Normal amount of heat cycling


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Old 01-04-10, 07:17 PM
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Normal amount of heat cycling

I apologize for all the questions, but does anyone know what is normal in terms of how much a furnace should be turning on and off?

Ours seems to be coming on for about 6 minutes, 4 times / hour bringing the total usage / hour to 24 minutes.

The temp here now is 25 degrees and we keep the temp in the house at 66. Any ideas? Just want to make sure I know what's normal here.

Thanks.
 
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Old 01-05-10, 04:32 PM
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There are various causes for this.

If your stat is located within the draft of the heat, it can cause short cycles.

If a digital thermostat's swing temp is too short, that can cause it.

If the furnace is oversized, that can cause it.

High limiting could cause it. Be sure to check your filter. However, another symptom might be that the house also does not ever reach set temperature. And this may become more obvious the colder it were to get outside.

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Not a cause: If the house were getting abnormally cold too fast (leaky house), that could cause the furnace to shut off, but then come right back on again - and to a worse degree the colder and/or windier it was outside. But, the furnace would also run for longer duration before shutting off(which is not what is happening in your case).
 
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Old 01-06-10, 04:22 PM
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Thanks for the reply. The furnace definitely seems to be on and off at a relatively normal schedule and the cycles don't seem to be too frequent (someone let me know if I'm wrong).

The real question is, is the amount that the furnace is on (40% of the time) appropriate for the temperature of the house vs. the outside temperature. In other words, am I using way more gas than I should be (due to windows, drafts, insulation, etc.) or am I within a normal range?

Thanks again.
 
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Old 01-06-10, 05:24 PM
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Ya, but your issue was that it is only on for like 6 minutes. By any standard, that duration is too short, without there being some abnormal acting force on the thermostat, that is making the furnace shut off sooner than one would like. I could maybe see such a time if the outside temp were 60 and you had the house temp set to say 70.

As far as an issue of how long it runs for out of each hour, it depends on issues that we do not know about, including how well the place is insulated and sealed. But I guess now, that is what you yourself want to find out - if your house is adequately sealed and insulated.

If you are on natural gas, you can check your meter in 24 hour time periods, and see how many therms are being used. Then compare to say a past gas bill that has about 25 degrees for the avg. monthly temperature. Then take the listed therms on that bill and divide it by the number of days you were billed for, and compare to your 24 hour gas meter read.

But that will only give you an indicaion if your house/furnace function still compares to how it has been in the past. You might also want to see if any friends, relatives or neighbors live in same size house with similar layout, and either ask them what their last months bill was, and compare to what yours was, or take some daily gas meter reads at their place, along with yours, and compare. But you will need to ask them what temp they keep their stat at, and or how they program it, compared to yours. If they do not hold temp to about what you do for yours, the test comparison would be useless.

And perhaps the web can provide some links as to what a reasonable amount of (gas)energy is required to heat a size/type home you have, to a certain temperature, during given outside temps. Although I'm not sure how accurate and useful such info would be, as there are so many factors that even include sun, wind, and trees on the property, and much more.
 
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Old 01-06-10, 07:22 PM
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Thanks for the detailed reply. After looking around some more, I believe that the reason the unit is cycling at that rate is due to the new thermostat, a Honeywell 6400D. These apparently keep the temperature exactly at the set point thus causing the unit to cycle for less time and more often.

Does anyone have any thoughts on the efficiency of this method vs having a unit that swings more? I'd consider swapping the thermostat out if it is going to be inefficient.

Thanks.
 
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Old 01-06-10, 08:04 PM
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Most programmable thermostats have a way to set the number of cycles per hour. I'd look through the instruction manual carefully for that feature, which probably also includes suggestions on an appropriate number of cycles for different kinds of heating equipment.
 
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Old 01-09-10, 08:48 PM
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Go to page 13 of the install manual.

Then go to setting "Cycle rates" #5. change that to 3. Will give you a longer run time.
 
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Old 01-11-10, 07:13 PM
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Thanks for the info Jay.

Is it better (more efficient) to run the system on longer cycles or does it not matter?
 
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Old 01-11-10, 07:45 PM
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Yes, it's more efficient to let the furnace run longer.. It takes about 10 min for the furnace to reach it's efficient rating.

Perfect example, in your car.. Do you get better mileage when you stop and go in town or on the freeway with a steady speed?
 
 

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