Smart Thermostats and Single Pipe Steam Systems

BillyS

I am trying to figure out if any progress has been made over the last five years. My original post was here:

https://forum.heatinghelp.com/discussion/167014/nest-thermostat-and-steam-heat

I have a one-pipe steam system and purchased a Nest Thermostat back in 2018 (still on a shelf). I had two wires (R / W) from the T-T connection to the thermostat, no common wire. When the boiler goes off on pressure, power goes off the the 24V transformer until the pressure goes down and the boiler starts making steam again.

Do any of the newer "smart" thermostats play well with steam systems that behave this way?

exqheat

Put thermostat on its own stand lone power, out of safety loop.

BillyS

exqheat said:

Put thermostat on its own stand lone power, out of safety loop.

Thanks for the quick response. Are you suggesting I power the thermostat with a transformer? Is there any thermostat that works well in this configuration?

To do this, I think I need the TT terminal to connect to a Rh/W on the thermostat and connect the new transformer to Rc/C?

Jamie Hall

Most of them do -- for what they are intended to control. Some smart thermostats are much easier to configure to handle steam systems -- or any high mass, slow responding system, for that matter -- than others. The Nest si one of the hardest to configure properly, although it can be done and if it is done, it works almost as well as a Big Box forty dollar unit... not quite.

Mad Dog_2

Not a fan of all the tinkering, but some have had success.  I still go back to the Best for Steam...Honeywell T -87....even the newer  non-mercury ones are better than the Smart ones, I have found.  If you can pick up an older model WITH mercury, at a Yard sale or what have you...GRAB IT and put it in... Mad Dog  🐕 

ChrisJ

Mad Dog_2 said:

Not a fan of all the tinkering, but some have had success.  I still go back to the Best for Steam...Honeywell T -87....even the newer  non-mercury ones are better than the Smart ones, I have found.  If you can pick up an older model WITH mercury, at a Yard sale or what have you...GRAB IT and put it in... Mad Dog  🐕 

I'm only joking Mad.
We all know you can't put mercury in the trash.

It must be properly disposed of, I believe by whoever collects hazardous waste in your area.

Gsmith

I have a 40+ year old millivolt single pipe steam system that now runs in a Honeywell (forgot the new name starts with R I think) T-4 thermostat that was installed with an A/C system last year., by the A/C guys. Works well, not wifi, but does have 7 day programmable settings, tho I keep it at a steady set point. I’m pretty sure the companion wifi models would also work ok.

Mad Dog_2

I used to have a Hellman's Jar full of mercury that got forced on my by an old timers who gave me a 300 Machine and tons of tools 🔧 for $300 bucks...it was part of the deal. At .49 lbs per cubic inch, this was HEAVY...Finally brought it to those hazardous waste days with bottles of chlordane..Actually the old Honeywell Chronotherm worked well on The Steam.  Mad Dog 🐕 

ChrisJ

I do not have a problem with mercury switches.
My pressuretrol has one.

I just don't care for the t87 anymore.

When I was a kid I used to watch the thermostat with the cover off to see the mercury arc when it moved.

I guess it's just another one of those things that used to be "just the way it is" that isn't anymore.

Like the big colorful circle that would shrink to nothing when you turned the TV off.  And that really annoying 15khz noise all TVs used to make when on.

AdmiralYoda

We just wrapped up our 3rd season on the Ecobee. It plays just fine with our single pipe, counterflow system. Very rarely overshoots and I'd say it performs just as well as any programmable thermostat at the box-store.

Steam works best when set at a set temperature. Set-backs tend to cause overshoots and no modern thermostat handles the larger thermal mass of a steam system well. I've played around with set-backs of various settings and I keep going back to "set it and forget it". A Smart thermostat will fail at deep setbacks just as poorly as any programmable one.

It needs to have constant power and needs to be tapped into the transformer or have its own dedicated transformer. There are a variety of ways to do this on the internet and any HVAC person should be able to help you out if you get stuck.

Where the Ecobee really shines (sorry...can't comment on the Nest) is that it monitors the outside temperature. If it is 55 degrees outside it knows it doesn't need to kick the system on early to maintain the set temp. Same goes with if it is zero outside... it is a bit more proactive and tries to stay ahead of the temperature loss. It is like a poor-mans outdoor reset.

Another feature that I like is that I can add temperature/humidity sensors in as many rooms as I want and the thermostat will display the "average house temp". I feel like this makes the whole house a bit more comfortable.

It will also use a "heat index" if I tell it too. So if the house is humid it will hold off on the heat a bit because the house "feels" like it is at the set temp.

The ability for me to monitor the house and individual room temps from an app or on their website is a novelty but I like it. Personal preference.

Steamhead

This is our go-to device for thermostats that require constant power:

https://www.supplyhouse.com/Resideo-R8239A1052-40-VA-Fan-Center-w-SPDT-Switching-Action-Includes-R8222B?utm_source=google_ad&utm_medium=shopping_neutral&utm_campaign=Shopping_Neutral_New_users&gclid=CjwKCAjwkLCkBhA9EiwAka9QRp5LxRy822tdtjObPv2AX2CDhY52_VydYvkF4xNX-18xmrIrVDwvfhoCVS8QAvD_BwE

Wire the normally open relay contacts to the thermostat terminals on the boiler.

If there is only a 2-wire cable between the R8239 and the thermostat, replace it with a 3-wire cable.

Wire R on the R8239 to R on the thermostat.

Wire W on the thermostat to G on the R8239.

Wire C on the thermostat to C on the R8239.

The transformer on the R8239 will power the thermostat all the time, as long as the power to the boiler is on.

Mad Dog_2

You're a Genius Frank!  That's Good to hear about The Ecobee... Mad Dog

exqheat

In multi family and rental , one sensor is enough. Less potential for sabotage.

AdmiralYoda

@exqheat 100% agree! Even in my single family it took a few tries to get the best spot. Turns out I have a couple exterior wall cavities that I didn't know were uninsulated and guess where I decided to attach those remote sensors???

I can imagine a tenant leaving the windows open and putting the sensor on the window sill!

exqheat

You need to place with a non tampering tenant. In extreme conditions, you can put sensor in tstat box.

STEAM DOCTOR

On the contrary. Put sensors everywhere. Just make sure only one is actually active.

BillyS

Thanks for all the information. I may give this another go with an Ecobee. I can relate to the T87 thermostat stories. My first job out of school was delivering boilers (sectional) to homes in Jersey City NJ. I was quite strong at the time and it came in handy. My dad was in the plumbing and heating supply business, and I even own (and read) Dan's The Lost Art of Steam Heating. In fact, my dad (now retired), brother, brother-in-law and nephew are all in the HVAC business.

I work for an electric and gas utility and I also know how dangerous a steam boiler can be... we had a guy about seven years ago go into a home where the owner bypassed all the safety devices. The boiler blew up as our techs went into the basement. It went through a cinderblock wall and somehow crushed the legs of the tech. This is why I'm so careful when servicing the boiler (and our pipes no longer bang thanks to Dan's book - water hammer...). Thanks again!

Big Ed_4

When my Dad moved to Arizona , he gave me his jar full of mercury . Thanks Dad , then I had to pay to get rid of it , Thanks Dad !

BillyS

Did some more research and it appears this might be the best set up. Apologies for the crude schematic. This makes sense to me... unless someone spots a fatal flaw.

BillyS

Revising this... I spotted a problem.

exqheat

Why not just close w-r on the TT. The thermostat has its own relay. No need for additional juice. Test TT for 24volts. If crossing TT causes the boiler relay to close, no need for other circuit.

Jamie Hall

Better circuit. and for @exqheat , the reason for the relay is to isolate the burner control -- and its transformer -- from the thermostat control and power. Not absolutely always necessary, but eliminates -- at much less cost than a burner control -- the likelihood of either overloading the burner control or, if one manages to get the phasing wrong (easy enough to do) frying the burner control.

Also to note -- some, but not all, burner controls will have the power to run the thermostat as well. Some will be marginal, and everything will be erratic.

Use the relay.

exqheat

What thermostat are you using? pwer to Rc C burner dry closure w r.

BillyS

@exqheat this is a Nest thermostat (not the learning thermostat), so I don't have Rc and Rh, only R. The issued I had was during very cold days and the boiler would cycle on pressure. When going off on pressure, there was no power at the TT connection. Eventually, the Nest would die, reset itself and overshoot the setpoint on the thermostat by around four degrees.

What actually happened is the thermostat would display the incorrect indoor temperature. So if the stat was set to 70 degrees, the thermostat would say it was 68 in the home, even though it was 72 degrees. I work for a utility that sells these thermostats and even gave this feedback to the Nest agent (although never heard back if this was a bug).

Tim McElwain

Stay with the T-87 forever you will not go wrong. Put the NEST up in the trees so the birds can NEST in it!!!!

exqheat

So what did you have before the nest? Put it back.

pecmsg

Another NEST?

Big Ed_4

I don't remember the nest had a proper cycle for steam ..

Steamhead

Big Ed_4 said:

I don't remember the nest had a proper cycle for steam ..

The last one I worked on had a "radiant heat" setting. That's as good as it's going to get on a Nest. But if the steam system responds quickly and evenly (MAIN VENTS!) this setting will work.

AdmiralYoda

Just for the record...here is how my Ecobee is wired. The thermostat wires are tapped right into the transformer. May or may not be the right way to do it... but it has been working just fine for three years.

Jamie Hall

That works, @AdmiralYoda -- becasue you have an outboard transformer which is dedicated to powering the Ecobee, and the transformer is in phase with the 24 VAC on the control board.

MisterInvisible

I’ve been running my Ecobee for about three years now using a c-wire adapter. Luckily had a power outlet in my basement not too far from where the thermostat wire comes out of the wall/ceiling. This is what I bought but there are others. https://www.amazon.com/dp/B07DJ7RHS5

trivetman

+1 on the Ecobee.  I’ve only had it in place for a few months but it seems to handle the steam cycle fine.  It does have constant power coming from the AC unit.

pgf

I installed an Ecobee Lite last winter. It was my second attempt at a smart thermostat -- the one from Sinope was a disaster: it did an excellent job of keeping the thermostat, in its location in a central hallway, with a radiator nearby, at the setpoint temperature. But the distant radiators never got heat. It was short cycling like crazy, all day long.

The Ecobee does a good job all on its own, as others have said. But we love our setbacks, and like to turn the heat down by 5 or 6 degrees overnight. That, of course, causes the boiler to short cycle due to pressure in the morning, turning on or off 7 or 8 times before the house comes up to temp. (It's a 30 y.o. Weil Mclean.)

So I took advantage of being able to do remote setpoint changes from my home automation server.

I installed a temperature sensor on the cellar floor, under the boiler. It's far enough away to never be damaged, but close enough to easily tell whether the burner is on or not. If the temperature under the burner is going up, then it's on, otherwise, it's off.

I have a program on the server which watches the house temperature, the burner temperature, and the setpoint. If it sees that the burner has gone off without the house reaching the setpoint temperature, it deduces that the burner has short cycled due to pressure. (See note below.) When it sees that a pressure cycle has occurred, my program reduces the setpoint to below the current house temperature, and waits for 10 minutes, keeping the boiler from restarting. This time was deduced empirically -- our house will keep rising in temperature for about that long, even with the boiler no longer firing. After the delay, the program bumps the setpoint back up to where it should be, and tries again.

It takes the house a little under an hour to come up 5 or 6 degrees to a daytime temperature (this has been acceptable to us, for 30 years now), with just one 10 minute delay cycle from my program.

Regarding the burner shutting off before the setpoint is reached: in addition to that happening due to over-pressure, the other reason that could happen is low water cutoff. But on my boiler, that will cut power to the thermostat. My program notices that condition and will quit.

There are other failsafes: for instance, the program will also abort if it notices that the setpoint has changed since it last looked. In that case someone is likely adjusting it manually.

paul

njwags95

I have been using Nest without issue for my one pipe steam system. I had already run modern 5 wire to the thermostat so all I did was install outlet next to boiler and bought a plug in transformer, wire nutted to one of the unused legs (I used yellow), then connected to back of Nest.

Robert_T

White Rodgers still makes at least 2 simple thermostats with adjustable anticipaters. In my 56 years of working on steam boilers, the only way to get proper control of one-pipe steam systems is an adjustable anticipater. The old Honeywell T87 works just as well functionally but was always a little more (fragile, tender) and subject to breaking. (snapping off at the base where the part that rotates is attached)

Logik

I have one pipe steam with a 300,000 btu boiler. The antique 6000 square foot house came with a t-87 at the bottom of a cold 2-story Foyer, remote from any radiators. It always overshot the set temp. I replaced it with a Honeywell Red link system. Both the thermostat and the "portable comfort control" are battery operated and wireless so they can be located anywhere and do not need 24v. So no new wiring needed to be run.
I added the internet gateway and use Alexa routines (and voice) to control the system. I use voice to drop the set temp when I leave the house for more than a couple hours. I use the routines to do a temp setback in the evening, and then beginning at 4:00am in the morning to slowly ramp up the temp 1 degree per 40 minutes or so from the evening setback. This helps keep overshoot to a minimum, and I wake to a warm house.
A disadvantage is that anything done using Alexa is in the cloud and so depends on working internet. The Honeywell receiver in the basement needs 24v. We sometimes get some scary lengthy power outages. So I am thinking of putting the 24volt transformer on an Uninterruptible Power Supply. This would allow the system to continue to operate during long power interruptions since it draws very few watts.
Any cautions or suggestions?

SteamDrew

We've been using the Honeywell T10 Pro smart thermostat. So far it's been my favorite smart thermostat that we have found to control steam systems. It actually has steam as an option when setting up the unit and when set up properly we get some nice long cycles compared to other units I've used in the past. You can also see the individual heating sensors and label the zones individually and also have the ability to easily turn the sensors on/off. I've used them in buildings up to 6 units with great success as an averaging control.

rberq

Hah! And I thought controlling a hot-WATER radiator system was hard. Best solution I have found so far, to avoid over-shooting the set point, is to put a timer in the thermostat circuit so the burner can run a maximum 15 minutes, then is off for 15, then on again if the thermostat still is calling for heat, and so on. This works pretty well unless the outside temperature is 20 below zero AND recovering from a nighttime setback. But I don't really understand steam -- I'm guessing this technique might not be suitable.

PEvans

I would be very appreciative to see more details on these monitoring/automation schemes like @pgf and @logik describe in a separate thread.

trivetman

@pgf

does programming the 10 minute delay increase efficiency much as opposed to just letting the system cycle on pressure until the final set point is reached?