I mentioned I would render a report of some kind on how the Hybrid functions. The season is about over up here in the mountains, but I've had it fired up enough times to gather observable, very consistent specs on its operation.
The stove is set up as both a catalytic, which is my preference, and a non-cat with stainless U-tube secondaries, which is Steve's Slatter's preference. It should be noted again the model is an 18," with an approx. 2.15 cu' firebox, and 2.90 cu' of internal heat surface for barrel and cook-top. This model has five rows of fire brick, two deep in the barrel.
Outside temps have been anywhere from 35 to 51 degrees, both clear and cloudy skies, morning or evening fires. Thus far no particular atmospheric condition has effected the stoves function (I haven't had opportunity to light or operate the stove on a cold rainy or snowing day yet). Draft and performance have been consistent with each burn cycle.
Each load has consisted of 5 medium splits of mostly 2 year old cherry, with some oak, hickory, or locust added which could be more seasoned and dry, and with 6 or 7 kindling strips, and a super cedar. I use some newspaper only to start flue suction at the back end of the stove.
Results have been very impressive.
Fires ignite quickly, with very little smoke in the firebox, and even while hearing some hiss from the less than perfectly dry wood, the fire rages on. The Air Intake is very effective.
In 5 to 8 minutes the U-tubes begin firing. Flue temps have been at 200.
In 10 to 18 minutes the Flue temps will range from 400-600 degrees, stove Body temps 400-500, and the combustor at 500 ready for closing of the bypass rod.
In 70% of the burn cycles the U-tubes stop firing once the bypass is closed.
Each cycle sees rapid changes every minute or two in rise of Flue, Body and Cat temperatures.
In 17 to 25 minutes with very fast, intense fires burning, with Flue temps reaching 650 degrees, I close the Air Intake to 1/4."
In 25 to 37 minutes the Flue will hover around 275-375 degrees, Body cruise 450-650, Cat at 1500. Stove Body temps will rise to 700 max with the Cat engaged.
If I open the Air Intake to half way after the Cat hits 1000 degrees, by 45-50 minutes into a burn cycle the Flue will top out at 450, Body at 800, Cat climb to 2000, which is maxing out Body and Cat thermometers. The safest and easiest operating procedure is to keep the Intake at 1/4," which is 20% capacity. Lazy flames will rise out of the load. At times the U-tubes will fire, but 90% of the action is at the combustor, which will glow at various temps starting around 900 degrees.
At 2 hours into a cycle I open everything up and throw in 3 medium splits. In 1-2 minutes the fire is ready to be returned to cruising at 1/4" on the Intake.
Thus far 8-9 hours renders a burn cycle down to a 3" to 5" deep bed of coals for reloading, with Body temps in the 300-450 degree range at that time. If I packed the firebox with some good size rounds thrown in, I expect to extend that to at least 60-90 minutes or more depending on wood species. I am told by Steve that some Elm owners burn 10" rounds in their Elms. I've not tried that, but shall next season. Man, the energy saved on my body splitting wood will be great, indeed.
Some observations on the negative side:
At the beginning of a cycle some flames are able to reach the combustor basket, which is an inch above the baffle and 3/4" back, which could cause some thermal shock, so we're going to work on extending the baffle in that area just a little to keep the flames under control.
Because the box is a round barrel, loading the stove erects a pyramid of fuel, which generates a combustion activity mostly aimed at the center of the baffle, north south. The U-tubes run north/south in the box, but are also east/west of the bulk of flaming activity. As an active fire builds flames hit the baffle center stage and splay east and west, or as an intense fire is able to shoot flames from the outside of the load they reach the tubes and they ignite. But as the load burns down some, the activity of the U-tubes ceases fairly quickly and only occasionally fire throughout a burn cycle. By then the Cat is ready for action, anyway, but the real action for secondary activity is at the center baffle, which cries out for the box beam. That will be installed this summer and by next season secondary activity will be increased exponentially before the Cat is ready for full ignition. Clean, efficient burn start to finish. I should add that in a 24" non-cat model the larger firebox seems to render more U-tube secondary activity. It has six rows of bricks which add to thermal mass and internal combustion temps. That's based on Steve Slatter's testimony of his own stoves.
I have to shut down to 1/4". This is phenomenal! Must be the full stove. What else could it be? At 50 outside and raining. Woo hoo!
