I’m installing Ecobee 3 thermostats. I really like the one at our lake house (1990s heating plant) so I started installing them in our regular home (1900s heating plant).
Things did not go smoothly. I’m mixing late 20th century and early 20th century electrical technology. The simple job became complicated. This is called the mushroom factor in some old-house maintenance communities: surprises in the infrastructure can make a normally easy task mushroom into a major project.