gusherb
Well-known member
I collect old thermostats, and I also have a stockpile of new digital ones. The general consensus is that digital is far more accurate than mechanical, and that is true. But there are some mechanical thermostats that are as accurate as the best digital ones, and there are digital thermostats that just plain suck at the one thing they're supposed to do.
Being the tinkerer that I am, I've tested just about every popular thermostat in existence. For heating; the two most accurate mechanical thermostats are the Honeywell T87 and T874 commercial thermostat. When properly leveled and the heat anticipator dialed in right, they're as good as the best digital thermostats available. Unfortunately they don't do so well with cooling, for that they tend react too slowly to load changes in the structure and therefore will let it get too warm inside as the temp rises and the sun bakes the building.
The big problem with mechanical t-stats is that the bimetal coil tends to lose accuracy as it ages, so a T87 that could keep temps within a degree or two may start letting it swing further and further as it ages. This starts happening when they get to around 15-20 years of age.
The best digital stats I've found are Honeywell, the pro line. Not the stuff you get at the big box. I've found them to have the most intelligent control algorithm of any stat out there, and are calibrated most accurately. The other most popular brand: Emerson/White-Rodgers tend to be about 2 degrees out of calibration from the factory, and some models came 4 degrees out calibration. The funny thing is they allow you to adjust that, whereas Honeywell doesn't. (Because Honeywell comes from the factory set correctly)
Being the tinkerer that I am, I've tested just about every popular thermostat in existence. For heating; the two most accurate mechanical thermostats are the Honeywell T87 and T874 commercial thermostat. When properly leveled and the heat anticipator dialed in right, they're as good as the best digital thermostats available. Unfortunately they don't do so well with cooling, for that they tend react too slowly to load changes in the structure and therefore will let it get too warm inside as the temp rises and the sun bakes the building.
The big problem with mechanical t-stats is that the bimetal coil tends to lose accuracy as it ages, so a T87 that could keep temps within a degree or two may start letting it swing further and further as it ages. This starts happening when they get to around 15-20 years of age.
The best digital stats I've found are Honeywell, the pro line. Not the stuff you get at the big box. I've found them to have the most intelligent control algorithm of any stat out there, and are calibrated most accurately. The other most popular brand: Emerson/White-Rodgers tend to be about 2 degrees out of calibration from the factory, and some models came 4 degrees out calibration. The funny thing is they allow you to adjust that, whereas Honeywell doesn't. (Because Honeywell comes from the factory set correctly)
