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Advice on choosing a replacement heat only t-stat


My wife and i moved into a 1912 farm house that has a hot water boiler\radiator heating system (Bryant Legacy BW series boiler made in 2002). The old mercury bulb manual t-stat is on the fritz and was wondering what I could replace it with? Do I need to use the same style or can I upgrade to a digital and programmable model? Do I need to use something that has an anticipator?




  • Big Ed_4
    Big Ed_4 Member Posts: 2,235

    I would use a digital thermostat today .. The heat anticipator set the on-off cycle of the thermostat to nudge up the temperature of the room for more even heat comfort . The digitals today have a programed cycle you can change if need be...
    I have enough experience to know , that I dont know it all
  • Sweet_Lew
    Sweet_Lew Member Posts: 116
    edited January 2010

    Thanks for the reply. I ended up purchasing a Robert Shaw digital and programmable  t-stat that has a anticipator feature from prothermostats.com.


  • Sweet_Lew
    Sweet_Lew Member Posts: 116
    Bringing it back from the dead.

    So I have been 0 for 2 on replacement t-stats. I just installed a 3rd. A Honeywell Focus Pro 5000 and it's no where near as good as the mercury was. With the old t-stat, the upstairs was almost as warm (if not warmer) than the first floor. Now, the second floor is much cooler than the first. I wish I never removed the mercury t-stat *bangs head on wall*. Any hot water boiler owners have luck with a newer t-stat?
  • ChasMan
    ChasMan Member Posts: 459
    edited October 2010

    The thermostat is not your problem. The old mercury stat if you set it to say 70 and assuming it was accurate and the anticipator was set corectly, would let the temp swing from 69 to 72 degrees. That wide swing probably caused the heat to stay on for long periods of time and is what gave you your comfort level. The new digital stat is not allowing that swing causing more frequent shorter cycles.

    You have one zone in the house and only one thermostat? I have five stats in my little house. All are digital. I also have a circ fan running. That tends to even things out a bit.
  • Sweet_Lew
    Sweet_Lew Member Posts: 116
    You're probably right

    I think I may try to get the old t-stat put back in. the house felt more evenly warm with it. I have one t-stat. Again, everything worked fine with the old t-stat. I need to remember if it's not broke, don't fix it..I guess I could put another upstairs.
  • ChasMan
    ChasMan Member Posts: 459

    Sometimes digital stats have a CPH (Cyles Per Hour) setting. You will want to make that as low as possible to mimic the old thermostat. Again, depending on how the old one was working. Sometimes the CPH is called Fuel Type like Oil / Gas What No Coal or wood? I have seen Steam (1 CPH) That might overheat way too much though.
  • Sweet_Lew
    Sweet_Lew Member Posts: 116

    I currently have it set to 3 CPH which is what the manufacturer had for hot water heat. I know steam is 1 and that is not recommended. I'll try 2 and see what happens.
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    I have a fancy programmable thermostat.

    Mine has many cycle time settings.

    1  radiant floor heat or gravity steam system

    3  hot water system or high efficiency furnace

    6  gas or oil forced air heating system

    9  electric heat system

    My other one has similar settings

    1  for steam or gravity systems

    3  for hot water systens & furnaces over 90% efficiency

    5  for gas or oil furnaces of less than 90% efficiency

    9  for electric furnaces.

    Note that one says 5 and the other says 6 for lower efficiency furnaces. I assume this means it is not that critical, or not that accurate. The second thermostat can set to 2, 4, 6, 7,10, 11, or 12 as well.

    These two are both Honeywell thermostats.

    I have two White-Rodgers thermostats that run hot air furnaces. Their cycle rates are in arbitrary numbers. If I remember correctly, they go from about 5 to 40. Higher numbers presumably run slower. I find this confusing, but it is probably usable if yo play around with it.
  • Ironman
    Ironman Member Posts: 7,119
    edited October 2010
    One Other Thing...

    Apart from adjusting the cycle rate lower, have you checked for air in your upstairs rads?
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Tucson_Joe
    Tucson_Joe Member Posts: 1
    Floor furnace, heat only digital thermostats.....

    I have an old house with a floor furnace. It is controlled by a single thermostat. I would like to replace it with a heat only, non-programable digital thermostat; however, I am having trouble sorting out all the data to find one that is simple, effective and inexpensive. I have looked at the Basic Honeywell PRO 1000 Non-programmable Digital Thermostat but am unsure if it will work on a floor furnance. Any thoughts?

    Will this also work as a zone thermostat for a radiant heat system (under hard wood floor)?Thanks.
  • JonS
    JonS Member Posts: 3
    Hot water boiler t-stats

    Sorry to report that I am having a devil of a time finding a good t-stat for my hot water boiler. My old digital Honeywell worked fine, now the replacements are running the boiler for 45 minutes straight - no cycling - it heats the radiators hot, then the boiler stays off for 2 hrs until the radiators are cold. I am posting on Controls in a minute to find someone here to suggest an answer.
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    I wonder what your problem is.

    I have a mod|con hot water boiler and two heating zones. Each has a Honeywell thermostat that, for historical reasons are not the same. One zone is radiant slab, and I have it set for one cycle per hour. The other zone has oversized baseboard; oversized so I can run lower temperature water in it. It, too, is set to one cycle per hour. The thermostats I have are fancier than I need, with all manner of fancy setback capability that really make no sense for radiant slab heating. And with large outdoor resets, they make little sense for baseboard .

    The thermostat for the radiant zone is a CT3600. I am not sure if it is still available. I could have it run 4 different temperatures each day, for a total of 28 different temperatures. I bought this to save money, but I cannot use it as designed. I did not understand setbacks and radiant slabs. Basically, you cannot do much over 1F setback, and that is not worth the bother.

    The baseboard one is a PRO TH4110D. It may still be available. I cannot remember if it is set at 1 or 2 cycles per hour; it can be set for 1, 2, 3, , ..., 12 cycles per hour. For hot water systems, Honeywell recommend 3 cycles per hour, but my boiler runs outdoor reset and I find lowering the cycle rate works better for me.

    I use 2F setback at night with this one as I do not use that zone at night. More setback does not work well because of the extreme outdoor reset I use. For example when it is 14F outdoors (design day), I put 130F water into the baseboard. When it is 32F outside, I put 121F water into the baseboard. That is not enough to recover quickly from a greater setback.
  • coltleader
    coltleader Member Posts: 1
    Thermostat advice

    I need some advice! I'm on the market for a new thermostat because mine is not even functional anymore. Can anyone suggest a brand or something along those lines? I have heard of prothermostats, and I was wondering if anyone knows anything about that type of thermostat. I appreciate any information!
  • Greg Maxwell
    Greg Maxwell Member Posts: 212
    Digital tstat

    For a basic nice stat, try the honeywell TH-5110d-1006
  • Sweet_Lew
    Sweet_Lew Member Posts: 116
    That's the one to get!

    That's is the same t-stat I ended up getting and it's working great.
This discussion has been closed.