Thermostats

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joemudd

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Wondering about modern thermostats. It seems when the weather is 30F and above, my house seems less comfortable (cooler) than when its cold. The stat is in a good hall location with no drafts. I realize that the heat is called more in frigid temps, but the temp in the stat area is the temp regardless of the outside. Also, is there a common setback set on these digital stats? Tia
 

Diehard

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Wondering about modern thermostats. It seems when the weather is 30F and above, my house seems less comfortable (cooler) than when its cold. The stat is in a good hall location with no drafts. I realize that the heat is called more in frigid temps, but the temp in the stat area is the temp regardless of the outside. Also, is there a common setback set on these digital stats? Tia
I have always attributed that cooler, less comfortable feeling to the fact that the length of time is longer during that slightly lower temperature, due to the outdoor temps taking longer to bring it down to the point where the heat starts up again.
 

joemudd

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What type of thermostat do you have
Its a Honeywell programmable from a few yrs ago.

I have always attributed that cooler, less comfortable feeling to the fact that the length of time is longer during that slightly lower temperature, due to the outdoor temps taking longer to bring it down to the point where the heat starts up again.
Thats what I thought but it still doesn't make sense to me. I also thought that the empty cavity wall behind the stat is colder due to colder temps in the basement.
When i say the setback, I think I meant offset, where the stat doesn't show it, but it waits for a degree or 2 below the set to send for heat which would keep the boiler from short cycling.
 

Diehard

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Thats what I thought but it still doesn't make sense to me. I also thought that the empty cavity wall behind the stat is colder due to colder temps in the basement.
When i say the setback, I think I meant offset, where the stat doesn't show it, but it waits for a degree or 2 below the set to send for heat which would keep the boiler from short cycling.
I thought sensors were located on the house side of the wall. Mine is.

I refer to the difference where it tells the heat to start or stop, as the Differential.

Google says, "Most thermostats have a built-in differential of +/-1 degree, while others will have a +/-3 degree differential. For example, a thermostat with a +/-1 degree differential that is set at 70 degrees will call for heat at 69 degrees and shut off at 71 degrees."
Of course depending on the type of system,radiators, etc., the resulting final temperature in the house can, and commonly does, end up with a wilder temperature range. In other words, "to hold a temperature as close as possible the thermostat has to anticipate the lag in time before the heating unit actually delivers heat to the room, and then to compensate for any overshoot ...

EDIT: Regarding "a boiler short cycling". Typically, in the case of a forced hot water system, it would be the circulators and/or the zone valves that would be short cycling. The boiler typically works to maintain a set temperature of the water.

 
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Mikey

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This idea isn't fully baked, but I've noticed that I often feel colder or warmer at the same thermostat setting, but depending on the outside temperature or appearance. We keep the thermostat (in an interior hallway) at 71°, but I feel cold if it's gloomy and 45° outside, but warm if it's sunny and 45° outside. May be influenced by having lots of window area. I'm thinking it may involve direct-radiated heat gain/loss from the body to the wall or window, more than conductive heat gain/loss from the body to the ambient air temperature. Basic theory explained at https://www.centracare.com/blog/2016/january/top-5-ways-body-heat-is-lost/.
 

Jeff Handy

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A common term that I have heard around here for the thermostat differential is “swing”.

Maybe it is just used in the Midwest?
 

joemudd

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I wonder if a mercury thermostat would be more accurate. Im probably overthinking it, its comfortable.
 

joemudd

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I thought sensors were located on the house side of the wall. Mine is.
Yea the stat is completely in the heated area, but the cavity behind between interior walls may be a few degrees cooler in colder weather 1/2 inch away from the back of the stat. shrug
 

voletl

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I wonder if a mercury thermostat would be more accurate. Im probably overthinking it, its comfortable.
The bi-metal spring that's in a Mercury thermostat makes them very unreliable they wear out over years
 

fixitron

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Have you measured the actual temperature with an accurate thermometer and compared it to the reading and setpoint on the thermostat?
We don't know how quickly your house loses heat, which could be a major factor. I can think of several things that could account for feeling colder when it is warmer outside, but I don't have much information to go on, starting with my first sentence. Another thought is if you have an Energy Kinetics System 2000, which runs the circulator for a while after the thermostat is satisfied to take off the extra heat from the boiler. When it is cold out, the boiler will run more frequently, with more of that extra run time. If your boiler has an Indoor/Outdoor Reset control, the boiler water will not be as hot at 30 degF as it would at 20 degF, so it will take longer to change temperature. Combined with a thermostat differential of more than 1 or 2 degF, there could be a notable swing in temperature in the house when it is not as cold outside.
Infrared radiation could be a factor, depending on several other factors, for which we don't have enough information.
 

joemudd

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Its a standard New Yorker boiler with a gas conversion. The temp at the stat is correct. House has been gone through and fitted with Roxul in 2x4 walls (great stuff, kudos Canada)) and new double pane argon windows. 12 inches in the attic rafters. Who knows what the differential is since ive never seen it reported on digital thermostats. I figure its the colder cavity behind th stat, or that the digital chip isnt so smart. Maybe ill fit some leftover Roxul in the area below the stat in the name of science.
 
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Mitchell-DIY-Guy

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There could be a lot of different things at play here. First, many modern thermostats are "adaptive" in that they try and learn how long it takes to get up to the temp setpoint, and many do this by sensing the temperature of the wall upon which they are mounted. Sometimes this adaptive feature can be turned on or off; for example let's say you don't CARE what the temperature is at 6AM in the house, but THAT is the time you want the boiler on, then you want to disable adaptive feature if you can. Others say, "I want the temperature in the house to be AT 70 degrees at 6AM" in which case some intelligence is used in the adaptive feature.

On my hot air system, I used to have simple Honeywell digital setback thermostats. One of the things they did, as part of the adaptive feature, is they used to call for heat in the middle of the night when you didn't expect it. I had the night setback to 62 degrees, and the morning temp to 72...but the stat must have thought that spread too great. So, while it kept the night time temp to 62, the heat would often come on briefly bumping the temp up to say, 64 or 65, beyond the setpoint...and I think the purpose there was to prevent an extraordinarily long anticipation time before the official 6AM call for heat. It did this during periods of extreme cold or when I had that setback to 62. After a call to Honeywell, their support folks said don't set back more than 5-6 degrees for "optimal" use.

Don't forget the concept of "thermal mass"; that is, you can heat the air in your room(s) to the comfort level you want, say 70 degrees, from 60 degrees, but for the first time it hits that setpoint, the room will not be comfortable because only the air at the stat has reached that temperature. It takes a LOT longer for everything IN the room (including walls, floors, etc.) to absorb the heat; and only when they do will you have a comfortable environment.

The location of the thermostat as well as the location of the heat sources (vents in a hot air system, or radiators in a hot water system) make a HUGE difference. Say you have the thermostat in an upstairs hallway, but everyone sleeps with the bedroom doors closed. Guess what? The heat will NEVER get to the thermostat setpoint! You have it set for 70, and it may get to 75 before someone wakes up in a sweat, opens the bedroom door, and finds the bedroom hot and the hallway cold. Hallway locations for thermostats in living area are a bad idea if doors are closed, doors to rooms that have the radiators or ductwork in them...and yet, in a two story home, the pros will ALWAYS put the stat in the hallway. I had to insist that it be put in my master bedroom just to prevent the scenario (which I experienced once) from happening.

There is also some intelligence and adaptive technologies built into some furnaces and I'd imagine, some boiler controls. One of them is the old school "anticipator" which is a mechanical device. They are generally on the boiler control and used with older mercury style thermostats. If your boiler has an anticpator, and you have a modern digital thermostat, unless either the adaptive feature is disabled on the Tstat, or the anticipator on the boiler control is bypassed you can have these smart features fighting each other.

Best to contact the boiler installer/manufacturer and find out what you have, and how best to install a modern thermostat. Digital stats with energy saving setback features (to turn off and on the heat to different setpoints) are pretty cheap these days. Ones with Wifi or internet control are a bit more costly, and then of course you can break the bank and get a Nest...
 
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joemudd

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Great post that gives at least some credence to my wall cavity suspicions.
I have always argued that the setback saving must be to a large extent negated by needing to reheat the surfaces. I try to just leave it on 71 but the wife dont abide.
 
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