Help needed! can't get a good draw

[MarcMunier]

Re: Help needed! can't get a good draw

This is my blast door. This is my insulating door.

Can't seem to see the links - can you re-share?

[Lburou]

Re: Help needed! can't get a good draw

You are probably getting more info than you want on these issues, but here is some more for you. I think there are some important variables involved in designing and using a blast door. You control the air charge in the oven with the size of the openings in the door, so you can be conservative with the air charge transiting the blast door by design. Secondly, a smaller fire with a blast door isn't as hard on the refractory as a larger fire and a blast door, so you can slow the heat charge that way. It is all under your control. I've controlled these variables with smaller openings in the blast door for the air charge and smaller fires that take about 70 to 90 minutes before getting the heat charge I'm looking for. A fairly conservative management protocol.

David s is correct in saying you can go too far with a big fire and ram air to feed a hot, hot fire. I have a lot of wind directly into the oven entry and do not have much choice unless I want to breathe smoke, which I don not. You pay your money and take your choice.

[Gulf]

Re: Help needed! can't get a good draw

Gulf

How do I preheat a chimney?

I am not disagreeing with any of the info which has been given on this thread. This technique just helps get the most out of some bad situations. IE: windy days, days when smoke seems to lay close to the ground, days when your chimney is colder than the ambient temperature. If the ambient temperature of the outside air is higher than your oven or chimney then the air inside is cooler (heavier). Cooler air in your chimney will fall creating a natural down draft. If you light a fire under some of these conditions the smoke will take the least path of resistance, straight out your door opening which it is already trained to do. That is probably why blast doors work so well.

As far as preheating your chimney goes, it is a pretty straight forward approach and real cheap to prove or disprove. Think of it as training the smoke to go where you want it to. This is assuming that you have dry wood and kindling which are properly stoked in the oven/fireplace. (It definitely works for fireplaces)

In the conditions which I mentioned above, if you light a match and hold it up high in the flu you will notice the flame/smoke being pushed back down. It may take a second match, a lit piece of kindling, or a rolled up news paper to get this draw headed up your chimney. Once you see the smoke going the right way slowly lower your flame to the kindling set in you oven/fireplace. I like to have a little kindling set on top of my wood bundle and once that is going, light the kindling under the stack.

[david s]

Re: Help needed! can't get a good draw

The use of a so called "blast door" creates extremely efficient combustion, which leads to a very rapid rise in temp. This rise is likely to exceed 500 C/ hr which is really way to rapid for the safety of any refractory, especially from start up and is likely to cause premature (usually unseen) damage. Refractory materials are not particularly good heat conductors relative to materials like steel for instance. It takes around an hour for the heat to penetrate right through the brick so uneven expansion leads to stress on the refractory. To be kind to your oven it would be prudent to allow the temp to rise at a more reasonable rate, which means not using the blast door.
However in practice we usually want to get the oven up to operating temp as quick as possible. Just be aware that it is probably not doing your refractory much good pushing it this fast.

[brickie in oz]

Re: Help needed! can't get a good draw

pic of a blast door -

Here is mine.

[Lburou]

Re: Help needed! can't get a good draw

This is my blast door. This is my insulating door.

[MarcMunier]

Re: Help needed! can't get a good draw

Thanks again everyone - great to know I haven't built a dud!

More follow ups,

Lburou

Couldn't see you pic of a blast door - can you repost? just to double check this sits on the very front of the door - not in between the cooking area and the chimney like a cooking door? Do people have 2 doors ?

Gulf

How do I preheat a chimney?

Thank you guys

[Lburou]

Five points Marc

Welcome Marc

• The oven smokes only in the early stages of the fire, after it heats up, it does not smoke so much, expect that to improve when you get a hot fire in there.
• An air tight chimney will draw much better than your trial fitting does.
• A 'blast door' is something many of us use every time we light the fire.
• If you light the fire at the top of a stack of kindling, you may have less smoke in the early stages of your fire, search for 'top down' fire starting.
• Your oven entry is very shallow, that makes it easy to access the inside of the oven, but a little more tricky evacuating the smoke efficiently.
• HTH

This is my blast door, I use it for every fire:

[Jaronimo]

Re: Help needed! can't get a good draw

The smoke will never flow correctly without a chimney. When the chimney is installed you will get some smoke out the front until the chimney heats up a bit and starts flowing upward from that heat. Heat rises, so when the chimney gets hot it actually starts to suck the air up into it which draws in the smoke. The taller the chimney, the more draw you will.

[brickie in oz]

Re: Help needed! can't get a good draw

IMO you need to try preheating the chimney before starting a fire in the WFO .

Its what his Great Great Great Grandpappy used to do, its a tradition.....

[david s]

Re: Help needed! can't get a good draw

Also new ovens are notorious for being smokey. Once it is dry, and this may take about ten fires it will be less smokey.

[MarcMunier]

Re: Help needed! can't get a good draw

Maybe I don't understand, but I believe you need a chimney and a door to get a proper draw. I did not try mine before had a chimney and door so I don't know for sure. I am in the process of building my final door (got the glass today!) so I used double thickness 3/4 exterior plywood for a test/seasoning door. I drilled a few 1" holes in the bottom to let air in.

So do you need a door to get a proper draw? I saw a post which had a you tube video which had very good draw with no door but was that the exception?

Also I have done a few larger fires(2/3 logs) now and I still get smoke coming out of the front, do I need to shape the vent more?

[Les]

Re: Help needed! can't get a good draw

Marc,

When I built my outside arch, I dropped it about an inch. My thinking was that the smoke would hit it and prefer to back up and out. Not sure how much it helps but the smoke out the entry is a minimum. Once the temps get up it will definitely go out your vent. And as gulf mentioned, ensure that the stack is sealed.

[Faith In Virginia]

Re: Help needed! can't get a good draw

If that is your first fire. a small fire just to start curing the oven then that is absolutely normal. Once you start bigger fires the heat generated will aid in the draw up the chimney. Right now your smoke is not that hot so it tends to just linger about. Once you get it hot it will want to rise. No worries your oven looks great. Get it cured as you should and I'll bet it will be fine.

[Gulf]

Re: Help needed! can't get a good draw

That chimney needs to be sealed to where it will not draw air between the top of the arch and the bottom of the chimney. But, for the most part, IMO you need to try preheating the chimney before starting a fire in the WFO .