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BenBaron 05-25-2009 01:55 AM

Newbie with an issue
 
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 05-26-2009 01:38 AM

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 05-26-2009 02:10 AM

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 05-26-2009 06:19 AM

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 05-27-2009 02:35 PM

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 :o
I assume from your question that it should have some sort of insulation layer below it???:eek:

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

BenBaron 05-27-2009 02:37 PM

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 05-27-2009 07:48 PM

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 05-28-2009 01:53 AM

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 05-28-2009 07:21 PM

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 05-29-2009 11:43 AM

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


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