How to Get a Hopper to Feed Into a Furnace
If you're trying to make item distribution for ovens, without minecarts or pistons(they are kinda noisy), this can be achieved with a inconsequential amount of redstone(although, redstone is common enough I've never been in any fear of running out).
I'm gonna try to explain what you're seeing in this picture, so I hope this works. This pic is from some early trial so it's missing a row of hoppers that is in the following explanation, but you should be able to get the gist of item distribution.
HHHHHHHH> (top row of hoppers, all pointing horizontal towards last oven)
HHHHHHHH (middle row of hoppers, pointing downwards)
HHHHHHHH (bottom row of hoppers, also pointing downwards)
OOOOOOOO (your row of ovens)
Now you'll want to build a row 2 row of blocks out from the the bottom row of hoppers to form a ledge 2 blocks deep. On that ledge you'll place a repeater going into each hopper(middle row), and then redstone next going into all 8 repeaters. Place a block just right of the last repeater in your array, then on that block place a redstone torch just next to the redstone line. If you've done this correctly you should see all the redstone and repeaters light up. This will keep your middle row of hoppers shut off, until you create an interrupt signal.
Now, to create your interrupt signal you need to place 3 blocks out the back of the middle row of hoppers. On the first block place a comparator followed by a repeater and finally redstone. Now, you'll need to place another 2 blocks so you can complete the circuit for the interrupt signal. Those 2 blocks need to be placed so that 2 redstone can run directly into that block with the redstone torch. If done properly this line will not light up until you try to load something into the top row of hoppers.
How it works... Well, items can only be passed through hoppers one at a time... so as the top row of hoppers has a line of items moving through it, when 1 hits the last hopper in the top row that comparator will fire. It will send a signal to that block with the redstone torch(I don't understand this part, I just know it works). Which will in turn interrupt that signal and the middles row of hoppers can pull down items from the hoppers above(Since they each only have 1 item, all 8 hoppers will pull down just that 1 item). now the top row of hoppers starts filling up again. But, while that is happening, the bottom row of hoppers can pull out those items to pass them to the ovens.
The main points to keep in mind here are the middle row of hoppers needs to be turned off, and the interrupt signal needs to come from that last hopper in the top row of hoppers. The bottom row of hoppers is to pull down out of the middle row, without this you would leave 1 item stranded here every time you tried to load your ovens. It's very similar to the one pictured above, but it eliminates the row of chests.
Now, keep in mind this is just one component to building a furnace(array of ovens)but this took me awhile to figure out. With a furnace this big you will need a fuel source(look into carpet duplicators, else I don't know how you would keep it supplied with fuel). You'll also likely want a delivery system that can supply items in a constant stream(I don't know if this possible with minecarts).
Source: https://gaming.stackexchange.com/questions/161115/fill-up-furnaces-all-at-once-by-hopper