I could not get any 4-2 wg to connect my air handler to my breaker box so I bought 4 copper and 8 copper single strand. Can I bundle these together and run them through the attic like romex or do they have to run in conduit?
Individual conductors like you bought need to be installed in a complete conduit system from the panel to the unit or junction box. You just cannot run conduit part way and slide the conductors through.
There are two 4's and an 8. I looked at a chart and it said 1" for three 4's, so I calculated it for two 4's and an 8 and got 3/4". Was your chart for two 4's and an 8, or three 4's?