I want to wire two attic fans from one new power source. Each fan to be wired to its own countdown timer. From the timer I connected the red wire to the black of the fan, black to the black from the hot, all whites are connected together and all grounds connected together. I connected the second fan and second timer the same way. When I turned the breaker back on, it didn't mater which timer I turned on, both fans would be running.

Before I can give a more informed answer, would you mind answering:
What color wires are coming out of your timer?
Can you explain your diagram a little more?
What type of timer are you using?
Thanks!

OK here's where you start to lose me. " red wire to the black of the fan, black to the black from the hot, all whites are connected " What timer are you suing, there should normally be no red wire. From your power source the neutral and black come into the swithc box, white/neutral bypasses the time and goes on to the fan. Black goes into the feed side of the timer and blacl comes out of the output and goes to the fan. Each timmer needs it own black feed but they can share the neutrals

There are three wires coming out of the timer. Red, black and white. The timer is a Leviton off, 2 hr, 4 hr, 6 hr and 12 hr timer.

I found out what I was doing wrong. I had both red wires (one from each switch) and both black fan wires all on one wire nut. I separated one red and back fan wire and now both fans are working independently as desired.

Thank you for your response.

The timer has three wires if used as a single pole timer, red, black and white. It actually has a fourth wire if I wanted to two switches on one fan and wire it as a three way. The directions on the timer said to connect the red to the black on the fan. I was okay with one fan but the directions didn't say anything about two switches, two fans and one power source. I got both fans and timers working by connecting the rd timer wire and black fan wire separately for each fan. I appreciate your input.

Can we narrow down the field, do you have the model #? Timer Switches > Residential Products > Residential Energy Management > Residential from Leviton Energy Management This could be an extra wire in case you want to set up a 3 way switch with a traveler

Glad you figured it out.