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  1. #14
    Join Date
    May 2006
    Location
    Austin, Texas
    Posts
    279
    You are correct. The CFMs for high and low are not chosen independently but they are not the same CFMs. Whichever dip switch you choose will have two different CFMs. Even if you can correct the furnace, you still have a 4 ton ac if I understand your post.

  2. #15
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,913
    The blower speed for low should provide a reduction in CFM to maintain the same temp rise as in high. If your is using the same CFM for bot, something is wrong.

    Your furnace may have been set up to only use second stage if you notice no difference in blower speeds.
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  3. #16
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    Quote Originally Posted by beenthere View Post
    The blower speed for low should provide a reduction in CFM to maintain the same temp rise as in high. If your is using the same CFM for bot, something is wrong.

    Your furnace may have been set up to only use second stage if you notice no difference in blower speeds.
    The furnace is using BOTH stages, only stage 2 if I make like a 3 degree delta T call for heat. Or at the tail end of a run. I am using the NEST thermostat generation 2 that supports 2 stage heat and 2 stage cooling as well has dehumidification/ Humidification. I am using 7 wire connection for 2 stage heat and 2 stage cool.

    I have used the 1st generation NEST at another residence for a long time. At this 3 apartment unit I am talking about in this thread, it is vacant while I work this. So I can get good controlled data on the running of this. I can see the duty cycle and run times etc. In addition I have IZON camera's in front of themometers scattered throughout all three of the units. I also have a NEST generation 1 installed in apartment 3 (the 500 sq ft one) that I had as a spare. It is only hooked to 24 volts and not a heating system. In this way I can see the temperature that unit and get reports.

    Sorry for all the info. I tried to paste page 48 of the manual to try and conclude this CFM discussion. As you can see the two position DIP switch controls 1 and 2.

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  4. #17
    I eat yummy crow and humbly apologize. The product specifications in another marketing document says high heat 1604 and low heat 1400. But I do not see that high of speed in the manual except for cooling mode. See what happens when a layperson tries to understand. At any rate because this sucker has to move air over the exchanger that is putting out either 74K BTUs or 92K bTUS it seems to have very high CFM and noise. Also the returns all seem to be racing to one side of the furnace. At 30 degrees outside, 70 degrees inside it stays in stage 1 heat mode and runs about 33% duty cycle. Just as a ref point aside from the noise.

  5. #18
    Join Date
    Nov 2000
    Location
    Eastern PA
    Posts
    68,943
    Even the low fire is too much for your home. The Nest thermostat is a sophisticated off/on switch with programming that is dedicated to turn the furnace off as much as possible. This means that more often than not, the Nest is bringing the furnace on in high fire when it is not figuring out a way to keep it from running.

    Also, no matter what, that furnace is forced into high fire every 12 minutes of run time. All staged condensing furnaces are forced into high fire with 12 - 15 minutes of run time to prevent damage to the primary heat exchanger.

    If you are looking for any sort of comfort level from your HVAC system, you have the worst of the worst case system installed. The combination of everything being oversized and a t-stat that is only concerned with energy efficiency, you'd be better off with the old coal burning furnace.

    Then again, the Nest stat is most likely not the only thing controlling your furnace's heat cycles. My guess is that during the colder days, the limit switch is what is turning your system on and off most times.

    Go back to whoever sized and provided that large of equipment and tell them to take it out and put in the proper equipment.
    Government is a disease...
    ...masquerading as its own cure…
    Ecclesiastes 10:2 NIV


  6. #19
    Quote Originally Posted by RoBoTeq View Post
    Also, no matter what, that furnace is forced into high fire every 12 minutes of run time. All staged condensing furnaces are forced into high fire with 12 - 15 minutes of run time to prevent damage to the primary heat exchanger.

    If you are looking for any sort of comfort level from your HVAC system, you have the worst of the worst case system installed. The combination of everything being oversized and a t-stat that is only concerned with energy efficiency, you'd be better off with the old coal burning furnace.

    Then again, the Nest stat is most likely not the only thing controlling your furnace's heat cycles. My guess is that during the colder days, the limit switch is what is turning your system on and off most times.

    Go back to whoever sized and provided that large of equipment and tell them to take it out and put in the proper equipment.
    I'm not seeing high fire unless I turn the t stat up about 3 degrees. If I leave the t stat at 70 degrees and it is 30 degree nights and 50 degree days the duty cycle is about 33 percent. Roughly 20 min run 40 min rest. Your input of 12-15 min is not anything I am seeing. Very rarely close to midnight a short bump to stage 2. How do you know what algorithm nest uses ? I doubt it is the high limit switch or the system would lock out. I agree it's oversized. The coal furnace comment is unfounded.

    As I said in my initial post I am going back to the installer so am fact finding here. Repeating that same comment is not useful to information gathering.

  7. #20
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    6,808
    Robo comes off as Mr. Know it all sometimes and he is wrong on occasion. Your two stage furnace with a 2 stage stat will only bring 2nd stage on when necessary. As for you being better off with a coal fired furnace, he's probably correct.

  8. #21
    Quote Originally Posted by jtrammel View Post
    As for you being better off with a coal fired furnace, he's probably correct.
    Not true

  9. #22
    Join Date
    Nov 2000
    Location
    Eastern PA
    Posts
    68,943
    Quote Originally Posted by makeithappen View Post
    I'm not seeing high fire unless I turn the t stat up about 3 degrees. If I leave the t stat at 70 degrees and it is 30 degree nights and 50 degree days the duty cycle is about 33 percent. Roughly 20 min run 40 min rest. Your input of 12-15 min is not anything I am seeing. Very rarely close to midnight a short bump to stage 2. How do you know what algorithm nest uses ? I doubt it is the high limit switch or the system would lock out. I agree it's oversized. The coal furnace comment is unfounded.

    As I said in my initial post I am going back to the installer so am fact finding here. Repeating that same comment is not useful to information gathering.
    I stand by every comment I made from a standpoint of working as a manufacturing and HVAC brand rep, including the brand you have in your home.

    As for my HVAC brother claiming I think I know it all, he is wrong....I do know it all...just ask me.

    It doesn't matter to me one ioda what you think you are seeing happening to your system. I deal with oversized systems every week, and I know how the furnaces must operate in order to prevent heat exchanger damage. I have also been following the Nest stat since it was first announced, and it's algorythym's are nothing new, just not utilized by HVAC controls companies because they are not designed for comfort. The intent of the makers of the Nest stat is to have the stat save as much energy as possible by turning the HVAC equipment off as much as possible. The Nest does not have any control over the programs that are built into the furnace controls any more than any other thermostat does. When a furnace has run for a certain amount of time in low fire, the manufacturers have now put into their programming to go into high fire until the thermostat is satisfied. I don't make any rules, I just read the white papers.

    You have been told how it is. I really don't care if you take any advice or not. Just seems like you are wasting everyone's time if you are just going to argue with us when we tell you how it is.
    Government is a disease...
    ...masquerading as its own cure…
    Ecclesiastes 10:2 NIV


  10. #23
    Join Date
    Nov 2000
    Location
    Eastern PA
    Posts
    68,943
    Quote Originally Posted by jtrammel View Post
    Robo comes off as Mr. Know it all sometimes and he is wrong on occasion. Your two stage furnace with a 2 stage stat will only bring 2nd stage on when necessary. As for you being better off with a coal fired furnace, he's probably correct.
    The thermostat will only bring on 2nd stage when the thermostat calls for it, but the furnace will go into high fire after a certain amount of time regardless of what the thermostat is telling it to do.

    There are now furnace controls that will anticipate heat need and turn on the furnace "before" the thermostat even calls for heat. Currently, all York brands have furnaces with these controls in them.

    The Nest thermostat changes it's programming depending on activity in the home. Any change in activity causes the Nest stat to start reprogramming. During any reprogramming, the Nest stat will call for 2nd stage of heat whenever it is recovering temperature and the difference in temperature of what the stat is calling for and what the temperature is withiin a certain variance for a certain amount of time. The temperature differential as well as the amount of time is a constantly moving target on the Nest stat, unless a household is absolutely timed exactly the same every day and the outdoor ambient temps never change.
    Government is a disease...
    ...masquerading as its own cure…
    Ecclesiastes 10:2 NIV


  11. #24
    Join Date
    Nov 2000
    Location
    Eastern PA
    Posts
    68,943
    Quote Originally Posted by makeithappen View Post
    Not true
    Why not? Other than not having coal available (which in PA is actually not a problem), new condensing furnaces that are oversized are often times running at 40-50% efficiency and are being constantly damaged by doing so. I've seen oversized furnaces burn out heat exchangers and controls within two seasons of operation. The whole time, the HO, who usually bought the furnace direct from a friend of a friend or via some internet company that could care less, and had it installed by the handyman who works at the office building where the engineering company they work for is located....has been complaining the whole time that it costs more to operate the new furnace than it did to operate their old one....and it's noisier!

    Any of this sound familiar?
    Government is a disease...
    ...masquerading as its own cure…
    Ecclesiastes 10:2 NIV


  12. #25
    As I said in my initial post, a 162K BTU Thermopride furnace was displaced.

    The system is not 100% ducted for a coal furnace. There are additions to the property of 500sq ft served by the same unit. There are signs that a coal furnace existed at one time. I feed the coal furnace at the farm house, not meeting my requirements for this property. This is a remote property, I doubt the tenants want to feed it. This is downtown Denver, coal furnace is illegal and would not pass code. Do you really think this system is running at 40% - 50% efficiency based on the data I have provided ? - wow


    Nest collects data with every device sold.

  13. #26
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,913
    Not unusual for an oil furnace to be 2 to 3 times as big as the home/structure needs.

    At 33% duty cycle in first stage, a 60,000 BTU 2 stage would have been more the size this place needs.
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