Hot Water Heater intake vent collecting frost - plumber says it's normal...

Discussion in 'Water Heater Forum, Tanks' started by tezakhiago, Mar 7, 2014.

  1. tezakhiago

    tezakhiago New Member

    Messages:
    5
    Location:
    Alberta
    Hi there,

    I just bought a new house in Calgary AB almost one year ago. It is fitted with a high-efficiency gas hot water heater, that has both an intake and exhaust vent to the outside, located about 8 inches apart on the exterior wall. Both pipes are simple ~2.5" PVC piping that end in a 90 degree turn facing downwards, with no bug screens on the pipes.

    We've had some bitter cold temperatures here in the last few weeks, and in the past week the hot water heater has stopped working 3 times. I am able to go outside and clear out frost that has built up inside the intake vent, which immediatly causes the water heater to start running again. We're not talking about a lot of frost, it's only a small amount. It's hard to tell if it's completely blocking the pipe because of the shape of the pipe, but it looks to me like it's just forming a layer around the interior wall of the pipe that's reducing the effective diameter of the pipe from ~2.5" to maybe 1.5". This is a recurring problem that has happened 3 times in 6 days but had not happened all winter long until now. As for weather, it was -30 degrees C when it first happened but had warmed up to -17 degrees when it happened last night. There has been no snow, but the amount of humidity in the air has increased.

    We are still covered by a warranty for one more week (until March 15th), and we had the builder's plumber out on Monday to look at it. His response was 'this happens all the time, you just have to keep the intake clear of frost. There's nothing we can do'. Problem is, this isn't happening to our neighbours, so what is different about the design of their hot water system that they aren't affected by the cold and we are? Also, my furnace air intake is not clogging up.

    Has anyone encountered an issue like this, and what can be done to fix it? Would poor design of where the intake vent is placed cause this? Any insight would be helpful.
  2. ankhseeker

    ankhseeker Member

    Messages:
    78
    Location:
    California
    as just an amateur, some thoughts come to mind. check your operating specs and see if the unit is designed to shut down in that cold of climate. Also, if the exhaust of the heater contains steam condensate, it might cause abnormal build up in the intake. Are there any installation instructions that might give you a clue as to a proper/recommended way to install the vents? Sometimes the installation pictures make it obvious. Just some thoughts. Maybe find another plumber to come and look at it for a second opinion. Take a pic of it and see if the manufacturer agrees with the install.
  3. tezakhiago

    tezakhiago New Member

    Messages:
    5
    Location:
    Alberta
    Ok, that helps a lot. I'm at work and don't have the model info right now but that's a good suggestion, then I can find a manual for it. I wonder if my builder will pay for a plumber's second opinion...

    The only thing that we can come up with that has changed is that when we first bought the house, the circulation pump was not plugged in for almost a year. We didn't know that it existed and were finally told by the builder when they did our final inspection that we can have that on, which solved the previous problem we had of having to wait forever for hot water. Now the pump is always on, so my guess is that that's putting a greater demand on the hot water heater, so it may be running more through the day and night. That would in turn cause both more exhaust to be produced and more air to be sucked into the intake, causing a faster frost build up.
  4. cacher_chick

    cacher_chick Test, Don't Guess!

    Messages:
    3,239
    Location:
    Land of Cheese
    It happens with condensing furnaces and heaters in freezing weather. As long as the vent piping is pitched as per the manual, there is little else on can do. Having the ports on the south side of the house can help.
  5. tezakhiago

    tezakhiago New Member

    Messages:
    5
    Location:
    Alberta
    Does anyone know what the guidelines are for exterior ventallation of a gas hot water heater? I beleive that the exhaust is being recycled into the intake, and since that exhaust is probably full of water vapour, it is condensing and freezing as it is pulled into the frozen intake pipe. It is currently installed with both the intake and exhaust at the same height off the ground. The manufacturer's guidelines are a little confusing to me, but I beleive that it says the exhaust outlet should be at least 12 inches above the height of the intake in order to prevent recycling of exhaust.

    Cacher_chick, I understand that it can happen in freezing weather, but why is it that just MY system is freezing up, but not the neighbours, and then why can't my system be adjusted to function in the same way as my neighbours to hopefully prevent this from happening?
  6. Terry

    Terry Administrator Staff Member

    Messages:
    14,804
    Location:
    Bothell, Washington
    You can take a bit of pipe and seperate them a bit farther apart. Moisture from the exhaust may in fact be happening on the intake.
    Last edited: Mar 8, 2014
  7. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,824
    Location:
    New England
    The installation manual likely lists the proper placement of the intake and exhaust ports...my guess is also that they are not proper and you're getting moisture from the exhaust closing off the intake when it freezes.

    When I had my boiler installed, they didn't follow the proper placement and on a cold day, it froze over. I checked the manual, saw their diagram, thought it was wrong, called the manufacturer to verify, and it was wrong. The installer came back and swapped things around, and it's been working fine for over 5-years without issues.

    The safety interlocks on the device are quite sensitive to pressure differentials and air flow...when it senses an obstruction, it will stop.
  8. tezakhiago

    tezakhiago New Member

    Messages:
    5
    Location:
    Alberta
    Ok so I've had a chance to review the manual, and I believe the installation is at least to code and to the manufacturers minimum guidelines. The manufacturer says "Clearance to non-mechanical air supply inlet to building or the combustion air inlet to any other appliance must be 12 inches", which it is. I've also driven around my community, which is all houses built in the last two years, and this type of installation is very common, on at least half of the houses around here. Here are some pictures to illustrate how it's installed:
    Labelled.jpg

    Because it's so common, I can't possibly imagine that it's not up to code at least.

    The other common type of installation is like my furnace vents, which I've seen on many houses as well:

    20140307_154735.jpg

    So why would one builder install vents the way they did on my house, and another builder would do it the other way? What are the advantages/disadvantages of the two methods?

    The manufacturer goes on to say "In locations where sustained outside air temperatures are below freezing, it is possible for the vent terminations to accumulate ice build up due to adverse local climate conditions. The optional concentric vent terminal is more resistant to this ice build up." It doesn't specify how to install a concentric vent or what that is.

    Anyway I'm anticipating an argument with the builder to get this fixed, any suggestions?
    Last edited: Mar 7, 2014
  9. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,824
    Location:
    New England
    A concentric system is less prone to ice accumulations because the heat from the exhaust helps to keep the intake from freezing over. The concentric adapter has the intake surround the exhaust once it converts from the two pipes. Mine isn't exactly a concentric vent cap, but it does incorporate both into the same fixture...in my case, they had the exhaust on top, and the condensation dripped down over the intake and froze it over...the installation instructions showed it reverses (there's a baffle in it to keep the two air streams from crossing over). But, I think the system where they direct the exhaust up into the T while the intake comes from below is probably an easy fix that should work. The hotter air will rise and take most of the moisture with it. If the installer won't do it for you, it wouldn't cost you much to resolve it yourself.
  10. Terry

    Terry Administrator Staff Member

    Messages:
    14,804
    Location:
    Bothell, Washington
    [​IMG]

    It would be so easy to glue in more pipe to the intake and locate if farther away.

    Just for an example, I had a laundry room in one home, and in the Summer I opened the window to that room.
    It was almost impossible to dry clothes with the window open. The dryer exhaust was looping and recycling through the dryer. Closing the window fixed the problem.

    You are $25 away from a fix on your frost problem.
  11. Reach4

    Reach4 Active Member

    Messages:
    1,932
    Location:
    IL
    That's an interesting fitting on the furnace exhaust output.

    I think that installation could benefit from PVC dye. I can see an advantage to having purple siding on a house: you can get purple PVC dye very easily. ;)
    Last edited: Mar 8, 2014
  12. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,824
    Location:
    New England
    Another thing to check is the minimum distance between the exhaust/inlet from those two combustion devices (furnace and WH). If there's a dryer being vented somewhere nearby, that can be particularly bad as it can contain some chlorine from bleach, and that can produce acids if it gets sucked into the intake of other devices. When I had my closed combustion boiler installed, I ended up crossing the house to the other wall (I live in a townhouse condo only has two outside walls) because both mine and my next door unit's dryer vent went out the back very close along with their furnace...I did not want to be sucking in their exhausts (plus, I couldn't get the required minimum separation distances).

    In your case, if you leave the intake as is, and turn the exhaust up and maybe terminate with a T like shown in the other examples, it should pretty much eliminate the condensation and icing on the intake. I'd also consider maybe a screen - some manufacturers require them, on the two vents.
  13. tezakhiago

    tezakhiago New Member

    Messages:
    5
    Location:
    Alberta
    Thanks for your help guys, I am trying to get my builder to make the switch for me but I will do it myself if they won't. I won't know if it worked for a year though...

    One more question, can anyone with industry experience tell me why it is common practice to install furnace venting as shown in the picture above, and why they might choose to install it a different way for my hot water heater?
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