Thermostat Guidance

MrMcSteamy

I could use some help dialing in my thermostat's control of boiler. I recently purchased a century home with an oil-fired one-pipe steam boiler system. Things were working reasonably well at beginning of first winter, had boiler serviced, on that recommendation I replaced all radiator vents with VentRite1 adjustable vents and was able to balance the heat through the home reasonably successfully.

The only issue was that the thermostat was in livingrooom and we also have a gas fireplace insert there and using it would completely throw off the thermostat's control of the boiler's heating of whole house.

So, this winter, I moved thermostat to the other main room - office/diningroom - my girlfriend and I both work from home so both livingroom and the office get a lot of use. When moving the thermostat, I discovered it was wired REALLY oddly and was the wrong type of thermostat for the system - confirmed by my boiler guy. On his recommendation, I got a Pro1 T701 thermostat.

The thermostat move really threw off the balance of the system and led to really uneven heating, but by readjusting vents, all is really good in that respect now ... the heat is now much more efficient, heat gets to the upstairs more successfully, and not unrelated, the system cycles far less often ... once, maybe twice, an hour instead of several times an hour.

Sorry for the long intro, but I am assuming all of that might be relevant. Here's the question/issue I could use some guidance on:

I have the thermostat set correctly for the system, and I have the cycling set as low as possible - .2 degrees. So, I would expect system to turn on when TSAT - set at 67 - hits 66.8 and then off when it hits 67.2 and with the radiators hot at that point, the temp would gravitate up somewhat over time. Here's the issue: the TSTAT kicks on the heat at 66.6 and off at 67.8 or 68. It's clear that we are now running more efficiently, and I expect the range of house temp to vary more than it was before, but that range it too much to be comfortable. Spots in the house will get too cold - perhaps 64.5 before the temp at the TSTAT gets low enough for boiler to kick in and 70 is just too hot. In case it's helpful, we live in NE US.

What can/should I do to make that range tighter. The thermostat is positioned well. It's on an inside wall, the wall is not cold, sun doesn't hit it, etc. The heat from the radiator in that room gets to the thermostat efficiently - they are about 7' apart.

Is there a better thermostat for my needs? I have just R and W wires, but could add a C if needed.

I'm wondering if a TSTAT with a remote sensor would be a good idea since I could experiment with positioning it to all system to cycle comfortably?

Otherwise, I'm out of ideas.

My boiler guy is admittedly not an expert on steam systems and I live in a rural enough area that there aren't but a couple of experts and they are too busy with commercial clients to have any capacity to help out homeowners.

I've gotten pretty smart about steam systems on my own, but I am not an expert and like a lot of folks in my position, I know just enough to be dangerous. But, I do understand that, so I tend to act cautiously and study up before doing anything.

Thanks for any guidance you can provide! Again, sorry for the long post and thanks for reading to the end!

Jamie Hall

Hmm.... well, that particular thermostat has no provision for operating either a steam or hot water system correctly. You may find that you would be much happier with one -- perhaps another simple one, such as the Honeywell/Resideo T87 --which does have provision for steam and hot water systems.

It might help, oddly, to widen the swing some -- but it will still overshoot badly in some spaces and not ever stay on long enough to warm up others.

MrMcSteamy

Thanks, Jamie! I didn't include this info since my post was already so long, but I initially tried a T87 since I found a lot of reference on the internet to it being a great choice in my case. It didn't work well at all, thus my trying the T701. After that experience, I found lots of folks saying the T87 USED to be great and isn't any more. Basically, I have found not found any definitive information on a thermostat that is good for steam heat.

If you, or anyone else, has a recommendation along those lines ... ideally one I can control with some precision - setting the swing to the .1 degree, for instance, maybe even different amounts of swing on the cut-in and cut-out ... maybe even that allowed for a remote sensor and/or management through an app, that would be GREAT. Again, I just have a R and W wires at the moment, but I could add a C if needed.

Thanks all!

Jamie Hall

You need either a thermostat with an anticipator -- a new old stock mercury T87 is one of the very best choices possible, if you could find one -- or one with a cycles per hour setting. Either will probably do what is needed. Swing is not a useful setting for any heating system which has significant lags, but it works well for any forced air system.

RTW

BY JAMIE HALL: You need either a thermostat with an anticipator -- a new old stock mercury T87 is one of the very best choices possible, if you could find one -- or one with a cycles per hour setting. Either will probably do what is needed. Swing is not a useful setting for any heating system which has significant lags, but it works well for any forced air system.

RESPONSE: I own an old stock mercury T87 that functions well and I set it and forget it as Mr Hall suggests. I too balanced the radiators vents, placed the thermostate in a better location and I sometimes keep a few doors closed in less used rooms in the house eg. laundry room. In my case, once the thermostat shuts off at the setting, the radiators continue to heat raising the thermostat temp. gauge another two degrees. Depending on the outside temp. my system cycles about every two hours on average and less as the day warms up.
Regards
RTW

RTW

P.S. I obtained my Mercury T87 just as they were phasing out mercury in all thermostats years ago. Maybe you could locate one at a salvage yard type business that sells home related items.

exqheat

What are the operating pressures for your boiler?

MikeAmann

@MrMcSteamy
I have a mercury heat & AC round Honeywell thermostat you can have for free (just pay shipping).
Something just fell against it and broke a tab for one of the screws. Nothing that a little epoxy wouldn't fix, I'm sure. I was going to take it to recycle soon. LMK.

EdTheHeaterMan

eBay has them for sale al the time. If you don't do eBay, then find a friend that does. https://www.ebay.com/sch/i.html?_from=R40&_trksid=p4432023.m570.l1311&_nkw=honeywell+t87f+2873&_sacat=0

You MUST ONLY PURCHASE T876F. Any other T87 may not have the Mercury switch that works so well with steam boilers. Look for NOS. It stands for "New Old Stock" which means that it has never been used. but well out of warranty because they stopped making them years ago.

MikeAmann

Strange, the first thing I did was an ebay search and all of the results were for NO mercury.

EdTheHeaterMan

MikeAmann said:

Strange, the first thing I did was an ebay search and all of the results were for NO mercury.

T87 will get you the new ones
T87F will get you the old ones. Try the link I posted

MikeAmann

Thanks Ed.

MrMcSteamy

I've ended up moving the thermostat to above the radiator. As you'd expect, that has helped dramatically to switch off the heat earlier and make the overall swing as the radiators continue to radiate heat manageable.

If this approach doesn't end up working well, I will check eBay for T87F thermostats. I had not been able to determine which of the many T87 thermostats were the magical ones that are appropriate for steam ... thanks for that clarification! I have to say that navigating the world of thermostats is journey fraught with confusion if you're not a heating pro.

Intplm.

MrMcSteamy said:

I've ended up moving the thermostat to above the radiator. As you'd expect, that has helped dramatically to switch off the heat earlier and make the overall swing as the radiators continue to radiate heat manageable.

If this approach doesn't end up working well, I will check eBay for T87F thermostats. I had not been able to determine which of the many T87 thermostats were the magical ones that are appropriate for steam ... thanks for that clarification! I have to say that navigating the world of thermostats is journey fraught with confusion if you're not a heating pro.

Nice that you have found some satisfaction in moving the t-stat above the radiator. Wow, that would not have been my approach. Glad it's working for you so far.

The advice @Jamie Hall started with above, using a Honeywell T87 thermostat is excellent. I have found that some of the newer snap action 87 series thermostats can work just as well.
The problem with finding a tried and true mercury version is that they will most often be used, and one would be taking a chance that they are up to spec. So keep that in mind when and if you decide to go forward.
The other thing that you can consider is what is happening when the t-stat is moved to a different location.

Some question come up:
Is the wall cold?
Is it on a outside wall?
Is there a mirror in the room?
Is there a window?
Does the mirror or the sun reflect off of the mirror or window onto or near the thermostat?
Is it in the path of the sun caused by another event? Drapes, blinds etc.
Is there a door or window near by that allows for temperature change that hasn't been thought of as a culprit of the problem?
Is there a sky light?
Is the heat anticipator set up and adjusted properly?
Is the thermostat level?
Is it wired correctly? ie. .. broken wire, loose connection, wired to far from the boiler, wires too small etc. etc?
So...some food for thought.

The old Honeywell 87 series t-stats are great when you can find one.
@MrMcSteamy, I hope you are almost done with this issue.

Chris_L

You really don't need a mercury thermostat. Just one that turns off when it is supposed to. (Are you sure you adjusted the heating swing and not the cooling swing?)

I have two units with steam boilers. Both have used electronic thermostats with adjustable swings for 20+ years. It is just a matter of picking the right swing setting and getting the right vents on the radiators to balance the system the way you want.