Secondary air tube location -- new insert advice needed

  • Active since 1995, is THE place on the internet for free information and advice about wood stoves, pellet stoves and other energy saving equipment.

    We strive to provide opinions, articles, discussions and history related to Hearth Products and in a more general sense, energy issues.

    We promote the EFFICIENT, RESPONSIBLE, CLEAN and SAFE use of all fuels, whether renewable or fossil.


Feb 12, 2019
A little background:

Napoleon s9

I heat my 3400 square foot well-insulated pole barn with a Napoleon s9 stove. This was Napoleon's largest pre-2020 stove with a 3.0 cf useable firebox. The s9 is an impressive heater and simple to burn efficiently. It it has a t-shaped secondary air manifold that runs east-west along the upper-rear of the firebox and north-south down the top-middle. The primary air enters in the normal fashion -- air wash above the door and "pilot" dog house under the door.

The north-south orientation of the secondary air, combined with the "vortex" baffles creates slow, spiraling, dramatic flames that start at the back of the firebox and spiral to the front. The secondary air stays in the firebox for a long time, swirling around "looking" for combustible gases or particulate matter. This efficient mixing of secondary air means less excess air is required for complete combustion and less heat is lost up the chimney. This design works particularly well with the s9's deep firebox.

Here is a short video of the s9. You can't see the spiraling secondaries very well because of strong primacy combustion, but you can get an idea of the flame show

Breckwell Wood Burning Insert

I heat my 3800 square foot 2-story well-insulated house primarily with a Breckwell insert. I bought the Breckwell as new old-stock in 2018 for $500. It was Made in the USA in 2007, before Breckwell was bought out and moved production to China. This insert has 2 cf useable firebox at most, but as a practical matter I only seem to fit about half the wood that I can fit in my Napoleon s9. To heat my large house I have to reload about every 6 hours in normal winter weather and every 4-5 hours on cold days.

The secondary air setup similar to what I have seen in most inserts -- 3 east-west tubes in the upper rear, middle, and front of the firebox that blow secondary air across the top of the firebox from the back to the front.

This design works reasonably well, but as compared to my Napoleon s9, there are at least two drawbacks.

First, the flame show is chaotic and not very nice to watch. The secondaries are fast, short, and they "fight" with primary combustion at the front of the stove.

Second, this design seems less efficient than the Napoleon s9. The secondary air does not mix as well; more excess air is required; more stack loss occurs.

Questions / Request for Comments

I am thinking about moving the Breckwell insert to my basement fireplace and replacing it with a larger non-catalytic insert. I am considering 3 options:

2. Osburn 3500
3. Napoleon s25i

All 3 will physically fit into the fireplace. All 3 will hold more wood than my Breckwell. Largest to smallest: Osburn 3500 > PE Summit LE > Napoleon s25i. Cost is not a deciding factor.

I believe that all 3 of these inserts use east-west secondary tubes similar to my Breckwell insert. If so, should I expect these to all have spastic looking flames? Are there any large inserts that have north-south secondary air or some other setup that creates slow, dramatic flames?

Since these are all epa-2020 stoves, I assume they are all very efficient. My #1 priority is long burn times. I assume that the firebox size is the biggest determinant of burn time. Does anyone have any experience with cycle time on any of these 3 stoves? I think that all 3 are new epa-2020 models.

Finally, I want to be able to shut down the air as much as possible once the stove is up to temperature. I have a 35 foot chimney in the house (brick exterior, block structure, clay flue, and stainless liner, sealed at top and bottom of clay flue) -- 20 feet of which is interior and the last 15 feet is exterior. Even with an uninsulated stainless liner, once the clay flue heats up the stove drafts very well -- too well most of the time. Because my liner is uninsulated it takes longer to establish a good draft. But once the chimney is heated, the stove tends towards overfiring even with air closed to the max. The tall chimney sucks massive amounts of air through the secondary tubes, and with no chimney damper or other way to restrict air beyond the EPA-regulated air control, little can be done to slow it down. Normal burns reach 700 degrees on the hottest point of the stove top, and a brief period of 750-800 degrees is not uncommon within the first hour of a reload.

If I close the air down too soon the Breckwell will smolder, but there is a very, very fine line between too soon and too late, if that makes sense. By comparison, my Napoleon s9 is very forgiving, perhaps due to the 25 foot perfectly vertical chimney that is 14 feet of interior black pipe and 11 feet of exterior triple wall stainless. It drafts like a dream from the start, and I can start closing down the air very quickly without smoldering. Does anyone have any insights as to whether one of 3 inserts I am considering will allow the best air control?

I would be grateful to anyone who can help me think through this decision. I am leaning towards the Napoleon s25i simply because I like my s9 so much, but the larger fire boxes on the Osburn and PE inserts make them very tempting.
With a 35' liner, no matter what is installed, it's going to be draft challenged which will result in shorter burntimes and a touchy air control.
If I close the air down too soon the Breckwell will smolder, but there is a very, very fine line between too soon and too late, if that makes sense.
This sounds a LOT like what I'm going through with my Lopi Freedom insert. I've been getting less than four hours out of each load by trying to keep it from smoldering and burning dirty. I also have a tall chimney with a liner I suspect may be uninsulated. Just like you say, there's too fine of a line between too soon and too late. Fully closed isn't enough, and bumping the rod in 1/8-3/16 seems like too much sometimes. It's just so stinking temperamental. I was much happier with a thermostatic, catalytic stove in my previous house.

I enjoyed your analysis of the S9. That was a pretty interesting read. I can tell you my Lopi also has the E/W tubes, and has chaotic secondary flames for the fleeting moments when I can get them to exist. Sorry I can't provide any input on the other models you're considering.