Planning on building an airwash, advice needed

Preheating of the air wash does not seem to be critically necessary, and actually may hurt a little bit. You want the air to be cool enough to sink down the entire face of the glass - if it's super hot, it will come out the air-wash and immediately begin rising back up. Though we're talking 'relatively cool' compared to the 1000º firebox here.

My inlet air comes in directly under the doors/windows, goes up each side through a 2"x2" square tube and out through an arched tube over the glass. Most new stoves seem to take the air wash air out pretty early, too. Secondaries are more critical on the pre-heat - you definitely don't want to cool the combustion gasses any more than necessary and if you can actually heat them up more, all the better.

What does seem to be important on the air wash is getting a good laminar/smooth flow covering the entire glass. You basically want a curtain of clean air to keep the smoke separated from the glass. If the glass does happen to get sooted, a hot burn + the fresh oxygen will help burn the carbon off the glass and you're left with a light white residue which wipes away easily.

I ran into a bit of trouble because I followed the arch of my doors - the air jets come straight out of the holes in the wash pipe, so as the pipe curves, the jets are no longer pointed straight at the bottom of the doors and I sometimes get a bit of soot in the lower / outer corners. But that has been mostly eliminated by drilling a few more holes. To sum it up in a very rough sketch:

you have to have the primary air comin in under the fire right Im talkin about where the outside air comes into the stove has to be below the fire then you can pipe it anywhere you want. if not wouldnt smoke come out when the door is open.

brokeburner - Yes, I think if you had an air inlet somewhere above the fire AND had an outlet somewhere over/in the fire, then I think you might get smoke back through the outlet in that situation. All my air comes in from below the fire. I think the primary air / air wash could come in from above the fire as the outlet wouldn't be 'in' the fire enough to let smoke out. ie the air wash outlet is so close to the door opening, if smoke is getting in the air wash outlet, then it's probably coming out the door already.

Beetle - I have a second opening at the base of the fire for primary air. Though I wish I would have done the control system differently so I could control primary air completely independently of secondary air. Maybe V 2.0 will have this mod. Flow control is via sliding metal gates.

We'll have to be careful using the word 'enter' I'm not sure if you mean enter as in 'where should the intake in the stove be' or enter as in 'where should the air be directed at the fire' As for the intakes, I'd always recommend they be at or below the base of the fire due to smoke issues mentioned earlier, though primary and airwash air could possibly have an intake higher up if they needed - as you break the draft when you open the door and not much smoke would leak back out. The secondary intake definitely needs to be below the fire as smoke could back up the pipes through natural convection when the door is open if the intake was above the fire.

As for where the primary air is directed at the fire, most new stoves seem to put it right at the base of the fire from the front.

Doesnt it make more sense for your primary air to come up under your fire (like through a grate system)? I know its a pain when the logs in the back of the stove doint fully burn. My primary is right at the front.

Another point to consider is whether you have adequate draft for that size of a single door. I remember on my old double door Vestal Stove that at times I could only open one door at a time to reload, check, or mess with the fire. Otherwise, smoke would roll out.

nojo - Air coming in under the fire will turn things into a blast furnace in short order. Of course I like the option to open the ash pan or have some other way to get air under the fire for quick start-up, but it does require some amount of “responsibility” to use and I don’t think you could use it effectively for the sole source of primary air. Plus, unless you have some type of ‘shaker’ grate it would always get plugged up with ash.

It seems the ‘perfect’ burn is to introduce air at the base of the fire to get everything up to temp, close the primary air and open the secondaries. The secondaries then light off and essentially ‘bake’ all the volatiles out of the wood.

wonder if larger fireboxes do better with secondary burns. I can only get mine to secondary burn for like 30 min. ANd the thing has to be HOT. If I turn the primary down past 3/4 closed I lose my secondary combustion. I have no control over secondary intake on my stove.


How are your ad on secondaries doing?

It seems you would have to have some kind of adjustment on the airwash air. if you have to much air comin in the airwash plus secondary air plus primary air with only being able to shut down the primary i could see a overfire in your future.it seems they have the airwash as the primary air in the new stoves to get the volume of air that you need to be able to keep the glass clean and not have 1,00s of adjustments.

I have been gathering ideas on modifying my Old Big Buck insert. I am going to add a baffle and secondary burn tubes such as has been seen on the forums before. The secondary air is going to come from the front, bottom of the stove and travel up along the inside of the stove from both sides. Then to a manifold and into the burn tubes. I am going to have an adjustment slide to regulate the amount of secondary air if need be. After reading this post, I wonder if I could add a burn tube right above the door and it work as a door wash? Can secondary air and door wash air come from the same place? What makes the air wash air not turn into secondary burn air?

Another semi related question, does the baffle typically need a bypass for loading of the stove? I don’t seem to see them in the new stoves but want to make sure no smoke escapes from the stove during loading.

Thanks for the input.

Michael

'82 Big Buck 28000