Oven not hot enough, flue issues?

[Lambooni]

Hello,

I have an 800mm ID refractory dome oven. It currently has an 5 inch single wall flu about 500mm long. I think this is probably too small.

My issues are;
- Hard to get a fire going (using seasoned hard wood)
- very smokey, lots pouring out the door
- Fire can even sometimes go out after I have had a raging inferno in there and lots of embers.

Its a real effort to start and keep the fire going at the moment and some help would be appricated.

If my flue is too small/short, can I use an adapter to go out from the 5 inch to and 8 inch, or do I really need to cut the concrete? Im not sure if cutting is an option so I was hoping that maybe going to a 1meter long and double wall flue could help me.

What are your thoughts?

Thanks in advance,
Adam

[shuboyje]

Re: Oven not hot enough, flue issues?

Our wood fired ovens do not rely on the flue to function, they will function just fine with out one. The only function is to keep the smoke out of your face.

What you describe sounds like a wet oven to me. Is it new? How is in covered?

[mrchipster]

Re: Oven not hot enough, flue issues?

Our wood fired ovens do not rely on the flue to function, they will function just fine with out one. The only function is to keep the smoke out of your face.

What you describe sounds like a wet oven to me. Is it new? How is in covered?

That was the first thing that came to mind for me also. WET OVEN....

[david s]

Re: Oven not hot enough, flue issues?

I agree, it sounds like your oven is wet. However a 5" flue is totally inadequate for an 800 mm diam oven. Your oven is more than three times the volume of mine. No wonder the smoke comes out the front. My oven is only 540 mm diam with a 5" flue and I wouldn't go any smaller.
I think you should replace the flue with a 6" diam pipe and an adaptor to the 5" as you suggested. A 6" pipe has almost double the cross sectional area of a 5" pipe so will give you plenty more draw. The 5" restriction at the bottom should work like a venturi accelerating the smoke draw at that point.

[scott123]

Re: Oven not hot enough, flue issues?

Beyond the oven potentially being wet, is your wood nice and dry?

[Lambooni]

Re: Oven not hot enough, flue issues?

Hi All,

Thanks for the replys, yes a wet oven sounds very plausable! Currently it is not covered and also has not been proofed with a water proof finish. I was going to fire it about 10 times before putting the water proofing over. It was originally covered with a plastic sheet but it kept blowing off and I left it in the end.

I assume the fix for this is just to run a long (or several) small fires.

I will also look at replacing the flu with a larger one. Would a double wall flu be of any help outdoors?

I always assumed that the flue helped to pull air through. I tried to fire my oven one night when it was very cold (before it would have got wet) and again I really struggled. I assumed this was because the flue was stone cold and that a double walled flue would help me, but I guess not?

Many thanks,
Adam

[mrchipster]

Re: Oven not hot enough, flue issues?

Just the act of building the oven it will be wet. Many very small fires over a two week time period will dry out your oven. You need to keep it covered if it rains because a single rain will slow your drying by several days to several weeks more than the two week dry process.

One large long fire will not dry your oven but may crack it.

[Lambooni]

Re: Oven not hot enough, flue issues?

Ok, well yes at this point my oven has been out in the rain many times. I will need to get a lot of fires going.

Is it best to fully dry my oven before applying the water proof paint or will it continue to dry from the inside also?

[mrchipster]

Re: Oven not hot enough, flue issues?

Ok, well yes at this point my oven has been out in the rain many times. I will need to get a lot of fires going.

Is it best to fully dry my oven before applying the water proof paint or will it continue to dry from the inside also?

Best to dry first yes,yes,yes,yes,yes or possibly yes.........but here is the real problem. I do not think paint alone will "wares proof" your oven.

Do you have photos and what type and how much insulation?

[Lambooni]

Re: Oven not hot enough, flue issues?

I have one of these ovens;

ukoutdoorliving

Its has a few layers of ceramic blanket but no more insulation than this. Then a concrete/lime mix render.

I was planning on using an acrylic waterproof paint for the final coat.

[mrchipster]

Re: Oven not hot enough, flue issues?

I would keep it covered when you are getting rain. Igloo style ovens will get wet when it rains unless covered.