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  • Which t'stat to use?

    I'm posting here because it looks like this is where the controls and hydronics experts hang out.

    I installed two separate small ( one room) hydronic heating systems in my forced air house, to warm up two cold rooms, 1- is a laundry room on a slab and 1- is the dining room at the end of the duct work with large windows.

    Anyhow, I installed 20 gallon electric water heaters, 30# safety valves, expansion tanks, pumps, and control the pumps using a relay for each. Sufficient baseboard was also installed to heat each of these rooms very nicely. The dining room also uses a V8043 to start the pump as it is on the same heater as a gravity fed radiator heating a room in the basement.

    The only problem is that I can't get the t'stats right. I have T87F installed in each room and no matter where I set the anticipator the stat over shoots the setting. I am used to gas fired systems and setting the anticipator at the same amp setting as the gas valve, but obviously there is no gas valve.
    I have been trying to find a stat w/o the anticipator but none of the suppliers have them. And I am not certain that would cure the problem, although simple on/off should do the trick.

    Does any one have any ideas? Is there an amp rating for the relay that could affect the anticipator? Do you know of a stat that is simple on /off for 24 volts. Or am I missing something??

  • #2
    Re: Which t'stat to use?

    How much does it overshoot?

    Honeywell T87K is what you want

    Comment


    • #3
      Re: Which t'stat to use?

      Thanks for the reply.

      I just Googled the T87K but Honeywell's description doesn't help much. What is the difference from the 87F?

      It over or undershoots 5-10 degrees from set point depending where I set the anticipator.

      Right now one room is 65 degrees, but the relay doesn't shut until stat is turned to about 58. I found a reading of .2amps on the relay cover and have changed all of the anticipators to that setting. Could the relay be taking the place of the gas valve and requiring a matching setting to operate properly?
      Last edited by APHCO; 12-10-2008, 09:27 PM. Reason: add content

      Comment


      • #4
        Re: Which t'stat to use?

        Check to be sure that the plastic protective holder for the glass bulb with mercury inside it was removed. Also, be sure there aren't any jumpers that might be shorting out the anticipator. It's a tiny resistive heater near the bi-metal coil what makes the thermostat think the room is heating up faster than it actually is.

        Try setting the anticipator slider to about 0.15A and let it cycle a few times. Then set it to about 0.7A and let it cycle a few times. You should notice a bigger difference in temperature swing with it set higher. The 5-10 degree swing has me wondering if current is actually flowing through the anticapator.

        Are you using a sub-base? Is there any chance of improper connection?

        2. If the rooms are at 65F and the pump(s) start about how long does it take for the rooms to reach 70F? I wonder if you may have far too much baseboard in the rooms. It does stay hot for some time once the pump stops. In cold winter you normally have it run in such a way so the baseboard is warm but not really hot at all times. That is it stays a good bit warmer than the air temp but also lower than the water temp in the boiler.

        3. Did you level the thermostats? There are markings and you need to use a level to check them.

        Info on T87K and T87N series: http://customer.honeywell.com/techli...69-1958EFS.pdf

        General Info: http://customer.honeywell.com/Busine...US/Default.htm
        Last edited by Woussko; 12-10-2008, 11:13 PM.

        Comment


        • #5
          Re: Which t'stat to use?

          Remove tstat from wall. Take one wire and wrap it around your amp clamp 10 times. connect the wires together. Take your reading in amps and divide by 10. (example .2 amps * 10= .02 amps). Set the heat anticipator to match the reading. The reading is how much amperage the valve draws. This setting determines how much of the heater in the tstat is exposed to fool the tstat before it overheats the area.

          How big are these areas (Cubic feet) and how much baseboard did you install. You probably should have installed the correct supply and return ducts.
          WE LIVE IN THE LAND OF THE FREE,
          ONLY BECAUSE OF THE BRAVE

          Comment


          • #6
            Re: Which t'stat to use?

            Originally posted by Woussko View Post
            Check to be sure that the plastic protective holder for the glass bulb with mercury inside it was removed. Also, be sure there aren't any jumpers that might be shorting out the anticipator. It's a tiny resistive heater near the bi-metal coil what makes the thermostat think the room is heating up faster than it actually is.

            Try setting the anticipator slider to about 0.15A and let it cycle a few times. Then set it to about 0.7A and let it cycle a few times. You should notice a bigger difference in temperature swing with it set higher. The 5-10 degree swing has me wondering if current is actually flowing through the anticapator.

            Are you using a sub-base? Is there any chance of improper connection?

            2. If the rooms are at 65F and the pump(s) start about how long does it take for the rooms to reach 70F? I wonder if you may have far too much baseboard in the rooms. It does stay hot for some time once the pump stops. In cold winter you normally have it run in such a way so the baseboard is warm but not really hot at all times. That is it stays a good bit warmer than the air temp but also lower than the water temp in the boiler.

            3. Did you level the thermostats? There are markings and you need to use a level to check them.

            Info on T87K and T87N series: http://customer.honeywell.com/techli...69-1958EFS.pdf

            General Info: http://customer.honeywell.com/Busine...US/Default.htm
            Answering in order of asking:
            I have installed hundreds of t'stats over the last 30+ years, most of them T87F. There are no red plastic shims,or crossed connections. There is no sub base or any need for one, the stats are level, I even used a level to do so.

            Originally posted by Chauncey
            How big are these areas (Cubic feet) and how much baseboard did you install. You probably should have installed the correct supply and return ducts.
            The dining room is 400 square feet, the laundry is much smaller. I calculated the heat loss and put in all the baseboard needed. The issue is not heat, it is control of the on/off cycles. When they call for heat, both areas get toasty. Heat isn't the problem. If I operate without stats, they run beautifully. Heat is not the problem. Did I mention that??.

            Remember, these are used for supplemental heat in two hard to heat rooms at opposite ends of the house. Each room already receives heat, but are always cold during the heating season.

            I installed them because for me, working with hot water baseboard and copper piping is the easiest and most fun way to provide a nice warm area. There is no way to get any duct into the laundry room and it has two registers already that are almost useless. The dining room is the farthest room from the scorched air furnace and has other issues that make it hard to heat. The baseboard works fine to heat the space required.

            If there was an easy solution I wouldn't of had to post it here.Easy I can do, difficult takes more heads. From what I have seen there is a lot of control experience on this thread and I thought something would pop out that was obvious to other heating guys.

            Actually I may have found a solution last night when I set the heat anticipators to .2 as is stated on the relay cover. Any other ideas?? And oh yeah, heat is not the problem!!

            Comment


            • #7
              Re: Which t'stat to use?

              Originally posted by APHCO View Post
              Actually I may have found a solution last night when I set the heat anticipators to .2 as is stated on the relay cover. Any other ideas?? And oh yeah, heat is not the problem!!
              When all else fails read the paperwork

              It wouldn't surprise me if you bought a bad t-stat. The T87F is a mercury stat and has been pulled from our shelves since 2004. I've had much better luck with the solid state T87K. No adjustments needed after setup. Seems to hold temperature better than the wildly swinging mercury bulb.

              You have probably solved the issue with the setting at .2

              BTW has your electric company sent you a dozen roses yet? They should

              Comment


              • #8
                Re: Which t'stat to use?

                Originally posted by plumberscrack View Post
                The T87F is a mercury stat and has been pulled from our shelves since 2004. I've had much better luck with the solid state T87K. No adjustments needed after setup. Seems to hold temperature better than the wildly swinging mercury bulb.

                You have probably solved the issue with the setting at .2

                BTW has your electric company sent you a dozen roses yet? They should
                Thanks for the further info on the 87K .I'll see if I can find one.

                Funny thing is that I had thought that all mercury stats were gone from production, but I have seen more on the suppliers shelves this year than the last few years combined. Both W/R and Honeywell seem to be readily available.

                No,haven't received the roses from the electric company,yet. I imagine they will send them when the really cold weather gets here. So far my wife is happy with the warm laundry room, except now it gets too hot in there from the stat not doing what it should.

                Having her warm and happy will be worth it, as the saying goes " if Mama ain't happy, ain't nobody happy"?

                I'll report back after a few days with the .2 setting

                Comment


                • #9
                  Re: Which t'stat to use?

                  you wont find the mercury T87 at a supply house they are electronic or bimetal t87's and yes if you dont have a amp meter try the amp rating on the primary control.

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