Thermostat Temperature Swings December 07, 2019, 07:20:43 pm Hi all! I'm enjoying perusing all of the topics but I think this might be my first post. I'm wondering if my thermostat is working correctly. When I am camping in the cold weather,I set the thermostat to a certain temperature, let's say 62. What happens then is that the camper gets VERY cold, then the heater kicks on, the camper gets pretty hot, the tstat kicks off, and the whole cycle starts again. I'm hoping that this might not be the way that it's supposed to work, and that the camper is meant to maintain a more steady temperature,.Thoughts? TIA
Re: Is my thermostat working correctly? Reply #1 – December 07, 2019, 11:03:15 pm Quote from: frayednot - December 07, 2019, 07:20:43 pmHi all! I'm enjoying perusing all of the topics but I think this might be my first post. I'm wondering if my thermostat is working correctly. When I am camping in the cold weather,I set the thermostat to a certain temperature, let's say 62. What happens then is that the camper gets VERY cold, then the heater kicks on, the camper gets pretty hot, the tstat kicks off, and the whole cycle starts again. I'm hoping that this might not be the way that it's supposed to work, and that the camper is meant to maintain a more steady temperature,.Thoughts? TIAHello, Frayed. Welcome to LDOG. We hope you find all the answers to your questions here. To help us do that, please share the year and floor plan of your LD with us. I will also add it to your visible profile.Chris
Re: Is my thermostat working correctly? Reply #2 – December 07, 2019, 11:07:06 pm Quote from: frayednot - December 07, 2019, 07:20:43 pmHi all! I'm enjoying perusing all of the topics but I think this might be my first post. I'm wondering if my thermostat is working correctly. When I am camping in the cold weather,I set the thermostat to a certain temperature, let's say 62. What happens then is that the camper gets VERY cold, then the heater kicks on, the camper gets pretty hot, the tstat kicks off, and the whole cycle starts again. I'm hoping that this might not be the way that it's supposed to work, and that the camper is meant to maintain a more steady temperature,.Thoughts? TIAIt sounds like the temperature swing from the set point is out of whack. Perhaps one of our tech wizards will be able to help you with that. Please tell us year and floor plan of your LD and if it is the original thermostat.Chris
Re: Is my thermostat working correctly? Reply #3 – December 07, 2019, 11:26:42 pm Thanks, Chris. It’s a 2003 midbath. 26.5. I’m not sure if it’s the original thermostat. I can supply a picture if helpful.
Re: Is my thermostat working correctly? Reply #4 – December 08, 2019, 12:42:11 am Hi frayedknot,I have never experienced this issue but your post got me thinking about hysteresis which in the context of furnace operation would be the point at which the thermostat senses when to turn the furnace on and when to turn it off. Some searching on this forum brought up a part of the thermostat to check out. It's called an "anticipator". Apparently the thermostat has a heated element that anticipates when to turn of the furnace so overheating doesn't happen. Yours may be out of whack or in need of adjusting. I don't know enough to give you good direction but I would search on the term anticipator in this forum for details. 1 Likes
Re: Is my thermostat working correctly? Reply #5 – December 08, 2019, 03:32:12 am Hi Tia,A thermometer at your thermostat would tell you exactly what the temperature is at the thermostat when it turns the furnace on/off and give you more clues.We learned with our new air conditioner that it:1) had a bad design that had the outflow right next to the thermostat which meant it cycled off way before the entire RV was cooled down (we made mods to fix that issue and have no problems now), and 2) that it worked a lot better with the fan up higher (we do level 2 out of 3) as it distributes the air better throughout the coach [most stick and brick HVAC installers say to run the fan all the time to prevent the hot/cold spots].Like others we have added insulation also which makes a big difference People often make coverings they can put on and off as desired - for windows using Reflectix insulation. And a blanket/sleeping bag between the cab (which has no insulation) and the rest of the coach.Keep us updated on what you figure out.Jane
Re: Is my thermostat working correctly? Reply #6 – December 08, 2019, 08:36:39 am Part of what you are experiencing could be the norm. The first part. If it is really cold out the air will be cold and feel cold at first and it does run for a little bit before it ignites, and then it takes a few to start pumping out the warm air. Now add to that a greater differential (when it turns on vs off) which is usually a few degrees. For example when it is set to 68 it may come on at 67 and go off at 69. Putting a digital thermometer near the thermostat could help tell you that what the differential is. Many thermostats have a way of adjusting that.If you are lacking insulation or have a lot of drafts that won't help. Also, forced hot air heat takes longer to heat up the objects in a home. This leads to them cycling on and off more in the beginning. Once they get everything heated up they will cycle a bit less. 1 Likes
Re: Is my thermostat working correctly? Reply #7 – December 08, 2019, 09:12:02 am "I'm hoping that this might not be the way that it's supposed to work, and that the camper is meant to maintain a more steady temperature. Thoughts?"Thermostats must have a differential (offset, hysteresis, deadband) to operate. This is the difference between the on and off temperatures of the heating system (or cooling for that matter). Two degrees has been considered the standard for comfort conditioning thermostats for a long time. The heat anticipator provides a small amount of heat to the thermostat to influence it slightly, (warming it) to cause the burners to be turned off a bit before the temperature setpoint of the thermostat has been reached. This prevents 'overshooting' of the setpoint. If the temperature is swinging more than two or three degrees, the thermostat is most likely bad, assuming no external influence that may be affecting the thermostat's operation.Bill 1 Likes
Re: Is my thermostat working correctly? Reply #8 – December 08, 2019, 11:04:06 am Tia,If you do a search of the archives, you will find some posts about installing programmable thermostats. One of the old posts was mine; it mentions installing a White-Rodgers thermostat in our 2003 mid-bath that reduced those temperature swings you are dealing with.It was an easy install and fairly inexpensive. The original thermostat was a mechanical one and led to wild temperature swings. I think it had something to do with the "heat anticipator" of the mechanical thermostat. Good luck,Steve K 2 Likes
Re: Thermostat Temperature Swings Reply #9 – December 08, 2019, 12:49:29 pm Hi Frayed. No matter which thermostat you have, it needs to have good airflow through it. I take the cover off of mine, once in a while, to clean the dust built up inside. That dust can insulate the sensor so it doesn't see the cold air as soon, then delay it shutting off soon enough, again because it doesn't see that it is getting too warm. Also make sure that there aren't objects nearby that would radiate heat or cold to the thermostat's location, or block air flow. With little or no air movement inside, my TK has greatly variable stratified temperatures inside. I've measured temps at the floor of 55 degrees, 70 degrees at waist high and 75 degrees at the ceiling. The small air flow from the heater does mix up the air, but once that stratified cold floor, warm ceiling pattern gets started it takes a bit to get everything evened out. Outdoor temperatures, big windows and lack of heater capability accentuate this fluctuation so it is more noticeable in the RV. As Steve (and Jill) mentioned, air out of the space heater has to establish proper airflow before it can light the pilot and burner, so there is some delay while it blows cold air. When the thermostat hits setpoint, the burner will shut off, but the fan will run for a bit to cool off the heater before the fan shuts off. That is a normal cycle. RonB 2 Likes
Re: Thermostat Temperature Swings Reply #10 – December 08, 2019, 08:37:33 pm Back to the heat anticipator, if it is working properly it should take some of the temperature swing out. If you take the cover off the tstat you will see it inside the thermostat. It is a little coiled wire that heats up while the tstat is calling. If you get very wide temperature swings then you can move the arm to either longer or shorter cycles, I think most are marked longer. Move the arm small amounts and let the furnace cycle some and see if it still over shoots the set point. Anticipators do fail and your only option is to replace the thermostat.Jon 1 Likes
Re: Thermostat Temperature Swings Reply #11 – December 09, 2019, 07:38:43 pm Quote from: JonS - December 08, 2019, 08:37:33 pm Anticipators do fail and your only option is to replace the thermostat. I spent a month one winter trying to tune the anticipator, cleaning the thermostat, adjusting louvers, and we still got too hot before it stopped, and too cold before it started. I replaced it with a digital thermostat from Walmart, set the control band to 1 degree, and it worked well in that motorhome and our current one (the mechanical one went back in the old motorhome when we sold it). Digital thermostats have a narrower on/off band, about half or less than the old mechanical style, and that reduces the temperature swings, improving comfort significantly for a cost of only $25. No anticipator to fool with, either. 3 Likes
Re: Thermostat Temperature Swings Reply #12 – December 10, 2019, 01:39:05 am Once you get the thermostat situation figured out, consider adding a catalytic heater as a steady, quiet and efficient way of maintaining an even heat in cold weather.Larry 1 Likes
Re: Thermostat Temperature Swings Reply #13 – December 10, 2019, 10:03:46 am Freyednot,I am sure I missed it in the posts, the old mechanical thermostats have two or three contact points that can get dirty and cause delayed starts until you move them. Take off the cover.1. Is the obvious one at the end of the large flat bi-metal coil, the primary temperature control. clean it; temp all the way down , stick a piece of paper between the contacts, Temp all the way up, pull out the paper, reset the temperature.2. Is the anticipator . It is a thin partial circle of wire with a little lever pushing on it, usually on the plastic base plate. The wire sometimes sinks into the plastic in the high summer heat and looses connection with the lever. Move it very slightly and it will regain contact.3. Is the on off switch. Many years of non use results in corrosion of this nondescript switch in the thermostat. If you can find it clean it by the same paper method. Off, paper in, on, pull the paper out. and at his time of year , turn it on . hopefully after 20 seconds delay the fan will start the purge cycle (20 seconds), then heat.
Re: Thermostat Temperature Swings Reply #14 – December 10, 2019, 12:25:56 pm The heat anticipator, as I said above, provides a small (subtle) amount of influence to prevent overshooting the thermostat setpoint. The range of temperature swing the OP described is far greater than the anticipator is intended to manage. Not impossible, but unlikely in my experience. Regarding a digital thermostat with a 1 degree deadband: keeping the space temperature within one degree of setpoint would cause the furnace to have shorter run times, more on/off cycles, and, depending on outdoor temperature, more gas used to warm the furnace heat exchanger up again and again. All of which would be more annoying (to me) than another degree of temperature swing which is unnoticeable, before the furnace comes back on. In fact, having the ability to adjust the deadband to a higher value, three degrees rather than two for example, could be better for the system. With a greater differential, when the furnace comes on, it runs longer to warm up the space, fewer on/off cycles, less demanding of the heating system components, and more efficient use of the gas. As always, YMMV.Bill
Re: Thermostat Temperature Swings Reply #15 – December 10, 2019, 02:57:31 pm Quote from: krmugn - December 10, 2019, 12:25:56 pmThe heat anticipator, as I said above, provides a small (subtle) amount of influence to prevent overshooting the thermostat setpoint. The range of temperature swing the OP described is far greater than the anticipator is intended to manage. Not impossible, but unlikely in my experience. Regarding a digital thermostat with a 1 degree deadband: keeping the space temperature within one degree of setpoint would cause the furnace to have shorter run times, more on/off cycles, and, depending on outdoor temperature, more gas used to warm the furnace heat exchanger up again and again.Most digital thermostats have an adjustable temperature differential, usually with a range of 1- 4 degrees, set it where it cycles at a point where you are happy with it. Whatever you do, the furnace will still produce noticeable hot and cold spells, as it cycles.Because of this, many use catalytic and electric heaters as their primary heat source, using the furnace only when the rig is very cold to bring it up to the desired temp and then letting the adjustable output of a catalytic or electric heater maintain the interior temperature.Ideally, you want to run the furnace as short a time as possible due to its inefficient consumption of propane, huge use of battery power and the lack of ability to run at lower outputs of heat.Larry 1 Likes
Re: Thermostat Temperature Swings Reply #16 – December 10, 2019, 07:32:44 pm Sorry, but what you described is pretty much how a thermostat works. It just feels worse in a camper because its not well insulated and you feel the temp changes.For constant heat, get yourself an electric space heater. Turn it on a LOW mode setting, not high. Then dial the thermostat on this heater all the way up. It will run constantly. The electric draw is about the same as a hair dryer if used in low settings. It will not make the camper feel hot. You will not freeze either. Set the furnace to run in the 60s or whatever you feel comfortable at. We have used 65 overnight. This is just a a simple method that has worked for us a few nights in the 30s and 20s ... Space heater runs all night in a safe place. Furnace runs as needed. Take all the precautions you normally would with one of these heaters.
Re: Thermostat Temperature Swings Reply #17 – December 11, 2019, 12:03:22 am Quote from: krmugn - December 10, 2019, 12:25:56 pmRegarding a digital thermostat with a 1 degree deadband: keeping the space temperature within one degree of setpoint would cause the furnace to have shorter run times, more on/off cycles, and, depending on outdoor temperature, more gas used to warm the furnace heat exchanger up again and again. All of which would be more annoying (to me) than another degree of temperature swing which is unnoticeable, before the furnace comes back on. In fact, having the ability to adjust the deadband to a higher value, three degrees rather than two for example, could be better for the system. With a greater differential, when the furnace comes on, it runs longer to warm up the space, fewer on/off cycles, less demanding of the heating system components, and more efficient use of the gas. As always, YMMV.The furnace will run more often with a narrower deadband, but for a shorter time. The heat exchanger will not cool off as much between cycles (because they are shorter), so there is no extra propane to warm it up. The fan and burner run just as many hours total, regardless of the deadband, so the only extra wear, if any, will be on the fan relay. The original poster was noticing the wide deadband (he was getting cold, then hot) so he should be making the deadband narrower, not wider.
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