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Condensate tank evaporation loss question

baj702 Member Posts: 44
Does anyone know approx how much water might be lost through the condensate tank vent? I do have a 10 foot riser off the tank to try and minimize the lost.

Also, when the boiler hits 1.5 psi and turns off, how long should it take to get down to .5 psi to turn back on?

I replaced the last 50 feet of the steam main that was leaking, but I'm still losing about 1 gallon a day on about 2000 EDR.


  • Jamie Hall
    Jamie Hall Member Posts: 23,276
    Not that much should be lost from the condensate tank -- unless the condensate is hot. And if the condensate is hot you may have a failed trap somewhere to add to your troubles...

    It's almost impossible to give any kind of exact figure for the timing for pressure drop. Depends too much on the mass of metal in the boiler.

    What is the rating of the boiler, in EDR?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • gerry gill
    gerry gill Member Posts: 3,078
    my condensate tank vent causes about 3 gallons evaporation a SEASON. A gallon a day is huge!
    Serving Cleveland's eastern suburbs from Cleveland Heights down to Cuyahoga Falls.

  • baj702
    baj702 Member Posts: 44
    @gerry gill I'm trying to eliminate some of the obvious possibilities. I don't think it's the condensate tank, though. Thanks for the metric.

    @Jamie Hall about 2000 EDR (575,000 BTU). I'm just looking for benchmarks. Right now it will go from about 2psi to .5 psi in about 5 minutes. Just wondering what a normal time might look like.
  • Jamie Hall
    Jamie Hall Member Posts: 23,276
    On a boiler that size, that probably isn't out of line. But as @gerry gill says, your water use is.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,576
    One pipe or two pipe?
    That slow drop in pressure seems out of line to me. Is there any whistling from the vents (one-pipe) after shutdown?
    Two pipe vapor systems, with cross over traps, can have slugs of air in the returns after the traps, and maybe that slows the pressure drop.
    Maybe you are just talking about the time needed to refire the burner, and not the pressure drop.
    Have you overfilled your boiler to rule out a leaky boiler section?—NBC
  • MilanD
    MilanD Member Posts: 1,160
    edited January 2018
    I have an LGB7. It's similar to your boiler in size. I don't run it past 8 oz now, but can tell you that before I installed 2stage setup and vaporstat, it didn't take that long for pressure to drop from 1.5 to 0. This is a 1 pipe. On a 2 piper, the only scenario I can conceive it taking that long would be when rads are full, rad traps closed, and tstat still calling for heat, so, only when system would be coming out of a deeper setback or trying to significantly raise the temperature.

    As to water loss, is this a 2 pipe or one? On one pipe, your vents may not be all closing, rads or main. You also may have several smaller leaks on rad valve unions. Those can loosen up on their own over time, and would necessarily visibly drip as the water woul dry on the surface of the hot pipe before having a chance to drip on the floor. Same on valve stems.

    2 piper, being a closed system, my only 2 guesses would be again rad valve union on several rads, or that one main air eliminator. Or perhaps some other union hidden from view and not obvious.

    It's surprising how much water can drip out of a tiny hole over 24 h. Look at any discoloration of the pipe at unions and fittings. Try also feeling for wet spots on the pipes behind and under what you can see, either with a small mirror or by hand after the system shuts off and pipes are not that hot to burn you.

    And last thing, check that the tank itself doesn't have a small drip at the bottom which then leaks into the ground, out of sight.

    It's important that you locate that leak or the combo of several smaller leaks and fix it.
  • baj702
    baj702 Member Posts: 44
    @MilanD Thanks. It's a 2 pipe system. I assumed it would take longer to decompress. I was expecting maybe a 1/2 hour of coast time between cut out and cut in.

    I'm trying to get the pressure down, but the stock pressuretrol doesn't have that fine of a resolution. I've ordered a vaporstat and it should be here this week sometime.

    The condensate tank is new, so I'm thinking the radiators too. There's somewhere between 40 and 50 of them.

    What is a 2stage setup? I've got a slant/fin caravan, with one 300,000 btu and one 275,000 btu. I was thinking about having them both go on until about 1.5psi, then shut one off and let the other keep the pressure. Not sure if it will work until I get the vaporstats, though.

    Thanks for the reply!!
    JUGHNE Member Posts: 11,060
    Are the returns of the 2 boilers tied together?
    Do you have a boiler feed pump or a simple condensate pump with it's own control?
  • MilanD
    MilanD Member Posts: 1,160
    Ok. So a small update: i have a 50 gal condensate return tank, one piper with traps on dry returns, and I too noticed some excess water loss after some repairs I did and was again paying closer attention. At any rate, the tank has 2 air vents, not sure really why, one low by the tank itself, large 2" pipe, and one up above the boiler, some 3-4 feet in the air 1-1/4"... Probably, the "it's always been there" syndrome, so 2 remained after the tank replacement.

    I now use that lower opening to add carbon filtered an then RO filtered water (our city water is high mineral and chloride water, so I do this and then add steamaster tabs for pH). Then I plug this pipe by stuffing a rag in it. I suppose I can get a cap...

    It's an approx 2,000edr building and with 3 big mouths, 2 Hoffman 75, and 30ish radiator vents. As such I have some 1/2 gal of water use per week on colder weeks, and almost none on warmer... I checked and rechecked for leaks and do have one rad connection nipple before the valve that's rusted and has a small small leak. As in, few drips per heating cycle. That's it. This will wait for a warm day to get repaired. I also have a float controlled boiler feeder pump, and after a blow down every 2 weeks, it requires an extra gallon or two. At any rate, I forgot to plug the pipe on Friday after I added water, and by Monday I had 4 gallons gone (I have a measure drawn on the tank's glad gauge.) I added 4 gallons to bring it back to where it was on Friday. So, with the rag stuffed in the lower pipe, it loses 1/2 gal week. Fwiw. I didn't check today and will check tomorrow how the level is after 36 hours of operations.

    As to 2 stage, yes, you should be able to have 2 boilers staged. You might not need to, tho. I have 2 large performance halls and one is on a zone valve which, when closed, reduces the system size form 2000 to 1200 edr. When this happens, pressure builds quickly and instead of cycling on pressure, the 2 stage gas valve train drops the burn down to low stage and, for my building, sizes the EDR boiler output to the connected load. If you are not oversized on the boiler side, you may not need it, however, it may work well on shoulder days, to build steam quickly, then drop one boiler out and run just one boiler on a long call. All this means, however, that you don't want to use overnight set-backs. For this setup you will also need 2 vaporstats.
  • MilanD
    MilanD Member Posts: 1,160
    Oh, as to pressure, once steam starts collapsing, pressure will drop quickly. If you want to delay fire, you can add a timer of some sorts in line with the vaporstat, on either break or make. Probably on break will be just fine. I don't see why this would be needed either. What are you trying to do?
  • baj702
    baj702 Member Posts: 44
    @MilanD Thanks for the details. That's weird about the 4 gal loss. I've got a 50 gal tank too, with a 2" vent that rises 10 feet. I just added the 10' riser the other day when I remembered reading about how the old timers used to run their vents to the ceiling. Before that it rose only about a foot or two. The 10' riser didn't make a difference, though, I'm still at about 1 gal/day.

    I've been checking the radiator valves. Every one so far seems really loose and there isn't any packing in them, so maybe that's my problem.

    If you do track down that anomalous 4 gal then definitely let me know what it was.

    They're new boilers, so I'm just trying to get a feel for them. This is also my first experience with boilers, so I'm not always sure what to expect.
  • MilanD
    MilanD Member Posts: 1,160
    I just checked the condensate tank after 36 hours and temp swing from 72 overnight to 75. No change in water level. Sorry. Mine was definitely caused by the 2 inch pipe I left unplugged...

    Yeah, 75F it's a bit higher temp setting on the thermostat. That's a whole another story: it's one of those 'smart' Honeywell RTH8320WF tstats, and it's cycle rates are all messed up if I don't swing it overnight nor keep it at 75. It just doesn't come on enough to maintain the indoor temperature at comfortable levels for anything below 75. Plus, it displays false temps when comparing to room temp on a thermometer - the room is more at 73-74 when tstat shows 75 and even lower when tstat is set to 71-74).

    Anyhow - back to your issue: go around and start slowly repacking all those valves. But I think, however, you have a combo between it and the tank, tank being the most plausible cause. 1gal/day is a lot, and based on my experience, I can see it go out of 2" pipe. I lost 4 gals over 4 days, which is similar.

    I also think you can easily reduce that vent pipe from 2" down to 1, or 1-1/4", and even less if you have main vents on your dry returns before the FT trap and sole venting is not done through the tank alone. Matter of fact, do it regardless. 1-1/4 is plenty for venting for 2,000 edr without creating any significant back pressure even without the main vents - your FT traps will limit venting rate anyway. You don't need 2" vent on the tank for sure!

    So, it's safe to assume venting that is happening at the tank does not require 2" pipe, and it needs to be sufficient but not too large. It's there also to break any vacuum between it and the boiler/system, so you can pipe that down. I would also suggest putting in a few 90s on that run, top of the pipe or elsewhere, and have the last run pointing up. All this can be done with rubber ferncos, and pvc, btw. It's only for air. I did something like that too, extended the higher of 2 vents I mentioned on the vertical run (it already had a 90), then added a fernco with a pvc "branch" from an old plumbing job, pointing both of it up again... This seems to have helped too keep the pipe cool and condensate dripping down into the tank on long calls for heat.

    You want to give any evaporation more surface to condense before going straight out the pipe and then let it drain back down. That's why 90s. Pipe going straight up will give no surface resistance.

    Attached is my set-up with the 2 vents. Doing this definitely reduced the amount of evaporation.


    Plus, since you asked about the 2stage setup: I took a pic of the 2 vaporstats: one controls the op limit, the other is low-high-low controller. Ptrol on the far left is high limit, probably superfluous, but needed by code. Op. pressure is at 4oz (0.25 psi) on low stage, and up to 8 oz on high, and only rising to 8oz at the end of a very long call for heat or when coming out of a deep set-back, and then it drops to low stage.

    Here is a whole low-hi-low setup album:

    Videos are from before I dialed it in to 8 oz drop-down to low fire limit.
    JUGHNE Member Posts: 11,060
    If your vent pipe has a 90, short nipple, 90 then short nipple down, then if the pump vent is passing steam from a bad trap you would get a drip on the floor. Otherwise just a chimney with (sometimes) invisible steam coming out.
    Sometimes the steam doesn't show up until you leave the room.

    Saw a job with PVC pipe drip cup under a feeder pump vent.
    It was near the ceiling. The PVC got so hot it bent as if an electrician put it into a hot box bender. Another melt down about 12' away where the condensation pooled.
    The installer told me that vent used to pass a lot of steam and then just quit doing it........no traps had been repaired/changed as to anyone's knowledge..........so sometimes traps "fix" themselves?? Pressure had always been low 1-2 PSI.
  • baj702
    baj702 Member Posts: 44
    @MilanD OK, I'll need to revisit the vent. I only have about 1' horizontal, so as far as condensing surface area, there's not much. I do like your two pipe vent setup. I think I'll do the same. I do miss the easy access I had to the tank before I put that huge 10' riser on. A tee at the bottom with another access pipe would be perfect!

    I can see "vapor" coming out of the pipe if I hold a flashlight on it just right, and my hand will condense it and get a little moist after a minute or so.

    I used 2" pipe because that was the size of the tapping on the tank, but I'll reduce it now.

    I'll report back in a couple of days!!!!
  • MilanD
    MilanD Member Posts: 1,160
    edited February 2018
    If you see any vapor, it's quite possible one of your traps has gone bad, but, if you can hold your hand there and it's not burning you like live steam would, it's probably just hot condensate evaporating away... My $$ would be on that.

    Depending on your venting, that is, if your sole venting point is not your condensate tank pipe and you have a vent before the trap, when the time comes to service the trap, if possible with your space restrictions, you may be able to just pipe in a p trap with black iron alone and get rid of the trap. Just like a trap on your kitchen sink, but tall enough for the water column to keep the pressure against the system op pressure, and voila - no moving parts to service, ever. In this situation, pipe in access on top and bottom of the p, so you can flush it out from time to time, as it'll also act as a dirt catcher.
  • Yet another reason to love gravity return, instead of a pump on a steam system!—NBC
  • MilanD
    MilanD Member Posts: 1,160
    @nicholas bonham-carter

    Sometimes due to system limitations you can't avoid it. But, I agree!

    @baj702 btw, you could pipe in a vent and p trap setup and get rid of traps when the time comes. It'll be cost of trap vs. cost of labor. But if it's your system, you can do labor, it's a viable option.