A few rack setup questions

I am setting up a Herpstat 1 as my primary thermostat with a Ranco as my backup. It is being used on a eight position rack with 16 qt tubs. What differential temp should I use on the Ranco? I was thinking of initially setting my Ranco at 92 F (differential 1 degree) and my Herpstat at 90 F. I will increase the temperature (Ranco always two degrees warmer then Herpstat) until I get to a belly heat temperature of 90 F. Please tell me if this approach is correct.

Also, I currently do not have any ventilation holes. Do I need them? There is a bout a 1/16 inch gap between the top of the tubs and the rack. How many holes should I put in each tub to get started and them check my humidity.

Thanks

the holes are not only for air flow but for humidity also.
what works in my house wont work in yours, you just have to ad holes as needed.

I would set the ranco straight at somewhere between 95 and 100 depending on what the actual inside the tub temps are at that setting.

with a 1 Degree variation it is likely the ranco will shut down the HS frequently. I would run a (with no snakes...) test to find the upper safe temp inside the tub use the ranco as this set point. For example my rack temps...

The herpstat is set for 94º this gives my 89-91º inside the tubs. The back up T-stat is set for 100º this temp delivers 95-97º tolerable range until the problem can be corrected.

The new herpstat one has a power down mode if the set point is low (under alarms I believe) and with the mechanical relay (typically will fail off not on) it is debatable if a failsafe is needed at all. I use one on my HS4 however in this case of this unit I have the failsafe set even higher to shut down when the temps hit 100ºF interior the HS is set for 5º shut down. so the two together make a seriously safe combination (triple redundant)

Hope this helps

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Oh it depends a lot on probe placement... I assumed the probe was located on the flexwatt in both primary and failsafe. If you have an interior mounting for the primary the secondary should go on the heat source directly and be set at a point I would say 10º over the highest operational temp.

I also always place the failsafe on the top rack slot as it is typically the hottest.

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Yes you need ventilation holes. VPI suggests that if you are unsure you should have more. High humidity and low ventilation is linked to RI and other nasty issues. The 'petri dish' syndrome...

Amount of air holes needed is going to vary, like Pit said, not going to be the same everywhere. I would start with a few and add more as needed. It's easier to make more, than to cover them up.

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My rule of thumb is a snake on paper when the water bowl is removed the RH should drop to the room in less than one hour. (one air change an hour) using the snakes exhaled breath to increase humidity is simply not a good idea at all. It is easy to control the room rh and have lots of ventilation.