Opened wood fired oven back up after 20 years

[Lumberyard]

We inherited a wood fired oven built straight into the wall of our dining room when we bought our house ... the only catch is that previous owners had built a stud wall in front of the opening to cover it up and removed the chimney. Finally got around to removing the wall and rebuilding the chimney this year, but now I have questions. Any insight would be appreciated.

Ash Dump
The oven has a slot at the opening that serves as an ash dump to an enclosed cinder block base that can be emptied from outside. The only issue is that the slot is inside the door which seems problematic for cooking with retained heat. I know a bit about the history of the oven and the people who built it seem to have known what they were doing (seems similar to an Alan Scott vault design) but this seems like an odd choice. Is there a reason for this? Do I need to come up with some sort of cover to avoid heat escaping through the slot into the less insulated ash chamber?

Repointing Mortar Joints
The oven has been boarded up for 20 years (and largely out of use for 30) though it has sat under a couple layers of metal roofing the whole time. It looks to be in fairly good condition, but there are decent gaps between some of the bricks on the ceiling of the oven in particular. Is this something I should be repointing to seal up the oven?

Small Vent in Back
This one is more of just a curiosity, but there appears to be a small pipe in the back of the oven with some sort of wire hanging out of it. Curious if anyone has any idea what its purpose is.

I've fired up the oven a few times with decent results -- didn't get it hot enough for pizza, though it's fairly large so maybe just needed more fuel, and it didn't retain heat well, possibly due to the ash dump. Looking to fine tune it a bit (and make sure it's really safe to use after being dormant all these years.

[david s]

The form of the chamber is typical of a bread oven. Low vault and tall sides at the perimeter.
It looks in pretty good condition. With the mouth of the oven being indoors, you may have issues with smoke in the house, particularly at start up, although this also depends on whether it is an updraft or cross draft chamber. An updraft chamber will have the entry to the flue at the same level as the top of the chamber's vault, while a cross draft oven pulls the flame down before exiting to the flue. Updraft systems smoke way less at start up while cross draft systems produces better heat circulation and lower fuel consumption.
The air vent at the back of the oven may be a modification to reduce smoke issues if it's a cross draft. This could explain the reason for the air vent the back because it would allow you to open the air vent while placing the oven door during the first 10 minutes or so, while the flue heats up to generate the required draw. preventing the house smoking up. Or if it's an updraft system, to improve cinrculation.
A pic of the base of the flue from the oven interior would be helpful.
Regarding the ash drop slot. if it were mine I'd be making a steel cover plate for it so it can be blocked off during retained heat cooking.

[Toiletman]

Small Vent in Back
This one is more of just a curiosity, but there appears to be a small pipe in the back of the oven with some sort of wire hanging out of it. Curious if anyone has any idea what its purpose is.

Since there's a wire hanging out of it: could it be a connection for either a temperature sensor or light? Have you found where it leads?

And sounds like a nice surprise to find in your house. Saves you a lot of work

[Lumberyard]

Thank you for the helpful responses. It's a cross draft chamber -- opening is a rectangle that the arch rises above. Haven't had trouble with smoke entering the house, but I've only fired it on really cold days so that probably helped the draft. A heavy door for retained heat cooking and a lighter metal draft door were left in there. Definitely designed for bread, which makes the ash drop inside the chamber more confusing. Metal plate idea sounds good.

Pipe in the back seems like conduit -- a light would be handy there but the bulb/enclosure would get a ton of heat.. You can see what the outside of the oven looks like in the image above and there's nothing sticking out anywhere, so not sure where a wire would end up. I guess I could venture into the crawl space...

Any thoughts on repointing larger gaps?

[david s]

If that hole in the back of the oven is only the size of a conduit it would be of little use as an air intake. Repointing the brickwork is often unsuccessful, but if it worries you give it a go. The important part is to get a decent bond and retain moisture in the area for an extended period which is difficult. Try this method. 1.Get the areas to be filled moist before pointing a soaked sponge held against the area with a stick or something works ok.
2. Then make up a slurry of 50/50 cement and lime and coat the cracks with this mixture.
3. Straight away fill the gaps with a 3:1:1:0.5 fine sand, Portland cement, hydrated lime, powdered clay mixed to a peanut butter consistency. Force the mix hard into the gaps.
4. keep moisture in the area for a few days maybe using the wet sponge technique again
5 give the whole oven a couple of weeks to dry before any fires.
6. Keep fingers crossed.

The cement and lime can be replaced with a calcium aluminate cement like Ciment Fondu if required. It has the advantage of setting and curing much faster, but repairs are also often not successful in the long term.