Smell of Gas - Navien Tankless Heater

Discussion in 'Tankless Water Heater Forum' started by cawhitehead, Aug 10, 2009.

  1. cawhitehead

    cawhitehead New Member

    Messages:
    2
    Location:
    Ottawa,ON
    Hello,

    Recently, we had a Navien tankless hot water heater installed in our home. We are satisfied with it's performance on the hot water side of the picture. However, we notice the smell of gas in our backyard often as the heater runs through it's cycles.

    We had the contractor back to investigate but they said there was 'nothing wrong' and the the unit normally releases a small amount of gas every time it starts up. In my opinion, the amount of smell and the frequency is unacceptable and I was wondering if my contractor is not doing enough to diagnose and solve this issue. One idea we have is to route the vent much higher up the side of the house so the smell dissipates further prior to hitting ground level. I am also considering getting the gas company out as well.

    Thoughts would be greatly appreciated!
  2. Dana

    Dana In the trades

    Messages:
    2,838
    Location:
    01609
    Routing the vent higher to dissipate more sounds potentially dangerous. Tankless hot water heaters & condensing boilers have well-defined limits on vent length not to be exceeded.

    The fact that there is unburned gas in the flue purges in quantities sufficient to smell in open air is suspicious at best, and possibly a disaster waiting to happen. In a longer vent pipe it may end up diluting to an explosive mixture, just waiting for an ignition source. Any unburnt released gas needs to be diluted beyond explosive levels ASAP, not hanging around in long flues until the flame front reaches the rapid-burn zone.

    DO have the gas company give it a well-instrumented sniff. It's possible that the amounts are small and the hazard low, but until it's actually tested by a disinterested third-party I'd remain concerned.
  3. Redwood

    Redwood Master Plumber

    Messages:
    7,450
    Location:
    Connecticut
    Consider me to be a skeptic as well.
    I just couldn't figure a way to say it as diplomatically... LOL:cool:
  4. cawhitehead

    cawhitehead New Member

    Messages:
    2
    Location:
    Ottawa,ON
    Thanks folks for your response.

    The Navien installation manual tells me the vent pipe can run a maximum of 100 feet and have six elbows. Right now we have about 6 feet and three elbows, so I have some additional room there.

    I am going to call the gas company on this one - I'm pretty disappointed in the contractor not taking this seriously enough and will likely file a compaint with the BBB. Like most HVAC contractors in Canada they are being run flat out by all these incentives being offered by the gov't for energy efficiency.
  5. Dana

    Dana In the trades

    Messages:
    2,838
    Location:
    01609
    That's a maximum of 6 elbows independent of total length, with each 90 degree elbow counting as 5 linear feet, every 45 degree elbow counting as 2 linear feet. So your 6 feet + 3 elbows counts as 21 feet (and yes, you have some room.) But more feet of vent increases your chances (and size) of a potentially explosive charge if indeed there is a malfunction that's causing the smell. With a shorter vent it hits the dilution of the open atmosphere faster, and the total volume/energy content of enclosed unburnt mixture is limited.

    Hopefully this will either test out as defective and the unit gets repaired or replaced, or that the mixture of the unburnt gas is well-diluted in the flue and not dangerous (in which case you could extend the vent.) Have you tried to contact Navien directly?
  6. Ian Gills

    Ian Gills Senior Robin Hood Guy

    Messages:
    2,777
    Location:
    USA
    I thought I could smell gas from outside when our old furnace started up (it vents through our chimney). After several months I called the gas company and they actually found a gas leak in the line under our neighbor's yard. It was all fixed with the minimal of fuss and mess (just a small hole dug and a valve inserted).

    They shouted at me for waiting two months.

    So the leak might not be where you think it is.

    It's worth getting the gas company out just to see the sniffer in action.

    It looks like a dog's nose on a stick and goes bonkers when it smells gas....just like a Republican voter responding to State healthcare...troublemakers.
    Last edited: Aug 12, 2009
  7. zl700

    zl700 DIY Senior Member

    Messages:
    237
    Location:
    Texas
    Many times the smell of gas is confused with the products of combustion, especially start-up and shutdown when CO is at it's highest, and the combination of formaldehyde and other by products including the burned/unburned mercaptan or a similar sulfur-based compound added to the gas.
  8. flamefix

    flamefix New Member

    Messages:
    71
    Location:
    Exeter, England
    It is quite common to detect a smell of gas at the flue from a boiler. But any smell of gas should be reported and investigated that's what would happen here. It could be a leak it could be an incorrect timing cycle between gas and spark, poor electrode positioning (ie failure to spark quickly enough, weak spark). So definitely worth having it checked through. Anyone you have come should have a suitable combustion analyser to check the flue gas and ratio. you would want the ratio of co:co2 to be much less than 0.004 anything approaching that would indicate a setup fault.

    I would suspect though that the smell is typically the residual gas air mix that is blown into the combustion chamber after ignition or before ignition takes place.

    Typically the burner will self purge on start up, running the fan to clear the combustion chamber then it will inject a controlled premix of air and gas before then starting to spark.

    If it is not a premix burner then gas will be let into the combustion chamber via a pilot whereupon a spark will be set to ignite the gas. Again a small amount of gas may be detected before the full combustion takes place when the main burner operates.
    If you have this type of system then I would suggest this is not the most efficient type of burner. A premix burner is the way to go with a new gas boiler.
  9. zl700

    zl700 DIY Senior Member

    Messages:
    237
    Location:
    Texas
    Clueless UK-

    A Navien water heater is not a boiler and is the only distributed tankless in the US that has a premix burner (with a spark igniter), unlike the rest that are a lean/rich burner setup.
  10. flamefix

    flamefix New Member

    Messages:
    71
    Location:
    Exeter, England
    semantics, xenophobia and "pot and black" spring to mind hardly helpful for the reader. end of :)
  11. ellrose

    ellrose New Member

    Messages:
    1
    Location:
    new york state
    ****
    My experience was exactly the same. The manufacturer's rep came to my house along with the local salesman from a large plumbing distributor. They came up with a number of possible reasons why we may be getting more smell than other people, but most of it was that the exhaust wasn't being dissipated by the wind, and that we should put the exhaust up higher. In our case he recommended going up an old chimney that we no longer use. That was helpful, but we still didn't feel comfortable. Then I found your post.

    I called the gas company after reading your post. He took a gas detector all around the unit and at the exhaust outside. There was Carbon monoxide, that you would expect but no gas. He said that is what you want to find. He also told us that the stuff we did smell was uncombusted gas from the shut off that had to be pushed out of the exhaust to keep from getting a "pop" when starting up again -- that was a big relief because we were somewhat concerned that there might be a safety hazard. Also, because we thought we weren't getting complete combustion made me concerned that I might be getting far less than optimal efficiency. ie not saving the money I purchased the unit for.

    He also said that if the manufacturer's rep said go up the chimney, it's probably OK to do so, as long as we don't exceed the maximum distance of 100'. If I didn't have that option, I think we would have to tell them to get the system out and put in something that works properly. It really stinks. :eek:
  12. gmrj

    gmrj New Member

    Messages:
    2
    Location:
    Edmonton
    Hi there,

    I realize this was posted almost a year ago but I am a gasfitter who has recently encountered several Navien tankless water heaters with similar problems.

    Within the last month I have responded to 3 customer complaints of gas odours outside of their homes. This is typically a small leak on the gas meter but in these 3 situations the home owners did not notice the odour at the meter but instead at the exhaust termination of their hot water heaters. What these customers were smelling was not natural gas but was an aldehyde odour associated with the improper combustion of the natural gas inside of the hot water heater.

    In each of the 3 instances, I checked the products of combustion with my gas detector and in all 3, I found 0% lel natural gas (perfect). However I detected large amounts of carbon monoxide. With the wand of my detector 2" away from the exhaust termination I was getting carbon monoxide readings ranging from 300ppm to 700ppm. An appliance that is burning properly should have carbon monoxide readings of 10-30ppm so as you can see, the amount of co exhausting from these 3 units was excessivly high and needs to be corrected before the problem becomes much more significant.

    Fortunately these units have sealed combustion chambers and are connected only to the outside air, but to be safe I checked the inside of the houses for carbon monoxide and in all 3 cases I found 0ppm carbon monoxide throughout the houses so it was safe to continue using the heaters untill the installers were able to make the repairs. All 3 of these units were installed in new construction and had not been operating for more that 3-8 months.

    I have spoken to a couple of colleagues about this problem and they have seen the same issue. I don't think the problem is common but clearly it's happening enough that it is a concern that is not isolated.

    If you are noticing an odour at the exhaust location of your water heater, try and characterize the smell but don't put your face directly in the exhaust. Put yourself in the path of the exhaust but remain a couple of feet away from the vent termination. If your appliance is not working properly this is more than close enough to detect the odour.

    1. Does it smell sulfuric? Natural gas is odourized with an 'eggy' type of smell.
    2. Does it smell a bit like car exhaust? This exhaust type of smell is called an aldehyde odour and indicates improper combustion.

    If you detect these odours, try calling your gas company and see if they will come out and check the exhaust with their instruments. It shouldn't cost you anything and they should give you some impartial and safe advice.

    Unfortunately I am at the beginning of my research of what is the cause of the problem and learning about how to correct it but I wanted to let you know what I have found and to let you know that this is not how the appliance should be running. It is very important to have this checked out and resolved as soon as you can. If anyone knows more about the problem and how it can be fixed, please let me know.
  13. Dana

    Dana In the trades

    Messages:
    2,838
    Location:
    01609
    I'd be curious to know if there are similar issues with other manufacturer's tankless heaters. Are you looking at Navien-only or a range of manufacturers & appliance types?
  14. gmrj

    gmrj New Member

    Messages:
    2
    Location:
    Edmonton
    I have only seen this problem in Navien units but I don't encounter very many tankless hot water heaters as they are not yet a common appliance in my city.

    I have seen something similar in a Lennox high efficient furnace but rather than the aldehyde odour and high co read existing for the entire heating cycle, the odour and co read would be begin at the time of ignition and disappear for the remainder of the cycle after 1-2 minutes of operation.
  15. ronrca

    ronrca New Member

    Messages:
    7
    Location:
    Canada
    I have noticed the same odor as well. The intake/exhaust is located near a window (4-5' away) and when I open the window, I smell sulfur.

    gmrj,
    Thank you for your response. Im out in Wetaskiwin and would be very interested what you find out. When you do find out, Id appreciate letting me know as well.

    Thanks
  16. zl700

    zl700 DIY Senior Member

    Messages:
    237
    Location:
    Texas
    They all do it to some degree. They fire from 10,000 to 199,000 BTU in variable steps then suddenly shut off when flow stops, as they must or they would boil the water and spit out the relief. What you are smelling is a combination of CO and unburned gas.

    The Navien is a little worse, since their premixed forced draft burner may have a little bit of gas in the mix chamber versus all other tankless may burn theirs off better with the lean/rich pre/post mix burner below the heat exchanger.

    Nothing to worry about and certainly not any reason to do a big study or research on it since the cause is so obvious.

    I have noticed, that in perhaps the last 8-12 months their newer units have a better purge operation after shutdown to assist in the alleviation of fumes.
    Last edited: Jun 29, 2010
  17. Holman

    Holman New Member

    Messages:
    1
    Location:
    Paso Robles, CA
    My Navien Tankless water heater is just 6 months old. I too get a strong smell of gas when it fires up. Unfortunately the tank is mounted just outside our kitchen window so the smell comes right into the house. I will have it check out.

    However, I also hear a great vibration as a loud deep rattle which can wake up anyone in the house...any ideas on that one?
  18. johninsask

    johninsask New Member

    Messages:
    1
    Location:
    Rockglen, SK
    I am currently experiencing this issue with the Navien, Model NR 240 NG. I followed your advice and called both the Gas Company and the Gas Inspector. Gas Company reported 4% LEL and 350 Carbon monoxide. Rep stated this is way to high. Gas Inspector called installation company. Company then called me. Plumber has apparently called Navien Tech Support and they informed him levels and odours are normal. Plumber now wishes to run exhaust outlets up former chimney to roof so I don't smell the gases. Inspector to visit next week to confirm installation conforms to Code.
  19. BizzyBeePlumbing

    BizzyBeePlumbing New Member

    Messages:
    23
    Location:
    Raleigh,Nc
    I had researched this problem on a tankless repair once, the gas company red tagged the unit, the gas valve was faulty, after replacement, the smell went away. I bet Navian has a batch of bad gas valves. In my opinion they are poor units, Noritz and Rinnai are top of the line units.
  20. BizzyBeePlumbing

    BizzyBeePlumbing New Member

    Messages:
    23
    Location:
    Raleigh,Nc
    this is either a venting issue or a gas valve issue. the unit sounds like it starving for gas or air. I have also had fan speed issue that result in this noise, especially when the air is heavy in the mornings and the venting has not warmed up
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