Need Recommendation for Electronic, Non-Prgmble, 2-wire, 24V T-stat w Cycle Rate Adjustability

D107

While I was able to adjust our old White-Rodgers t-stat anticipator, it appears my old Honeywell MagicStat32 is on its way out, 30 yrs old etc. Shuts off after two minute cycle. Somehow the room temperature reaches setpoint and shows it on Temp indicator. Don't know how that's possible unless heat is coming from large 1.25" uninsulated pipes just below in basement boiler room. The anticipator screw is supposed to be turned one revolution counterclockwise for hydronic cycles, but screw falls out if I loosen that much.

Anyway, wondering what the recommendation would be for an Electronic, Non-Programmable, 2-wire, 24V w cycle rate adjustability. Most of the simple ones don't have all this. Don't really need programmable as with our new properly sized boiler there will be no setbacks. But want it to run with 24v with battery backup.

mikeg2015

Honeywell T4. Supplyhouse.com has them. In the setup, you can disable the schedule program. Cycle rate is adjustable.

D107

@mikeg2015 Thanks; I believe they say it runs on AC and/or batteries. I need 24v. There is a T1 too that I think is 24V. I was alaso looking at the RTH11B. or CT30 or 31 one of which has some kind of numbered adjustment system. Not trying to save money here, want something reliable and built to last but so far that's what I found.

mikeg2015

It can be powered from the 24AC system transformer (3 wires needed R, W, Com) which also allows continuous backlight (makes a nice nightlight), or use batteries (simple 2 wire, R & W). Honeywell T series all use the same wall base so it can be upgraded if you want ot integrate it with a heat pump for dual fuel, or AC system as well. Each heat source having a unique cycle rate setting.

In my current setup I have a Lennox iComfort stat for the heat pump, ended up adding a T4 because I would have to give up communicating AHU features to go to a hardwire interface for dual fuel.

I also use the heat pump as a passive backup, setpoint set much lower, in case the boiler fails while I’m away from home, I’ll at least get enough heat capacity for freeze protection. It held 54F indoors when it was -10F outside 2 winters ago when my power damper failed when I was on vacation.

D107

Thanks yeah i guess i feel safer with 24v and backup battery. This is just atmospheric boiler with three zones. I’ll check put the rth11b. We only have two wires.

D107

@mikeg2015 I ended up getting the RTH111b which should hold me for awhile. It works well. There's one setup choice I could use advice on. Their instructions are a little confusing. They say: "If your system type is Single Stage Heat and Cool OR Heat Only then heating system type is #5. Then they explain that's for standard gas or oil furnace less than 90% efficient.

System type #3 is for 'Heat Pump, Hot Water or high-efficiency furnace. greater than 90% efficiency. I chose that one since it mentions hot water, though I have an atmospheric boiler. What would the cycle rate or anticipator difference be?

mikeg2015

Probably type 3. It would have a slower cycle rate. Probably 2 or 3 CPH. But... good chance it’s just a minimum run time with a max differential Allowed and a max run them with a minimum differential. Not the same as cycle rate which uses the rate of change to determine cycle times.

D107

I noticed first cycle overshot by one degree, then rose another degree. If that continues I may check out the furnace settings. Or the 'electric furnace' or 'steam or gravity system.' This t-stat was just to get us through the cold wave. I can take my time and get something with a few more options. I don't like to overshoot, since then we're always making up, in effect, for a two or three degree differential, which is not a money-saver. We don't use night setback anymore. though they often label things as 2-3 CPH, with our insulation and cast iron piping we tend to get a cycle every two hours. Thanks.

EdTheHeaterMan

Wow! So concerned with numbers. I would like to shoot the person who decided to put temperature numbers on thermostats. But he is probably already dead.

if you blanked off the numbers and just put
WARMER < A B C D E F > COOLER
on thermostats, there would be a lot less discussion on numbers and more on how comfortable you are.
The discussion might be more like this:
"Honey are you a little cold?"
"Yea"
"Can you check the thermostat?"
"It is between C and D"
"OK put it on C please"
"done"
"lets see how we feel in an hour"

But with the numbers it goes more like this:
"Honey are you a little cold?"
"Yea"
"Can you check the thermostat?"
"It is set on 68 but the temperature reading says it is 67"
"Well that not right"
"I'll call the service man"
"He will have to come out to fix it and I will complain about the bill when he says there is nothing wrong"
"that sounds like a great idea"
"That is why the numbers are on the thermostat in the first place...right?"
"Sure is!"

"By the way, if we turn the thermostat up to 70, we might feel warmer but the gas bill will be higher"

"I think we should leave it at 68 and complain to the the service company for overcharging us for a service call and telling us there is nothing wrong."
"Yea... Nothing wrong service calls should be free... right?"

neilc

EdTheHeaterMan said:

if you blanked off the numbers and just put
WARMER < A B C D E F > COOLER
on thermostats, there would be a lot less discussion on numbers and more on how comfortable you are.
The discussion might be more like this:
"Honey are you a little cold?"
"Yea"
"Can you check the thermostat?"
"It is between C and D"
"OK put it on C please"
"done"
"lets see how we feel in an hour"

I thought "D" was warmer , , ,

mikeg2015

I agree. The reality is that a steam system almost always overshoots even when sized correctly because total radiation, for good reasons, Exceeds design heat loss by at least 50% in most cases and there’s a big lag between heating the iron and warming air bear the thermostat. A true CPH thermostat helps with that. A differential based one is pretty worthless. Best is often an old school mercury anticipator to respond to true rate of change with some de-bounce.

Similarly, forced air gas furnaces are often oversized with poorly laid out and installed ductwork. Also can overshoot by a lot.

HVACNUT

Look at the Honeywell T6 Pro. It's a little more than you're looking for but is has many CPH options. It is programmable, but guess what? You can program it to be non programmable. It's like the Bizaaro world.

D107

@HVACNUT yes, Bizarro world it is-- I miss the DC comics character. I'm also a little partial to White-Rodgers/Emerson. Hoping honeywell hasn't been sold to another company--I think they've pushed their support to a group called 'Resideo'....But thanks I'll check out T6 --as long as it can work with two wire, 24volt with battery backup.

HVACNUT

> @D107 said:
> But thanks I'll check out T6 --as long as it can work with two wire, 24volt with battery backup.

Yes, it takes 2 AA batteries. With a 2 wire hook up, I'm assuming R and W. It is a 24v thermostat, but with your configuration, its not "24v powered". You would need a third wire to make a Common (ground) side of the circuit. Hence the need for batteries in your case.

D107

@HVACNUT Not sure I understand the distinction. My current t-stats--all from the 80s except the new RTH111B I assume would all work without the batteries but use batteries for backup for power failures etc. Others I've seen are completely powered by batteries--which I never like to do. If the T6 would not be powered by the 24V, then the RH wire is useless and only the W would be needed to communicate with the emitter(?)

HVACNUT

Rh is 24v power to the thermostat. W brings that same 24v back to the zone relay to energize the circulator and boiler. A common is already in the relay for switching, but not at the thermostat. If there is no "C" connection at the thermostat, then it's not 24v powered, its 24v switching, but 3v D/C battery powered.

D107

@HVACNUT Thanks for the tip on the T6 Pro. Just ordered one from Supply House, should be in today. There are some choices in the advanced options that are not clear to me.
1. Heating system type: I have atmospheric boiler; their choices are conventional forced air, heat pump, radiant.
2. Heating equipment type: gas forced air, hi eff gas forced air, oil forced air, electric, hot water fan coil; air to air heat pump, geothermal heat pump, hot water radiant heat, steam.
3. Adaptive intelligent recovery: If I am using non-programmable--meaning same temp 24/7, then this may not apply since there is no setback to return from?
4. The 12 heating cycle stages would seem to be where I could control length of cycle and degrees from target temp that would start call for heat.

Right now even on a cold day the zone in question has 3 hours between cycles, so hopefully that can be corrected to hourly.

HVACNUT

You made me look. Honeywell certainly changed their wording from the retired Pro 6000 manual. That was bad enough. Now its worse.

Heating System Type will be Radiant. I guess they're covering all hydronics in one word.

Heating Equipment Type will be Hot Water Radiant Heat. To start anyway. We'll come back to this.

The Adaptive Intelligent Recovery option will be deleted once you make it non programmable.

The Heating Cycle Rate I think you're referring to (#ISU 370) is not an option with your system so it will be deleted from the set up as well.

Heating Equipment Type (#ISU 205) will play the role of anticipator or CPH setting. The numbers don't correspond to CPH but you can play with the numbers if Option 9 doesn't work for you.

D107

Gee, that's too bad that cycle rate doesn't apply for me. That was the main reason I wanted that t-stat. I have to increase my cycle rate. I guess it's likely the forced air choices would be most likely to do that. RIght now there's hours between heat cycles with the RTH111. The T6 probably won't overshoot like this one I hope. Thanks for checking.

HVACNUT

#ISU 370 is for staged heat. It has no bearing on your system.

D107

@HVACNUT Actually when I started setting up the unit--as nonprogrammable--it did allow me to make a choice for 370. I know it says 'stage 1' which I think is what they refer to when there's only one stage. Interestingly, on the installation instructions for their T6 hydronic unit is where I found an actual description of the 12 cycles. See attached. Default is #3. Would be nice if they gave us a more detailed listing of the characteristics of all the various cycling choices so we wouldn't have to experiment. So between the system type, equipment type and the 370 --if it works--I have a lot of variations.

HVACNUT

This is BS. My manual shows that option is used for staging. It says nothing about CPH. Like you said, playing with a variation should get you where you need to be.

D107

@HVACNUT We must have different models. Mine is TH6210U2001 T6 Pro. Having now experimented, I can definitely say that ISU 370 is adjustable, likely 1-12 for CPH. At first i used the default which was '3'; cycle was really short. I lowered it to 1 and cycle was much longer, probably adequate given how warm it is outside. Too bad in my manual they don't really hint what number cycles per hours is recommended for what kind of system; they just say Stage 1, 1-12. They seem to allow user to mix and match between system type, equipment type and cycle rate. Sometimes when you choose one system type you'll find their default for equipment type or cycle rate but that's generally changeable. So far so good.