Smoke

[Greenman]

Re: Smoke

Hey Max

Nothing is beyond redemption. I am sure that with a bit of tweaking that you will get that oven drawing acceptably well and if a bit of initial smoke stains the entry then you will probably have plenty of company.

It is easy to post he pictures of the perfect things and we all appreciate that but the reality is sometimes a little different a little short of perfect.

Perfect will be 'Build II' for all of us on build 1.

[Massimilliano]

Re: Smoke

Hi everyone
Thanks for your valuable suggestions.
I have persevered and today we had our first wood-fired pizzas.
I have come to the conclusion that I have/had two separate issues:

1. Horrible smoke; and
2. Not all of the smoke going up the chimney.

Smoke
I was originally using gum tree. This created noxious smoke. I have since switched to New Zealand Ti Tree. This still smokes during ignition but is nowhere near as acrid as the gum smoke.
Another design flaw is that I built the oven upwind of my house - that was just plain dumb!

Chimney issue
I think my major problem is that there is no 'throat' or funnel from the arch into the flue. Therefore, only smoke that is directly in line with the flue gets extracted, whereas smoke that comes through on the shoulders of the arch continues on straight out the front. See attached photo

To answer some of your queries:
1. I have attached some photos of my build. For more details go to Wordpress.com and search for claypizzaoven and you should come across my blog, which tracks my build.

2. My oven is 850 cm or 34" in diameter and 425 cm or 17" high.

3. The entry is 185 sq" in area. The 6" flue is 28 sq ", therefore it is 15% of the entry - probably a little small according to David's calculation

4. I wanted to go for an 8" flue, but couldn't see how I could do that, given that my arch is one brick length in width. That would leave only 1/2" on either side of the arch, which seems to be insufficient to me. I found the Pompei instructions a little vague on that point (or maybe I am just stupid)

So, it seems that my major problem is that I don't have a 'throat' or 'funnel'.
It would be major surgery to retrofit one, so I guess my options are:
1. to try and carve a throat (albeit shallow) into the underside of the arch. I am not sure how I will do that. Probably with an angle grinder; and
2. Extend the flue. I have a piece of ss flue left over, so I will try and attach that to see if it makes any difference
3. Put a 'blind' extending down about 2.5" at the front. I experimented using the plywood arch former (until it caught fire). This worked quite successfully by redirecting smoke back into the arch and up the flue (see 3rd attached photo).

All further comments are welcome.

[Massimilliano]

Re: Smoke

Restricting the air intake from say 1500% down to around 25% of the flue area actually creates an extremely efficient combustion atmosphere, as some members have found by using a blast door.

Davis
I am not sure what you mean by "reducing the air intake. Do you mean cut down the entrance size?

Also, what is a "blast door". I can't find any reference to one on this site

[david s]

Re: Smoke

Davis
I am not sure what you mean by "reducing the air intake. Do you mean cut down the entrance size?

Also, what is a "blast door". I can't find any reference to one on this site

It is a door that blocks off all the air from the outer arch bar about 25% of the flue cross section at the bottom of the door. I'm not a real fan of this technique because it can lead to too rapid a rise in temperature which can be damaging to the refractory. Apart from not having any funnelling to the flue pipe I think your 6" flue should be adequate, but the alterations you suggest should all give an improvement. I think your oven is probably still wet and or your wood was too wet or green. Judging by the water dripping from the bottom of the floor in the third photo, this is most likely your problem. Usually you need to keep wood for 12 months before burning it. My guess is that if you keep firing and make sure your wood is well seasoned and dry, your oven will fire up fine. The other thing to check is that your oven opening height should be around 63% of the internal dome height, give or take an inch or so either way.

[david s]

Re: Smoke

To illustrate how inappropriate the 10% rule can be, take a medium sized oven say a 36" neapolitan oven with a 14" internal dome height. With a semi circular inner oven door opening 9" high and 18" wide (127 sq") !0% of this (12.7sq") would suggest a flue diameter of only 4", which is clearly way too small for a 36" oven. Even at 15% of door opening (19 sq") would suggest a 5" flue. Again this would be inadequate IMO, but a 6" should do the trick.

[bobmurphy]

Re: Smoke

One thing that has helped me a lot with smoke is making sure the wood is dry. I struggled with a few fires being hard to light and smoking. Then I read someones post about putting the wood for the next fire in the oven to dry. This has worked great. I usually wait until the temp is down to 300 degrees or so then just stack it in there. This works great. My oven also smoked more when I first started to use it. I think from the masonry still having a lot of moisture in it. So, keep making some fires, and dry your wood in the oven. Good luck.

[Massimilliano]

Re: Smoke

Thanks again guys
FYI:
A) my door is, or should be, approximately 63% of the dome height
B) The water you can see on the bench is the result of me trying to scrub the door off the facing bricks.
C) the ook on the landing is what leached out of the plywood form that caught fire while I was using it to deflect smoke

I guess the blast door is a version of the old trick of holding a sheet of newspaper over the face of an open fireplace to hurry along ignition.

Today I added a 2ft section of flue. It has made little, if any, difference to the smoke coming out the front. That may be due to the fact that it is not sealed to the bottom flue, just perched on it. The good thing, though, is that by elevating the discharge height the smoke dissipates a big better.
I am getting the hang of lighting if too. Some of my initial problem was that the fire kept going out when I was trying to start it. , resulting in lots of smoke.
The top-down method and a pine cone get the fire going with minimal smoke.

[Tscarborough]

Re: Smoke

Just throwing this out, any tree with "gum" in it's name you probably want to stay away from.

[wotavidone]

Re: Smoke

Just throwing this out, any tree with "gum" in it's name you probably want to stay away from.

I, on the other hand, use nothing else.
"gum tree" in Australia is a catch all term for many varieties of eucalypt.
Red Mallee, e. socialis, and river red gum, e.camaldulensis, and white mallee e. Dumosa are fine fire woods, abundant here in south Oz. Really dry stuff doesn't make much smoke.
Mallee type eucalypts, like the one in my front yard, are brilliant in that they can be coppiced. i.e. you can take to 'em with a chainsaw and just about cut them to ground level for fire wood. A couple or three years later you can cut them again.
I don't use mulga, various acacia species, because some of them smell really bad when burned.

[david s]

Re: Smoke

Thanks again guys
FYI:


I guess the blast door is a version of the old trick of holding a sheet of newspaper over the face of an open fireplace to hurry along ignition.

Some of my initial problem was that the fire kept going out when I was trying to start it. , resulting in lots of smoke.
The top-down method and a pine cone get the fire going with minimal smoke.

The newspaper trick is the same as the "blast door" thing.

Fire going out is typical for a wet oven.
Keep firing I'm sure you'll find it will get better with each burn.

[Massimilliano]

Re: Smoke

Well guys
I am now too sessions of entertaining down and can report that I am happy with the results.
The pizzas, venison, sardines, corn, and zucchini turned out belissimo.
I am still getting smoke coming out the front but a mate mentioned to me, between mouthfuls of pizza, that he is an expert with an angle grinder and has a variety of smaller machines, which he reckons he can use to carve out the funnel/throat.smoke chamber.
Incidentally, the gum I am using is homegrown and is eucalyptus nitens, which I use to great effect to heat my home in winter. I guess my woodburner is more efficient than the pizza oven.

[brickie in oz]

Re: Smoke

I guess my woodburner is more efficient than the pizza oven.

No, your woodburner was built properly by experts, your oven wasnt.