Wiring new thermostat to the furnace

Discussion in 'Boiler Forum' started by keano016, Nov 13, 2009.

  1. keano016

    keano016 New Member

    Messages:
    35
    Location:
    Mass
    Hi

    I would like to install a new thermostat on my second floor of my steam oil heating system.

    Few questions for you.


    1. How difficult is to connect the wiring to the boiler. Can I do it myself? Is it two wires that just need to be connected to two screews or is it more complicated? The current thermostats that are connected to the furnace are all 2 wires.

    2. What kind of a wire I need to buy so that I can run it from the thermostat to the boiler?
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,003
    Location:
    New England
    It depends...

    Most thermostats use 24vac, but some could control 120vac or 240vac. Then, without knowing if your system has multiple zone control capabilities, you may not be able to add another thermostat without changing the controls at the boiler.

    Exactly what does the thermostat turn on/off? A zone valve, a pump, or other?

    In its simplist form, a thermostat is just like a temperature controlled on/off switch. There's power on one lead, when the thermostat determines heat is required, it closes and applies that power signal on the other lead - just like a wall switch to turn on a light. It depends on what that switch is trying to turn on.

    Depending on the voltage on the wires, and the distance of the run, would determine the size and type of wire required. So, without knowing more about the system, it isn't safe to say. Often this is something like 18g bell wire, but it could require larger or smaller, or some other type depending on what the system design.
  3. keano016

    keano016 New Member

    Messages:
    35
    Location:
    Mass
    Thanks for your response.

    The thermostat will be turning on a Steam Boiler. I want to have a thermostat upstairs in my bedroom so that when the temperature upstairs at night reaches the desired level the boiler would turn off. Right now, the downstairs needs to be heated up to the desired temperature to have the boiler turn off and to me that is just a waste of heat and expensive oil.

    The run would be from second story to the basement, I would say about 25 ft.
  4. Eldan

    Eldan New Member

    Messages:
    14
    Alternative

    Changing the location of the thermostat may not work as well as you think and could make the overall comfort of the home worse. It sounds like the upstairs is getting too warm when the downstairs is comfortable, a common problem. If so, you should look into installing thermostatic radiator valves on the upstairs radiators. If you have one-pipe steam it's not hard to install these yourself.
  5. keano016

    keano016 New Member

    Messages:
    35
    Location:
    Mass
    Well, my reasoning is this.

    Right now the thermostat kicks on downstairs. The boiler creates steam that shoots upstairs to the attic, then the steam gets to the second floor, then to the first floor. My first floor is wide open area, there is a family room addition, so the system has to work extra hard to raise the temperature there by 2 degrees, compared to increasing the temperature in my bedrooms upstairs. So in essence, if my desired temperature downstairs was 65 degrees, my attic may reach 73 and second floor 70 before the first floor reaches 65.

    with the new thermostat (note I want to add one, not reposition the existing one) When the temperature reaches the desired temperature in my upstairs bedroom, the boiler would shut off once the temperature upstairs reaches 65, let's say 15 minutes prior to it should have been had it needed to heat up the downstairs to the desired temp.


    Mine are one pipe radiators. I need to do some further research on the thermostats per each radiator. My understanding was that steam is very hard to control and fine tune.
    Last edited: Nov 13, 2009
  6. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,003
    Location:
    New England
    It sounds like it is a conventional, 24vac, heat only thermostat. The gauge wire required would depend on the distance you need to run the wire. Having two thermostats that turn the whole system on or off still means either one would do that unless there was some way to zone it. So, depending on the weather, the house room layout, and your desired settings, satisfying the upstairs needs might still have the downstairs cold, keeping the heat on. Assuming you wire these in parallel, either one will turn the boiler on. Wiring them in series would only allow heat if both were calling for it.

    If there is something like a zone valve for steam, you may be able to zone it, then two thermostats could control the zone valve rather than the boiler. You'd need a controller so the boiler turned on if either zone valve was activated, but it wouldn't be too messy to install.

    I'm not sure it would help that much. Now, whether you could zone things or add thermostatically controlled valves to the radiators, I'm not sure. I know they make them for hot water, but not sure about steam.
  7. Eldan

    Eldan New Member

    Messages:
    14
    TRVs

    The steam will go wherever there is less pressure, which is not necessarily the way you think. What's probably happening is that the upstairs radiators are oversized, or you have faster vents upstairs than downstairs. TRVs are definitely what you want. If the attic is not inhabited you can install a TRV and set it to 55. Set the bedroom TRVs for your sleeping comfort or to match the downstairs setting.

    You will save money because the TRV controlled radiators will close earlier, directing all steam downstairs and satisfying the thermostat or the pressuretrol faster.

    To install a one-pipe TRV you need three components, a valve adapter that replaces the existing air vent, a thermostatic controller that screws onto the adapter, and a new air vent with a straight configuration instead of a 90. One thing to note is if you have radiator covers or drapes you will want to purchase a model with a remote mounted controller.

    My TRVs are from Danfoss and they work well. We had terrible overheating upstairs and it's been completely eliminated.
  8. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,003
    Location:
    New England
    Googled a few articles on this, and one article indicated about $50 a valve installed. http://www.danfoss.com/North_Americ...e6f/c5fda1d6-28ad-4d20-9200-06094abb234a.html

    Probably others that make similar valves. Sounds like this is what you need. You'd want to leave your existing thermostat in the coldest room, and put new valves on the hot areas. the hot areas now would start shutting off, leaving only those that were in the cold part. Then, the current thermostat would shut off the boiler. So, you'd probably only need to add these in the hot areas, and leave the remaining ones controlled by the existing thermostat.

    They have a bunch of different models, but this was the only one I saw that was for a one pipe steam radiator.
  9. Eldan

    Eldan New Member

    Messages:
    14
    The hardest thing about installing TRVs is figuring out which parts to buy. The part you referenced is just the 1 pipe steam adapter. You also need an contoller and a vent. You have choices on the controller. You can get a direct mount, or one with a remote thermostat connected to the actuator by a capilary tube. This would let you mount the sensor on the wall or outside a radiator box for unobstructed air flow.

    This PDF explains all: http://na.heating.danfoss.com/PCMPDF/RA2000%201PS_DS.pdf

    I've also heard good things about Macon Controls: http://www.maconcontrol.com/opsk1204.html
  10. nhmaster

    nhmaster Master Plumber

    Messages:
    3,189
    Location:
    S. Maine
    The easy thing about a steam system is that you can leave the old thermostat where it is and turn it down. The new thermostat can be wired in paralel with the old one. That way either one can call the burner depending on which is set higher. Just find the TT terminals the original thermostat is wired to on the primary control and bug on to them with the new wire.
  11. wallygater

    wallygater New Member

    Messages:
    133
    Location:
    long island
    steam radiators

    I have had steam radiators for the past 18 years and have never understood how they worked. there is one room in particular upstairs that gets ridiculously hot. all the other rooms in the house are comfortable. I would like to install a trv on the hot room. How can a valve on the end of the radiator possibly control how hot it gets? I just don't get it. I have tried valves with bigger holes in them and ones with smaller holes. It just does not seem to make any difference. That room gets hot as shit. I have the baseboard type of radiators. this one upstairs is the only one that is not enclosed. I never got around to getting a cover for it. Will covering it up make the difference? Or should I try one of these trv`s first?
  12. Eldan

    Eldan New Member

    Messages:
    14
    wallygater, the radiator is probably oversized. Covering it won't help. A one-pipe TRV works by closing off the air vent when the room comes to temperature. If the air can't get out, the steam can't get in. The radiator is effectively shut off.

    Without a cover or other obstructions you can get the simplest TRV with sensor mounted on the valve. I think it will cure your problem, with one caveat. You need to check the pressuretrol on your boiler and make sure the cut-out pressue is around 1.5 psi. Over the years it's possible that some heating person cranked up the pressure to "fix" some other problem. That's a mistake.

    By the way, the air vents should be sized so that on the coldest day all the radiators fill with steam at about the same time, regardless of distance from the boiler. Sometimes you have to make the vent in the room with the thermostat a little slower.
  13. wallygater

    wallygater New Member

    Messages:
    133
    Location:
    long island
    Trv

    Thank you. I think I will try it. They look like they are about 50 bucks. It might take me a while to get the money together for this but when I do I will post back and let you know how I made out. sorry about hijacking this thead.
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