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Thermostat Swing Settings

JohnCT
JohnCT Member Posts: 35
in Strictly Steam
I'm using a Lux programmable thermostat with steam heat. I'm trying to follow recommendations I've read to limit cycles per hour, but this thermostat only lets me control that by temperature cut in and cut out swing, rather than cycles per hour. Settings are in .25 degree increments between .25 and 2.5. Factory default is .25. 1,800 SF house with 8 radiators, all get steam pretty quickly. I'm thinking of setting the swing to 1 degree. So, if set at 66, would come on at 65 and cut off at 67, for example. Has anyone had experience with this type of thermostat setting with a steam boiler and what are your thoughts to limit heating cycles?

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 24,842
    You really can't set a specific cycles per hour with thermostats of that type. What you can do -- and should do -- is experiment with it until you get a comfortable balance between the temperature swings in the house and the number of cycles per hour -- which, if the radiators heat quickly, as you mention, is of somewhat less importance.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • SuperJ
    SuperJ Member Posts: 609
    Ideally you would run it a little tighter than that. You are likely going to be tempted to nudge the stat to get it going, and then nudge it back to shut if off if your swing is too wide.
    I would only go to a 2 (1deg up and down) degree wide control band if I was trying to combat known short cycling. Try tightening it up to 0.5degF and watch the cycle rate over the course of a day or two. Thermostat location and building envelope are going to have a significant effect on what the optimal setting is. A stat that supports setting cycles per hour is not too expensive though, might be worth the upgrade.
  • JohnCT
    JohnCT Member Posts: 35
    Thanks, Jamie!
  • JohnCT
    JohnCT Member Posts: 35
    Thanks, Superj! Good advice. I'll try a narrower setting and see how that goes. I realize I probably have the wrong thermostat for steam. But, I just installed it last season after buying the house, replacing a very old manual mercury filled thermostat, so hate to waste that money. I'm new to steam heat and didn't know to look for that type of setting when buying a thermostat.
  • Jamie Hall
    Jamie Hall Member Posts: 24,842
    Pity you didn't keep the old one... they're bullet proof, and very nearly the ideal gadget for controlling steam heat...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • JohnCT
    JohnCT Member Posts: 35
    Well, Jamie, that's just part of my ongoing steam education. I had no idea that you really don't want to program big temperature setbacks when using steam heat. Completely different approach from forced air heat I was used to. It amazed me that they had that crappy 40 year old $8 thermostat in a house in New England. Now I know why.
  • SuperJ
    SuperJ Member Posts: 609
    edited October 2018
    The mechanical anticipator is a beautiful thing that's under appreciated. Pretty elegant way to get some integral action on a mechanical device.
  • rlev11
    rlev11 Member Posts: 8
    I have my Lux that I have had for a number of years set for a .5 degree swing and am very pleased with it. On the coldest days in PA I go about 2 hours between cut out and restart of the boiler. I much prefer my Lux than the honeywell programmable I had before. If I have it set for 70, after the end of a cycle it may work its way up to 72 until the radiators start cooling down, but it feels nice and I don't mind it

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