Anticipator Setting

Scott Kuchta

Ok, so I've insulated the pipes on my one-pipe steam system, got radiators venting properly and fairly evenly balanced - heat is getting to where it needs to go. Now I notice on heating cycles to maintain the heat at the set temperature, the boiler shuts off before the upstairs warms up. However, if we are away and turn the heat down, upon returning and turning the heat up, the boiler runs longer to heat everything up, the upstairs gets nice and warm. I now have a smaller rad vent on the room with the t-stat so I don't heat that one up too quickly. Now I'm looking at the anticipator setting. I looked at the PDF offered by Honeywell for the T87. I'm not sure what the "current rating for the primary control" (I have an oil burner) is or where to find it if I did. So setting the anticipator that way is out unless someone can tell me where to look. I don't have an ammeter to measure, otherwise I could do that following Honeywell's directions. But I do understand that moving the anticipator to the left makes the burner run a longer cycle and also makes for less cycles per hour. I could use some advice on setting this until I can either find the current rating or measure with an ammeter. I also get the feeling that if I did measure it or set it according to the current rating that this might just be a "good place to start" and that some adjustment may be necessary anyway. Am I correct in that?

t. tekushan

anticipator

I don't have all the answers but the beauty of the original Honeywell round T-stats is that wonderful analogue anticipator.

If the anticipator is set too "short" for the current drawn for a long time the excess current may destroy the anticipator. It doesn't appear that this is the case here. Don't go any shorter and you won't do any damage. "Long" settings do no harm but can cause larger room temperature swings between off and on cycles. If you set it really long, the system will overshoot the desired temp.

What I'm trying to say is that there is no risk involved in experimentation. Set the anticipator incrementally longer until a satisfactory balance is achieved. I lived with a system like this in a rental. I set the anticipator quite long. The temp variation didn't bother me at all, and I really liked the fact that the system operated a peak efficiency because it would run longer and less frequently. My distinct impression is that it lowered fuel consumption.
I look at it as a crude heat timer...

Pat Clark_2

Adjusting anticipator

Make sure you have the power turned off before making any adjustment on the anticipator. If not it may burn out immediately when you move it. Then you will have to replace the thermostat.

Pat

Scott Kuchta

how can i tell

I must admit I did move it toward the left (longer) without killing the power. How do I know if I killed the anticipator? Thanks though, if I didn't kill it already, I will turn the power off before experimenting further.

Dick Charland

Not difficult

With a T87, it is very important that it is installed properly, the backplate needs to be level and fastened securely to the wall. There are two ways of determining the thermostat current, one to use an ammeter(capable of reading less than an amp) or two read the current setting off of the primary control. A standard cad cell control usually has a .2 amp draw. Verify this off of the control. Then slide the heat anticipator setting to the appropriate setting. To check the heat anticipator itself, examine the coil to see if there are any points where it appears burned or damaged, if so replace. This should not be the case in your situation. It will not hurt the anticipator to move it with the power on. A little experimentation with settings may lead you to end up probably around .4-.6 setting. Moving to the left cuts down on the amount of coil available to generate heat allowing longer cycle before "tricking" thermostat.

Fred Harwood

Anticipation

Try to get three cycles an hour. If rads overheat, reduce venting. If some are still cold, vent them better. Then you approach the sweet spot.