Steam Thermostat Question

CamAid

So I was told not to lower the Thermostat more then a few degrees when going to work, bed etc because you want to keep everything warm in the house to act as radiant heat. I understand that but Why would you want the Steam setting on a thermostat to only come on ever hour? Wont that allow too much time for everything to cool down (100 year old home with average insulation)? I would think you would want it to be like forced hot air and run multiple cycles per hour? (will that break the boiler)? As of right now I notice if my setting is 69 degrees the boiler will still kick on short cycles here and there? I thought it wouldn't come on until it dropped 68 or less? This is a wifi Honeywell

Different question. After my boiler has been running for a little bit and all the vents on the rads are closed I notice the second the thermostat shuts down I hear the vents open? Its like as soon as the pressure drops they open yet no water or steam comes out? Seems very quick to me?
Thoughts and you guys rock by the way!

Jamie Hall

Steam -- and hot water -- responds rather slowly to either being turned on or off. A steam radiator, once warmed up, will usually still be perceptibly warm even half an hour to an hour after the boiler shuts off. Conversely, even with a well vented system it may take ten minutes or so for the radiators to really come up to temperature after the thermostat calls for heat.

So... you don't want the system to cycle on and off in short bursts. What often happens that way is the slower radiators never get any heat at all!

That said, some people have found better results with a setting of two cycles per hour for steam rather than one. It depends so much on the individual house and system.

Now setbacks are another story. Setbacks do work moderately well for forced air, where the only thing you are heating is the air. They do not work well -- indeed, may actually use more fuel -- for either hot water or steam. Again, your mileage may vary -- but there seems to be a sort of consensus that a three degree setback is about as far as you want to go.

On the vents opening -- it truly is amazing how fast the pressure drops in a steam system once the boiler stops firing. Even on very big systems, it is often less than a minute. The reason is that the steam condenses that fast. Neither water nor steam will come out -- the steam is condensed, and there shouldn't be any water anywhere near the vent anyway.

CamAid

Also if the thermostat is at the set degree how do those old round thermostats know to keep coming on every hour if the temp in the room hasn’t dropped? They aren’t digital ? Thanks again

Jamie Hall

CamAid said:

Also if the thermostat is at the set degree how do those old round thermostats know to keep coming on every hour if the temp in the room hasn’t dropped? They aren’t digital ? Thanks again

No, they aren't digital. And they don't actually know to come on every hour. Instead, they use an anticipator -- which is really just a very tiny heating element which runs along with the boiler -- which is adjusted so that the thermostat heats up a bit faster than the air and, thus, turns the boiler off sooner, depending on the residual heat in those big cast iron radiators to finish the job. Properly adjusted they can maintain the space temperature within very narrow limits -- half a degree or less.

The beauty is that they respond to the actual conditions of the space, so that if it is cooling faster than normal (say a windy day) they will come on sooner than they otherwise would.

The downside is that if they are improperly adjusted -- which happens all too often -- their ability to hold a constant temperature is no better than a modern digital thermostat -- and they require more skill and patience to adjust.