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Customer Discussions > Home Improvement forum

Is this how heaters are supposed to work?


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Showing 1-25 of 45 posts in this discussion
Initial post: Feb 15, 2012 11:08:49 AM PST
Last edited by the author on Feb 15, 2012 11:14:31 AM PST
JC says:
Pardon me for my extreme ignorance, but was just wondering if this is how house heaters are supposed to work:

(I havent lived in this house very long, but never really used the heater. But now that we have a newborn in the house, we like to run the heater at night since it can get pretty cold!)

- house is not too old (~15 years old)
- gas heater

So what i do is set the temp on the thermostat to 72, for example. And i set the schedule for it to come on at 10PM and run until 7AM. Let's say at 9:59PM the thermostat says the house temp is 67.
At 10PM, the heater will kick on like expected, and run. Warm air is coming out of the vents and the house heats up. Everything is fine until the thermostat reaches 72. Once it reaches 72, the heater turns off (again, as i would expect). But from that point on, the darn thing turns on for a couple minutes, then turns off for a couple minutes, then turns on for a couple minutes, etc. etc.

It is incredibly annoying (and noisy) and sometimes the "stop and go" noises of the heater wake my baby up.

Is this how heaters are supposed to work? Or am i programming something incorrectly? or?

edit* According to the Honeywell website, it says that normally a heater will cycle on/off about 5 times per hour. This sounds about right with what i experience, maybe i experience a little more frequently. So i guess its normal. But if anyone has any other experiences, let me know! thanks

Posted on Feb 15, 2012 12:07:02 PM PST
DCP123 says:
You need a thermostat with an adjustable "span" (some manufacturers use a different name for this, but I forget what it is). Span is essentially the difference between the temperature at which the thermostat turns the furnace on and the temperature at which it turns it off. If your thermostat has a span of 1 degree and you set it for 72, it will try to keep your house between 70.5 and 71.5 and will cycle very often. With a span of 3 degrees, it will heat the house to 73.5 and let it cool to 70.5 before turning on again. You'll get more peace and quiet. Your existing thermostat may have an adjustable span, check the manual. If not, buy a new one that does. They're pretty easy to install.

Bad insulation and a poorly sealed house can also contribute to frequent cycling of the furnace and also to high heating bills, but it doesn't sound like that's your problem.

Posted on Feb 15, 2012 1:10:39 PM PST
JC says:
thank you

i will check when i get home if my thermostat has a span feature. i dont think it does though.

Posted on Feb 15, 2012 1:38:44 PM PST
DCP123 says:
I remembered: The other term for it is "swing." Honeywell doesn't generally, if ever, include an adjustable swing/span setting. Instead, some of their thermostats determine the cycles per hour based on the type of heat you have (high efficiency gas/oil or regular, steam or electric). How exactly that works, I don't know, but if it runs less often, the temperature variation will be higher, so it is effectively controlling the span/swing, but with Honeywell it's not explicit what temperature range you're getting and you may have to lie to your thermostat about what kind of heat you have to get your desired cycle rate/span/swing. I think some Honeywell Thermostats have only two cycle rates (3 and 6 times per hour), but apparently some do 9 times per hour for electric, 6 for standard gas/oil, 3 for high efficiency gas/oil or hot water and 1 for gravity or steam heat.

I imagine Honeywell uses some sort of calculation based on how fast your house cools and how long it takes to heat and the thermostat uses that information to determine when to turn on and off to get about the requested cycle rate. I'm sure it's terribly sophisticated, but I was very surprised and disappointed to discover that the programmable digital thermostat I had bought couldn't control something that was adjustable on even the ancient mercury thermostat I was replacing.
Unless money is short or you think you'll freeze or wilt if temperatures vary by more than a degree, throw away the Honeywell and buy a Hunter or a Lux, both of which usually, if not always, have a setting for span/swing.

If money is tight, figure out how to convince your thermostat that you have a high efficiency furnace or steam heat.

If you like a very narrow temperature range, you're not like JC or my family, so this post isn't for you.

Posted on Feb 15, 2012 1:57:45 PM PST
Last edited by the author on Feb 15, 2012 2:00:43 PM PST
JC says:
thanks again!
Through the power of google image search, i found the model number of my thermostat at home --- Honeywell CT3300.

You are exactly right - Honeywell doesnt let you control swing/span. There are switches behind my thermostat (according to the manual) that let the thermostat know what kind of system you have. The manual doesnt say how many cycles each option correlates to, but i bet you are right. I called my wife and asked her to time the cycle for me (lol) ... she says from the start of one to the start of the other it was ~11 minutes, so 6 cycles per hour like you said. Maybe i will try and set the switches to something else to get me to hopefully 3 cycles per hour. Like you said i dont care for a narrow temp range, 69-74 is fine for baby

thanks!
edit* i wouldnt be hurting my heater in any way by setting lower cycles, would i? the only downside is that i would have more temperature variation?

Posted on Feb 15, 2012 2:41:02 PM PST
DCP123 says:
I'm not an HVAC expert, but I think some systems are damaged by frequent cycling. I've never heard of one being damaged by infrequent cycling. I guess in theory one could overheat from running too long, but they have thermal limit switches to protect them from that and the run times when you're heating should be shorter than they are at the time when your program first increases the temperature setting. Also, I've read on another forum that Honeywell sometimes tell people who aren't thrilled with the frequent cycling to go ahead and change their cycle setting. "You can go ahead and reset the cycle rate but it is possible that you will not have very good temperature control."

If there's something I'm missing, I'm sure an HVAC pro or a Honeywell lover will point it out.

BTW, Has anybody ever heard of the theory that part of the reason people are so much heavier than they used to be is that we no longer expend much energy maintaining our body temperature? I've seen no real proof, but I find the idea believable. Our ancestors did not evolve in a world kept at a constant 71 degrees.

Posted on Feb 16, 2012 7:37:29 AM PST
oldflyer says:
One cause for frequent cycling is a draft hitting the thermostat, especially in the heating season. Check to see if the hole in the wall where the thermostat wires come through is plugged with insulation or other material. I can guarantee that most are not. In many installations, if not almost all, you will find air flowing through the hole. This can drastically affect the operation of the thermostat in both the heating and and cooling modes.

In reply to an earlier post on Feb 16, 2012 12:49:25 PM PST
Jimbo says:
Some furnaces have a sensor that will turn the fan on several times (even after the flame goes out) just to cool the heating chamber. You may have a similar set-up. Your furnace should not make enough noise to wake people up, you may want to have that looked at.

Posted on Feb 16, 2012 1:16:22 PM PST
Wayne says:
AC systems can be damaged by frequent cycling, but good thermostats have built in delays for that. It should not hurt for heat though, but is not something you want.

Based on your description, you don't have a top of the line thermostat. Those will keep track of how long it takes to heat your house based on starting temperature, and over time will figure out when to turn on in order for your house to be at the desired temperature at the desired start time.

Some thermostats let you adjust the swing and some do not. I think many Lux models do, but you'd have to check on a unit by unit basis. Honeywell units may not, but they are pretty good at figuring out what to do. (At least the top of the line ones are.)

Another problem that causes frequent cycling is the relative placement of the thermostat with respect to the air return and the heating ducts. If the thermostat is getting warm air more directly than most of the house, it will hit the desired temperature when the average temperature is lower. As the air mixes within the house, the temperature will drop, the system will go back on, and shut off prematurely again. Likewise, the return can suck hot air by the thermostat causing the same issue.

Sometimes this can be fixed with a different thermostat. Sometimes it can be fixed by not leaving a door closed, or leaving a door closed. And sometimes it's best to move or shield the thermostat. Sometimes something as simple as the pictures on the same wall can affect things.

Posted on Feb 17, 2012 8:06:37 PM PST
One thing that you could also look at is the placement of your thermostat. Your thermostat should be place on a inside wall, it should also not be place in direct sunlight or over a supply duct vent, near a door or window. Also you might want to make sure you have duro dyne seperating your furnace from your duct work. If there is no give between the furance and the duct work youll get more noise then usual. Another thing you could do is to leave your fan constantly on. The fan that circulates the air through the house is actually some what inexpensive to run continuously.

Posted on Feb 24, 2012 12:52:22 PM PST
Last edited by the author on Feb 24, 2012 12:57:56 PM PST
In engineering control devices, this is called hysteresis. Read up at Wiki; the section mentioning control systems talks spefically about thermostats.
http://en.wikipedia.org/wiki/Hysteresis#Hysteresis_in_engineering
In theory, if you set to 72°F, then when it gets to 71°F it comes on, then off at 72°F again. If you can set a range with your thermostat, like 70-74, it will keep the house 72°F on average, but come on less frequently. I believe my thermostat automatically has a little built-in span, since it comes on about 1° under the set point, and off at 1° above..

Posted on Feb 24, 2012 4:51:00 PM PST
Last edited by the author on Feb 24, 2012 5:19:39 PM PST
Stix says:
What happens in the other hours of the day? Some older furnaces do not like newer stats. Your anticipator could need to be set to have it go longer cycles. There is in the advanced setting of most newer stats that lets you set cycles per hour. So you could have a few things going on.

Easiest way to check is use a old stat and see how it acts. If it acts the same it could be the blower just cooling down the heat exchangers as older furnaces are not time cycled; they are working of a fan switch that has a piece of metal that bends and reacts to heat to turn on and off the blower.

Next check and see in the manual if it has a cycles per hour setting. If so set it to 4. Next you may have leaky walls. Feel for a draft behind the stat in the hole where the wire comes thru. Any draft, silicone the whole as insulation will not stop wind.

I would need more info to help you further. What type of stat? Model number of furnace? How long does it cycle like that for ? Indefinitely? Furnace could be to large for the house and cannot get a long cycle.

Also check for dirty filter!

For that stat make sure switch is in Gas not electric and unscrew A 1 turn.

In reply to an earlier post on Feb 24, 2012 4:53:40 PM PST
Last edited by the author on Feb 24, 2012 4:59:56 PM PST
Stix says:
That is not how it works. In a auto switchover stat you can set it to heat at 70 and cool at 74. If you set a dead band of 4 degrees on a heat only you will be most uncomfortable. You want the furnace to come on at 1 below the set point and cycle off at the set temperature. If you have to set otherwise your furnace/duct system is installed wrong or is to large for the house.

Posted on Feb 24, 2012 6:39:47 PM PST
My advice: have the furnace checked by an HVAC professional. We had our furnace doing the same thing, cycling on and off every 2 minutes. It turned out that a sensor in the furnace was malfunctioning ... apparently the gas starts flowing, the burners start up, but then don't ignite the gas fast enough, and the sensor automatically shuts off the gas as a SAFETY feature. End result, we had symptoms exactly like you described in the original post. The technician replaced a part in the igniter (I think) and the problem disappeared!

So: have it checked. The constant cycling you describe could be the safety features kicking in for some reason.

Luis Rodrigues

In reply to an earlier post on Feb 24, 2012 6:44:56 PM PST
Last edited by the author on Feb 24, 2012 6:45:30 PM PST
Stix says:
Your talking about the flame sensor. Flame sensors if they do not sense the flame they will lock out after 3 tries then some auto try again in a set amount of time. It would not continue to do so. If it was the ignitor the flame would not start and he would not have any heat. You do not replace flame sensors you clean them. They very rarely go bad. Companies just replace them to charge the customer more money.

Posted on Feb 24, 2012 9:02:48 PM PST
DCP123 says:
Joseph Miller,

What Motorius described is exactly how span/hysteresis/swing works. They are all words for what you're calling a "dead band." They describe the difference between the temperature at which the heat turns on and the temperature at which it turns off (or the temperatures at which the A/C turns on and off). The difference between your heat setting and your cooling setting is an entirely different issue.

If you're setting the a/c to come on only 4 or 6 degrees higher than the temperature at which your heat comes on, you're just doing it wrong. Humans did not evolve in a world where the highest temperature was only a few degrees higher than the coolest temperature. If you're convinced that 75 is too hot to survive and 69 is too cold for life to be worth living, you need to spend more time outdoors. You're also wasting an ungodly amount of energy to avoid the horror of having your body exert any effort to maintain it's temperature.

If you're severely ill, rail-thin and having trouble maintaining your weight, maybe avoiding any exertion is a good idea. Otherwise, maybe you should try living with a more normal, variable, temperature range. I find it pretty comfortable, but I do a lot of crazy things like wearing less clothes in the summer than the winter. Maybe that makes me a hippie environmentalist.

I'm sorry if I'm having trouble discussing your idea of what's comfortable as a valid opinion without sounding sarcastic, but I just find it hard to believe that anybody but a furnace salesman would really find it "most uncomfortable" to live with a furnace that heated their house to a broiling 74 before it switched off and still let it chill to a freezing cold 70 before it came on again.

In reply to an earlier post on Feb 24, 2012 9:07:03 PM PST
DCP123 says:
BTW, Motorious, Thanks for using the word hysteresis. That's what I originally searched for when I couldn't figure out how to set the span/swing on my Honeywell thermostat. When I found the thermostat makers calling it span and swing, I thought maybe I was confudes about what hysteresis means and didn't bother to check. Good to hear that I was on the right track.

In reply to an earlier post on Feb 24, 2012 9:21:00 PM PST
Last edited by the author on Feb 24, 2012 9:30:13 PM PST
Stix says:
Your post on this right here tells me you know very little on the subject. Your post is nonsense. I was just generalizing for comparison. You only want a 1 degree temp drop and then shut off at desired temp. Where did I say any given temperature was correct temp for everyone? If you have to change it to any other setting than a .5 to 1 degree drop to make furnace come on and then shut off at desired temp then something is wrong. If you have to overshoot desired temperature to make things comfortable or to make it work there is something wrong with your duct and or equipment.

A swing of four degrees is ludicrous! A salesman I am not. Why the heck would you ever want to heat a house to 74 then let it fall to 70 before coming on again??? You want to maintain the desired temperature all the time.

Posted on Feb 24, 2012 11:36:37 PM PST
DCP123 says:
Joseph,

I appreciate that you have knowledge of HVAC systems and want to be helpful by sharing it and I really do apologize for the sarcasm of my first response to you, which was brought on by your mention of the possibility of setting your cooling temperature only 4 degrees higher than the heating temperature and by your claim that variation in temperature of more than a few degrees would be "most uncomfortable". I found both of those ideas pretty absurd.

I gather that you probably don't really recommend setting heating and cooling temperatures that close and perhaps you were just exaggerating a bit about the whole "most uncomfortable" thing. So, I'll take some of the blame for the tone of your latest response. And, to be fair, your latest post is right about one thing: I wouldn't particularly choose to have a swing/span of 4 degrees. I see no particular advantage in that and only discussed it in response to your exaggerated claim that a swing that big would be "most uncomfortable," which isn't the case for me and shouldn't be true for anyone in remotely decent health. I'd probably choose a swing of about 2 degrees as a good trade-off between maintaining a fairly constant temperature and not listening to the furnace turn on and off all bloody day.

However, you are dead wrong when you say "you only want a 1 degree temp drop." That's apparently what you want, but it's not what I want and it's pretty clearly not what the original poster wanted. He was annoyed by the frequent cycling (about 5x an hour) of his furnace with a thermostat set up just the way you like and said that he doesn't care for a narrow temperature range and that 69-74 degrees is fine for him.

And, no, neither I nor the original poster "want to maintain the [one exact] desired temperature all the time"

Your welcome to want that, but I'd hope you can consider the possibility that not everyone on the planet may agree with you.

I am a little puzzled about what aspect of my post brought you to the realization that I know very little about the subject? You haven't said a word to contradict anything I've said about how furnaces and thermostats work. All you've done is denied the possibility that the original poster and I may not want to keep ourhomes at an exactly constant temperature.

Oh, yeah. You're also right on the money with your comments about flame sensors. But you really should ease off on your belief that everyone must share your desire to keep their house at one constant temperature all winter. Some of us prefer to have the furnace off until the temperature leaves our comfort zone, which just isn't as narrow as yours.

Peace

In reply to an earlier post on Feb 25, 2012 5:44:17 AM PST
Last edited by the author on Feb 25, 2012 5:46:03 AM PST
Stix says:
I am not gonna argue the point with you anymore. Systems are designed today for comfort. Not for one persons but for everyone. A furnace that is installed correctly will not go on and off constantly with a small temperature swing. They will run run longer cycles and stay off for longer periods after shut down. You do not need to have a 4 degree swing to have the furnace not cycle on and off for extended periods.


If you have that problem then you have other problems.

1. Furnace is to large for the house. 90% of houses have furnaces way to large for the home. This causes excessive cycling and they can be loud.
2. Your house leaks like crazy and infiltration is causing the furnace to cycle way to often.
3. Filter dirty and or blower speed to high.
4. Bad stat or one that does not work correctly for that particular furnace. Not all furnaces like all digital stats.
5. Stat not set up correctly.
6. Bad duct design and or broken leaky ducts.
7. Get a humidifier they let you keep the temperature at a lower setting and still feel comfortable.

I could go on and on. When we go to a job we look at the whole job. Someone tells us there bills are to high and or the furnace cycles to much that is where we start. Can I diagnose the problem by typing here? No it is not easy. I need to see a job to properly diagnose it.

We know how to make a building and or a house work with existing equipment until it is time to replace it with the correct size.

More money is thrown wastefully up peoples chimneys instead of staying in their pocket just do to incorrect sizing. Which leads to "uncomfortable" swings and rapid on off cycles. Furnaces today are meant to run really long cycles. That is why we do not even install single stage furnaces anymore. The price difference is nill and the comfort and quiet of them is fantastic.

I could type all day but I am better at doing my job than typing about it. I am not good with words lol.

Posted on Feb 25, 2012 8:23:03 AM PST
DCP123 says:
You say you're not going to argue the point anymore, but then you do - badly.

A Honeywell thermostat set up for use with a non-condensing gas forced-air furnace is designed to cycle approximately 6 times per hour. It makes a calculation based on how quickly the house heats and cools and determines how far below and above the set temperature it turns on and off to get it to cycle about 6 times an hour.

You think that's great. JC doesn't and it was him I was trying to help. Neither JC nor I have a furnace that cycles every couple minutes. He said that in his first post, but he was exaggerating and clarified in his second or third post that it was actually about 6 times per hour.

I've tried being nice, but your suggerstion that the decision Honewell has made for its customers (to cycle gas furnaces 6 times an hour) rather than allow them to choose their own swing setting is "designed for comfort. Not for one person, but for everyone" is just kind of dumb. JC's thermostat was operating exactly as designed - cycling 6 times an hour and maintaining a narrow swing - and, whether you lkike it or not, his family wasn't happy with that. Mine was doing the same and it kind of bugs me too, but not as much as JC. So, no, that setrting does not ensure comfort for everyone and not everyone thinks a little temperature variation is a pronlem. No matter what you learned in HVAC school, not everyone wants to spend their entire life at an over-climat controlled 72 degrees. If you can't accept that fact and respond to what real people want in their own homes, you should not do residential HVAC work.

If I ever have an HVAC guy come to my help ignore my preferences and try to tell me what I want, I can guarantee you that guy will get fired in a heartbeat.

And please stop harping about a 4-degree swing. I only mentioned it because you did. In any house with the door closed, you should be able to maintain a reasonable cycle rate with a smaller swing than that. If you can't, you need to invest in insulation.

In reply to an earlier post on Feb 25, 2012 9:15:13 AM PST
Stix says:
I would let you waste money anyway you want; then when I left I would tell people at trade shows and shop talk how silly some customers are. I was being nice and you are a condescending home owner who knows very little about what your talking about. You post tells everyone how little you actually know. I need not point it out anymore.

Have a great day :)

In reply to an earlier post on Feb 25, 2012 11:17:32 AM PST
Jasoturner says:
Actually, the temperature will always overshoot when reaching setpoint temperature, and this acts like the deadband to which you refer. You don't need anything as fancy as a deadband T-stat for a normal heating system to cycle reasonably. This sounds like it may be a boiler control problem.

In reply to an earlier post on Feb 25, 2012 11:22:11 AM PST
Last edited by the author on Feb 25, 2012 11:25:35 AM PST
Stix says:
Thank you. Thats what I been saying!! Only disagree on the over shooting for sake of you wont see it on stat always. Most we set up they work with a 1 degree below and a .5 overshoot but it does not show up on temp reading on stat.

Posted on Feb 25, 2012 12:21:08 PM PST
DCP123 says:
J. Turner,

Thanks for your input, but if you read the first 5 or so posts, I think this is the situation.

JC's furnace is a gas furnace that was cycling about 6 times per hour. He has a Honeywell thermostat. If you set up his Honeywell thermostat for use with a non-condensing, forced-air gas furnace, by design, it is intended to cycle about that often. He doesn't like that, so I gave him some information about the settings that control cycle frequency on a Honeywell thermostat and he looked up some similar information on his own that was specific to his thermostat. I believe his problem is solved.

Mr. Miller has been so kind as to inform us all that he does not believe that any homeowner could ever possibly prefer to have his furnace run less frequently for longer cycles even if that causes temperature to vary more than a few degrees. However, JC was very specific that that is his preference.
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