Smart thermostat

ispern

Has anyone hooked up a smart thermostat to a steam boiler? 



I bought an Ecobee Smart Si, and it needs a common wire, 24V constant.  I have an Ideal No. 7 boiler cerca 1940, which is now fired by a Carlin Combustion gas burner.  I asked Carlin if 24V is available anywhere on the unit and they said no.



Where might I get 24V from that the Ecobee needs?



Thank you.



Jeff P

Melrose, MA

Si_zim

Depends

If its a millivolt system (did they mention that?) you are probably out of luck. Mine is a recent gas boiler and 24v control so my smart thermostat is ok. (Its not an ecobee)



Might be possible to rig something up with an external 24v AC power supply and a relay if you needed to.

bill714

This may help

its a power extender kit to power your thermostat.





https://ecobee.zendesk.com/entries/21681115-Installing-the-Power-Extender-Kit-with-ecobee-Si-thermostats

ispern

Ecobee tech support response

Here is what Ecobee says:



"Typically every boiler has 24V at the controller. If your boiler does not provide 24V, you will need to add isolation relay on your boiler TT terminals wires, the isolation relay will prevent back feed into your boiler controller, from the external transformer."



I've never heard of an isolation relay. Is this something I can attempt without an electrician's help?



Thank you.



Jeff P

Melrose, MA

Mark N

Relay

If you don't understand what they're asking you to do I would say no. Hire a pro. Why do you need such a high tech thermostat for a 74 year old steam boiler? Steam works best if you just leave the the thermostat set to one setting.

ChrisJ

Nest

I tried a Nest and didn't like it.



My recommendation is send the Ecobee back and buy this.  Save your self a lot of money and a big pain in the butt for nothing.



http://www.pexsupply.com/Honeywell-TH5110D1022-The-FocusPRO-Large-Screen-Non-Programmable-Digital-Thermostat-Premier-White-4088000-p

ispern

Saving energy with steam heat

Interesting.  I assumed that I would save energy with a programmable thermostat no matter what type of system I had.  When you say 'works better,' do you mean I save money by leaving the stat at 68 all day when I am not home?  Seems counterintuitive.



Jeff P

Melrose MA

Mark N

Set backs

Set backs work best with Forced Hot air Heat.  There is a lot of energy stored in your steam heat system.  It is stored in the water, in the boiler, in the pipes.  You do a big set back and all that is lost.  That is a 100% standby loss.  Steam systems behave better when left at one setting.  To recover from say a 10 degree set back the whole system has to be brought back to temp before you get any heat.  The system will begin to cycle on pressure, most likely all the vents will be hissing and spitting water, you will have banging, and maybe even trip off on low water. If you have an auto water feeder that will feed water and when the condensate comes back the boiler will be over filled.  Finally the thermostat is satisfed,  but the the rads are smoking hot and will continue to put heat into the house.  By time you're done you have probably over shot by 10 degrees.   To compensate for that you might open the windows.   

steamedchicago

setback heatloss

All those BTUs that you have to put back into the system are BTUs you'd have lost if you kept the building at the higher point.  The savings from a set back is the difference in heat loss at the high point versus the heat loss at the setback temperature.  The only loss from a set back is if your controls are bad, and you overshoot the temperature.  That's true of lots of residential systems, but it's a control failure, not an inherent one.  



In a house with modern windows, door weather stripping, and attic insulation, the originally installed radiation is much larger than the current heat loss.  Such a house can use that extra radiation to raise the temperature fairly rapidly, which makes a set back reasonable.  

RoiiRaz

Did not find setback useful...

I have a LUX thermostat which monitors boiler run-time per 24 hour period. I tried to drop the temp to 62 and bring it back in the morning (after 8 hours). My boiler ran the same overall time to bring the system back to the original temp as it did without the setback.



I haven't tried to do the computations, but intuitively: Once the pipes get past the pickup and reach 215, the boiler can pump more heat to them much faster than they cool back down (because of all that hot metal). If you are trying to come back from a setback, the thermostat will call for heat until the original temp is reached, which means the boiler will continue to pump heat into rads which are already at their heat capacity. Adding more steam at this point will not give you more heat, but just raise the pressure (because the vents are supposed to be closed at 215).



Along the same lines: I had my thermostat set for a 1-degree swing. I thought that once I get past the pickup of the pipes, I would let the system overshoot and then slowly come back down. But, I cut the swing to 0.25 degree, and I found that my boiler run-time is SIGNIFICANTLY lower -- like 30%.



Has anyone else had the same experience?

RoiiRaz

RE: 24V...

The LUX is battery operated. I've put it on a millivolt system at another house without a hitch.



To counter my previous point: I have a friend with a 125k BTU boiler who _does_ setback to 62 at night, and he found that his system recovers back to the original temp in 30 minutes. He's happy with it (although I don't think he compared it to boiler run-time without setback).

steamedchicago

setback pressure

If the boiler produces steam faster than it can be condensed, then

pressure will rise.  With proper controls, and a balanced system, the

boiler will shutdown on pressure, until the radiators have condensed

enough steam to drop pressure below the cut in.  When the boiler isn't

running, it's not using fuel, so as long as the pressure cutout isn't

excessive, there's not much loss there.   Also, keep in mind that the

240 BTU/hr per sq ft of EDR assumes a radiator temperature of 215, and a

room temperature of 70.  If the room temperature is lower, they'll

condense more steam.  It's not a huge difference, but it does increase

the amount of steam the system can consume. 

ispern

Value of a smart thermostat

One of the reasons I wanted to install a smart thermostat was so that I could make calculations like this. Ecobee keeps track of set temp, room temp, boiler status, and outdoor temp. I'll know how fast the house loses heat, and what thermostat settings save me the most energy. I'll try all kinds of different settings and see what happens. I maintain that generally speaking lower stat settings save energy based on the laws of thermodynamics (or, you don't get something for nothing, and vice versa).



I did decide to have an electrician help me with the install. I'll let you know how the system performs once I get it done.



Jeff P

Melrosesf MA

Si_zim

Data would be useful

Yep- I agree on the logging... It was something I pondered when looking at thermostats also. Ecobee has nice logging and graphing capabilities which would help show how the system is operating and how efficient its being. I do wish I had some visibility into this. Not all the data you may want is there though- even if the thermostat calls for heat you may not know if the burner is firing due to pressure related cycling.

All the fanfare about the Nest learning capabilities was muted by reviews showing unreliability and people setting the schedule when the AI did weird things.

I just opted for a thermostat that had features I needed and reliability - will have to tweak the system the old school way. But once running efficiently I am not sure I would be checking the logs that often.

ChrisJ

More data

Data logging was the entire reason I tried a Nest and I probably would've used it more than a few hours if it didn't lock up right off the bat.



The other problem is you need more than just outdoor temperature, at least in my house wind has a huge effect on heat loss.