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  1. #1
    Join Date
    Aug 2003
    Posts
    48

    Question

    Would someone please explain anticipation? I have a White-Rogers digital comfort set(?) thermostat. The settings number from 2 to 35. The manual says the higher numbers are for hydronic heat. I heat with gas.

    thx

  2. #2
    Join Date
    Mar 2004
    Posts
    1,042
    Anticipation is used to compensate for how some systems deliver heat with a lag factor. This isn't usually a big problem with forced air systems, unless they are severely oversized, but can be an issue with hydronic.

    With zero anticipation (in a general sense, not with regard to the settings on your particular thermostat), the thermostat will keep calling for heat until it reaches its actual setpoint. Then it stops calling for heat. You'd think that's all there is to it, but there is always some heat that remains to be delivered at that point, and in most cases it's still going to get delivered to the space even if the thermostat is satisfied. In a forced air system, you've at minimum got hot air that's still in the ducts and will probably get blown out before the blower stops. With gas forced air, you've got a hot heat exchanger; the thermostat causes the burner to turn off but there's still residual heat there that needs to be delivered. With hydronic, the thermal mass of your baseboards/radiators/slab is hot at that point; stopping the flow of hot water doesn't make them stop radiating heat into the room until they give up all of that heat at their own pace. So regardless of the system, once the thermostat clicks off, there is almost always more heat that is still going to be delivered to the space. Depending on how much heat there is after that point, you might be fine, but you can also drastically overshoot your setpoint.

    Anticipation is internal thermostat logic (or a mechanism, in nicer mechanical thermostats) that can be adjusted to make the heat cycle off sooner than the setpoint would otherwise suggest. You tune the system so that the thermostat stops calling for heat early, but the residual heat that comes after that point gets you to the setpoint you intended. It prevents the overshoot on systems that would otherwise overshoot.

    Overshoot is generally only an issue with heating systems (not so much in cooling systems) so except in unusual cases, anticipation is only applied on the heating side. Unless you're having problems with overshoot, there's no need to adjust the default settings. Lots of more basic thermostats don't even have the feature.

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