| Supply Voltage | 20 to 30 Vac |
| Electrical Ratings | 18 to 30 Vac |
| Operating Humidity | 5 to 90% RH |
| Mounting | Square |
| Application | Heat Only |
| Dimensions | 3 1/8 in. high x 3 1/8 in. wide x 7/8 in. deep |
| Stages | 1 Heat |
| Color | Premier White® |
| Sensor Element | Bimetal |
| Accuracy (F) | ±3 F |
| Switching Action | SPST |
| Switch Type | Snap action |
| Terminal Designations | W, R |
| Setting Temperature Range (F) | 50 F to 90 F |
| Heat Current | 1.0A running, 2.5A inrush at 24 Vac |
| Fan Current | 1.0A running, 5A inrush at 24 Vac |
Description
The T812A1002 is a non-programmable thermostat from Resideo (Honeywell Home), heat-only.
A non-programmable thermostat holds one setpoint until someone changes it. That is the whole design, and it is the right design more often than the market admits: in a shop, a rental, a spare room or anywhere occupancy has no schedule, a programmable stat gets overridden permanently within a week and then behaves like this one with extra steps.
Heat-only means there is no cooling changeover and no fan switch to get into the wrong position. On a boiler or a furnace with no air conditioning, that is one less thing for a tenant to set wrong.
Where it hangs decides what it reads. A thermostat measures the air touching it and nothing else, so an interior wall about five feet up, out of direct sun, away from supply registers and doorway drafts, and clear of the back of a wall carrying hot water or flue pipe. Most complaints that a stat is “off by three degrees” are placement, not calibration — the stat is reading the truth about a spot nobody lives in.
These are also the straightforward answer to the C-wire problem. A smart thermostat needs a common wire to power itself continuously, and in an older house that wire is often not in the bundle — which turns a thermostat swap into a wire pull. A non-programmable stat does not draw a continuous 24 V supply for itself, so the wires already on the wall are usually the wires it needs.
If the stat has an adjustable heat anticipator, set it to the current stamped on the primary control rather than leaving it where it arrived. Too low and the burner shuts off early and the room never reaches setpoint; too high and it overshoots and then coasts cold. It is the one adjustment on a stat like this that changes comfort, and the one most often skipped.
Confirm the system type before ordering — low voltage, line voltage and millivolt thermostats look similar and are not interchangeable.
- Brand: Resideo (Honeywell Home)
- Manufacturer Part #: T812A1002/U
- Type: Non-programmable thermostat
- Stages: Heat-only
- UPC: 085267233736
- Category: Thermostats