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Need new thermostat for single-pipe steam system

Our thermostat just broke so it's time for a new one. I was hoping that we could solve a persistent problem with the new thermostat.

On warm winter days the general temperature around the house is hot and on cold days it's really cold even though the thermostat is reading the same temperature in both cases. I've assumed that this is because the thermostat is located in the center of the house and there is generally a temperature gradient between the center and the edge of the house. On cold days the edge is going to be really cold and on warm days it will be pretty close to the temperature at the center. Since we do most of our living towards the edge of the house rather than the center of the house this is a problem. It makes it seem as if our heat is very inconsistent and causes us have to manually adjust our programmable thermostat all the time.

I've figured there are couple good solutions to this.

1. A thermostat that has an external (outdoor temp) temp probe in addition to the internal one and it uses the external temperature to adjust the target temperature for the internal thermometer.

2. Move the thermostat to a better position that more accurately reflects what the temperature feels like. But how do I choose that better position. I either need expert help on this or I need a thermostat thats easily movable so that I can experiment. For easily moveable I would think a thermostat with a remote/wireless temperature probe would be perfect but all the "wireless" thermostats are way more feature rich and expensive than I need. They are generally $200+ which is crazy. So help finding a thermostat with a remote temperature probe that doesn't have wifi connectivity and other expensive stuff would be great.

3. A thermostat that does have wifi connectivity and uses it to get the local weather report and uses that data to adjust the target temp.

We also have some issues with the wind direction. If the wind is blowing in one direction one side of the house will get cooled off a lot more than the other and if it's blowing the other way the opposite happens. This really messes with the temp because if the thermostat is in the cool area the rest of the house gets way too hot and if it's in the hot area the rest would get way too cool. To somewhat solve this it would seem reasonable to have multiple remote temp probes communicating with the thermostat and the the thermostat just takes the average of the probes and uses that as the actual temperature.

So does anyone understand this issue better than I and know the best way to solve it and what products to buy?



  • JStar
    JStar Member Posts: 2,752
    edited October 2013

    I would put in a Honeywell Pro4000. You can set it up for 1 cycle per hour (appropriate for steam), and balance the system with radiator vents. I bet all of your "cold-room" problems come down to poor venting, in the radiators and the mains.

    With steam, thermostat location is not as critical as you would think. Radiant heat will get everywhere in the house in a very short time. Think about it this way...The sun is 92,960,000 miles away from Earth. It is still able to heat us with radiant energy. The radiators in your house should have no problem keeping you warm.
  • Jamie Hall
    Jamie Hall Member Posts: 21,568
    Probably at least two

    separate problems here.  First off, the Honeywell Pro4000 which Joe suggests is indeed close to an ideal thermostat for steam.  Easy to hook up, easy to program, reliable.  All good stuff.

    As Joe says, though, the problem of cold edges and warm centre on cold winter days may well be due to problems with venting.  As you may have read around here, if the air can't get out of the system, the steam can't get in.  Therefore, it is necessary for even heat that the mains be vented very fast, so that steam can get everywhere in the system at about the same time.  Then it is also essential, in single pipe steam, that each radiator be properly vented.  You don't want the radiators too fast, but you do want them so that they all heat more or less evenly.  If you do have colder rooms, then you can speed up the venting on the radiators in those rooms (up to a point) to get more heat there.  It's worth experimenting with.

    Also -- at the risk of sounding like a broken record -- make sure that the pressure on your boiler is low enough.  1.5 psi is ample.  Oddly, the higher the pressure the more uneven and slower the heat will be (it also costs money...).

    Make sure your new thermostat is mounted in a representative room -- and one which you often use!

    The problem of uneven heat on a windy day is common in older houses, and is caused by infiltration.  Storm windows, if you don't have them, help a lot.  Just tightening up the windows and doors can help. 
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
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