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    Venting a condensing boiler through chimney? (21 Posts)

  • Steve Goldstein Steve Goldstein @ 8:06 AM
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    Location

    Webster, which is a suburb of Rochester.
  • Steve Goldstein Steve Goldstein @ 6:21 AM
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    Luna HT is condensing

    The Baxi Luna HT is a modulating condensing boiler, if that makes any difference in your recommendation.
  • Steve Goldstein Steve Goldstein @ 6:31 AM
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    natural rise

    Are natural rise boilers the less efficient (not condensing) models? In fact, that's one of my decisions. Do I spend nearly twice as much to get the efficiency of a condensing model, or is the payback too long to justify the extra expense? I have a big (3200 sq ft), old house in Western NY. I spent $3500 in 2005 for natural gas. I plan to be in this house another 20 years. It's possible, if the venting options don't work out, that I may have no choice but to pick a lower efficiency boiler that can vent directly into the existing chimney flue without PVC or any other modification. But before I am forced to go that route, I want to know if a condensing boiler is even possible, with the constraints my house presents (wrap-around porch going around exterior wall that furnace/chimney is near; 18" thick stone foundation walls with fat beams for the sills; a furnace flue that shares a chimney with a wood stove flue).
  • Tony Tony @ 7:31 AM
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    Stick with it

    Stay with condensing/modulating. The efficiency stickers are NOT an accurate way of comparing boilers. One thing is for sure, do not stray from the installation manual. If you have problems later and it's not to the book, you're out. Maybe the HT isn't the right fit for your house. There are other mod/cons out there. My guess is your quote is coming from someone who has access to other products as well as Baxi. Since Baxi is represented by one supplier in WNY, and they have more than one product, maybe you should keep looking. Years of high gas bills is no excuse for taking the easy way out now. Where in WNY are you ?
  • Joe Brix Joe Brix @ 8:54 AM
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    A natural draft boiler

    Doesn't excuse the need for a liner in many cases. But check out other options. Burnham Revolution can use Z-flex stainless liner.
  • Bob Harper Bob Harper @ 10:00 PM
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    Hmm

    You cannot put PVC in a flue adjoining a woodstove. The chimney itself requires a 1-2" clearance to combustibles. You might be able to run AL29-4C stainless if you have a lot of money in the bank and the applaince is listed for that application. Still you would have the combustion air issue. So, does that woodstove have a listed insulated liner?
  • Steve Goldstein Steve Goldstein @ 10:18 PM
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    No liner

    No, the woodstove interfaces with the chimney tile at the bottom of the flue, but the chimney isn't lined (other than the tile itself). I had the chimney inspected when we bought the house 10 yrs ago, and it passed. But there wasn't a PVC pipe in the adjoining flue at that time.
  • Mitch Mitch @ 7:23 AM
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    Every condensing boiler

    or furnace or any other item I have worked on that is sealed, takes combustion air from and vents to the outside requires both terminals to be located in the same area. Going up a flue passageway is typically not a problem as long as it is independent of any other appliances and the exhaust pipe is not in danger of cooling to the point of ice build up blocking the exhaust gasses. Have you thoroughly read the instructions. Mitch S,
  • Steve Goldstein Steve Goldstein @ 8:35 AM
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    not my job

    It's not my job, as the home owner, to read the installation instructions. However, when I speak to three different boiler installers, and only one suggests venting up the chimney, I get nervous that this may not be a reasonable suggestion. I'm not an HVAC pro, but I know more than most homeowners do--enough to be dangerous and ask some tough questions. I don't want to get bamboozled into buying a suboptimal, dangerous, or potentially damaging heating system. I want the job done right. My chimney, from the basement to the top, is approximately 30' long. That length doesn't include any additional length or elbows that would be required to get from the boiler to the chimney entrance. Baxi doesn't post their installation info online, but Viessmann does. With the Viessmann, vertical venting lengths like I'm talking about are not acceptable. And they don't mention specifics like having a wood stove venting through another flue nearby. So I'm concerned about the length. I'm concerned about the wood stove. I'm concerned about the pressure differential, if he brings intake air from under the porch (I think he mentioned using a bigger pipe in the flue to compensate). I'm concerned about insulating around the PVC pipe in the chimney. I'm concerned about whether PVC is an appropriate material, if there's hot exhaust from the wood stove nearby. I'm concerned that this contractor didn't think that neutralizing the condensate pH value was necessary, but another contractor wants to do that. I'm concerned about ice build-up doing damage to the top of my old brick chimney. Like I said, I know enough to be dangerous and to have concerns. But I rely on you guys to tell me if my concerns are unfounded, or if this contractor is trying to pull the wool over my eyes.
  • Joe Brix Joe Brix @ 9:02 AM
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    Manuals here

    http://www.blueridgecompany.com/download
  • Steve Goldstein Steve Goldstein @ 9:35 AM
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    Venting Baxi into unlined masonary chimney?

    Thanks for posting the link to the manuals. Very helpful. Check out the attached image from the Baxi manual. This is amazing, if I'm reading it right. It almost looks like they're saying you can exhaust the Baxi directly into an unlined masonary chimney. That can't be right, can it?
  • CHARLES CHARLES @ 3:58 PM
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    Venting

    What else is venting into that chimney? The PVC would need to be insulated if the chimney is being used by other appliances. And that piping will diminish the inside diameter of the chimney. If no other appliances sharing the chimney, the PVC would need to be insulated through the chase. When all else fails, read the I&O manual. It's that thick booklet the installer uses to cushion his knees when he kneels on the floor during the install.
  • Steve Goldstein Steve Goldstein @ 8:53 PM
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    chimney

    The chimney has two flues. One flue is devoted to a wood burning stove. The other flue currently supports a boiler and a FHA furnace. The old boiler will be replaced with the new high-effieciency boiler, and the FHA furnace will be replaced with an air handler connected to the new boiler. So in the end, the one flue will only handle the one boiler, and the other flue will continue to handle the wood stove. When you say "If no other appliances sharing the chimney, the PVC would need to be insulated through the chase", I assume you mean that the cavity between the PVC pipe and the chimney tile will need to be insulated or filled somehow, right?
  • rob rob @ 9:29 PM
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    Nope, no way

    Dormant chimney can be used a chase for the vent, no other appliances may share this chase. Temporary or otherwise, nope, no way. Besides, you will probably need to run the intake parallel so both terminals are in the same pressure zone and you will need to insulate the exhaust. Let me introduce you your new best friend, Mr. Installation Manual. Nope, no way common vent. Sorry, charlie.
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  • Steve Goldstein Steve Goldstein @ 3:25 PM
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    Venting a condensing boiler through chimney?

    A heating contractor is suggesting that I have installed a Baxi Luna HT condensing modulating boiler. Because of the configuration of my basement, the boiler will be installed near an exterior wall that also has a wrap-around porch. He's suggesting that the intake air come from under the porch, and that the exhaust be vented through 3" PVC pipe running up my brick/tile chimney. My best guess is that this would be a 30' vertical rise. Is this acceptable? I thought high-efficiency modulating condensing boilers couldn't be vented vertically like that....
  • Jim Jim @ 3:36 PM
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    It depends

    Most high efficiency boilers require that the vent intake and exhaust are located and terminated in the same vicinity. If not you can have a difference in pressure.
  • Brad White Brad White @ 3:38 PM
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    Jim is right

    but by all means follow what the manufacturer recommends. Dual parallel make-up air, if that is the way they do it, may have to be balanced in length depending on the manufacturer. At least you are not losing any efficiency by giving up coaxial pipe-in-pipe venting.
  • rob rob @ 9:24 PM
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    Warning- Warning- Will Robinson....

    > A heating contractor is suggesting that I have
    > installed a Baxi Luna HT condensing modulating
    > boiler. Because of the configuration of my
    > basement, the boiler will be installed near an
    > exterior wall that also has a wrap-around porch.
    > He's suggesting that the intake air come from
    > under the porch, and that the exhaust be vented
    > through 3" PVC pipe running up my brick/tile
    > chimney. My best guess is that this would be a
    > 30' vertical rise.
    >
    > Is this acceptable? I
    > thought high-efficiency modulating condensing
    > boilers couldn't be vented vertically like
    > that....

  • viccipe viccipe @ 1:24 AM
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    Steve Due Dilligence

    Steve, impressed with your need to know. ALl of the threads info u recieved sounds good. A power vented unit sucking in fresh air from outside and running 30 ft. high terminating above roof line sounds OK. My feeling are the chimmeny is not best place. Especially with sharing wood stove. run your piping seperate from chimmeny. or find natural rise boiler?
  • Dennis Dennis @ 10:37 PM
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    This Baxi may not be a condensing model

    Running the 3" up the chimney should not be a problem, it would not have to be insulated. The intake could also run up with it if there is room, if there is sufficent room surrounding the PVC the the intake could just be connected to the base of the chimney and draw from around the space not taken up by the 3" PVC. I would have the chimney well cleaned. I would also check the flue the wood stove is using as there may be leaks through morter joints, that would contaminate the intake air. I think it would be best to line the chimney of the wood stove. In a pinch the side wall intake would probably work, most 90+ furnaces can intake from the basement while venting through the side wall, I don't see why boilers would be any different. This method is approved by Weil Mclain.
    Just do it, right.
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