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Thread: T Stat Question

  1. #1
    Join Date
    Mar 2011
    Posts
    7

    T Stat Question

    I have a question about the operation of a White Rodgers 1 F87-361 prgrammable digital thermostat. It operates a gas furnace/a/c in a converted garage we use as a family room. Here's the issue. If I set back the temperature at night to say 64* from 69*, and ramp it back up in the morning back to 69*, the thermostat will not "catch-up" to the proper temperature, and the furnace will continue to run until the temperature well exceeds 69*. The furnace won't stop until the thermostat temperature reading finally gets to 69*. But by then, it's roasting, since the actual temperature (actual readings with a digital thermometer) show temperature far above 69*, and it feels it). This happened with a prior White Rodgers 1 F87-361 that contractor replaced because he thought it may have been faulty. Same thing with the new one. Once the room temperature and the thermostat temperature balance out, it works fine. I can also tell you years ago I had a mechanical thermostat and this was never a problem. I was able to even shut off the furnace, and ramp it up manually the next morning and it would always stop at the correct temperature. What's going on here? What I've done in the meantime is stagger the upward temperature. I set it to go to 66* and then a half hour later to 69* in order to minimize the excessive heat. Sorry for the long thread, but I just don't think the thermostat should operate that way.

  2. #2
    Join Date
    May 2008
    Location
    Central Fla.
    Posts
    311
    Is it located on an exterior wall? Near a return? Is there an insulation/barrier where the wires come through the back plate on the tstat?

  3. #3
    Join Date
    Mar 2011
    Posts
    7
    It's located on an interior wall that is part of the closest that houses the furnace. It is to the right and above a large return on the same wall.

  4. #4
    Join Date
    May 2008
    Location
    Central Fla.
    Posts
    311
    So when it shuts off what is the room temp. right then and there? It should be taken 5' from the floor in the middle of the room. It would be ok if it coasted up to 71* if you set it to 69*. you are working with a 3 degree spread, heats up to71* cools down to 68* Back and forth. You can have the dead band adjusted but it will short cycle and drive you crazy.

  5. #5
    Join Date
    Mar 2011
    Posts
    7
    It definitely exceeds that temperature, but frankly I haven't done a proper recording of the readings. I'll do that and get back to you. Thanks for your input. (By the way, what's a dead band?)

  6. #6
    Join Date
    May 2008
    Location
    Central Fla.
    Posts
    311
    The temp. degree between when it shuts off and comes on.

  7. #7
    Join Date
    Dec 2010
    Location
    La Honda, CA
    Posts
    83
    Might just be that your old mechanical T-stat had an incorrect heat anticipator setting and was short cycling and you just got used to that. White Rodgers makes a very good product in my opinion. With single stage equipment (if that's what you have) you could expect a 2-3 degree temp swing. How far off is the temp in the home (with your thermometer and a reading near the thermostat) from the reading on the new T-stat?

  8. #8
    Join Date
    Jun 2009
    Location
    Midwest
    Posts
    5

    Answer from White-Rodgers

    My name is Tim Burke, an employee of White-Rodgers. This is purely my own personal opinion expressed here.

    In addition to some of the submitted comments keep in mind that digital thermostat temperature readings are buffered. By that I mean that it does not recognize a temperature change in real time. By design it moves slowly. That way if someone opens a door on a cold day and a blast of cold air hits it for a short time the equipment will not turn on and then turn off (short cycle) right away.

    If your heating equipment is over sized for the area you are conditioning this could explain the overshoot in temperature upon recovery. The room is heating faster than the thermostat can sense. From what you described after it recovers the first time it works fine the rest of the day.

    Here is a link to the operating instructions:
    http://www.emersonclimate.com/Docume.../0037-6763.pdf

    Go to the configuration menu and ensure item 2, Heat Cycle Rate is set to Fast, and item 5, Energy Management Recovery is On It is worth a try, but may not help.

    If the equipment is over sized like I suspect, you need to reduce the amount of heat entering the room so the thermostat can keep up. Have a qualified HVAC Contractor review the application.

  9. #9
    Join Date
    Mar 2011
    Posts
    7
    Thank you for your reply. This explains a lot. The room can quickly heat up. I'll check with my HVAC contractor (not the one who installed the unit, which is oversized) on air flow, and check those settings you mentioned as well. I'll also play around with "staggering" the recovery (going from setback temperature to final temperature with two steps over a slightly longer period of time). Like I said, once the temperature stabilizes, it works well. By the way, for all out there (especially the professionals), this is a great site.

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