottom left and right corners, so it shuts using gravity. However, the ash pan gasket does not compress enough to make a tight seal without a latch. This causes overflowing pellets and caked ash in the burn pot.
The ash pan latch on newer Mini-A stoves seals the unit properly. The latch itself can be purchased and added to the older Mini. The is latch $43.00 and it's a solid one. You need to drill a hole in the ash pan to install it. The hole required is approximately 13/16" and most metal drill bit sets go up to 1/2". However, new Titanium Step Drill bits can easily solve the problem. I got some step bits from Harbor Freight. Just find the center of the pan and measure approximately 1-1/2" down from the top. An ash pan gasket and fire door gasket in good condition are also necessary for a proper seal. An impregnated graphite gasket is recommended because of its durability. With these changes, you won't see any more overflowing pellets in the burn pot from caked ash building up in the bottom. It also prevents black ash from collecting on the back of the firebox. What a difference!
Enviro addressed many of these issues with quite a few upgrades to the Mini in the newer Mini-A. These upgrades include:
1. Newer Control Panel & Decal with plate - new combustion trim control to adjust the exhaust blower speeds for different heat level settings
3. Ash Pan latch - to stop air leaking thereby reducing the draft needed for a lively fire.
Not addressed by Enviro but recommended by Harman for their own stoves.
4. Higher current combustion blower upgrade with larger impellers.
To see the old Enviro Mini now running on heat level 2 with old control board and old burn pot view my youtube video!
For a similar solution to the Breckwell vacuum problem -see my blog > http://www.eastcoasthearth.com/blogs/pellet-stove-parts-101/13615545-boost-your-breckwell-run-on-heat-level-1-without-re-adjusting-the-damper
To summarize, the more lively the flame, the better the heat transfer. Better fan petal blades, ash pans, gaskets, and blowers make a difference. Harman pellet stoves have one of the most intense flames and they really crank out the heat! The double fan blades in those stoves contribute to that power. These improvements reduce black smoke on the back fire box wall, caked ash in the burn pot, and pellet pile up in the burnpot. The pellets will burn completely.