I just moved into a 7 year old townhouse. Turned on the a/c yesterday and noticed that although I have the thermostat set between 76-78, the thermomoter part of the thermostat read 70 in the house. The a/c cycled what I felt was a normal amount. Does this mean the thermostat is faulty and I should replace it?
I doubt if I’ll be able to help but does the room temperature feel like 76-78 or does it feel like 70?
Many thermostat thermometers are adjustable. Check it’s accuracy against a known true thermometer and see if you can effect correction. If you can’t figure it out, try to tell us what kind of thermostat it is and we can probably tell you how to improve things.
Clearly at least one of the readings is faulty. Personally I would guess the thermometer, but it doesn’t really matter. set the thermostat to a point where you are comfortable, note the arbitrary number associated with that setting for possible future reference. If you are curious about what temperature it is in the house, get a thermometer and place it at various points around your house. The one I have near my computer (about as near to the computer as I am which is why it is there), reads about 4 degrees warmer than ambient in other rooms of the house. Absent a heat source I am surprised by the low horizontal gradients in my house-but the temperature does vary. The little thermometer on the thermostat is such low quality that it is hardly worth paying attention to.
But doesn’t the thermometer tell the a/c (or heat) to turn on? If you have the thermostat set to 72, when the thermometer hits 73, that signals the a/c to start? Or does this happen internally (like within the box) and the thermometer on the outside of the box is just for show? So the thermometer on the box could be wrong but what matters is what the temp reads inside? Perhaps this question should be retitled “how does a home thermostat work?”
It depends on the type of thermostat. WIth the older style thermostats which are common in most homes the thermometer which displays the temperature is not connected to the internal heat sensing switch that turns the furnace on or off. In the newer digital themostats the temperature readout and the control come from the same sensor. Here is an article aboutHow Home Thermostats Work.
This is the correct answer. In other words, as long as the A/C is cycling on-and-off a reasonable amount (i.e. it has a typical period and duty cycle), and as long as the temperature is what you want, then the actual reading on the thermostat is irrelevant.