Page 2 of 3 FirstFirst 123 LastLast
Results 14 to 26 of 34
  1. #14
    Join Date
    Feb 2004
    Posts
    2,458
    Originally posted by BobbyBJr
    On natural gas, can you not clock the meter and find out how much gas is actually being used?

    Bobby
    I was typing like a mad man & didnt see your post

  2. #15
    Join Date
    Sep 2001
    Location
    Vancouver Canada
    Posts
    996
    Higher pressure = more btu = overfired. That is how a 2 stage furnace works. 1st stage lower pressure than 2nd stage. That is the only thing that changes on the gas valve is the pressure. So if 1st stage is 36000 btu and second stage is 65000 btu then obviously higher pressure = more gas consumed.
    "Go big or Go Home"

  3. #16
    Join Date
    Jun 2003
    Location
    New Hampshire
    Posts
    2,666
    Some manufacturers require 4 inches w.c. gas valves. Thats a pretty broad brush to assume you always should have 3.5 inches w.c.
    Also if gas company has a high pressure coming into house it may be the responsibility of homeowner to reduce gas pressure at each appliance.

  4. #17
    Senior Tech Guest
    Things that make ya go hmmmm....

  5. #18
    Join Date
    Nov 2000
    Location
    Upstate, SC
    Posts
    2,919
    Hmmmmmm.....wouldn't properly installed and adjusted regulators take care of those minor flunctuations in gas pressure?

    Bobby

  6. #19
    Join Date
    Feb 2004
    Location
    michigan
    Posts
    677
    I'm not really sure that there's much of a discussion here if all you are concerned with is .5" difference in gas pressure. I think that if you were to monitor the gas pressure for serveral days you would find swings greater than .5" several times. The supplied, incoming pressure directly effects the manifold pressure and like electricity that will fluctuate according to demand.
    If you are talking 5" or higher I agree that that would cause an overfired condition but 4" really isn't. I don't think that it would show much difference when you clock the meter either. Have you tryed clocking the meter at both pressures yet? It would be interesting to see what the BTU difference really is. Let us know what you come up with. I'm on natural gas and my conduct my own experiment and see what diference there is at home.

  7. #20
    Join Date
    Jun 2003
    Location
    New Hampshire
    Posts
    2,666
    My response to individual regulators on each appliance is based on the "what if factor". It is my understanding that certain areas of the country will provide gas at a higher pressure(2 psi). In most parts of the country you get inlet pressure around 7 inches w.c. and with properly sized pipes you should get a flow pressure of 5-7 inches w.c. and the manifold flow pressure of whatever it is set at at the factory(either 3.5 or 4 inches w.c.) if we are talking a typical 80% furnace.
    If the gas pressure is 1-2 psi then the house piping is usually sized for that high pressure and individual regulators are required at each appliance.
    There are a bunch of possibilities and the original poster could answer his own question if he thought it through because he can look at the situation better than any of us ever could over the net.

  8. #21
    redneck hvac-r Guest

    How do you clock an appliance?

    I was never taught this in school but would like to know for future reference. Do yo just turn all other gas appliances off and use a manometer or do you actually "clock" the meter?

    Thanks for your replies in advance.

    Redneck.


  9. #22
    Join Date
    Sep 2001
    Location
    Vancouver Canada
    Posts
    996
    I really can't believe that gas pressures at the meter will fluctuate according to usage. The delivery pressure on a low pressure meter is 8" wc. I know that winter to summer the main gaslines will fluctuate from 30 to 60 psi. I have never seen a meter pressure change from summer to winter if the reg was properly setup. As far as saying that it is only .5" difference from 3.5 to 4" wc. Put a manometer on the valve and I can guarantee that when you adjust your regulator from 3.5 to 4" you will see and here a difference in the burners. As far as a unit being designed to run at 4" instead of 3.5" it will state what pressure is required on the unit. You may have to derate it for altitude but other than that always use manufacturers recommendations.
    "Go big or Go Home"

  10. #23
    Join Date
    Nov 2004
    Location
    CA
    Posts
    238
    redneck hvac-r

    if you have installed a furnace, the Manual will tell you how to clock it.

    Also, there is chart on the Net for even easier "clocking"

  11. #24
    Join Date
    Nov 2004
    Posts
    2,927


    here is a place to look:

    http://www.bacharach-training.com/

  12. #25
    Join Date
    Feb 2004
    Location
    michigan
    Posts
    677
    Originally posted by Black Adder
    I really can't believe that gas pressures at the meter will fluctuate according to usage. The delivery pressure on a low pressure meter is 8" wc. I know that winter to summer the main gaslines will fluctuate from 30 to 60 psi. I have never seen a meter pressure change from summer to winter if the reg was properly setup. As far as saying that it is only .5" difference from 3.5 to 4" wc. Put a manometer on the valve and I can guarantee that when you adjust your regulator from 3.5 to 4" you will see and here a difference in the burners. As far as a unit being designed to run at 4" instead of 3.5" it will state what pressure is required on the unit. You may have to derate it for altitude but other than that always use manufacturers recommendations.
    Oh I wasn't thinking of a huge , as in 1 or more inches, change but there are observable changes at times under certian conditions. I guess I'm just saying that a half inch increase does'nt indicate an overfire condition. We've got some residential on the same mains as heavy industrial and you can tell when they go on line

  13. #26
    Join Date
    Feb 2005
    Location
    small island in the Pacific Ocean
    Posts
    558
    A unit is overfired if its actual burner firing rate, which is obtained by clocking the meter, is greater than its manufacturers rated input. So to say a unit is overfired because it is getting 4"WC as opposed to 3.5" WC I would say is wrong. All you could say is the pressure is to high and you either need to correct it or get a smaller orifice. High pressure may cause overfiring, but a unit is not considered overfired because of it.

Page 2 of 3 FirstFirst 123 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event