Tstat "will not work efficiently on steam or gravity systems"

malex

So I was looking at the tstat earlier in the heating season and set it to the setting that seemed best. It did not have a steam or CPH setting so I knew it was not optimal but have not paid much attention to it until today when I was looking through the manual and saw the words "will not work efficiently on steam or gravity systems". Its a Magicstat/32 CT3200.



Things are working well but I do notice some weird cycle patterns where it runs for 10-15 minutes and shuts off but not due to pressure and start back up in 5-10 minutes.



My question is if its worth plunking down $100+ on a decent steam tstat. How would it really make the system run better? I have been considering a vaporstat, as making sure that system stays under 1psi seems to be the next priority. Ptrol is not very accurate and sometimes on cold days (and nights) it pushes 2psi and the vents starts to act a bit crabby.



Let's just say 'mom'is is with you in the candy store and you can only pick one, which one will it be? New Tstat or a Vstat?

Mark N

Thermostat vs Vaporstat

A thermostat controls the boiler each and every time it runs. A vaporstat would only come in to play if the pressure went above the cut out. If boiler is sized properly and you have enough venting that might be never. I'll take a good thermostat every time. I have a FocusPro 5000 and I think it was about $40.

nicholas bonham-carter

New thermostat

I think the new version of the old round Honeywell thermostat (set table for steam) is less than the focus pro. As the consensus here is that setbacks are a waste of energy, you really don't need the vision pro unless you wish to use its remote sensor feature. If you are going away for days instead of hours, then it's easy to dial down the temperature.

Spend the difference in price on a low pressure gauge, and you may find that your boiler is so perfectly sized as to be never exceeding the "speed limit". Also the gauge will tell you how your venting is performing.

Thank goodness the magic stat people were knowledgeable enough to tell you about the steam incompatibility, unlike the "nest" , group, who believe in their supremacy over every hvac system!--nbc

malex

Basic tstat it is

As I mentioned, my low pressure guage does show up to 2psi even though the ptrol is set to cut out at 1.5psi and vents become noisy. Will the way a proper steam tstat work remedy any of this or is the only solution a vstat?



If anyone has the time, I would be very interested in how exactly the boiler/tstat will work together with the proper settings as compared to the Magicstat.

Mark N

New Thermostat

A new thermostat isn't going to cure the pressure being to high and neither will a vaporstat. Switching to a vaporstat will most likely cause the boiler to start cycling on and off till the tstat is satisfied. High pressure is usually caused by an oversized boiler. What size boiler do you have and how many sq ft of EDR do you have?

malex

Mark

I have a Peerless ECT03 rated for 283 sqft and my estimate of the radiator load is approximately 260 sqft using the generic charts. I am trying to get a more precise estimate but I can't find the edr for all my rads, which is a mix of sunrads, richmonds and an Aero and even a fintube. But this should be close and it doesn't seem that off from the boiler. I am also missing a rad in a walk in closet that I am planning on replacing.



But again, I don't generally have pressure problem but on cold days (especially cold mornings) when the rads are saturated but the tstat is not satisfied the pressure can raise to the cut out point.



I was wondering if the steam designed tstat would work differently or what would the difference be if I replaced the magic stat? Longer cycles and longer off periods?

Mark N

Boiler

It seems that your boiler is sized properly. Do you use a set back? On the cold morning when you observe that the rads are saturated and the thermostat isn't satisfied how long has the boiler been running? If all the vents are closed I would expect the pressure to build. What are your current cycles how long does the boiler run on average. I would expect 20 to 25 minutes. The amount of time off in between would vary depending on how cold it is outside.

Dave in QCA

proper thermostat for steam

If you install a proper thermostat for steam, you will notice fewer cycles, longer cycles, and longer off time between cycles.  This can still be balanced to the point that you do not feel much temperature fluctuations.  



In your first post, you stated, "Things are working well but I do notice some weird cycle patterns where it runs for 10-15 minutes and shuts off but not due to pressure and start back up in 5-10 minutes"   This is exactly what will change with a proper steam thermostat.  You will not have a bunch of very short on/off cycles.  Remember, every time the boiler shuts off, the steam will condense and then it will suck in a great big breath of air.  When the boiler starts again, the first thing it has to do is get the air all back out.  This type of cycling is not efficient on steam.

Jshine

honeywell thermostat

fyi - I have a 1 pipe system

I replaced an old round honeywell last winter with a honeywell RTH5100B - non programmable - digital display.  For steam - they recommend to set at "1 cycle" - It's been perfect.  System comes on once an hour - stays on 15 minutes or so (depends on outside temp) - keeps room temp very consistent.

By the way - I had tried the round digital T8775 - but found that the display would go on and off and just didn't want to work with my system?

Good luck

John

malex

I went with the TH5110D (Focuspro)

also nonprogrammable and looks about the same. Hopefully I will have the same good results.



If the boiler only comes on once an hour doesn't that create some temperature swings or are the rads able to keep the heat constant that long?

Dave in QCA

Not normally

For cast iron radiator systems, one hour cycles usually works perfectly.  There is a lot of residual heat in the cast iron and it will continue to give off heat for a long time.  For most systems with copper fin tube convectors, cycles are set for 2/hr because the convector will cool down very quickly when the steam shuts off.

Jshine

1 cycle per hour

When I first came across "1 cycle" - I thought there was some sort of timer involved.

 - to be clear - the "1 cycle per hour" is variable based on temp.  A colder day will shorten the '1 cycle" to maybe every 40 mins - 50 mins while a warmer day will lengthen to maybe every 75 mins - to 85 mins.  Your thermostat will react to the changing conditions.

malex

Hoocuspro to 1 cph?

SO I just put int he Focuspro 5110D1006 and it is working right out of the box but I don't see any settings to set it specifically to steam and to 1 CPH. Anyone has any insight as the manual is very sparse.



EDIT: nevermind, found it. Why wouldn't they include the installer setup instructions in the box?

Jean-David Beyer

New Honeywell manuals

I have an older Honeywell digital thermostat that has everything in the manual.



I also have a Honeywell TH4110D. Its operating manual sucks. They also have an "Installation Guide" that has the information that was left out of the operating manual. After 4 pages of how to wire it, it explains how to adjust the hidden settings, such as cycle rate, adaptive recovery, C|F, etc.



I think Honeywell are afraid if the homeowner learns about those settings, they will screw up. Maybe they are right, but I was pretty angry with them until I found there was the Installation guide on their web site. My former contractor, who installed it, did not seem to know about that, and left it set up for low efficiency forced air, when he had just installed a high efficiency hydronic system. I really did not need a 5 cycles per hour setting, 3 would have been better and actually, I now run it at 1 cycle per hour for various reasons.