Even though the Weepmizer can work with either NO or NC solenoids, I would use the NO type, like mentioned here on the forum many times. (Good Advice). In a power failure, your weep system will come on. With a NC solenoid, it will stay closed until the power comes on. Not good.....
After buying our 4 bay ss 2 months ago, the weepmizer was the first thing I made changes to. My solenoid was a 24v type and relied on input voltage from my floor heat boiler transformer. This required the power to be "On" to my boiler just so the Weepmizer would cycle the solenoid. When the temps dropped to 30° - 32°, the boiler would kick on. Needless to say, I had a very large Jan.-Feb. Natural Gas and elect. bill. I could have changed the T-stat setting, but I made this change instead.
I changed my solenoid to 120v. which allowed me to iscolate it from my boiler and not add an aditional 24v transformer. Now I can leave the breaker off to my boiler when not needed. I put a switch inline to the 120v input to the weepmizer/solenoid circuit. This allows me to flip the switch off which kills power to my NO solenoid, thus opening water flow. Now I can test all my weep guns to make sure I don't have any that are clogged. I'm sure many do the same thing here. Hope this helps....