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  1. #14
    Join Date
    Mar 2002
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    Concord, CA
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    2,635
    You're a lawyer too bigbird? Talk about convenience! You could do some new construction condominium work and then represent the buyers when they sue you - all in one value added package.

  2. #15
    Join Date
    Apr 2005
    Location
    illinois
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    257
    Irascible
    Thanks for your reply. The the furnace is in the basement and the furnace room is fairly large about 20x12 ft. The entire basement is about 2000 sq feet. From what I have heard the furnaces use a lot of air for combustion.
    I saw in your article that you recommend an oversized blower unless you have textboook ducts. I already have high static pressures. Won't a big blower make the static pressure go up? I was thinking that a 2 stage furnace system would decrease the static pressure since less air would need to be moved.
    Regarding running the VS blowers 24/7 it seems that there would be less infiltration if all the ducts were in a conditioned space. About 70% of my ducts are in a conditioned space so I would conclude that there is less theoretical chance of air infiltration than if 100% were in an unconditoned space. Is my reasoning correct?
    I hope I am not misquoting Jim Davis but I believe that he says that when the burner flames are on low, the flame is farther from the heat exchanger and that this lowers the efficiency of the heat transfer. He gave the example of holding your hand above a flame. The heat you feel rapidly declines as you move your hand away from the flame.
    I think he also thinks that the heat exchanger is less efficient at removing heat when the temperature of the air entering the HX is less. He said that a better way would be to decrease the number of burners that are on high and that a company called Nordyne[sp?] actually is making a furnace that does this. He thinks the companies should make single stage furnaces with a VS blower. He teaches his
    classes to modify the 2 stage furnaces so that they run on low stage for a very brief time such as 1 minute before going to hi fire, He claims that when this is done peoples bills go down.

    [Edited by heetseeker on 05-31-2005 at 11:56 PM]

  3. #16
    Join Date
    Nov 2000
    Location
    Eastern PA
    Posts
    68,944
    Jim Davis is a smart guy...but...
    Government is a disease...
    ...masquerading as its own cure…
    Ecclesiastes 10:2 NIV


  4. #17
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    Apr 2005
    Location
    illinois
    Posts
    257
    RoBoTeq
    Please share your doubts about what I wrote. I am trying to learn and to hear what others think about what I think Jim Davis said. He says that nobody has proved him wrong yet.
    here is a quote I found
    Jim Davis
    Professional Member

    Registered: Aug 2002
    Posts: 434
    The statement is based on actual field testing of the BTU's the furnace delivers to the duct. If a furnace is rated at 100,000 BTU input at high fire, it may be 60,000 BTU input in low fire. By meausring the Temperature of the plenum and the temperature of the return we get the Temperature rise. Then we measure the air flow or CFM. Take the Temp. Rise times CFM times 1.08 and you calculate actual BTU's being delivered. No one to date has found a conventional 2-stage furnace(VS or otherwise) delivering more than 55% of the actual input!. Some have been tested as low as 40%.
    Efficiencies of furnaces are not based on real measurements but rather fictitious calculations that can't even exist in the real world.
    __________________



    [Edited by heetseeker on 05-31-2005 at 11:42 PM]

  5. #18
    Join Date
    Mar 2002
    Location
    Concord, CA
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    2,635
    An oversized blower will increase static pressure. But static pressure is not a sin unto itself. A flex duct can handle 10 inches of positive pressure. Trane's blowers are approved to run at up to 0.9 inches. But it will only deliver its rated tonnage at 0.5 or 0.6 inches. So if you can't get your ducts big enough to deliver the air you need at 0.5 or .6 inches then you fix the ducts and/or oversize the blower. If you can't get the airflow you need at 0.9 inches (or whatever your furnace is approved to run at) then your ducts are painfully small and must be upgraded. Typically if a customer doesn't want to spend a lot of money on their ducts I'll at least upgrade the return duct if at all possible and then oversize the blower.

    The purpose of a two stage furnace in my mind is for more even comfort and quieter operation.

    I’ll have to test Mr. Davis’s observations the next time I get a chance. If it pans out... I too would like Robo to expound on his cryptic remarks. At the very least I’d like to know if he thinks OEM AFUE calcs are reasonably close to reality.

    If the ducts are in the conditioned space then yes, there is no infiltration caused by those ducts.

  6. #19
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    Nov 2000
    Location
    Eastern PA
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    I have not done any of the testing that Jim claims to have done but find it very odd that all manufacturers of furnaces have falsified their data sheets.

    My guess is that Jim has been testing wrongly. The temperature rise method will be quite accurate but only if all other data is accurate.

    Does it not seem odd that only Jim Davis has ever proven that furnaces claiming to be 80% efficient are really only 55% efficient? No one else in the industry ever picked up on this? I don't think so.
    Government is a disease...
    ...masquerading as its own cure…
    Ecclesiastes 10:2 NIV


  7. #20
    Join Date
    Aug 2002
    Location
    Westlake, Ohio
    Posts
    2,477
    Originally posted by RoBoTeq
    I have not done any of the testing that Jim claims to have done but find it very odd that all manufacturers of furnaces have falsified their data sheets.

    My guess is that Jim has been testing wrongly. The temperature rise method will be quite accurate but only if all other data is accurate.

    Does it not seem odd that only Jim Davis has ever proven that furnaces claiming to be 80% efficient are really only 55% efficient? No one else in the industry ever picked up on this? I don't think so.
    "I HAVE NOT DONE ANY OF THE TESTING THAT JIM DAVIS HAS DONE"
    pretty much says it all. It is not just just me any more that has measured the same thing but thousands of others. It is more amazing that no one has actually proven this information wrong. Not sure how you use the formula CFM X Delta T X 1.08 = Actual BTU's delivered then divide by input for true efficiency the wrong way? And we check static pressure and blower performance specs minimum. Those that actually measure CFM are coming up with lower efficiencies than I have. When checking manufacturers specifications you can sometimes actually get outputs greater than inputs using their own data. Manufacturers are forced to follow what I call antiquated standards that are supposed to compare all equipment equally when in fact they allow a lot of fudge. But until this changes they merely will comform. As I noticed in another post a homeowner wanted a guarantee that his equipment would perform within 10% of its rating or a 90% efficient furnace would run at least 81% and he was told this is a ridiculous request.

    captain CO

  8. #21
    Join Date
    Nov 2000
    Location
    Eastern PA
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    I figured you were lurking Jim How the hell are ya?

    Now I'm gonna have to do some testing of my own, which is not as easy as when I was a tech rep with my own lab set up.

    Hell, I put in one of the first two stage units made for my sister back in the 70s. It was a Ruud two stage that was eventually discontinued for lack of interest in it. I loved it. The thing ran nearly all the time on low fire and my penny pinching sister raved about how cheap her heating bills had become since I replaced her old unit.
    Government is a disease...
    ...masquerading as its own cure…
    Ecclesiastes 10:2 NIV


  9. #22
    Join Date
    Aug 2002
    Location
    Westlake, Ohio
    Posts
    2,477
    Originally posted by RoBoTeq
    I figured you were lurking Jim How the hell are ya?

    Now I'm gonna have to do some testing of my own, which is not as easy as when I was a tech rep with my own lab set up.

    Hell, I put in one of the first two stage units made for my sister back in the 70s. It was a Ruud two stage that was eventually discontinued for lack of interest in it. I loved it. The thing ran nearly all the time on low fire and my penny pinching sister raved about how cheap her heating bills had become since I replaced her old unit.
    Was on the road when this all started. I heard things changed with you. But still enjoy our conversations. As far as your sister I can't imagine how much more she could have saved. I really wish two-stage could be efficient and many more problems could be solved!
    captain CO

  10. #23
    Join Date
    Jul 2004
    Location
    West TN
    Posts
    983
    Heetseeker

    I'd prefer both pipes for your furnace be located away from the dryer vent.

    Inlet pipe due to chemicals in laundry.

    My reasoning for the outlet pipe is just me being 'overly'
    cautious. I run too many "what if" situations sometimes
    so I can try to avoid becoming a victim of Murphy's Laws.
    i.e. What if Heetseeker moves out and the new owner is the
    big time cook that has this huge vent-a-hood installed.
    The house ends up in a negative pressure and the easiest place to pull in air through the dryer vent (Sucking air from outside through the clothes dryer). And low and behold, the fumes from the furnace get 'sucked' into the house.
    A very unlikely situation to say the least....
    But I figure.. If I can think it... it might happen hehe.


    Somewhere in this thread, I saw you mention your ducts have high static. How are you determing this?

    I sure wished I could come to your house and evaluate the situation.
    Bring me up to speed on what you got going on.






  11. #24
    Join Date
    Nov 2000
    Location
    Eastern PA
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    Jim; my sisters old furnace was very old and very oversized so it really didn't matter what I replaced it with, she was going to see a savings.

    Now you really have my curiosity up. I like the idea of two stage and modulating furnaces and assume that because they have longer run cycles they must operate more efficiently.

    Since I am quite aware of the farsical means that we design cooling equipment to test out more efficiently on the bench, I am reluctant to think you may be missing something.
    Government is a disease...
    ...masquerading as its own cure…
    Ecclesiastes 10:2 NIV


  12. #25
    Join Date
    Apr 2005
    Location
    illinois
    Posts
    257
    Wormy
    Thanks for your replies and your interest. I wish you could see my house too. For my static pressures I had a contractor come out who checked the pressures. Search under my name and see my post on high static pressures.
    I have been busy. I took down the drywall in my basement and found out that my 3 supply ducts to the master bedroom are all faulty. The two long runs to the addition to the bedroom were basically disconnected from the main trunk. When they added the flexduct they probably moved the hard duct enough to have the connection to the main run fall apart. The ducts were held together with dried up duct tape.In addition the connection between the hard ducts and the flex duct had big gaps. The third duct to the bedroom has a big air leak where the hard duct meets the supply vent. No wonder the bedroom was cold in the winter. I guess the best solution for this last problem is lots of mastic.
    I also found out that one of my wall return ducts was blocked by a piece of metal at the floor after I opened the metal between the joists in the basement . Apparently the original installer when they built the house had tacked up metal to seal the return but forgot to remove it.
    This should reduce the return static on my big furnace. The return static on the big furnace was .5 and the supply was .35 the first time they measured it. They came back and when they remeasured it they got the following measurements. There is an open grill on the return drop of the large furnace. we measured the static with the grill open and covered. Unfortunately they had no solution to the static. They said they install lots of furnaces with similar static.


    grill open
    .18 filter .5 blower .25 A coil .18

    grill closed
    .26 filter .58 blower .25 A coil .18

    The numbers are placed where the readings were taken in relation to the various furnace components. With my limited knowledge I figure my static is normally .83 [.58+.25] since I plan on closing the grills when the furnaces are replaced. With my newly functioning return I suspect the static pressure will fall closer to the .75 that I get with the grills open. I am thinking that if I get a vs 80 2 stage furnace that the static will be lower most of the time when the furnace is running on low fire[altho with less thermal efficiency].
    The a/c will still be a problem. I don't really want to go to a two stage a/c because of cost. Can you comment on how bad you think these pressures are?
    Again thanks for your interest.





  13. #26
    Join Date
    Mar 2002
    Location
    Concord, CA
    Posts
    2,635
    Why the obsession with static? The measurement of static serves only to tell us what we need to do to get our airflow up to appropriate levels. A low reading serves no purpose unto itself. Proper airflow is the goal. A LOT of systems have an ESP of .8". I'm not saying that's good. It's just a fact. You can get the airflow you need at the pressure and even higher if forced to.

    If the ducts literally can't be upgraded due to space limitations then you'll have to embrace the high static and put in a blower that can handle it. If space isn't a limitation then upgrade the ducts. This isn't rocket science. If it seems like rocket science to your contractor then get a new one.

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