I'm trying to replace an old t451a thermostat that controls a zone on a oil heat Hydronic system.
The guy at the big box store sold me a lux elv4.
He said even though it says not for hydronic heating systems that I could us it.
There are 2 wires (white and black) in the electrical box.
He told me connect both wires to the line-in(red wires) side.
Is this correct? Shouldn't one wire go to the line-out (black wires) side
Also are there any better thermostats that can be used on a Line voltage oil heat hydronic system? There seem to be very few choices out there..

Thanks in advance...

Watch out for the guys in the big box store. Its rare to find one that knows what they're "specialty" is. In this case you need to convert the 120 Volt line serving the 24 v thermostat. I'm no expert. That is why I'm at this site now. I have dealt with this exact unit before. I was given bad info with regards to the conversion at the big box (HDepo) near Levit. PA. What you want to ask about is a RELAY I have the Honeywell R458A to take care of the conversion.

I have the r845a Honeywell relay. This unit or something similar deals with a low volt conversion. The Lux whatever - I'm not familiar with it. Is it a low volt thermostat? I guess not if it's line voltage.