Still puzzling out overshoot

Charles_8

My insulation and vents arrived today, so this evening I insulated the main loop with 1" thick fiberglass. (Except for about five feet exiting the boiler, and the last three feet going back in, there was none at all). The risers still are bare and I'll be ordering the appropriate insulation for them next.

I also put a C-size vent in the living room (the long but low radiator) which is also where the t-stat is, and a #6 in the upstairs bathroom since I want more heat there while showering. The new vents are now quiet - the old ones were probably crudded up and whistling through smaller than normal openings...

The overshoot is worse if anything, which makes sense as the steam is now heating the living room rad even more before the thermostat satisfies. Set at 65, cycles between 65 and 71 (boiler off at 67).

As posted in another thread, I think I need some kind of heat anticipator "tuning". Changing vents seems like it would just alter the distribution of heat in the various rooms.

Is it possible that the radiator is just too large for the room? It's been +10F high, -18F low for several days now and the room heats up well (actually too well including the overshoot) but the radiator never gets hot all the way to the end. -20 is a pretty typical coldest-morning temp up here.

Any steam gurus in Aroostook County (Maine)?
-Charles

Ken_40

You may have exacerbated the problem...

By installing a 'C' in the LR, the rad that effects the 'stat the most!

ALWAYS use a #4 in THAT rad (the one that impacts the 'stat most).

Unless you have a truly anomolous case of huge rad in small room, or the opposite, huge room with undersized rad, never use anything but a 4 in the 'stated room, and 5's and 6's in the other rooms.

Your 80% home-free already. The 'stat now sounds like the culprit! Please re-iterate the make and model 'stat you're using.

Did you mention the end of main, vent array? They too are impacting. The insulation of individual risers is not a high priority at this point. Let that go for now.

And pressure? We're in the "under 1-1/2 psi max" at any time - setting range?

We'll get you throuh this. Promise.

John Roberts

Are there any other Aroostook counties?

Charles_8

Thanks for helping. I *hope* we'll be able to get this sorted

For the last two winters I've only heated part of the house (usually just the master bedroom, bathroom, and LR). 2nd BR and the DR are shut off. Mostly on weekends I'll heat the 3rd BR where I have my radio station.

The MBR and bathroom were warmer than the thermostat setting, too. Since putting in the larger living room vent I have noticed that the two other rooms are now the correct temp, as I expected, since the stat is in the living room and shuts off sooner, although not soon enough.

Heating the room with the stat quicker (with a bigger vent) will cause all the other rooms to heat less, correct?

I'm not sure if the size of the stat-room vent affects the amount of overshoot though: It's got to get hot enough to satisfy the stat, no matter what, and then that mass of hot cast iron keeps putting heat into the room...

The main vent is very old and rusty looking and sounds like it's leaking even when hot. I have a new vent and plan to install it tonight. I'll leave the risers alone for now, as you suggest.

The thermostat was an old beehive, now a digital Honeywell RTH110B (non-programmable). Trying to find tech info on it. It doesn't have a normal heat anticipator settings by amps, only a setting for two through six heat cycles per hour. I've tried both ends (2 and 6) and it doesn't make any difference. As has been suggested here, I may put the old one back in and turn up the heat anticipator. If it burns out I'm no worse off!

Regarding the pressuretrol, there has never been any measurable pressure in the system (I have a 0-15 psi gauge) so it never cuts out on the pressuretrol, only the thermostat. I think the leaky main vent is letting the pressure out - although as this site makes clear, it only takes a few ounces of pressure to heat a two-story house.

I'm basically satisfied with the system's ability to heat the house - it's the 6 degree swings in temp that bug me. If I could get that down to 3 degrees I'd be happy.

Charles

Charles_8

Not to my knowledge, but I didn't want to assume that everyone knew where it was

(Or how cold it gets up here!)
-Charles

Ken_40

If the main's insulated,

and the vents replaced, you must consider the 'stat as a likely culprit.

Two CPH would be the correct setting for steam. One, would be better!

Consider this: If the LR, where the stat is is swinging 3+ and 3- from the setpoint, the problem MUST be the 'stat!

Balancing the remainder of the house is a whole plethora of "other" issues/dynamics. If you set the 'stat at 68 and actually have swings from 65 to 71, AND the rad in the LR is reasonably well sized to the "load," AND a # 4 Gorton vent - presumably in new condition is in that rad, AND the steam valve to that rad is wide open:

THE THERMOSTAT'S BLOWN!

Charles_8

Thermostat

The thermostat when set to 65, does indeed come on at 65. It cuts off at 67. But then the temp in the room continues to rise over the next several minutes until it reaches 71.

That doesn't sound like the fault of the thermostat, since it cuts out (and I can hear the boiler stop) at 67.

Can you please explain to me the idea behind the "number of cycles per hour" setting? Don't I want the boiler to kick in ANY time the room is down to 65, never mind how many times an hour it got there??

thanks
Charles

Charles_8

Reintalled the beehive, now working properly

The cheap Honeywell RTH110B electronic thermostat does not have an anticipator, apparently. So I reinstalled the T87 beehive. I also fixed the following things: There was a 3/4" hole through the plaster and lath into a cold inside-wall space, which I stuffed with insulation. Also the beehive base plate was not mounted level before and now it is...

Finally I set the anticipator to its lowest setting, .1 amp, even though my R8184G control recommends .3 amp. (I don't have an ac ammeter handy). That actually caused short-cycling! At the .15 amp setting, I barely notice the room temp swing and a thermometer sitting next to me on the couch shows 2 deg or less

Of course it's a heat wave today, 24 this morning after 5" snow but now it's down to 15. I turned on the radiator in the hallway, which is also the other side of the wall the thermostat is mounted on. That may have made a little improvement too.

Anyway, if (when) the outside temp goes back down to -15 perhaps a tweak of the anticipator might be needed.

-Charles

chapchap70_2

Hi Charles,

I went back and read a section of my heating text book on thermostats because of your above post. I thought the higher the anticipator setting amperage, the shorter the burner run cycle which, of course, is backwards.

I don't know if you will have to do much tweaking with the thermostat anymore because as it gets colder, the temperature swing may be less because of the increased heat loss. I don't think there is any danger of burning out a control or a thermostat by changing the anticipator settings.

I think you fixed the problem by plugging the cold air behind the thermostat. If that is the case, the other thermostat will work the same way.