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chimney liner rating?

Jim Davis
Jim Davis Member Posts: 305
What you state is the theory behind venting but not the reality. Again the pressure of the mechanical room has just as much affect on the draft of the chimney and is not addressed in the tables. If one would measure the temperature of flue gases above a drafthood they would find old appliances actually had cooler flue temperatures more often than not than the new induced draft furances without dilution air.


  • KBP&H
    KBP&H Member Posts: 48
    Chimney liner rating?

    Have a customer that a chimney co is relining is chimney,, installing a 5" liner rated @ 205,000 BTU,, Can I REDUCE a 6" Draft hood to the 5" liner ( BURNHAM SERIES2 205) or does the 6" Draft hood have to stay a min of 6" to the chimney opening at top of flue?
  • RianS
    RianS Member Posts: 104
    Chimney liner

    How high is the chimney? 5" seems kind of small for 205,000 BTU unless chinmey is very high.
  • KBP&H
    KBP&H Member Posts: 48
    chimney liner

    I talked to Burnham today, for this installation they allowed a ONE size reduction from the draft hood size of 6".> 5"
  • Saggs
    Saggs Member Posts: 174

    I recall doing a stainless liner for oil on a 30ft chimney and I think 150K btu was about max for that height w/ a 5" liner. You may want to check this out further. Check w/ your wholesaler or Z-Flex.
  • Empire_2
    Empire_2 Member Posts: 2,343
    This might help

    FOund this to be very useful. 5" liner is not rated at 205Mbtu/hr 6" would be useful in your application. Is there any other appliance going to the chimney?
  • tim smith
    tim smith Member Posts: 2,743
    flue liner

    In the international fuel gas code they state that you not reduce the liner to any smaller than the draft hood connection, just a little tid bit.
  • Robert O'Connor_12
    Robert O'Connor_12 Member Posts: 728

    Depending on where you live and which code(s) your state adopted can results in conflicting answers. That being said, here in the "Great State of New Jersey" we have the 2003 International Mechanical & Fuel Gas Codes adopted (with exceptions*)

    03 Fuel Gas Code,Section 504.2.2 states that.
    Where the vent size determined from the tables is smaller than the appliance draft hood outlet or flue collar, the smaller size shall be permitted to be used provided that all of the following requirements are met:

    1. The total vent height (H) is at least 10 feet (3048mm).

    2. Vents for appliance draft hood outlets or flue collars 12 inches (305mm) in diameter or smaller are not reduced more than one table size.

    3. Vents for appliance draft hood outlets or flue collars larger than 12 inches (305mm) in diameter are not reduced more than two table sizes.

    4. The maximum capacity listed in the tables for a fan assisted appliance is reduced by 10 percent (0.90 x maximum table capacity).

    5. The draft hood outlet is greater than 4 inches (102mm) in diameter. Do not connect a 3-inch-diameter (76mm) vent to a 4-inch-diameter (102mm) draft hood outlet. This provision shall not apply to fan-assisted appliances.

    Robert O'Connor/NJ
  • Robert O'Connor_12
    Robert O'Connor_12 Member Posts: 728
    KBP&H Follow up commentary

    In addition to the 2003 International Fuel Gas Code, Section 504.2.2 Minimum size, the commentary is as follows:

    If a vent complies with all of the items 1 through 5 (as I've listed in the above post) and is sized in accordance with the appropriate table, it is allowed to be smaller than the appliance connection, primarily because of the increase in capacity of the vent resulting from its height and because vent capacity is based on the Btu/h input rating of the appliance and not the size of the appliance flue collar. The code section "suggests" that flue collars are sized for "worst case" vent designs and are thus somewhat oversized for vents with higher venting capacities. Item #4 that I too have listed above is necessary to prevent positive pressure from developing in the vent seving fan-assisted appliances. A 6-inch draft hood connected to a 5-inch Type B vent, "your" example, might look like an installation error, but section 504.2.2 (above) could allow it in some cases, and operating a vent nearer its maximum capacity is ALWAYS desirable.

    Another section I'd look at would be 504.2.10 as well.

    Good luck, and have a Happy and Safe St.PATRICKS DAY!

    Robert O'Connor/NJ
  • Jim Davis_3
    Jim Davis_3 Member Posts: 578
    Probably won't work

    The capacity of a pipe is determined by the force exerted on it. All flue charts assume that the mechanical room is neutral or slightly positive pressure, the inside and outside temperature never change and there is no wind in your area. They assume that as the height of the flue is increased so is the force. This is theory not reality. Flex liners are more restrictive to flow than smooth pipe of the same diameter and have less capacity. If you use a 5" on this boiler the odds of the boiler venting properly are minimum if not nil. I would have recommended a 7" liner and wouldn't even trust a 6". I get many calls after liners are put in where the equipment doesn't vent at all.
  • Robert O'Connor_12
    Robert O'Connor_12 Member Posts: 728
    Jim, remember Goldielocks!

    Goldie Locks Saves the 3 Bears from Certain Asphyxiation: The last time we saw Goldie Locks, she was a mere child being chased around by 3 bears. But alas, Goldie has grown up and is now an appliance installer. As we peek in on Goldie Locks, she is attempting to connect a furnace to one of three vent pipes in the three bears house. The first vent pipe was toooooo small, the second vent pipe was toooooo big, but the third vent pipe was just right. At one point we were simply worried about vent pipes being big enough but as technology has progressed, we are now worried about vents being too big. Vent pipes for new Federally mandated mid-efficiency appliances have to be "just right" When a vent pipe is too small there isn't sufficient area to vent the products of combustion. When a vent pipe is too big it will be subject to excessive condensation. The corrosive nature of this condensate will cause the vent pipe to deteriorate. This issue, as well as the dangers associated with vents and chimneys that don't funtion properly have led to incresed concern about using existing chimneys and vents when appliances are being replaced. You have probably seen some articles on the subject. An article called "Carbon Monoxide--The Silent Killer" , "Danger Lurks in Local Neighborhoods: Dangers of Carbon Monoxide," written by George E. Lucia and Trica Branley of Hillsboro, NJ and it appeared in the Feburary 1994 issue of New Jersey Municipalities Magizine. Both of these articles are worth reading. Some questions I ask as a applicant who is proposing to use an existing chimney or vent with a replacement appliance are: 1. Is the chimney/vent clear and free of obstructions? 2. Is the chimney lined, and is the liner in good condition? 3. Is the chimney/vent size appropriate for the new appliance? Often it is not possible for an inspector to see the inside of the flue or chimney. In most cases, an inspection is done after the new appliance is installed. For this reason getting some certification about existing conditions from the installer probably makes sense and is in fact code in the great state of New Jersey (counter form: F370). In addition, a spill test performed by the contractor should be performed. If possible, this spill test should be witnessed. We now return to Goldie Locks, who has just completed the furnace installation in the 3 bears house. The 3 bears are so happy with the installation that they don't chase Goldie Locks out of the house, but rather, invite her to sit down and have some porridge with them. And they all lived happily ever after--untill the bears got the bill. Papa Bear thinks Goldie Locks' prices are toooooo high! The End.............Robert O'Connor/NJ
  • KBP&H
    KBP&H Member Posts: 48

    I was initialy told the liner company was putting in a 5" liner because of the offset in the chimney,, after they found out the btu requirements they changed the liner size to 6"... I wonder how efficent the liner will be after installation.,,,,, The whole thing is that the chimey co doesn't want to loose the sale......... I say we should go 85% direct vent, tekmar control w/ deep outdoor reset, straight thru the chimney, have them cap the top,,,, put in a indirect fired w/h and get the homeowner $750.00 back as a rebate. AND SAVE probably 25% in gas bills over the standard 82% draft boiler.
  • Robert O'Connor_12
    Robert O'Connor_12 Member Posts: 728
    As I understand it

    Draft refers to a phenomenon created by the buoyancy of lighter (less dense) gases. Draft is measured as pressure in inches of water colum (kPa) and is a negative pressure, meaning that it is less than the atmospheric pressure at the point of measurement. Draft is produced by the temperature difference between the combustion gases (flue gases) and the ambient atmosphere. Because hotter gases are less dense, they are buoyant and will rise in the chimney, causing negative pressures to develop that are directly related to the height of the chimney or vent and directly related to the temperature difference between the flue gases and the ambient air. The type of vent or chimney used in a given installation is generally based on the temperature of the flue gases produced by the appliance and the appliance category. The development of higher efficency appliances continues to produce lower flue gas temperatures, and the diversity of mechanical venting systems continues to expand. Many of todays appliances are deigned to be vented by "more" than one type of venting system.

    Robert O'Connor/NJ
  • Robert O'Connor_12
    Robert O'Connor_12 Member Posts: 728

    I'm not saying that 5-inch can be used in the posters application. If we use the chart provided by MikeT below, we can only come up with (based on the info by KBP&H) that at base minimum he would need to go 30-feet in height @ 6"diameter. Manufacturer's of liners all have their own capacity charts. KBP&H said the liner was rated for 205,000 and the boiler used (I'm assuming its at or below this number) is within the 205 rating of the liner system.

    When the code is silent, it will go by the manufacturer's installation instructions on a UL listed and approved appliance. IMHO it would appear that the chimney guy in this equation is overstating his liner's capacity by quite a bit and by using this system could result in an unsafe condition.

    I was simply pointing out in my posts above what the code states, not wheather or not it applied to "his" application and it would appear that it does not meet the exception.

    Robert O'Connor/NJ
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