Replies

1. 
   BobChapman | Feb 06, 2006 07:28am | #1

   I should have added two more things to my description:

    

   1.  When the thermostat and furnace are bringing the house up to temerature at the start of the day, the furnace runs full-time, just as you would expect.

    

   2. The behavior that I have reported above, and which baffles me, is when the house temperature is at the desired temperature (actual temp = set-point on the thermostat).  And as it happened today, the outside temperature was relatively high, in the mid-fifties, so that there was very little heat loss going on.

    

   Bob Chapman
2. 
   cvjxn | Feb 06, 2006 07:54am | #2

   this could turn out to be a wild set of comments as there is wildly diverse opinions about why there should be the cph settings in the thermostat...... but here are the basics you need to start with so you can ultimately make your own decisions....

   Cycles Per Hour this is the electronic version of the old "heat anticipator" adjustible resistor (potentiometer coil for those who took physics long enough ago) in "all " "mechanical" thermostats. basic intent originally was to apply a little heater under the bimetal strip so it would warm up just a bit faster than the room air coming from the "furnace" -- thus anticipating the need to turn of the furnace and let the coast down of the system finish the actual heating -- thur preventing "overshoot" in the room when the thermostat doesn'r catch up with reality quite fast enough........

   now --- with the electronic thermostats ---- that approach doesn't work --- so the concept of forcing or limiting the number of cycles per hour the furnace is allowed or encouraged to use got started..... it sort of works in some cases of forced air systems and in some cases of hot water systems........ but two stage furnaces and boilers and using outside air temp is much better -----

   so --- bottom line for your case is to get into the program of that very good thermostat and set the cph to 1 and than let the rest of the system do its job and let the thermostat do the things its good at...

   these "new fangled" things really are great --- but all this sophistication only works if we know enough to control it......

   cvjxn

1. 
   BobChapman | Feb 06, 2006 03:18pm | #3

   cvjxn-

   Thanks for your very informative post.  I shall try adjusting cph, and I imagine that it will stop the "cycling" that I'm seeing.

   Bob

1. 
   seb | Feb 06, 2006 07:43pm | #4

   I have one also, it is on a gfa furnace...It recycles to fast imho.
   The original one would over run the setting a couple degrees, and not start till under a couple degrees,which is, I think the most efficient.
   I finally had to move the t stat to a diferent place, and that helped a bit....Still not like the old one,Post how yours comes out, I would be very interested....Tnx..
   Bud

1. 
   Norman | Feb 06, 2006 09:18pm | #5

   I have one of these on my hot water boiler, and I too think that it cycles on and off way too much. If one uses the standard 'hot water boiler' setting in the themostat, you lose the capacity to change the number of cph. Any other thoughts on how often a hot water / radiator system ought to cycle in a Chicago winter?

    

   Thanx much.

2. 
   cvjxn | Feb 06, 2006 10:46pm | #6

   okay guys -- gather round and I will try to condense three out of nine evenings of a BOCES heating fundamentals class into a coherent posting......first -- the most efficient (heat or cool btus in the comfort space versus btus paid for from the utility company) and also the most comfortable for the people in the comfort space is for the "furnace" to run 24/7 and for the temp in the space to stay within +/- .75 degree of set point. ----- that of course requires a very complex (read: $$$ and subject to subtle failures) infinitely variable gas valve (or a/c comp/cond unit) --- so we live with compromize ----- but 2 degrees over and under run is UNACCEPTABLE --- get a new thermostat/fix the aquastat on the boiler/relocate the thermostat/control the cycles/etc.for boilers ---- the thermostat should not turn the gas on/off --- only the circ pump and or the zone valves..... turning the gas on and off is the duty of the aquastat as moderated by the outdoor temp sensor. the space wants heat so calls for water to flow in the local loop and the space takes heat out of the water... if the water flowing through the boiler is "too cool" the boiler fires. by always circulating the water, the living space gets all of the heat out of the water that was put in --- not the "dead" spaces the piping goes thru to get there. the outdoor temp sensor takes care of whether it is chicago or tampa or greenbay and adjusts the temperature of the water available to circulate to the living space when the space calls for it... the bigger the heat loss rate in the living space --- the hotter the supply water has to be to still have any heat to give off at the end of the radiator!so bottom line is ---- except for older brute force forced air gas or gravity gas furnaces where cph of 3 is usually good or electric heat where 6 or 9 is practical ---- set the cph at 1 and trust that the rest of the system is "smater" than the thermostat can ever be by itself.....hope I haven't been TOOOO professorial..... cvjxn

1. 
   seb | Feb 08, 2006 05:28am | #7

   cvjxn, Thanks for the benefit of your seminars...I really appreciate it...
   As I mentioned my system is an old GFA ...I replaced the gas valve with a new honeywell elect. ign , and did the new honeywell t stat...
   It was "short cycling" in my opinion....The thing was set on 3 (3CPH).
   I set it to 1 cph and now it runs over temp 2 or 3 degrees, which I think is more efficient than no over shoot.I may be totally off in left field about the efficency, but it seems logicial that with this type of system, there is a loss due to the heat up time befor the blower comes up..Thanks again for the info...
   Bud

2. 
   DonCanDo | Feb 08, 2006 01:53pm | #8

   I set it to 1 cph and now it runs over temp 2 or 3 degrees, which I think is more efficient than no over shoot.I may be totally off in left field about the efficency, but it seems logicial that with this type of system, there is a loss due to the heat up time befor the blower comes up

   I think that depends on whether or not the furnace and ducts/pipes are in the heated area or not.  Heat can't really be "lost".  It can only go where it's of no use to us (like outside the house).  If the furnace and it's associated ducts/pipes are in an area that gets heated anyway, then it shouldn't really matter (from an efficiency perspective) whether or not the system "short-cycles".

   My furnace is in the basement which I don't purposely heat.  However, if my basement were any colder (it's about 10° cooler than the living area in the winter), I would heat it.  So, I don't mind any "heat loss" to the basement.

   -Don