Miner Cooling Which is Better, Push or Pull?

I've been thinking about different ways to use the hot air from miners for heating purposes. To make cooling work effectively, is it smarter to blow cool air into the miners or suck the hot air out?

There is no difference, all that matters is total airflow through the systems and both ways can do it. That said, it is always easier to provide positive pressure vs suction even if only because positive pressure makes it easier to overcome leaks and eliminates any building ventilation concerns when using gas appliances such as water heaters, stoves and heating.

what would the CFM requirement be to push the air through something like a Avalon 1246?  I saw some silent inline duct fans that have a cfm of 1200.  Wonder if that would be good for 2 or 3 machines?  Was thinking put a  duct and  an inline duct fan + box filter to the machine, each rated for 1200cfm.  Add another inline duct fan for the exhaust side only if needed Can the fans on the machines be removed, and just use the inline duct fans to push the air through, if it has a high enough CFM? Got my miners running now in the attic, luckily its cool weather.  Will do the duct work now, as I make it more sound proof in the coming week(s).

As long as the duct fans are rated to deliver that airflow under pressure, sure. The fans on miners are so loud because they have to move the air against a fair amount of resistance (back pressure) caused by the heat sinks. That entails using fan blades with a steep pitch moving at high speed to generate enough pressure and that is where most of the noise comes from.