Weil McLain Product 381-356-586

If you have a boiler controller that supports this sensor it is a pretty easy upgrade. I installed it on a GCa Series 3 Gas boiler only used for heat (no domestic hot water). When this is installed the boiler will dynamically adjust the temperature set points in relation to the outside temperature. So if it is a little warmer out the boiler will cycle off at a lower temperature then it will if it is colder and vice versa, up to the boiler's thermostat set point. It will also change the temperature the boiler will turn back on, again down to the boiler's "efficiency" set point. After using it for a month I think it probably does save a little gas and money although year-over-year average temperature is higher this month, and I'm comparing the old boiler which was very basic. Note that you want to keep the sensor out of direct sunlight or away from any potential heat sources such as a drier vent. Installing on the north side of the building is best and what the manufacturer recommends. In my case I was able to run a cable through the attic and install it under the eve. Using the graph included with the instructions I was able to verify the location was OK by comparing outside temp and where the boiler was cutting off. This is a low-voltage part and certainly within the realm of a DIY project, although routing the cable might be a bit more of a chore if you can't wall-fish or run in an attic or crawlspace.

good value for dollar