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Question about adding a fresh air pipe to boiler room

stefnstefn Posts: 25Member
So here’s my story and question. We have a high efficiency Dunkirk gas boiler in a separate room in finished basement alongside a direct vent on demand Rinnai tankless hot water heater. We installed the water heater 10 years ago and the boiler 16 years ago. Once we replaced the hot water heater and it no longer vents through chimney we’ve had issues with carbon monoxide in home. The chimney has a new liner that we installed two years ago hoping to resolve the issue. The hvac guy seems to think that the chimney gets cold and when the heat does kick on it takes a long time for the air to go up the chimney so the carbon monoxide comes back into the house. Actually had the fire department here last night. There is a louvered door to the boiler room. There is a window in the basement that we now have cracked open. The hvac guy wants to come and cut a 5 inch hole in the side of the house and run a pvc pipe into the boiler room to bring in fresh air so we don’t have to leave the window open. Is this right? There isn’t a baseboard in the basement and the only heat down there comes from the warmth of the boiler room itself. There are also most of my hot and cold water pipes exposed in the boiler room as well. I’m afraid the basement will get cold, the pvc pipe will condensate, the water pipes will freeze as well as a million other concerns. Anyone have any suggestions? I live in New York where our winters can be very cold. Thank you


  • Jamie HallJamie Hall Posts: 10,407Member
    NFPA 54 requires 1 square inch free opening area per 4000 BTUh for gas fired appliances, as I recall. If that louvered door has that much free area (not gross area) for the louver, and opens into a big space (say a thousand cubic feet or better, it might be adequate -- but I'll bet it's not. You need a fresh air intake properly sized to the boiler plus the water heater assumed to be operating at the same time.

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • EBEBRATT-EdEBEBRATT-Ed Posts: 5,732Member
    Have your HVAC guy put in a properly sized pipe or duct to provide combustion air for the boiler. Question, if your Dunkirk is a high efficiency as you mentioned above it would have a induced draft fan venting into the chimney. The flue pipe should be sealed and it's probably AL29C metal flue it??..... so how are you getting CO??

    you can also put a damper on the new air intake duct wired to the boiler to only open when the boiler fires. It must also be interlocked with the boiler to prove the damper open before the boiler fires.

    This should keep the basement warm enough
  • stefnstefn Posts: 25Member
    So thanks for the responses. The boiler is 80 percent efficient but does not have a draft fan as you mentioned. The liner is the metal you stated and is sealed. The HVAC guy seems to think it’s a backdraft of Carbon Monoxide as the chimney is warming up and trying to draft the air out as the water heater used to warm the chimney but the new one vents directly outside now. Once it gets really cold here and the boiler is running more often we don’t have this issue because the chimney is warm. I just worry about a hole in the house causing more issues than helping. He did mention the automatic damper one but it seems to be way more expensive and come with its own set of issues. I’m just trying to figure out if I should stay with the window cracked open for the season rather than go and cut a hole in the house and chance making the basement really cold, which is my kids playroom, freezing my pipes, causing condensation, etc.......thank you
  • DZoroDZoro Posts: 756Member
    Have the MUA sized correctly, installed with the interlock damper. Then no worries about freezing pipes and cold kids. Make sure the chimney pipe is also sized correctly, that should take care of the CO worries.
  • JohnNYJohnNY Posts: 2,249Member
    Resolving chimney problems requires a specific skill set in many cases. Like you, I'm leery of the HVAC tech's approach. A draft reading under various conditions in the home should be the first test. Something is preventing the chimney from doing what nature wants it to do, i.e. draft upward toward lower atmospheric pressure. Please consider hiring a specialist.
    For installations, troubleshooting, and private consulting services, find John "JohnNY" Cataneo here at :
    "72°F Mechanical, LLC"
    Or email John at [email protected]
    John is a professional Master Plumber, licensed by The Department of Buildings of The City of New York, and works extensively in NYC while consulting for clients in and out of state.
  • DZoroDZoro Posts: 756Member
    That tankless water heater is probably 3-4 times the btu's as your old tanked water heater. @JohnNY is right, we don't know how tight your home is, # bath/exhaust fans, or main house MUA.
  • stefnstefn Posts: 25Member
    So I’m not sure who to hire to do a draft test. It’s really hard to find reliable chimney companies here on Long Island. We have two bathrooms with exhaust fans and my roof is 12 years old and has a ridge vent. The house is 3200 sq feet including the basement.
  • HVACNUTHVACNUT Posts: 2,132Member
    Does the Rinnai take in outside or room air?
    A Fields Controls Fan In A Can will work if the tankless uses outside air, which it should.

    Above all, have both been serviced and maintained?
    CO and "I think it could be..", or " just crack a window" isn't what you want to here. It needs a proven resolve.
  • Jamie HallJamie Hall Posts: 10,407Member
    Look. This one really is a no-brainer. Get adequate ventilation into the boiler and hot water heater space, preferably yesterday morning. Also get good CO detectors and place them in both the utility room and the playroom area.

    Not to be alarmist, but a cold play area won't kill you. CO will.

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • captaincocaptainco Posts: 424Member
    You need an HVAC contractor that has a combustion analyzer and a draft gauge and knows how to use it. A chimney sweep does not know how boilers and flues work together. A piece of toilet paper in front of the drafthood will tell you if air or negative pressure is the problem. Does it suck in when the boiler is not running?

    How did you know you had carbon monoxide problems? Did you have an alarm? How long have you had it? Is it possible you have had CO problems the whole time and didn't know it?
  • stefnstefn Posts: 25Member
    edited December 2018
    So to answer a bunch of the questions...the Rinnai uses outside air through it’s own pipe that is direct vented to side of house. The toilet paper test? Where exactly would I hold the toilet paper in relation to the boiler to do this? We have had CO detectors since owning our first home in 1995. We have detectors on every level and multiple ones in basement with one even being attached to alarm on home. Alarm company called and sent signal through phones to evacuate and call fire department as well. Oh and we service our units yearly. Thank you
  • EBEBRATT-EdEBEBRATT-Ed Posts: 5,732Member
    I am not against bringing in outside combustion air if it needs it it must be done.

    Is you chimney an inside or outside chimney? How tall is you chimney? Any trees or other obstructions? Is the chimney higher than any roof within 10' of it's termination? I would have the liner rechecked and make sure it is properly sized.

    You may have to insulate around the liner. Other than you bathroom exhaust fans which I assume only run occasionally do you have any fireplaces with open flues or any other exhaust fans running
  • stefnstefn Posts: 25Member
    So it’s an outside chimney without obstructions. Yes it’s higher than any roof. Just had liner installed and had a different company come out to check it and said it’s sized properly and they insulated around it. We have one other fireplace that is wood burning but we don’t use it and have it capped and flue is closed.
  • DZoroDZoro Posts: 756Member
    How large is this room? My thought is to put in the boiler air intake system, and a solid door on the boiler room? Has your contractor looked at a larger temperature differential to keep the boiler on a longer run cycle?
  • JUGHNEJUGHNE Posts: 5,652Member
    If he went with a Fan In A Can type air inducer, should you change the louvered door out to a solid?

    It seems we are trying to force the added fresh air up the chimney, the louvered door would let some pressure be lost into the rest of the basement. The air pressure proving switch would probably close and start the boiler without establishing the draft up the chimney.
  • captaincocaptainco Posts: 424Member
    The fact that the CO alarms you have don't do anything until the CO is over 70 ppm for at least an hour doesn't mean you haven't had a CO problem the whole time. It has just finally reached life threatening levels.

    You hold the toilet paper in front of the drafthood opening. This just lets you know if the room is positive or negative. The does not verify the boiler is venting, just room air.
  • stefnstefn Posts: 25Member
    So both thermostats, two zone system, have one degree diff. So the cycle time is long. We do lower temps at night and during day. The CO detectors we have give reading below 70. At this point I am at a loss. My HVAC guy even brought in someone else to check the system. He could t find anything wrong and went with the same idea of cutting a hole in outside walls and running pipe to close to floor to bring in outside air and thus shutting the window. I want my family to be safe but I also want to be sure I am doing the right thing.
  • Jamie HallJamie Hall Posts: 10,407Member
    There seems to be a certain level of obstinacy here. First off, your CO readings should be 0. Anything over that is a long term risk to your health and your family's health.

    Period. End of discussion on that.

    Now your two outside people have come up with the idea of bringing in outside air for combustion. What's the problem with that? Several of us have come up with the same idea.

    Do it. I like the bringing it into the floor idea better; it is what is recommended in general...

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • stefnstefn Posts: 25Member
    Ok. So I just had someone here who said I have a five inch liner in the chimney. He says I should have a 5.5 or 6 and that my boiler is 174 BTU. It’s going to cost me almost $2000 to replace a liner I just installed two years ago. Do I replace liner or cut hole in wall or both? Thank you
  • JUGHNEJUGHNE Posts: 5,652Member
    The Fan in a Can is better than the hole in the wall, runs only when you need it.
    Would pressurize the room (with solid door) to push air up the chimney before boiler lights.....IMO
  • SuperJSuperJ Posts: 478Member
    edited December 2018
    Area of a circle =πr2
    3.14 x 2.5^2 = 19.625 sq inches for a 5" hole
    19.625 x 4000 = 78.5kbtu per 5" hole

    I'm not in a position to comment on what you need, but based on the 4000btu square inch, you would need more like 3 5" (ID) holes to support 174kbtu and whatever your hot water heater is. Tankless water heaters can be big btu's. I bet the power vent on the hot water heater is drawing the space negative. Does the hot water heater support a fresh air intake pipe?

    I wonder if you have derate (enlarge) the hole if you run it thru a length of pipe, since the pipe would add further restriction.

    You need combustion air, no matter what you do with your liner.
  • JUGHNEJUGHNE Posts: 5,652Member
    Does the water heater have it's own combustion air inlet pipe?
  • stefnstefn Posts: 25Member
    The hot water heater has its own pipe to the outside for fresh air intake
  • EBEBRATT-EdEBEBRATT-Ed Posts: 5,732Member
    If your liner is too small no amount of fresh air will fix this problem. You need the right size liner sized for 174.000 btu/hr and the liner should be insulated because you have an outside chimney.
    As far as combustion air is concerned what is your basement like? Storage and a work shop or finished off? What is the cubic footage of the basement? L X W X H

    What size is the boiler flue? I would guess 6". What size is the liner? How high is the chimney?

    It may be possible to use a draft inducer
  • stefnstefn Posts: 25Member
    The basement is finished except for two rooms by outside wall. One is a very small room with electrical panels and main water line. Other room houses boiler and tankless hot water heater. Ceiling is unfinished in these rooms and pipes are exposed. The rest is finished walls, drop ceiling with tiles and carpet. One small window. I was told liner was insulated originally when installed however one new guy today said it wasn’t. My head is spinning. Everyone gives me a different solution with a different price. I will spend whatever I need to in order to resolve the issue correctly and make sure my family is safe. Boiler flue is 6 inches
  • stefnstefn Posts: 25Member
    Here is a photo from the boiler. There is a BTU input and output. Not sure what difference is.
  • EBEBRATT-EdEBEBRATT-Ed Posts: 5,732Member
    A 6" liner is safe. I would put in a 6" insulated liner and be done with it. If you liner is undersized it probably backdrafts on a cold start, once it get going and the chimney is hot the undersized liner pulls enough draft. If your old liner is un insulated in an exterior chimney it cools rapidly.

    As far as combustion air, once the liner is fixed you problem MAY be solved. Depends how much air infiltration (how much your basement can leak air inward) you have. This can only be found by testing.

    can you put a damper on your cellar window with a bird screen and wire and interlock it with the boiler?

    Seems to me the guy that installed the undersized liner 2 years ago screwed up.

    5-6" liners doesn't sound like much. It's only an inch....right. NOT
    a 5" liner is 19.6 square inches. A 6" is 28.2

    6" is about 45% larger than a 5"

  • STEVEusaPASTEVEusaPA Posts: 2,866Member
    edited December 2018
    The person who installed your liner 2 years ago had, or should’ve found, the proper information about your boiler to size the liner properly. If it is undersized, they should replace it.
    But I still think the proper evaluation needs to be done first, as recommended by @captainco & others
  • Bob HarperBob Harper Posts: 811Member
    Air is stupid. It doesn't know where to go unless you put arrows on the pipe. JK. ASHRAE did a study proving passive MUA is wholly unreliable. If the inlet is on the leeward side of the home it will become an exhaust and further depressurize the CAZ. If the outlet is too high it can allow warm room air to create draft and exhaust out the air intake again, further depressurizing the CAZ. Just because you make a hole in a wall doesn't mean the air has to obey. You need a pressure gradient across an orifice or duct to move air.
    A 5" chimney liner is way undersized because, unless its smoothwall you have to de-rate it 20%. A 5.5" smoothwall or a 6" corrugated would suffice.

    You need a combustion analyst with his draft gauge and analyzer backed by training. A trained tech and perform a draft interference test and a depressurization test to see what's going on. If you're really lucky and he has a micromanometer he can measure the pressure gradient in Pascals to document what's going on.

    If your CO alarms are alerting that means you probably meet the medical definition of CO poisoning because that's what the alert algorithms are based upon- 10%COHb. You need a low level unlisted CO monitor.
    John Pilger at Chief Chimney in Smithtown doesn't know combustion analysis but he should be able to size and correct the liner. HTH
  • stefnstefn Posts: 25Member
    Thank you for all the responses. I was hoping the person I hired a few years ago was sizing it properly because this was the exact problem he was trying to fix for me. Unfortunately I don’t even trust him to come back at this point. Bob Harper your suggestion is interesting as I already have John Pilger coming here onThursday to assess the situation. I have also read many discussions that say the MUA is not reliable and can have its own repercussions. I’ve also read that it can help. Unfortunately the internet can be a scary place. I’m hoping John can help me on Thursday at least with the chimney and liner information.
  • stefnstefn Posts: 25Member
    I have also just been informed that I have a 7 inch flue pipe. Don’t know if that makes a difference but I’m assuming it does.
  • NY_RobNY_Rob Posts: 1,369Member
    stefn said:

    ...I was hoping the person I hired a few years ago was sizing it properly because this was the exact problem he was trying to fix for me.

    So this is an ongoing problem at this point, not something new?

    You had this problem before installing the liner?

  • flat_twinflat_twin Posts: 203Member
    If I was faced with a $2k chimney repair to keep a 16 year old atmospheric boiler running safely, I might consider abandoning the chimney altogether and put the $2k toward a modcon boiler.
  • NY_RobNY_Rob Posts: 1,369Member
    ^ That, and for a typical 1,500 to 2,000 sq/ft Long Island home that 174K boiler is probably wayyyyy oversized which just adds to the problem.

    Square footage (heated area only) of the home?
    Age of home & chimney?
  • stefnstefn Posts: 25Member
    So my house is around 3200 sq feet with the basement. It was built in 1970. We replaced the roof 12 years ago and it now has a ridge vent. The chimney is brick and is original. We thought about replacing the boiler but other than this it works well and we plan to sell the house in the next 5 years. This has been an issue since replacing the old hot water with a tankless hot water heater that does not vent through the chimney. We had one prior incident with low levels of carbon monoxide and decided that the way to help the draft issue would be to install a liner since there were some minor cracks in the chimney (so we were told). Hence we brought in what we thought was reputable company to put in an insulated liner. We are finding out that might not have been the case. The flue pipe is 7 inches. The chimney is on the outside of the home and is unobstructed.
  • GBartGBart Posts: 753Member
    My god people, this is exactly how the entire CO awareness began................. I read these posts and ideas and I am floored.

    A couple had a brand new house in the late 80's, it had the furnace in the basement in a closet just like this, they had a slumber party for their daughter in the basement, 13 or so girls all around 12, the guy tried to light a fire in the fireplace, the house like many was tight, NO AIR coming in, he finally got it going by drawing down the furnace chimney because it wasn't running at the time, later the furnace came on and all the exhaust went into the basement and those girls went to sleep and never woke up.

    The tragedy of this story continues because the TV news and so called experts said you need a CO detector and anyone around in the biz should remember this and they flury of CO calls that followed.

    As much as everyone home should have detectors they are supposed to have dedicated combustion air coming in for each fuel burning appliance. PERIOD, the CODE book is so screwed up on this it isn't funny, there is no such thing as free air space I don't care if you have a 10,000 sq ft basement for fuel to burn and exhaust the same amount of air or more has to come in to replace it or at the least you will get soot and poor combustion.

    In my state Ct most of the inspectors won't accept anything but fan in a can because it adds extra air. can't have any CO in the house, you need a fresh air kit and a qualified contractor to install it and test your system. Open windows if you have to for now and keep an eye on your CO meters, hopefully you have digital with real time PPM.
  • GBartGBart Posts: 753Member
    edited December 2018
    I couldn't find that article it's so old but here is another that is very similar in situation.

    It amazes me the code book and inspectors haven't taken this issue by the horns and settled it.

    One thing to do for proper testing is to close the house up and then run the unit, when we are there many times the cellar door or hatch is open, that won't show any issues in fact the unit will run great. With the house closed up get the system running and check draft, go to window and open by a crack and see if air pours in, I've seen houses sucking the exhaust fumes down the chimney of the fireplace or woodstove.

    Bottom line is if there is any kind of fuel burning appliance in a home it HAS TO have combustion air supplied to it from the outside and sized correctly, it doesn't matter if you cut two vents in a closet one low and one high, it's all nonsense the basement is still sealed to the outside, no air is coming in at the rate it is going out, add to that kitchen exhausts, bathroom exhausts, clothes drier exhausts and central vac exhausts, everything in the house is exhausting and just about every home in America is in a vacuum.
  • stefnstefn Posts: 25Member
    You have my attention GBart. My HVAC contractor has not mentioned fan in a can, only putting pipe to outside from the boiler room. We have digital CO detectors throughout the house. What do you suggest as fresh air kit and who exactly installs it and tests system? I can’t seem to get a straight answer from anyone I have had here. It’s all.......”this should solve the problem” which doesn’t really work for me. I’m willing to spend whatever I need to in order to remedy this issue CORRECTLY and make sure my family is safe. Thank you
  • JackJack Posts: 1,044Member
    I wonder how many houses don't have CO or draft problems because the tank water heater doesn't allow the space to go negative pressure? I would not put a hole n the side of the house for just the pipe. The F in Can or the Tjernlund Enforcer, which I prefer, will operate only on a call for heat, so you are not flooding your finished basement area with cold air 24/7. One thing that will improve the draft on the flue is a B-vent connector.
  • GBartGBart Posts: 753Member
    Some of those Dunkirk boilers had a recall for high CO, did any contractors test the combustion exhaust gases for CO to see what the unit is putting out?
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