Two-Stage Thermostats

[Dave]

I recently had a Trane two-stage variable speed furnace (model TUY060R9V3)installed along with a White Rodgers 1F80-261 single-stage thermostat. My installer noted that the single-stage thermostat, properly jumpered, works as well as using a White Rodgers 1F81 two-stage thermostat, as the 1F81 model operates by timer in the same way as the single-stage, properly jumpered, would (i.e., ten minutes on low fire, then switch to second stage heat).

Based on what I've read and discussions I've had with others, it seems that a two-stage thermostat would in fact take into account temperature differentials, etc., in determining when to switch to high fire, not just time.

Is anybody familiar with this issue, specifically with respect to White Rodgers thermostats? Apologies in advance if this is an obvious question to some of you. I am no expert on heating, but it seems that my two-stage system should be running with a multi-stage thermostat.

Thanks in advance for any comments. Dave

[modervador]

The algorithm in a 2-stage stat is much more sophisticated than what the furnace board can hope to achieve. The furnace can only take into account how long the thermostat called for heat and how long the furnace spent in low and high fire mode to satisfy that call, and perhaps how long it has been since the last call. As you note, the thermostat can take all that into account as well as the rate of temperature change.

Here's your answer from the horse's mouth:

"1F8X-XXX Series Multi-stage and Heat Pump thermostats are designed to determine the optimum time to activate the second stage. Simply raising the temperature in heating or lowering it in cooling will not always force the thermostat to bring the second stage on quickly. There is a time delay from 0-25 minutes. The time element (0-25 minutes) of the delay varies depending on the performance of the first stage. In Heating for example, assume for the last 2 hours the thermostat is set on 70 and the room temperature is 70 with the equipment using only the first stage of heat. The thermostat calculates (internally) the performance of the system. Since the equipment is keeping the temperature within 1 degree of setpoint the thermostat will delay second stage for a longer time if you manually raise the temperature or if the room temperature quickly changes. Once the second stage comes on it will come on sooner the next time there is a difference between the setpoint and the room temperature. The net effect of the staging program is when the first stage is capable of making temperature the second stage will delay longer. When the thermostat calculates first stage cannot make temperature in a reasonable time the second stage will come on sooner. This is a built in function that automatically optimizes the use of additional stages of heat or cool. Most thermostat models have a method to bring the additional heat or cool stages on quickly for testing purposes listed in the installation instructions under the heading of "Testing Your Heat/Cool System."

%mod%

stanford [e-mail] (Dave) wrote in message news:...