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Typical venting for high-efficiency wall-hung boilers?

Dan_GCDan_GC Member Posts: 7
I currently have a gut/rehab underway on 3rd floor of a building. In the next phase we may be adding a high-efficiency boiler on second floor. With everything open above 2nd floor up to the roof now, it would be very easy to add vent pipe to be connected to the boiler in the future. Is it possible to take a good guess at vent requirements, and what would those be? Possibly 3 or 4" PVC for intake and exhaust? We are not ready to make a boiler selection now.

In this phase we added a tankless water heater and in researching it, typical models (but not all models of course) use 3 or 4" PVC. If we could make a best guess on the boiler venting now, it may save us a whole lot of trouble and expense in the next phase. Any thoughts?


  • SWEISWEI Member Posts: 7,356
    A heat loss calculation

    will answer that for certain.  With some basic information, we should be able to get close enough that you can size the flue(s.)

    How many square feet will this boiler be heating?  What type and age is the building construction?  Any envelope upgrades?  Where is it located?
  • Dan_GCDan_GC Member Posts: 7
    edited June 2014
    additional info

    Thanks, SWEI. The boiler will heat an area of the building of about 2,000 sq. ft. total, two floors, one on top of the other. The building was built in 1890, but is being gradually upgraded with closed cell spray foam insulation and other details. Before the boiler is added, it will all be highly insulated with walls at R-20 or higher, top floor ceilings at R-60 or better, Marvin windows with double or triple glazing, etc. We've already added a tankless water heater in this phase, so the boiler may or may not need to supply domestic hot water. (We estimate we're close to capacity with the tankless as winter water comes in from the city at about 38 degrees.)The building is located in Chicago.
  • icesailoricesailor Member Posts: 7,265
    Exhaust Venting:

    Will the AHJ approve of a uninspected vent system for this future gas appliance with the pipes buried where they can't be seen or serviced?

    My old dead boss used to always tell us, "First, establish your vent".

    I would suggest that no matter what you do in the future, if you plan on putting a boiler on the second floor, you place it so you can easily vent it and it all can be seen for inspection. Don't give AHJ's any reason to squeeze your nuts.

  • SWEISWEI Member Posts: 7,356

    this at perhaps 20 BTUs per square foot, or roughly 40,000 BTU/hr.  Even if it's 50% higher, you're looking at no more than a 3" flue, quite likely a 2" depending on developed length and the particular appliance you choose.

    Ice beat me to it -- you need to make sure this gets a mechanical inspection and that may well require pulling a permit for the yet-to be-installed boiler.  If it were my job, I'd install polypropylene venting.  FIrst, it's the right thing to do, and second, PVC might not be allowed in your jurisdiction by the time you actually install the boiler.
  • SnowmeltSnowmelt Member Posts: 1,192

    Try the Ncb units Fromm navien, they have 2 inch venting and does domestic and space heating.
  • Dan_GCDan_GC Member Posts: 7

    The vent pipe will be viewable by looking up the chase from below and will be further accessible by removing a medicine cabinet on third floor, which will give an opening directly into the chase. Worst case we can cut an opening somewhere for inspection, but that is still far easier than trying to install venting after everything is finished. I'm a carpenter/contractor and know the local practices. The reality is these things are seldom inspected anyway.

    So, are these wall hung boilers then typically vented using plastic pipe (i.e. PVC)? When putting in the tankless water heater, I found some required stainless steel venting (Rinnai) and others used PVC. We chose the Noritz primarily on the basis of being able to use PVC. With the 199,000 BTU Nortiz, the smallest PVC allowed was 3".

    Right now the difference in cost between putting in 2", 3", or 4" PVC is negligible. Is there any downside to running 4" PVC just to be sure the pipe is large enough for anything? And why was the statement made about polypropylene being "the right thing to do"? If we follow manufacturer's specs we should be good, right? Do many of them require polypropylene venting?

    The run is less than 20' vertical through the roof, with maybe a couple of elbows.
  • RobGRobG Member Posts: 1,850

    As well as getting it inspected, take plenty of pictures. I have seen too many instances where the inspector who approved something in one phase was not the one who inspects the second phase. As well, anyone who needs to work on the system in the future will know where everything is at. Label the pipes also so that the future installer knows what is what.

  • SnowmeltSnowmelt Member Posts: 1,192
    Your ?

    About running the pipe bigger, yes it does make a difference but it's about back pressure. Although most of time going up one pipe size is ok follow specs. If it calls for 3 inch up to 100 feet you really don't want to install 4 inch at 20 feet. It may set the machine off in an error code.

    The other question is about other material vs pvc, although lots of jobs are done with pvc, the fact is that pvc is claim to melt at about 140 degrees.

    There is a nice product out there called central-therm, it may be one what your looking for....
  • jonny88jonny88 Member Posts: 1,139
    with Swei

    I think we have all learned over the years about venting mod/cons.Unless stated by manufacturer polypropelyne is your best bet.If you are using chimney as a chase I like to use centrotherm.
  • RobGRobG Member Posts: 1,850

    I prefer using central-therm  :)
  • icesailoricesailor Member Posts: 7,265
    edited June 2014

    Personally, not to sound like a pruck, but you're a Carpenter/GC. I think that you should stick to point loads and other construction issues. Leave the piping, installation and venting of gas appliances to the trained, licensed people that specialize in doing these installations. I'm sure that you can find someone that will install what you bought and is willing to take the responsibility of what YOU did. Some of us will not.

    There's never enough time to do it right. But always time for someone else to do it over.

    I've dealt with inspectors that wanted to see EVERYTHING before it was covered up before an inspection. Some inspectors don't like to sign off on things they can't see. Like flue joints in a chase, with PVC pipe on a 199,000 BTU gas heater. 1,000 more BTU's puts it into another category. Why do you think they all stop at 199,000 BTU's?
  • RobGRobG Member Posts: 1,850

    The most simple solution is to pick the equipment that will be used and run the the vent accordingly. To try and guess what MIGHT be installed is a crap shoot.


    Occam's razor, the easiest solution is usually correct.
  • Dan_GCDan_GC Member Posts: 7
    PVC vs. Centrotherm

    What is the advantage of Centrotherm over PVC?

    I realize it would be ideal to do the final boiler selection now, then install the venting based on that. But I do not live in an ideal world. The boiler will not be installed for 2-3 years. We're not in a position to do the selection now, and we don't even know what will be available in a couple of years. So we have to do the best we can.

    I've been doing some searching, and the ones I've found all seem to use PVC.
  • SnowmeltSnowmelt Member Posts: 1,192
    edited June 2014

    Pvc seems to be a material that will melt when temp gets to high, so I think I'm not sure but local codes saying anything above 140 degrees is to hot for pvc , so they want you to use central therm which has a higher rating.

    Just an FYI the central therm has a flex with a cap so it can be used in a chimney application
  • icesailoricesailor Member Posts: 7,265
    Sch 40 PVC:

    Is there any manufacturer of PVC pipe and fittings (Like Charlotte Pipe & Foundry) that specifically approves their product for venting gas appliances? Are there any suppliers of gas appliances that manufacturer Sch. 40 PVC pipe and fittings for venting their manufactured gas appliances?

    There's still a lot of Ultra Vent and Plexco out there that was supposed to be removed. And it was never removed. Fun when you crawl into a crawl space to service a gas appliance vented with Ultra-Vent, and the clips are rusted away and it has come apart. You didn't bring your CO detector with you and in panic, you wonder if you're going to get out. That dizzy feeling is either an oncoming heart attack, a panic attack, or CO poisoning. Anyone that has experienced that, knows what I am writing about.

    When you see a gas appliance, vented with snow white PCV pipe and fittings that is now the color of Cappuccino, you should know that there is a problem with overheating. Even CPVC is limited. PP or Stainless will be the choices some day.

    Maybe some asking here need to have a nice sit down chat with their liability insurance provider and have a close and personal discussion about just what their liability covers and who does what.

    Someone I used to do work for, just had a 72 YO Mason/bricklayer type, fall off some pipe staging, without outriggers or safety nets, no harnesses etc, landed on his head and was killed. I'm sure that there will be discussions with the insurance carriers over what is a "Sub Contractor. Is this 72 YO "Subcontractor" qualifying as a subcontractor
  • Steve_210Steve_210 Member Posts: 585

    Be careful using pVC even if the local codes allow right now it may not be legal by the time the boiler is installed
  • icesailoricesailor Member Posts: 7,265
    Rotating blades:

    Unlike Plex-Vent and Plexco, where it was sold as high temperature gas venting, the PVC pipe and fitting manufacturers have never legally approved the uses of their products for venting heating appliances. So, when the effluent hits the rotating blades, they will have absolutely no responsibility for its use. Just because XYX gas heaters approved it, doesn't make it really "approved".

    Centro Therm, PP and Stainless Steel like Dura-vent is.
  • HenryHenry Member Posts: 965

    S636 ULC approved PVC venting is essentially grey PVC sch 40 with a different colour and new labelling. They used the standard for sch 40 PVC which is max 75 PSI at 140F! ABS is actually a better material as it only starts to deform at 217F. The best materials are PP or S/S.
  • icesailoricesailor Member Posts: 7,265
    Alone on the dance floor:

    That may be so. Is that Charlotte?

    It may be gray, but the high temperature is still 140 degrees. If there is any discoloration of the pipe or fittings, and have they made all the fittings you need in Gray?

    If there's any issues, and there is discoloration, the pipe manufacturers will leave you on the dance floor to find new partners.

    Once installed, hope that there isn't a code change and when a final is done, that the AHJ inspector approves it. I have a LOT of trust for AHJ's.

    In the jurisdiction I came from (Massachusetts), whomever applies for the gas permit, is responsible for the gas piping and the venting. It can not be transferred to a third party without a new permit. Most Massachusetts plumbers and Gas fitters would never risk accepting something unpermitted that they did not install. First of all, because the vent installation requires a permit and an inspection, if there is no permit, it is 4X the cost of the permit as a fine. And it might need to be totally exposed. I can see a AHJ inspector wanting to see each and every joint under a pressure test. Just to keep his/her inflated head in place. I used to work around an inspector, a rather large fellow, that refused to go into crawl spaces through an access in the floor unless it had a proper ladder down to the dirt. No 2X4 job site ladders. If he didn't like it and it wasn't to OSHA standards, you'd be paying for a re-inspection. And he didn't like going on jobsites that looked like the dump.  His favorite expression was "A clean job is a happy job. I'm happy". Or, ",,I'm not happy. I'll be back".
  • SWEISWEI Member Posts: 7,356
    If this were my job

    I would size it, design it, and then get a letter from the Mechanical Bureau accepting the proposed phased construction approach.  Then pull a permit, install the vent and probably the NG line for the boiler, and have it all inspected.
  • RobGRobG Member Posts: 1,850

    Why can't the owner pick the equipment now? If the right equipment is specified now, it will still be available in two years. I would think that an inspector is not going to approve a vent that he does not know what appliance is going to be attached to it.

    Pick it now, put it in writing and be done with it. Or just leave a chase that will be accessible for inspection down the road.


  • CMadatMeCMadatMe Member Posts: 3,066
    Where Are You Located

    Is the question that needs to be asked. Cause if you live in the 5 Boroughs of NYC come Sept 1, you cannot vent ANY piece of equipment with PVC regardless of what the install manual says.

    There are also a few municipalities out in LI that already will not allow it. It's a slowly changing thing so I'd make sure that there are no changes being made to the building code in your, city, town or village.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • Dan_GCDan_GC Member Posts: 7

    We will not be picking equipment now for the reasons mentioned, including the fact that the final size and footprint of the apartment has not been determined, wall assemblies for the next phase have not been determined for heat loss calculations, and we may or may not need additional domestic hot water capability depending on how well things work out with the newly installed tankless water heater.

    It seems that the choices are fairly simple: 2", 3", or 4" venting, with 4" posing little downside.

    PVC or polypropylene, with polypropylene such as Centrotherm being the safest choice. So... 4" polypropylene? Seems easy, what am I missing?

    For you guys that use polypropylene, I am assuming there is no reason to use it for the intake air and you still use PVC for that, right? Or do you use polypropylene for both, and why?
  • ZmanZman Member Posts: 5,830

    I don't see a need for bigger than 3". Unless you have very long runs(over 60') or a very large boiler(over 250k). 3" is more than enough.

    Polypro is going to be the standard soon. The code they are a changing, don't get caught with the wrong product in the future.

    The intake can be PVC.

    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Dan_GCDan_GC Member Posts: 7
    HVAC "Professionals"

    Icesailor, I don't want to sound disrespectful, but would love to hire someone to do it for me and have it done "right". However, as I found out yet again when trying to have the tankless water heater installed, many of the HVAC people out there don't have much of a clue what they are doing, so I might as well try to understand as much as possible myself, to avoid problems.

    On the tankless WH, I had 6 different companies come out and tell me what they would do for me. Not one of them thought that I would need a larger gas meter, even when specifically asked. My own simple research showed that I clearly did, and the gas company confirmed it. None of the companies was clear on the gas pipe sizing. My own calculations showed that I needed 1-1/4 gas pipe to ensure adequate supply, given the lengthy distance and number of elbows. Most of the companies could not answer the basic questions, the answers to which are available in the install manual, which I actually read.

    In the end, I bought the tankless on Amazon, installed it myself, and had my licensed plumber make the pipe connections. If I would have used the professional HVAC guys I talked to, I am fairly certain that this unit would not function correctly.
  • Dan_GCDan_GC Member Posts: 7
    edited June 2014

    So I completed the venting. 4" Centrotherm Innoflue and 4" PVC for the intake.

    The PVC run cost about $50 in materials. The Centrotherm cost about $230. This is for about 15' of pipe, and a couple of elbows and clamps.

    I'm not in the HVAC business and I'm doing this only once, so the additional cost of the Centrotherm is not a concern, if it avoids tearing into the wall later to do a retrofit. But if I was in the business, I would be pretty skeptical as to whether the additional cost is warranted, unless the manufacturer requires it instead of PVC.

    I called around to about 8 larger HVAC suppliers in Chicago, and nobody had ever heard of it. I finally emailed the company and found that there are only two suppliers in Chicago and one in the nearby suburbs that carry it. So it is apparently rarely used here.

    The supplier I went to to get it is also unfamiliar with it. Luckily Centrotherm has their catalog online, and I was able to give them part numbers. Even with that, they still managed to give me the wrong parts, but I was able to show them the very clear and helpful pictures in the catalog, which allowed me to get what I needed.
  • Rich_49Rich_49 Member Posts: 2,540
    Rest Easy Dan

    in several years when PVC venting becomes more of an issue and the problems associated are more well known you will be glad you did this .  Many of us have seen the bad stuff that happens on older installs , this pipe is used by professionals who give a damn . Sufficed to say there are many whom money means more to than the safety and well being of the end user .
    You didn't get what you didn't pay for and it will never be what you thought it would .
    Langans Plumbing & Heating LLC
    Serving most of New Jersey, Eastern Pa .
    Consultation, Design & Installation anywhere
    Rich McGrath 732-581-3833
  • CMadatMeCMadatMe Member Posts: 3,066

    Centrotherm is nothing new. Been dealing with them for 4 years now. Just because

    you've had an experience from the uninformed and what seems like suppliers that

    are not keeping up with advances in the industry isn't the product or Centrotherms issue.

    Here's where that additonal cost makes sense. I'm giving Mr and Mrs Homeowner a UL

    Certified and tested venting product not a vent system that is installed with material that

    moves waste into a sewer or septic system. Secondary Mr and Mrs Homeowner I'm

    providing a venting system that carries a 10yr warranty.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
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