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Could someone verify my thermostat theory?

I recently decided to adopt the steam system for my building.  There are 11 units, all of which are over-heated, yet there is no indoor thermostat -- only an outdoor thermostat that is set to 55 degrees. 

I'm trying to understand how the boiler should cycle with only an outdoor thermostat.  Could someone verify for me...

1. If the temperature is above 55, the boiler should not fire, right?

2. If the temperature is below 55, and none of the building radiators are open, the boiler should not fire, right?

3. If the temperature is below 55, and any one of the radiators are open, the boiler will continue to fire until a) the cut-out pressure is reached, b) all radiators are closed, c) the outside temperature rises to 55 or above.

Here's my real concern: If all three of these points are true, then given a sunny winter month that never warms above 55 outside, regardless of how much solar heating may be happening inside, if any single radiator is open (or has a badly leaking control valve), the boiler will cycle continuously the entire month.  Is that correct?

Am I missing some important points or is it just plain crazy that we don't have an indoor thermostat?


  • Steamhead
    Steamhead Member Posts: 16,468
    What you need

    is an outdoor control, not just a thermostat. The Tekmar 279 is a good choice. 
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,576

    what make of control is now controlling your building? is it possible that it once had an indoor sensor, which has now been lost?

    with the price of gas, and the great possibility for waste, the installation of a proper control system, supported by a current mfg should be on your list for your "adopted child". when you say the apartments are overheated, can you estimate how much gas has been wasted?  i suspect that the changeover to an effective control would save enough fuel to pay for the control in a few months! if the budget is very limited, a honeywell visionpro, or tekmar thermostat would at least monitor the inside temperature.

    while you are deciding what to do about the control system, why not check out the rest of the system, as far as main venting, over-pressure, and pipe insulation.--nbc
  • will smith_4
    will smith_4 Member Posts: 259
    Controlling anything...

    Sounds like all you're doing now is controlling the system based on outdoor air temp-the notion being, if the OA is below 55, you'll allow the system to cycle as long as the operating control is "calling" for heat. There's nothing wrong with having an OA lockout, but I'd also have either an averaging temp controller (that uses multiple temp sensors) or at the very least a sensor/stat which you would locate at a point in the building that you'd consider to be the coldest spot that still gets heat. Thought I'd emphasize that because I ran across a stat once that was in a closet. Took a while to find that one...

    Also make sure your pigtails are cleaned and primed, that they are oriented the proper way (if you have mercury 'trols), that the gauge is accurate, and that the operator is set up properly. You didn't note if it's 1 or 2 two pipe, or if it's vapor/vacuum-each carries it's own peculiarities that can affect overall setup/performance.
  • sreja
    sreja Member Posts: 175
    thermostat theory and logic


    I think what you are experiencing is the same kind of shock and awe that many of us novices have faced when dealing with our steam systems:

    The standard control decision for firing the boiler just seem so crude.  Turning on the boiler when the outside temperature drops below some point and then off when it increases beyond that point -- doesn't seem to very accurately mirror the actual needs of the building.

    As you say it seems so wasteful.

    But the reality is that it seems like many (most?) multi-unit steam heating buildings are set up like this.

    The idea seems to be that while it's not perfect, it's good enough and that chances are when the temperature outside is below some point, SOMEONE in the building is going to need some heat.

    As has been suggested, there are controllers out there that have indoor sensors.  That would seem a much more logical option.  We just upgraded to one and we'll see how much it helps -- though one must remember that none of these systems does anything more than measure temperature at one or maybe two indoor locations, so it's still a bit of a guessing game regarding different temperatures in different locations of the building.

    In an ideal world each apartment would be able to send a signal to the boiler room indicating that they wanted heat, and the decision about whether to fire the boiler and for how long could be made based on that.. That would be the logical solution -- i'm not sure why we don't see such systems -- it wouldn't be *that* hard to do.  But they don't seem to exist.
  • Mike Kusiak_2
    Mike Kusiak_2 Member Posts: 604
    Multi sensor temperature averaging

    The Tekmar 279 and other controllers using thermistor indoor sensors can be set up for multi room indoor temp averaging. By using an array of 4, 9 or 16 or 25 (or more) sensors, you can take an average measurement of building temperature and control the boiler accordingly. The array is simply a series-parallel connection of the sensors, whose electrical resistance appears the same to the controller as a single sensor at the corresponding average temperature.

    This arrangement will not give any weighting to the colder apartments unless you locate more of the sensors in the colder parts of the building, but by proper location the building temperature control will be much better than just using a single indoor sensor.
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    Some apartments must get a minimum of heat.

    In some places, such as New York City, there are regulations that during the legally defined heating season, require that in the day time the building must be heated to at least some legally defined temperature, and at night it must be heated to at least some other legally defined temperature. And the temperatures are different depending on what the outside temperature is. I do not know what any of these temperatures are, nor do I know what the legally defined heating season is. But the building super must ensure that these are met or the owner is subject to fines. It may be that the system needs no controls at all, but that would mean that the super must ensure compliance manually. Or maybe the controls do it all. Depends on the owner, I guess.

    I used to live in Buffalo, N.Y., in a one-pipe steam heated apartment building. I do not know the laws there, but there was an outdoor sensor, sort of a bulb, that pushed a microswitch with a roller at the end of the actuator into a wheel that was reminicent of a circular sawblade. This wheel turned around once every 24 hours. At one extreme,  there was no heat and at the other the heat was on almost all the time. There were no thermostats. It worked pretty well most of the time, though there were times when it was too hot. I remember trying to turn the heat off in one room, but the valve did not work right. It did not really turn off all the way, so steam escaped around the packing nut, and the radiator still heated until it filled up with water. The super got mad at me for adjusting the valve. I suppose there was water hammer, but I do not remember that. But the alternative was to open the windows, and I felt guilty doing that.
  • BoulderBeginner
    BoulderBeginner Member Posts: 3
    Many thanks!

    Thanks for all the great feedback!  I'll have to do a bit of reading on the function of the outdoor control component.  As I mentioned, I'm a newbie.  Our steam repair guy (Carl) said that he believes there used to be an indoor thermostat -- he's seen the wiring -- but believes it was covered up by a remodel.  Sounds like a common fate with various parts of these old steam systems.

    And it seems that neither Carl nor I have been able to locate any main air vents either!  In addition to replacing some missing pipe insulation, venting the mains sounds like a high priority. 

    I don't have a clear picture on how to estimate how much fuel or BTUs are being wasted, but all of the residents seem to feel their residences are too warm and our fuel bill is our single largest expense through the HOA.

    However, since we're funded through limited monthly fees, we may be able to afford only one significant repair this season (in addition to wrapping exposed pipes).  Any opinions which would be the most effective correction to focus on first -- outdoor control or main air vents?
  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,576
    best use of funds

    i would do the main [not rad] vents, plus honeywell visionpro thermostat [installed in the north west corner inside wall], plus good a low pressure gauge. try to get the pressure as low as possible [my 55 rad system does most of the main venting by 2 ounces, and rarely goes above 8 ounces, using a vaporstat. i do have 17 gorton #2 main vents on 6 dry returns. if your building is tall, then you may need some riser vents.--nbc
  • BoulderBeginner
    BoulderBeginner Member Posts: 3
    edited March 2011
    Was this a Main Air Vent?

    Thanks again!  It sounds like you're confirming where I thought our system might be heading -- main air vents and indoor thermostat.

    I believe that Carl (our boiler guy) is pretty intimidated by the effort and expense of cutting into the main lines.  So, I'm hoping that we might be able to find some pre-existing spots where air vents may have existed in the past and have been capped.

    Do you think this looks like the previous site of a main line air vent?

    (Shoot, I can't seem to get the photo uploaded.)
  • Rod
    Rod Posts: 2,067
    Installing Main Vents

    Hi- I'm not quite sure what you envision when you say "cutting into the mains". All that is needed is to drill and tap a hole into the top of the main for 1/2 or 3/4 pipe. Your steam system is running  (or should be) at under 2 PSI so high pressure isn't a problem. If when the vent pipe is attached, you feel that it needs to be firmed up a bit you can put a fillet of JB Weld around where the two pipes join.  Venting wise a 1/2 inch pipe will support 2 ea. Gorton #2 s. Be sure pick a spot that has enough over head clearance for the vent(s) and make sure the vents are oriented so that any water entering them will drain back into the main.

    Attached is a excellent drawing by Brad White of an "antler/menorah" arrangement . Note the use of a pipe union. This makes the multiple vents much easier to attach and service.

    Pictures- This website will only accept  pdf or jpg (picture) files.

    - Rod
  • Steamhead
    Steamhead Member Posts: 16,468
    Another way to do this

    if you need a lot of vents, is to have a welder attach threaded sockets ("thread-o-lets") to the steam main where the vents will be installed. See the pic below for an example of this.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
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