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  1. #1
    Join Date
    Nov 2007
    Posts
    30

    Vision Pro Stat and CPH setting?

    I Have A honeywell Vision PRO 8000 2 stage stat on a Trane XV90 furnace .. The CPH is set to recommended setting fo 90% Effec. @ 3....My understanding of this is that the Unit will Cycle on and off 3 times an hour @ 50% load, on 10 min off 10min...now does 50% load depend on the outside temp,,lower temp higher load?......I guess this is good for efficiency...but isn't every house different with different heat requirements?.. my house is a split 3000 sqf.....Now if this CPH @50% load is true... what happens when the temp drops below the set point and its in that 10min off cycle, the systen does not come on untill it reaches the next 10min on cycle? This leaves my house cold with this cycle...If I set the stat to 4 or 5 CPH, running more often and shorter periods of times would this be more comfortable? of I would have to experiment with it to get the right combo.....I would rather have a t-stat with no CPH and run the furnace for the exact set point I have @ the t-stat, cycling on and off as needed to maintain the set point.

    Please any suggestion of maybe finding a new t-stat ( White Rodgers?) or setting this on up for better controll of the set point to be more comfortable without that many cold times..

    Thanks
    Rock142

  2. #2
    Join Date
    Mar 2006
    Location
    Great white north
    Posts
    57

    Robertshaw...

    Just my Humble Opinion.
    We were at our neighbors house last year, and I timed his furnace run times, on & off cycles. He had his Honeywell thermostat set to 6 CPH, which then ran the furnace for 3 minutes, off for 7. I found it very uncomfortable in there. Just the time you started feeling warm air, the furnace would shut off. And, according to the pros on this board, that is an ineffiecient way to have the furnace run as the heat exchanger is just warm when the furnace shuts off, causing that heat to be wasted.

  3. #3
    Join Date
    Dec 2002
    Location
    North Central Ohio
    Posts
    230
    My question would be is the stat/furnace wired correctly for 2 stage heat?
    It seems that the default/recommended CPH setting for furnaces (gas,oil)over 90% is 3. The setting of 5 would be for furnaces (gas,oil) less than 90%Are you satisfied/comfortable at this setting? You may need to increase or decrease this setting as every house/person is different. I have found that the default settings seem to work for most homes but have played with them in rare situations. Play with it and time the cycles as it pertains to your comfort level.

  4. #4
    Join Date
    Dec 2002
    Location
    Rochester, MN
    Posts
    5,304
    On mild days, the furnace is going to run avg 3 CPH, but as it get colder, it will run longer, and less cycles.

    The house won't get cold, the t-stat will figure it out ahead of time to turn on as needed. This advoids the temp swing that is found in others... Just set it and forget it.

    On my set up, when it gets down into the teens the furnace starts running longer, less on and off, and when it gets down to single digit, then it runs much longer, and below 0, pretty much runs none stop, and -10 2nd stage starts cycling on and off.

  5. #5
    Join Date
    Jun 2003
    Location
    Florida
    Posts
    9,548
    Set your fan to on instead of auto before you replace the stat, that's a good stat. That stat is a learning stat which will take a week to set your schedule up...it's SMART. Give it a chance...
    If everything was always done "by the book"....the book would never change.

  6. #6
    Join Date
    Dec 2002
    Location
    Rochester, MN
    Posts
    5,304
    Quote Originally Posted by smokin68 View Post
    Set your fan to on instead of auto before you replace the stat, that's a good stat. That stat is a learning stat which will take a week to set your schedule up...it's SMART. Give it a chance...

    I agree, it's a great stat..

    I've owned this line for 3 years, I've put in this line in family members, and the like the comfort it provides.

  7. #7
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,721
    As the OD temp gets colder, the off cycle time will become shorter.
    If your feeling cool before the next on cycle, your furnace may be over sized.
    The 3 CPH algorthym works fine on systems that are not over sized.
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  8. #8
    Join Date
    Jan 2008
    Location
    Lehighton, Pa.
    Posts
    178
    I have the Vision Pro TH8110U stat. It's hooked up to a Lennox X16 HP, variable speed blower, with a Harmony III control board. The Harmony controls all of the stages, both HP and electric. Therefore, the stat is just used to send the signal to the system to go on/off. I'm confused with the CPH setting process for my individual set up.

    Right now the CPH is set to 5. Depending on the outside temps, the system will either cycle on/off multiple times in the warmer temps or will remain running almost non-stop when the temps go say around 30. What actually would change if I adjusted the CPH to let's say 3?

  9. #9
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,721
    You wouldn't have those inefficient short cycles in the milder temps.
    You should have them adjust how quick the second stage of the HP comes on, and AUX also.

    The CPH setting may be the cause of your high electric bill.
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  10. #10
    Join Date
    Jan 2008
    Location
    Lehighton, Pa.
    Posts
    178
    Quote Originally Posted by beenthere View Post
    You wouldn't have those inefficient short cycles in the milder temps.
    You should have them adjust how quick the second stage of the HP comes on, and AUX also.

    The CPH setting may be the cause of your high electric bill.
    The timing of the second stage and HP settings are built into the algorythym of the system. When initialized, the system starts in stage one, if after 4 minutes the temp is not at 90, it goes to stage two, assuming that the temp stays in a range of 90-120, the aux, will not kick on. There is another 4 minute spread to determine this.

    If you think the CPH may be causing a problem, what should I have the setting read?

  11. #11
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,721
    3 CPH for the stat.

    15 to 20 minutes before going to second stage. And 15 to 20 minutes before bringing in the AUX heat.

    The heat pump uses less electric then the strip heaters, let it have long runs.
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  12. #12
    Join Date
    Jan 2008
    Location
    Lehighton, Pa.
    Posts
    178
    OK, I'll change the CPH to 3. May sond like a stupid question, but I'm looking for an education. While the term CPH is self explanetory, what actually does reducing the number do? The stat determines when a heating call is required. Let's say the stat is set to 73. The actual temp showing on my stat never changes from the setpoint number, so both numbers say 73, yet the system cycles on and off. Assuming that the on/off cycle occurs in a fraction of a degree, (since the actual number never changes), does reducing the cph number increase that fraction, thus reducing the cycles?

    I guess what I can't comprehend is the entire CPH function. If the number is set to three and three will not be a sufficent amount of cycles within a given hour to heat the home, what happens?

  13. #13
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,721
    The lower the CPH the more temp droop the stat allows. It will allow the temp to drop alittle lower and to go alittle higher. In tenths.
    The on time will be longer, and the off time will be less. Making the house feel warmer.
    As it gets colder outside, the off time could drop to just afew minutes, and then back on for 20. If the set point is not reached, the stat contimues to call for heat no matter what the CPH is set to.
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