Thermostat Anticipator Setting

mel rowe

When you say that it should take 20 minutes to fill the radiators, would that be 20 min. from the time it starts to steam, or 20 minutes from when it kicks on?

Dave Braunegg

I have a one-pipe steam system in a two-story (plus basement) house. If the thermostat anticipator is set correctly, how wide should the temperature swings be? (This is an old, round, mercury-bulb thermostat.)

For example, if thermostat (1st floor) is set to 68 degrees,
- How low should the thermometer on the thermostat read when the boiler kicks in?
- How high should the thermometer read after the boiler shuts off?
- How high should the thermometer read after the boiler shuts off *and* after the house has coasted on up to its maximum temperature due to the heat still in the system?

Thanks,
Dave

P.S. I know about reading the current rating at the burner to find the anticipator setting, but I want to find out if it is working correctly.

Big Ed_4

old T87....

....has a 4 degree differenial. I like to set them 2* below and 2* above. And you adjust it from level.

With steam you want to set the cycle to three times a hour. Take a amp draw on the whole thermostat circirt. Start off setting antisipator to that reading. Then push it to the next number following the "Longer" arrow. Setting it on the money would set cycle six times a hour.

Hop this Helps

Dave Braunegg

Big Ed,

Thanks for the response. I used to think that the thermostat setting would equal the lowest temp.

I'm guessing that adjusting the level of the thermostat to get the 2* above/2* below is just trial and error, right? I start with the thermostat level, then tilt a little bit to adjust the lowest temp (where the boiler would kick in). Wait for next heating cycle, then repeat until the heat kicks in where I want?

Is it best to check the amp draw right at the thermostat? I would take the thermostat off the wall, unhook one wire, and insert the ammeter between the loose lead and the thermostat. Does the boiler need to be firing when I do this?

By "cycle three times an hour", to you mean that the thermostat should call for heat three times an hour? That is, three times in one hour the room temp hits the low point, thermostat calls for heat, room heats up and thermostat shuts down the boiler, then finally the room cools down to the low temp again?

Thanks,
Dave

mel rowe

I'm always glad to see a discussion about the heat anticipator function, since it has baffled me for some time. I understand about checking and setting the anticipator to the correct amperage. I get lost when you talk about being able to get 3 cycles per hour. My boiler takes about 40 minutes to get up to heat, fill all rads and and satisfy the stat. It then stays off for about 60-65 minutes. I have often thought that a shorter cycle that did not allow the boiler to stay off for so long would be more efficient and more comfortable, but it seems that whenever I move the anticipator setting down a bit, the boiler shuts off well before the stat is satisfied. Any clarification or suggestions will be greatly appreciated.

Dick Charland

Unforunately, the T87 was a great thermostat and its demise regretable considering some issues I have heard re: new and improved electronic versions. The function of the heat anticipator in the thermostat is to "trick" the thermostat which is nothing more than a switch to turn the heat on/off. Depending on the type of heating system there will be residual heat in the radiators, baseboard and ductwork etc. When the thermostat turns the system off the residual heat will continue to heat the space. Accordingly, the heat anticipator is a small heating coil in the thermostat that heats up as current flows though the unit. Typically, properly set, it will turn off the sytem at or about 1-2 degrees below set point allowing the residual heat to raise the temperature to the one selected.

Depending on the control that the thermostat is connected to, there will be an amperage rating that the anticipator should be set to. Typically a cad cell control is .2 amps, an old stack relay was generally .4 amps and at the other end a Taco zone valve .9-1.2 amps. To get an accurate spec it is recommended to take an amp reading. The amperage factors into how much heat the coil will give off in the "tricking" process, with a smaller amperage, more of the coil is used thus anticipator is set to the right. As amperage increases anticipator is moved to the left. The unfortunate installation of a thermostat with a high amperage draw and an incorrectly set anticipator will generally result in the coil burning out.

When the thermostat is installed level and the anticipator is properly set the temperature should be held pretty much at the set point, generally falling a degree or two turning on the system, but you should not see high overides of the room temperature. Accurate measurement of the amperage should allow for proper cycling requiring at most minor tweaking of the anticipator.

Rarely have I ever had to put a thermostat out of level, would usually "recalibrate" when a new thermostat was installed and the customer would insist it was defective because the old one always raised the temperature higher then the set point.

Fred Harwood_2

Anticipation

Part of the confusion may be due to down in current or down in physical motion. The T87 anticipator is just under the bottom right of the dial, which means that the slider moves from about 3 o'clock to about 6 o'clock. Moving the slider down toward 6 o'clock increases the current setting, and moving it up toward 3 o'clock decreases the current setting.
The numbers are stamped on the plate underneath, but require a strong light and reading glasses for most of us.
So then, a longer runtime means moving the slider down toward 6 o'clock, and a little movement can mean a lot. The principle is to move it a bit, then observe, etc.

mel rowe

Thanks loads for that information. Any idea why my stat seems to shut off so quickly when I move the anticipator toward the 3 o'clock position, even before any steam starts getting to the radiators? I have encountered this numerous times as I have adjusted the anticipator in an effort to get more frequent cycles, under the belief that this might be more efficient, rather than letting the system and piping cool down for so long between cycles. What do you think would happen if I just left the anticipator set at the lower setting and let it run like that for a longer time? Will it ever really heat up?

Dick Charland

First, what control is it attached to? Without getting an accurate amp reading we'll start with that. As you move the anticipator to the right (3:00) you are allowing more of the coil to heat up and depending on the control this will cause the bi-metal to react and turn off. The actual room temp still being "cold" the bi-metal then springs back and turns the system on. It will bounce back and forth like that, not an efficient way to run the system. If you are seeing this, you want to move the anticipator to the left in small increments. Knowing the control amperage will provide starting point.

mel rowe

I have measured the amp draw on the thermostat circuit. It is 1.9 amps. If I set the anticipator to that setting, will that give me the minimum cycle time I can expect with the capacity of my boiler and the attached load? I'm asking this dumb question because when I set the anticipator at 1.9, the boiler will run for about 35-40 min. and then will be off of about 60 -65 minutes, as I said. I was hoping there was some way that I could shorten up the overall cycle time and gain efficiency.

Fred Harwood_2

Anticipation

Yes, because you should be moving toward the 6 o'clock position to increase boiler run time.

Big Ed_4

Cycle time

With steam you want to set the cycle to how long it takes to fill radiators which should be around 20 min. But if your radiation is too large and you get a over ride . You can decrease to nudge up the heat. The main thing is comfort. You try to soften the heat swing. Mataining proper humidity levels is just as important. Don't forget the other part of comfort.

Dick Charland

I'm sorry, something doesn't sound correct with the amp rating. Is this an oil boiler or gas? A T87 range goes up to 1.2 amps, how did you measure the amps?

mel rowe

****, you are right. I was going by what the tech. told me he had measured. Obviously that was incorrect. I do have a gas system. I got my flashlight out and a magnifying glass (LOL) and I found that when I have the anticipator set below about .75. the system kicks off without really heating up the rads. When I set it higher than .85 It runs for about 35-40 minutes and then stays off for about 65-70 minutes. So I'm not sure if I can get a better cycle than that, with this system. Any suggestions?