Drowning by numbers

January 3, 2007 10:13 AM

Plumbing question. Bring your knowledge of water use.

Suppose a safety valve of a gas heater/boiler is defect (or, you know, the plumber installed a cheap piece of cr*p he salvaged on another project and it - surprise surprise - dies within a month of installing it).

The water is running through it 24/7, during at least four months and at most nine months. (The plumber claims that, at most, this causes a small stream of water.)

Is it reasonable to expect to see a use of 600 m3 (cubic meters of water: one cubic metre = 1000 liters) for that year? (The plumber says it's impossible: 600 m3 is like six swimming pools, he says, you must be crazy to think a small stream of water can cause this).

For the morbidly curious: the bill came in at 2000 $. (Thank you, plumber.)

posted by NekulturnY to Home & Garden (16 answers total)

Depends on how large the orifice is. Put a bucket under the outlet and see how much water you accumulate over an hour. Multiply by the time you estimate it's been running.
posted by electroboy at 10:26 AM on January 3, 2007

How big is the valve opening? 600 m^3 in 4 months is 3,422 cubic centimeters per minute. If the valve opening is 2 square centimeters (completely guessing about that), that's a linear fluid velocity of 28.5 cm/second through the valve, which isn't completely unreasonable.

If you look up the manufacturer and part number of the valve, it should give information about its flow characteristics that would be pretty helpful. Either way, the plumber will say anything to keep from claiming liability.
posted by muddgirl at 10:28 AM on January 3, 2007

Best answer: Look at the third illustration here:

http://www.city.brandon.mb.ca/main.nsf/Pages+by+ID/488

Seems like a moderate stream of water could waste enough water to account for your bill.
posted by jellicle at 10:29 AM on January 3, 2007

If the valve is still leaking, place a bucket with gradation marks underneath and time how long it takes to fill a gallon, liter, etc.. Use this number to extrapolate over the course of 4 or 9 months.

If it takes 1 hour to fill up a liter, then in 4 months it would leak 2,880 liters (4*30*24), which is 2.88 cubic meters.

Where was this water going? Is there a drain nearby?
posted by ajr at 10:33 AM on January 3, 2007

Response by poster: The safety valve is connected directly to the drain (which is logical, I guess), so the water disappeared into the sewer system immediately. Which is also the reason why we never found out before we did.
posted by NekulturnY at 10:39 AM on January 3, 2007

Response by poster: The only info I can see on the type of valve is:

Groupe I
anti-pollution
10 Kw
posted by NekulturnY at 10:42 AM on January 3, 2007

Best answer: I had a leaking toilet valve which (silently!) generated a bill of several hundred dollars over a three month period. But more than two thirds of that bill was for water treatment of what went down the drain. When I explained what had happened to my utility, they simply dropped that part of the bill because the water was clean.
posted by jamjam at 11:01 AM on January 3, 2007 [1 favorite]

Back of the envelope for 4 months gives me 3-4 liters per minute flow rate accounting for 600,000 liters total loss. That does not strike me as an impossible flow rate (too many variables/unknowns to be sure). If you've accounted for normal water use, and given that however much longer it may have been running just makes it more possible, and given your plumber is in clearly the cause of the primary issue - and if he doesn't think it is the problem, isn't it his problem to figure out what the other mystery water waster is? I think your plumber is just trying to cover his ass and avoid helping with your water bill. If someone did this to me I'd haul their ass to small claims court. And get a new plumber, obviously.
posted by nanojath at 11:13 AM on January 3, 2007

I hate to bring this up, but if your boiler has been leaking, you may have lost even more money from wasted fuel heating water which then just goes down the drain, than you have from the water itself.
posted by jamjam at 11:25 AM on January 3, 2007

Was there any warranty on the boiler (including the T and P valve)? If so, the plumber's professional insurance should likely take care of at least some of your expense.
posted by notsnot at 11:39 AM on January 3, 2007

In a full year, you'd be looking at 25 gallons an hour for that level of flow. That's a gallon in about 2.5 minutes. Sounds a little excessive. For 6 months, it'd be 50 GPH, or about 1 GPM.

You'd HEAR any of those flow rates, too. Like the tub or toilet constantly running.

I'd check for leaks elsewhere, perhaps on the outside of the structure if the meter is outside.
posted by FauxScot at 1:01 PM on January 3, 2007

I dispute the idea that you'd hear it. I took a .5L bottle to the kitchen and checked how fast I could pour it out without it glugging air, so it was about as fast as you'd pour coffee. Took just under 7 seconds, meaning I could have done 4L in a minute no problem. At that speed falling 3 inches onto a flat surface and draining immediately away I heard nothing.

600,000L divided by (30 * 4) gets us 5,000L a day. Divided by (30 * 9) it's 2222L a day. Divide that by the 1440 minutes in a day and that's between 3.48L and 1.54L a minute. 1.54L/m is fairly leisurely, though it's a visible trickle.

If your plumber wants to dispute that, get a 1L bottle and a stopwatch and make him watch you pour it out.
posted by phearlez at 3:18 PM on January 3, 2007

It really depends on the system configuration if you would hear the failed relief valve or not.

I'm sort of a plumber - I'm a mechanic in a nuclear submarine. I've heard loud, low flowrate leaks (think soda can with a hole in it) and silent, high-flow systems. The high-flow ones usually have to be high enough flow to pressurize the pipe, though - smooth flow in a pipe doesn't make very much noise.

I think a roughly 1 gpm leak (sorry, I'm used to using english units) would be possible. A 200F boiler would have about 11psi pressure in it, which may not make a very loud sound.

verdict by SWAG: plausible
posted by ctmf at 8:00 PM on January 3, 2007

Response by poster: Ok, thanks for all your answers. BTW: we could definitely hear it (it even kept us awake at night - drove us crazy), it's just that we didn't know it was leaking - we thought it was the boiler.

The pressure on the pipes where I live is 7 bar (day) and 8 bar (night). I guess it was the valve and only the valve after all.
posted by NekulturnY at 5:46 AM on January 4, 2007

pherlez...

I added a zero! Whoops! (Used 6000 cu Meters, instead!)

Now he's only looking at 2.5 gallons an hour.

It's not the drain that will make the leaking noise, however. It's the supply lines. They are under pressure, quasi-rigid, and afforded abundant opportunity to resonate on coupled structural components. The HW heater, OTOH, drains into a gravity fed, large diameter pipe with only turbulence to generate accoustics.

At my house, I heard a similar size leak from a flapper valve in a toilet. Squealy, little, steam sound... all from the supply lines.
posted by FauxScot at 11:55 AM on January 4, 2007

Response by poster: Follow up: I followed jamjam's advice and wrote the utilities company. I inserted heavy doses of begging and voila: they cut 700 $ off the price. Thanks, AskMe!
posted by NekulturnY at 9:34 AM on January 17, 2007