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adding outdoor thermostat to control boiler second stage

Dan_53 Member Posts: 20
I have a two stage 300,000 btu boiler (NG) that has a high fire gas valve as well as the regular gas valve. The thermostat on our operating temp is set at a boiler inlet temp of about 170. The high fire valve also has an adjustable thermostat, which in the winter is set at about 145-150. So when the water temp at the boiler inlet is below 140-150, the high fire gas valve opens, and all 300K btu's are used. Currently, I have the high fire valve turned off. I only turn it on Dec-Feb. We live in northern CT. Is there any simple outdoor thermostat that I can wire into the high fire gas valve circuit that will allow it only to function when the outdoor temp is below 20 degrees? The boiler never has a problem with inlet water temps being too low. So I only need to run that high fire valve on the coldest days when all three hydroair zones are running as well as DHW. Thanks.


  • Just a,,,

    Normal HW spdt (single pole double throw)grey box t'stat with the proper range and a remote bulb will work. Sorry I don't have a number for you. I've used them myself for similar applications. Johnson makes a digital of the same configuration that works nicely as well. It needs power to operate though so the wiring is slightly more involved. I live in Hebron FYI. ;)
  • Dan_53
    Dan_53 Member Posts: 20

    does anyone know a model number of one that goes from say 0-50 and is compatible with 24v? I have found some, but they are compatible with 240v and 120 v. Would that mean that they are also compatible with 24v AC?
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