My furnace recycling more often after installing a new thermostat. Is this bad?

itguy

The CNG technician was here to repair my natural gas heating system with hot water radiators (some leaky valves problem). He offered to replaced my 20+ year old Hunter (Set'n Save I) thermostat while he was here. I let him install the new thermostat (Honeywell T1 Pro non-programmable).
Now, I am noticing that the new thermostat is displaying 70 degrees room temperature all the time (I set the thermostat to 70 degrees) and my furnace going on and off more frequently. I used to set my old one to 70 degrees also. I used to see varying room temperature readings 69, 70 and 71 degrees, not 70 all the time and the furnace didn't cycle as often.
Should I reinstall the Hunter back (or buy a similar current model) or should I live with the new thermostat? I don't want to cause any problems with my furnace due to recycling more often.

HVACNUT

epmiller

I have not used that exact thermostat but some units can have very tight regulation and the displayed temperature will not vary more than a degree. What exactly are the installer settings on your tstat? From your post I would conclude 125 - 0 (fahrenheit), 200 - 3 (radiant heat), 205 - 9 (hot water radiant heat), 218 will not be displayed. If the thermostat is not programmed properly it can cycle the boiler too often which would explain the "going on and off more frequently". For example, if it's set for electric heat it will cycle way too often. For a boiler I would like to see no more than four or five cycles per hour. Even then, that's short cycling in my book. There may be other things involved here that we can't tell from your description of the problem so if you don't understand what you are doing call someone who does.

itguy

I was on the phone with Honeywell support. We checked the installer settings. They are all correct. The support guy confirmed that the Honeywell thermostats were designed to keep the room temperature constant to provide the best "comfort". This explains why I am seeing 70 degrees all the time. I checked the room temperature with an accurate thermometer. The variation was less than 1/2 degrees. So, it is obvious to me that the furnace has to go on and off more frequently now. It seems to me a very logical result. With the old Hunter thermostat room temperature had to drop to 69 for furnace to come on and reach to 71 degrees to stop. This 2-3 degree variance makes the furnace go on and off less frequently. Am I wrong? By the way I read this in Hunter's user manual: " Your thermostat set at factory to cycle when the temperature rises 2 degrees above or 1 degrees below the temperature setting". I would love to know which scenario is better if my goal is to keep my furnace longer. 2-3 degrees of temperature variation does not make me "uncomfortable" at all.

LS123

Hello @itguy, I experienced same when I put a digital tstat (talking about that have temp up and temp down button type of Tstat) because some digital Tstats try to be with in 0.5 + or - of what the temp is set. I had put a Tstat like the old clock and you set the temp you like on the top, and it indicates the temp in the room... although this type of Tsats dont have mercury, they are less sensitive to meeting exact temp within 0.5 + or - from what you set it to... best!

HVACNUT

You don't need to strictly adhere to the installer setup. You can make changes until you find the CPH that's comfortable for you. 

itguy

I decided buy a new thermostat. The only feature I care about the thermostat is this: It has to have to have 2-3 degrees temperature variance. Does anyone know about a model like this? My current thermostat Honeywell T1 Plus has only a variance of 0.5 degrees. Honeywell does not make such thing.

Jamie Hall

Honeywell doesn't make such a thing because the job of a thermostat is to maintain a constant temperature. Personally, if I had a thermostat which couldn't do that I'd junk it. However, you may be able to find a commercial control which will do what you want.

EBEBRATT-Ed

Try this one it has CPH settings. @Supply House.com

PRO 1000 Non-Programmable, Heat Only, Horizontal Thermostat Honeywell

itguy

I have a discontinued Robertshaw 9620 programmable upstairs. It allows me to set the variance I want 1, 2, or 3 degrees. Very nice feature!

BrassFinger

I have the PRO 2000 Honeywell and when I first installed it I didn't like the constant on-off cycles. The user's manual doesn't help but the installers manual has the setup instructions for cycles per hour and other things. I think I just set it to "4" from the default "5" CPH and that was enough.

Chris

itguy

Chris,
Very interesting, thanks. If I am reading the manual correctly you can set the "cycles per hour' to 2 through 6. Setting it to "4" gives you 15 minutes cycles instead of 12 minutes cycles at "5" setting. Were you able to notice this 3 minutes small difference?

BrassFinger

itguy said:

Chris,
Very interesting, thanks. If I am reading the manual correctly you can set the "cycles per hour' to 2 through 6. Setting it to "4" gives you 15 minutes cycles instead of 12 minutes cycles at "5" setting. Were you able to notice this 3 minutes small difference?

Most definitely. It doesn't sound like a big difference but at least in my system it was quite noticeable. I will add that my house, approx. 1800 sq.ft. Cape Cod style, 1969 construction but newer windows, doors, etc. in N. Illinois is running a 110K BTU (!!!!) 80% gas furnace. Even with the recent cold blast the furnace runs barely 50% of the time, averaging 12 to 15 minutes on, 12 to 15 minutes off. In milder weather the run time is quite short and with the stock thermostat settings it hardly had a chance to run before it shut off. I've only owned the house for 4 years but the HVAC system is pushing 20, so needless to say it will be downsized drastically when replaced.

itguy

Thanks! I will buy one of this Pro 2000 thermostats. I don't like the ON/OFF pattern of my furnace. Last night I captured the noise pattern in the furnace room to find out how long the furnace is on during a 9hr period (11pm to 8am). My guess by looking at the pattern is about 20%-25% of the time during 9hr period. The only thing that I don't understand is the large number of the "short" periods. There are only 4 long periods and about 30 short periods. This is not what I would have expected to see. Both upstairs and downstairs thermostat temperatures were set to 69 degrees. The outside temperature was 12 degrees (average). Here is pattern: