Newbie with an issue

[BenBaron]

Hi guys,

How many times have you heard...I wish I had found this forum earlier???

Anyway, I've built a barrel type oven, not to any specific spec (which is probably the problem) and tried cooking a couple of days ago. Not entirely a disaster, got a fantastic garlic bread out of it but the heat seemed to disappear within minutes of moving the coals. Had it burning for about 2 hours, it got nice and hot but then 1 garlic bread later (which cooked in 2 mins or so) and the by the time Id made up the next pizza, that one took around 8 mins to cook, next one even longer.

So I will get some piccys up later on and some sizes but I was concerned about the airflow, essentially I could put my hand in the oven (at the bottom) for a good number of seconds, where as halfway up the doorway there was no chance, felt like it would strip my finger nails off. So..Im thinking there is too much airflow at the bottom where its sucking it in?

I have no chimney (no room) so its just the barrel then the front opening, I have concrete over the dome top (about 2'') but not a mixture of vermiculite.
No concrete on the face or the back wall (back wall ( think I can remedy) but the front is just going to get a render.
~4'' concrete base, with firebricks for the entire oven.

I know its a long shot without seeing photos and sizes but any recommendations from that description? I was thinking of perhaps drilling some ventilation holes to help with the air flow? or adding a thicker concrete layer on the top?

All help comments greatly appreciated...

Ben

[brickie in oz]

Re: Newbie with an issue

More insulation is needed by the sounds of it, mine takes 1 hour to heat and stays hot for 4 hours, its even still fairly warm 2 days after a firing.

Thermal mass+Insulation=good oven.

[Frances]

Re: Newbie with an issue

Hi Ben,

I think it sounds like not enough insulation, too. (Or none at all?)

If you post some pictures, maybe we can suggest some way of adding insulation, but from what you've said, I doubt that airholes or more cement would improve matters. Retro-fitting insulation has been done before, and with any luck there'll be a solution for your oven, too.

[Ken524]

Re: Newbie with an issue

Do you have any insulation under the floor? It sounds like whatever is directly beneath your brick floor is sucking heat out of the floor instead of reflecting it (insulation).

[BenBaron]

Re: Newbie with an issue

Hi guys,
Thanks for the replies.
Ok so insulation sounds like the problem, so I can easily wack a good dollop ove the top, maybe get some down the back, none on the front though.

My concrete base is just that, a 4'' slab of concrete laid on normal bricks along the edges, so there is nothing under the slab at all apart from air
I assume from your question that it should have some sort of insulation layer below it???

Soon get some piccys up, just been a little busy..

[BenBaron]

Re: Newbie with an issue

PS Since figured out my opening to roof height is only 52%, how will that affect the temperature? Presumably not enough airflow? so will it burn at a lower temp?

[Ken524]

Re: Newbie with an issue

Ben,

The biggest problem (most difficult to solve) is the lack of insulation under your cooking floor. Are you cooking on the concrete or do you have bricks on top of the concrete??

You need to have some insulation on top of the hearth and under your cooking floor bricks. This is why your floor refuses to get hot. The 4" slab of concrete is like a giant heat sink, sucking your heat away from the cooking surface.

If it's possible, put some 2" thick refractory insulation board on top of the concrete hearth, then lay some bricks on top of that for a cooking surface.

[Frances]

Re: Newbie with an issue

If all else fails, maybe you could add some insulation underneath the concrete hearth? It'd be better than nothing at any rate...

[Jed]

Re: Newbie with an issue

BenBaron,

How many fires have you had in your oven?

If it is brand new the second issue you will have is the moisture in the masonry takes a good 10 fires or so to cure or dry out. Until that point, the oven has a real hard time getting to and holding temperature.

This is a secondary issue compared to the 'no insulation under the floor' issue which will take a big long fire to heat up all that concrete.... or get some good insulation under the cooking floor.

JED

[geisen]

Re: Newbie with an issue

Ben
Firebricks that line your oven are heat sponges. They absorb heat.
You have to have insulation between the firebricks and anything else (360deg all around) to keep the heat from being sucked out of the firebricks. Anywhere concrete or air touches your firbricks is BAD.

The floor of your oven needs to have insulation under it or you will loose all heat quickly.
The dome of your oven needs insulation around it or same thing.

Possible solution for floor: add 2" insulation board and then low duty firebricks. This will raise your floor 4.5 inches but it beats tearing the whole thing down.

What is on the outside of your dome....touching your bricks? If nothing, good. add insulation (FB blanket best, vermiculite also good). If plain concrete....not good. not sure what to do at that point.

good luck
Greg

[BenBaron]

Re: Newbie with an issue

Okaydokay guys thanks for all the help on this, Ive got a few piccys.

Fires, Ive had about 5 now, started small then bigger.

Had another session tonight but still not much luck with it, one of the piccys which shows the fire, clearly shows the level of heat from the smoke layer, anything under the smoke is relatively cool, in the smoke hot as hell.

Other piccys show the top, which is refractory concrete, this Im going to add a good layer of vermiculite mix.
Other piccy shows the front which is direct into the oven, I dont really have much solution to getting insulation on the front so will have to live with that one, the back is the same but I can get some insulation on that so will do a mix of vermiculite as on the top.

Im wondering if it would be worth while cutting a slot in the top to act like a chimney, Im pretty sure its starved of oxygen as when I shove the fire to the back it kills it or almost does, the piccy shows flames but Ive had to keep blowing it to keep it lit.

Sides are a double layer of firebricks with about ab inch of concrete between them, they havent yet got warm....


Below the concrete is a little tricky but Im either going to cut a hole in the base and bodge some insulation in or go for heat resistant expanding foam (easier to install). Anybody used expanding foam??

To me it just seems like its not hot enough, reading a few threads and other places people say its hot enough when the carbon burns of the bricks, hasnt happened yet.
Does different wood burn at diff temps?

Thanks again
Ben

[mfiore]

Re: Newbie with an issue

Ben, do you have temperature measurements? How big are the fires? The fires that burn off the carbon are big (scary big). Yes, different woods burn at different temps. Somewhere in these threads someone published a chart with different woods and burn temps. With big huge, hot, long fires, you may be able to get to high temps, but if not insulated, you won't be able to retain.

Good luck

[Rastys]

Re: Newbie with an issue

Ben,
just looking at your thread and now your pictures, you have a variety of problems which are not 'easy fixes'!
As mentioned, you are :
1. seriously lacking in insulation:
- especially under your hearth bricks,
- at the back of your oven,
- on the sides and top, and
- on the front of the oven.
2. your fires are not hot enough to achieve the better temperatures to get those pizzas cooking crisping in a short time,
3. your oven entrance/arch is a little low (which is beneficial in preventing heat from flowing out of your oven) but may be too low if you plan on insulating under your floor, which is in my opinion a 'must do'!
When you cook your pizzas, try as I do, push your fire to one side rather than to the back and get more wood and flames into it. The flames should be high enough to run up your walls to the centre of your barrel. You don't have enough heat to start with, and are loosing too much through your floor sides, top and back.
If it were mine, I would:
1. remove the hearth bricks and put a double layer of insulation board (yes it will be more expensive than vermiculite cement, but you will save considerable height inside your oven). Then re-install your hearth brics.
2. Remove the second layer of firebricks from your walls From what I understand is that you have a full 9" plus cement bonding them as a heat sink which is way way too much. A single half brick )4 1/2") is more than ample. Put an insulation blanket over your single barrel bricks or 3 to 4" of vermiculite cement insulation.
3. Carefully cut out the mortar in your oven arch bricks and using a diamond blade, carefully replicate the arch around 4" higher than it is at present (to allow for the 2" of insulation board and an extra 2" for easier access for you if you require it. This should be quite easy to do as your front face bricks are more like larger blocks and will easily hold in place during the 'renovation'.
Re install your arch bricks using your original form work and pack the top mortar joint with mortar to ensure that it is good and completely through.
From your pictures, I can't see how you can insulate behind them without removing them and bringing then 4" forward into your oven and losing valuable cooking space.
I think then that with better fires, you will enjoy your oven as it will get hotter with less wood, hold the heat longer, and be more enjoyable.
Sorry mate, but I don't see any easier way to fix the problems.

Cheers.

Rastys

[brickie in oz]

Re: Newbie with an issue

Does different wood burn at diff temp?

There is the same energy per kilogram of wood in most species, so wood type isnt the factor.

Your design is all wrong and no matter how much you dick around with it, it just wont change or work.

The first pic you put up showed slow lazy smoke, now Ive built many a fire place and chimney and know all about how they should work correctly to achieve a decent draw and hence a decent fire.

A properly designed and built wood fire pizza oven is nothing more than a chimney that is laying down, or more correctly, a well designed chimney is nothing more than a good designed and built wood fire pizza oven that is standing up seeing as how the ovens were here first.....

You have to have a restriction in the fire box to make the thing draw properly, its called a ventura.
Without the ventura the fire wont burn.
The ventura restricts the flow of air/oil/vapour/fuel(what ever), etc, with any restriction there is an increased flow/velocity.

Its the restriction that causes the fuel to burn correctly.

Ill post some diagrams of how it all works later.

Uploaded, the pics are a cross section of a fire/pizza oven.

Without these basic elements in your oven/fireplace, the fire just wont burn.