Used red brick or new fire brick ?

I have access to a couple tons of used red brick. Question @1 is can I use this old used red brick for the construction of the whole J tube assembly fire channel and heat riser or just stick with the HoDe fire bricks. Any feed back will be welcome. And question #2 sense I have to drive 100+ miles to cut WOOD I am debating on a 6 or 8" system can I use smaller pieces of wood like for a 6" system in a 8' system? Now my stove vent pipe is 8" already or should I switch over to a 6" {material is a whole lot cheaper} and just burn smaller stuff I can go out in the desert and find all kinds of smaller pieces up to 6" round or so but finding logs that need to be split Well not going to happen on a regular bases out there. {. I will be heating a 2000sq ft home? TIA David

David ; Stick with firebrick in burn tunnel & heat riser, you can use the red brick on the rest. Yes you can burn smaller wood in an 8" system, homedepot sells 5' pieces of 8" hvac pipe at very reasonable prices, they will even mail them to you. I would definitely stick with an 8" you only need the black pipe near the horizontal transition area, then you can switch to hvac pipe thats much cheaper. Don't forget used pallets and construction waste as sources for free firewood.

Davin Marin : Be very careful what you put in your cart for ''FIRE BRICK" Especially right now at LOWES, HO-DE's and other big box stores !

The kind of F.B.you want is 9" x 4.5" x2.5/3'' and weighs 28-30 ounces, less than quart of milk. In many places in the U.S. and Eastern Canada You can not get
any kind of F.B., sometimes all that is available is a Hard/dense F.B. that weighs over 7pounds almost a gallon of milk.

The best use for the heavier brick is to place Them in a kiln to prevent rapid drop in temperature after you shut off the Heat !

Again, the best Fire Brick (1) weighs less than a quart of milk, Then (2) the next best brick is 100 yr old red/red orange house brick, (3) the heavier 'Fire Brick'
weighing almost as much as a gallon of milk comes in a very distant 1/3rd.

Instead of reradiating the heat radiating from your combustion Chamber back into the heart of your fire- It just absorbs the heat just like the hunk of high density
Thermal Mass it is, and slows the growth of the high temperatures you need to create the Efficient Burns we expect from our Rocket Mass Heater !! For the good
of the Craft ! Big Al !