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Converting mechanical thermostat to wireless technology

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I am working on balancing my single pipe steam system in a 2 family that was split into 4 apartments and decided to locate the thermostat in a second floor room, which is the coldest in the house. Currently, I have a mechanical thermostat that is wired in series with the pressuretrol, spill switch, and low water cutoff and bought a wireless thermostat kit. I made the mistake in thinking I could just connect the two wires that serve the mechanical thermostat and be done. Wrongo!! Initially I wasn't sure how it would work and found out the hard way I need some additional equipment. Does anyone have any experience converting from two wire mechanical to a wireless device? It looks like I may need an additional transformer, and a relay (to take the place of the mechanical tstat).
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  • ratio
    ratio Member Posts: 3,627
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    How 'bout some pics and model numbers?
  • mikeg2015
    mikeg2015 Member Posts: 1,194
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    Might be a 120V system or a millivolt system.

    Also, the mechanical stat was unpowered. So it used W and R only but no common.
  • BoilOver2
    BoilOver2 Member Posts: 38
    edited December 2018
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    Assuming the current stat is low voltage, check into buyimg a transformer online to provide the c wire you need to power the stat where it's currently installed. Search for something like transformer for ecobee c wire.

    The ecobee also has a wireless remote sensor that might be helpful for your use case.
  • nicholas bonham-carter
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    I would use a Honeywell VisionPro thermostat down in the boiler rom, where it is easier to wire it up properly, and it’s remote sensor, whether wireless, or wired (only 2 wires needed), could be put up in the coldest area. A wired sensor is more reliable in maintaining communication with the base in older buildings with thicker walls, and floors.
    Make sure that you have generous main venting, and good balance, before doing this, or the warmer apartments will roast!—NBC
    RPK
  • SteamingatMohawk
    SteamingatMohawk Member Posts: 1,007
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    The existing thermostat is one of the famous round Honeywell T87s that have been in existence forever. The wireless thermostat kit is the YTH5320R1000 basic kit with the EIM, thermostat and return air sensor. The system specific wiring guide (not a schematic) for heat only lists three wires; R (including jumpers in the EIM for Rh and Rc), C and W. After searching the internet, I found relays and combination units that have both the transformer and relay. Some are near or over $100 and as low as under $25. I am skeptical of the lower priced ones, having learned you get what you pay for over the years.

    I already have a Honeywell AT72D 40VA transformer and plenty of wire.

    Regarding venting, I have been working on that, but have a living room on the second floor of my 4 unit that cools down faster than the room with the tstat installed. So I decided to install a wireless thermostat (in case I want to put it somewhere else) to avoid running wires in a 90+ year old house. I can then tweak the other rooms so they don't overheat. I learned a lot about venting by researching and comparing vent valves with data from the 2005 Balancing Steam Systems report by Gerry Gill and Steve Pajak. It is mentioned in several of the discussions on this web site. Everyone working with steam should look at the extensive table comparing the vent capacities of a large number of steam vents. It's pretty amazing what you can learn about how Gorton, Maid O' Mist, Heat Timer (Varivalve) and Vent Rite compare in capacity. For example, the Varivalve when shut still passes the equivalent of a #5 and Vent Rite #1s only go as high as about a #5, but can be completely shut off.






  • Jamie Hall
    Jamie Hall Member Posts: 23,324
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    The famous round Honeywell T87 has been around forever for a very good reason: it works. Reliably, every time.

    No "upgrade" you make is going to improve your temperature control or save money (want a setback? Stroll by the thermostat and dial it down...). However, there's a lot of sizzle, even if there isn't much steak.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    1Matthias
  • Kjmass1
    Kjmass1 Member Posts: 241
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    There is certainly value in being able to average ecobee remote sensors across rooms or floors. While the living room with the stat may be 71, the kitchen is 70 and the office is 69. Average those all together and you’ll have better cross room comfort.
  • SteamingatMohawk
    SteamingatMohawk Member Posts: 1,007
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    I bought the Honeywell switching relay ( which includes the transformer) RA89A and have a question. The RA89A shows two options, one with the jumper installed between 1 and 3 and TT terminals connected to a thermostat and another option with the jumper removed and a controller connected to 2. I am not sure which option applies to the YTH5320 wireless thermostat kit I bought. It appears the second option just eliminates the transformer, TT connection and relay from the circuit.

    Does anyone have enough experience with this equipment to give me an answer that won't do any damage? No guess work please.

    https://customer.honeywell.com/resources/Techlit/TechLitDocuments/69-0000s/69-2041.pdf
  • ratio
    ratio Member Posts: 3,627
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    If you're talking about the jumper from 1 to 3 in figure 2, that jumper allows the relay to put out line voltage. If your original thermostat was low voltage (almost certainly if your T87 didn't explode off the wall) then you in no way want that jumper installed.

    Actually, you won't need the relay if you're using an EIM. Feed the EIM with the supplied 24 volt xfrmr (power it with contac constant AC from somewhere), but remove the l'il wire jumpers from R to Rc & Rh on the EIM. That separates the control relays. Take the wire that was on the R terminal of the T87 & put it on the Rh terminal & the wire that was on the W terminal of the T87 & put that on the equipment W terminal of the EIM.

  • SteamingatMohawk
    SteamingatMohawk Member Posts: 1,007
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    Eureka! After much searching and talking to guys in the stores (some familiar with what I am trying to do), I connected with someone who has specific knowledge.

    I think I understand what you state, but, to keep peace in the family I have to put the lights on the Christmas tree.

    If the attachment is readable, here are the schematics for the EIM and RA89A.

    I will be back on as soon as I keep the boss happy.
  • SteamingatMohawk
    SteamingatMohawk Member Posts: 1,007
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    So, if I restate what you said above, I will have the following:

    Separate transformer for 24vac:
    Incoming 110vac to the primary terminals
    Outgoing 24vac to R and C on the EIM

    EIM:
    Incoming 24vac stated above
    Disconnect jumpers to Rc and Rh
    Connect Rh to one of the wires to the mechanical thermostat
    Connect W to the other wire to the mechanical thermostat


    With this arrangement, when the EIM turns heat on, a contact will close between Rh and W to complete the circuit the same way the mechanical thermostat closes the circuit.
    It does not provide any power. If I got this right, it's simpler than adding an intermediate relay (with it own power supply) to merely complete the circuit in place of the mechanical thermostat.

    I will draw a schematic to make sure I have a terminal to terminal wiring diagram.

    Thanks.
  • ratio
    ratio Member Posts: 3,627
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    So, if I restate what you said above, I will have the following:

    Separate transformer for 24vac:
    Incoming 110vac to the primary terminals
    Outgoing 24vac to R and C on the EIM

    EIM:
    Incoming 24vac stated above
    Disconnect jumpers to Rc and Rh
    Connect Rh to one of the wires to the mechanical thermostat
    Connect W to the other wire to the mechanical thermostat


    With this arrangement, when the EIM turns heat on, a contact will close between Rh and W to complete the circuit the same way the mechanical thermostat closes the circuit.
    It does not provide any power. If I got this right, it's simpler than adding an intermediate relay (with it own power supply) to merely complete the circuit in place of the mechanical thermostat.

    I will draw a schematic to make sure I have a terminal to terminal wiring diagram.

    Thanks.

    Correct. The R & C provide power to the EIM only. The Rc & Rh are internally tied to the Y & G relays and the W relays respectively. Once they're out, the equipment calls are dry.
  • SteamingatMohawk
    SteamingatMohawk Member Posts: 1,007
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    Thanks, I'm not an electrician or electrical engineer, so I am not familiar with the "dry" term. This helps a lot.
  • SteamingatMohawk
    SteamingatMohawk Member Posts: 1,007
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    So, I can use the AT72 (40VA) transformer I already have laying around and return the RA89A switching relay (with transformer). Saves me $80 plus tax. I like that. It probably makes sense to run two 18/2 cables (one for power to the EIM, the other for the conductors to the mechanical thermostat connections in the boiler control circuit) rather than a cable with enough wires to meet all needs, since I have to locate the transformer somewhere and the wires to the control circuit go through the pressuretrol box and there isn't much room to mount the transformer near the pressuretrol.

    It's a lot simpler than adding a separately powered relay between the EIM and the mechanical thermostat connections in the control circuit.

    Does this make sense?

  • ratio
    ratio Member Posts: 3,627
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    Yes.
  • SteamingatMohawk
    SteamingatMohawk Member Posts: 1,007
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    I am somewhat surprised I could not find anything on the internet for doing the "simple" conversion I am doing from T87 to YTH5320 (or similar). But then, steam is not all that popular these days and anyone wanting to spend the money to install a several hundred dollar wireless and wifi capable thermostat probably needs to have their head examined. My reason is that this is in a 90+ year old two family house converted to 4 units with no zones and one thermostat.

    I have been struggling with balancing the steam to the apartments and may want to change the location of the thermostat, so wireless is a plus. Another plus, having the wifi capability can help me check things out without actually going to the house, since I don't live there.


    Thanks for all your help.


  • SteamingatMohawk
    SteamingatMohawk Member Posts: 1,007
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    I installed the transformer and EIM yesterday. System test was satisfactory. Now all I have to do is tweak the room the thermostat was in because it is a bit warmer than it was. The apartment where I have the wireless thermostat is fine and the two others seem to be fine so far.

    The installation turned out to be a lot simpler than having to add the extra unneeded relay.

    Thanks for the help.
  • SteamingatMohawk
    SteamingatMohawk Member Posts: 1,007
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    Still tweaking the vents, but taking days off until after Christmas. I picked up the RedLink device today for connecting to the internet.
  • Jamie Hall
    Jamie Hall Member Posts: 23,324
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    When you install the RedLink, do yourself -- and the rest of the world -- a favour and set a really strong login and password for it, please. Don't use the factory defaults...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    Erin Holohan Haskellethicalpaul
  • SteamingatMohawk
    SteamingatMohawk Member Posts: 1,007
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    Good idea, thanks.
  • SteamingatMohawk
    SteamingatMohawk Member Posts: 1,007
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    Twice now, I noticed the boiler came on and ran for a couple of minutes then shut off and not on the LWCO check. It seemed weird. I went to the room where the thermostat is located and it read, "Heat On", so I went back to the boiler and it was on.

    Does anyone know if the wireless thermostat I installed has some kind setting for a periodic run of its own, or if it's a reaction of the thermostat to changing temperature in the room? The radiator and pipes didn't even get warm in that room. I read in one of the discussions that the sensors in this modern stuff may be very sensitive.

    The wireless thermostat kit is the YTH5320R1000 basic kit with the EIM. I'm going to read the manuals.
  • ratio
    ratio Member Posts: 3,627
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    That thermostat has a 'cycles per hour' setting that should be set to 1, or possible 2 or 3, for a steam system. That said, it may be the pressuretrol stopping the burner due to the boiler pressure climbing. Had it been firing for a long time before it cycled off? Maybe trying to recover from an overnight setback?
  • Jamie Hall
    Jamie Hall Member Posts: 23,324
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    Any idea why the boiler shut off on its own, and exactly how long did it run? A couple of minutes is one thing -- but if it was shorter -- say a 30 second pre-purge, then 15 to 30 seconds run, then off, it may also be that the flame sensor didn't prove flame on the first try, and shut off. Some controls will then retry after another short interval. Might have a tech. with good instruments and skills check and see that the burner and ignitors and flame sensor and all that sort of thing are adjusted properly.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • NY_Rob
    NY_Rob Member Posts: 1,370
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    As mentioned above, you could set the t-stat "Heat Cycle Rate" to 1... that will 100% stop occasional "phantom heat calls". It will also produce larger swings between heating call and setpoint though. If the swing is too large on 1, give 2 a try... supposedly your t-stat can "learn" and will eventually workout a proper runtime to make CPH setting 1, 2, etc.. not overshoot or let the room get too cold. From what I have read, it takes time for the t-stat to "learn" and adjust to new "Heat Cycle Rate" settings.
  • SteamingatMohawk
    SteamingatMohawk Member Posts: 1,007
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    I was in the basement when the boiler started and it ran for a minute or two, definitely not 30 seconds or less.
  • SteamingatMohawk
    SteamingatMohawk Member Posts: 1,007
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    NY_Rob, is your comment specific to my thermostat or generic?

    I looked in the manual (https://customer.honeywell.com/resources/Techlit/TechLitDocuments/69-0000s/69-2092EFS.pdf) page 4 item 5 is first stage heat. I will check the setting to see if it is set for steam. the manual does not indicate the default setting or the CPH. That setting may be a clue.

    Thanks.
  • SteamingatMohawk
    SteamingatMohawk Member Posts: 1,007
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    Jamie Hall The boiler has a standing pilot and I am not aware of any prove flame device, other than the thermocouple having to be hot enough from the pilot before the pilot will stay lit.
  • NY_Rob
    NY_Rob Member Posts: 1,370
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    NY_Rob, is your comment specific to my thermostat or generic?

    I looked in the manual (https://customer.honeywell.com/resources/Techlit/TechLitDocuments/69-0000s/69-2092EFS.pdf) page 4 item 5 is first stage heat. I will check the setting to see if it is set for steam. the manual does not indicate the default setting or the CPH. That setting may be a clue.

    Thanks.

    Yes, my comment was for your Focus Pro.
    Steam should be set at 1 or 2, and that will also prevent "false starts" because if it runs 1X or 2x an hour (depending on your setting it to 1 or 2 CPH) it's prevented from making another start for another hour after the thermostat was last satisfied.

  • SteamingatMohawk
    SteamingatMohawk Member Posts: 1,007
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    Why would that function be built in to the thermostat? What happens when it's -15F in the middle of winter and the house cools enough for the heat to be needed to come on?

    I don't think the original round Honeywell had that capability.

    I've seen mention of CPH in reading the discussions, but didn't really see anything explaining why. Letting the system cool down for an hour only makes it take that much longer to warm up when the boiler is allowed to fire..

    I guess I am about to learn some more about steam heat.

    Thanks in advance.

    Al
  • ratio
    ratio Member Posts: 3,627
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    The thermostat knows how fast the house is loosing heat, and how fast it gains it when the heat runs. A while back, I found a description of sorts of the cycles per hour operation. After chewing on it, I think what it does is that you'll have at most 'cycles per hour' starts, spaced appropriately, and the on time is reduced if you require less than ½ the output of the furnace and the off time is reduced if you need more than ½ the output of the furnace. This is all steady state, I believe somewhere I saw that if the temperature drooped too far it will fire the heat regardless of the cycle rate.
  • Jamie Hall
    Jamie Hall Member Posts: 23,324
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    The old round Honeywells -- the T87 series -- had an anticipator instead of a cycles per hour setting. They haven't been beat for steam yet, in my not very humble opinion. If the anticipator is set correctly -- which takes some fiddling, granted -- it does the job of maintaining set point temperatures very well indeed.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • SteamingatMohawk
    SteamingatMohawk Member Posts: 1,007
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    Holy cow! I wonder what happened to "when its cold turn it on, when it gets warm enough turn it off?" like the way it was done 100 years ago.

    The Dead Men must be rolling in their graves laughing at "technology".

    Thanks for the info. I will look into it further and if I find anything worthwhile, I will mention it here.

  • ChrisJ
    ChrisJ Member Posts: 15,706
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    > @SteamingatMohawk said:
    > Holy cow! I wonder what happened to "when its cold turn it on, when it gets warm enough turn it off?" like the way it was done 100 years ago.
    >
    > The Dead Men must be rolling in their graves laughing at "technology".
    >
    > Thanks for the info. I will look into it further and if I find anything worthwhile, I will mention it here.

    It sucked, that's what happened to it.

    The closest you'll get to that is 1 CPH.
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • SteamingatMohawk
    SteamingatMohawk Member Posts: 1,007
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    I'm aware of the heat anticipator and have always what it did. I surmised it is a way to account for the residual heat in the system piping and radiators that would eventually dissipate into the rooms after the boiler flame is turned off. But I never looked further into the concept.

    If saying it sucked, means that the fine control of temperature was opening the windows, when overheated, I can understand it.
  • SteamingatMohawk
    SteamingatMohawk Member Posts: 1,007
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    Since we're talking about the electrical side of steam heat, my LWCO runs the self test about every 10 minutes. I often wonder if it needs to occur that often, since the system pressure drops while the flame is off, potentially drawing air back into the system or creating a vacuum, which seems counterproductive. Perhaps this should be a separate discussion.

    Any thoughts?
  • ethicalpaul
    ethicalpaul Member Posts: 5,704
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    Do a search for cycleguard or psycho guard and you’ll see what people think of them (they hate them)
    NJ Steam Homeowner. See my sight glass boiler videos: https://bit.ly/3sZW1el
  • NY_Rob
    NY_Rob Member Posts: 1,370
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    I'm aware of the heat anticipator and have always what it did. I surmised it is a way to account for the residual heat in the system piping and radiators that would eventually dissipate into the rooms after the boiler flame is turned off. But I never looked further into the concept.

    IDK who invented the Heat Anticipator, but Honeywell pretty much perfected it in the T87F "Round" t-stat.
    It's such an elegantly simple design (along with the rest of the T87F) that if it was placed in a clean environment it could probably run properly for 100 years or more due to the fact that there are basically no moving parts to wear out and no solid state electronics to burn out.

    Interestingly enough, when I first connected the T87F to my mod-con (which uses Taco Zone Sentry zone valves) the T87F's anticipator was set way too low and the boiler literally fired up for 30 seconds then turned off. I then set it to 1amp and the room overshot setpoint a bit... but at least it didn't short cycle. I finally found the Taco Zone Sentry heat anticipator rating (.5amps) and the correct anticipator formula for a mod-con (1.4) which brought me to an anticipator setting of .7 on the T87F. Since setting the T87F anticipator at .7amps it's been almost perfect at keeping my downstairs zone at desired temp with minimal swings while producing long run cycles.
    It's quite amazing actually that this 70+ tech can make a modern computer controlled boiler work so well.

  • Jamie Hall
    Jamie Hall Member Posts: 23,324
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    The interesting thing about the anticipator design is that it accounts for so many variables using a very simple, though ingenious, all analogue/no moving parts design. The same thing could b done with a "modern" thermostat, but it would take multiple sensors and a small computer and some interesting programming. All feasible, but...

    Among the variables:
    Stored heat in the system after the burner shuts off
    How fast is heat being lost by the structure
    What is the set point temperature
    What is the actual room temperature

    And it uses those to determine how long to run the boiler, and when to shut it off.

    And it's pretty close to bulletproof... and no batteries or C wire...

    What's not to like?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • ChrisJ
    ChrisJ Member Posts: 15,706
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    > @Jamie Hall said:
    > The interesting thing about the anticipator design is that it accounts for so many variables using a very simple, though ingenious, all analogue/no moving parts design. The same thing could b done with a "modern" thermostat, but it would take multiple sensors and a small computer and some interesting programming. All feasible, but...
    >
    > Among the variables:
    > Stored heat in the system after the burner shuts off
    > How fast is heat being lost by the structure
    > What is the set point temperature
    > What is the actual room temperature
    >
    > And it uses those to determine how long to run the boiler, and when to shut it off.
    >
    > And it's pretty close to bulletproof... and no batteries or C wire...
    >
    > What's not to like?

    You could install the same exact style anticipator in a modern thermostat and just have it warm the pcb the thermistor is soldered on. A simple smt resistor would work.

    There's a good reason they stopped using them. They're not so great.

    There are also other mechanical thermostats that worked good besides the round T87.
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • Jamie Hall
    Jamie Hall Member Posts: 23,324
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    One thing about anticipators which is often overlooked -- they not only heat, but, since they have mass, they cool slowly -- and the rate at which they cool is a complex function of room conditions.

    And what's not good about them? I've had a lot more trouble getting even stable heat with a range of fancy modern thermostats than I've ever had with an anticipator equipped thermostat. Of course, I used to enjoy the delicate work needed to get the most out of a Rochester QuadraJet, too...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England