Thermostat rant

[Jabberwocky Dragons]

Maybe I'm over thinking this or just too dense to understand the reasoning.

I use Herpstat 2's. After reading the thread Eric provided, it seems that you are just gambling on which unit will fail first, or conversely, which one you have MORE confidence in. It seems that if your secondary fails it may shut everything down. Thus, where's the back up to the backup?

Unless someone can dumb it down to me I see no reason for a back up to a Herpstat but maybe for other brands.

Sure, here's it simplified. Your secondary (on/off) thermostat should always be on. If your primary fails in the "on" position, your secondary will turn power off to both. Gambling or confidence doesn't factor in here.

If the secondary fails in the "on" position, it doesn't matter because it's not providing heat to anything. It will simply allow your primary to continue functioning as normal. Your secondary should always be on anyways. Herpstat is reliable but should still be backed up. Losing a clutch of eggs or a rack of snakes in not a fun experience, especially when a fool-proof method of prevention is so easy and relatively inexpensive.

There's a much greater risk when a thermostat fails in the on position than the off position. Herpstats are designed to fail in the off position. Cheaper stats typically fail in the on position. If the secondary fails in the typical manner here, the worst it would be doing would be supplying power to the primary Herpstat.

This kind of backup is designed to work if the primary were to fail in the on position. Since this is so unlikely with a quality stat like the Herpstats, I personally don't see much reason to back a Herpstat up. Would it hurt? No. Is it overkill? Possibly.

From Spyder Robotics: http://www.spyderrobotics.com/home/s...edocument.html.

It's been a long day so I may not be reading correctly. What I'm taking away from your link though is that Spyder Robotics says that their Herpstats are inherently designed to fail in the "on" position (per the Triac component). They have taken steps to help prevent this in the higher end models but the default failure is still the on position regardless. They also give this prominent warning:

Also keep in mind that even with the highest quality components ALL electronics have the possibility of failure.

It then goes on to recommend backing Herpstats up with a secondary on/off.