How can my gas pipe be too small?


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Old 11-26-10, 11:29 AM
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How can my gas pipe be too small?

My water heater doesn't produce enough hot water in the winter months, yet it's perfectly fine during summer months. My online research suggests the problem may be that my gas line is too small to run both the water heater (40,000 BTU) and the new gas boiler we added to this line shortly after buying the home (130,000 BTU). Both gas appliances run off of a 3/4" natural gas line, with 40 feet of pipe between the meter and the appliances (located next to each other). If I'm reading the charts correctly, it looks like 40 feet of 3/4" pipe only supports 136,000 BTU. But here's what I want to understand, and I'm hoping someone on this forum can explain to me: since my boiler is not running constantly -- let's assume it's running for maybe 10 minutes out of every hour -- shouldn't the water heater be able to function just fine most of the time, struggling with a smaller flame for just the limited period of time when the boiler is on simultaneously? In other words, regardless of the pipe size, when I wake up in the morning and nobody's used any hot water for at least 8 hours, shouldn't there still be a full tank of hot water in the winter, just like there is in the summer, because the water heater has had all night to maintain the temperature? I mean, doesn't the internal thermostat in the water heater tell the flame to keep running, small or big, until the tank is full of hot water? I don't understand why would it matter that the water heater doesn't get its full capacity of gas for a fraction of each hour.
 
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Old 11-26-10, 12:01 PM
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Can't comment on the supply line but I do know we had to adjust the heater on a hot tub I managed at a former job because the water coming through the supply line was colder in the winter than summer so that may also be a contributing factor

By the way, welcome to the forums
 
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Old 11-26-10, 12:06 PM
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Well..same answer as mitch for me. Our incoming water temp varies by almost 30 degrees between winter and summer. Though my WH will heat it to set temp..I need to use much more of it when bathing since the cold is so much lower.

Have you actually measured the hot water temp from a 2 handled faucet? I say 2 handled since single handles CAN allow a bit of bleed over..depending on the type. Esp a shower or bath which may a mechanical limit on the lever/knob.
 
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Old 11-26-10, 12:27 PM
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Thanks, Mitch. I realize the incoming water temp is much colder during the winter, so this means the water heater will need to run more frequently in order to reach the same output temperature as in the summer, and the recovery time will drop too. I totally get it. But I'm still baffled as to why the water heater can't do this using a 3/4" gas line, which is WAY more than is required for a standard 40,000 BTU water heater. Even if the boiler completely cuts off all gas supply to the water heater when the boiler comes on for a few minutes here and there, it seems like the water heater could compensate for this when the boiler is NOT running.
 
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Old 11-26-10, 12:32 PM
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Thanks for responding, Gunguy. The two-handled faucets in our home suffer the same problem as the one-handled faucets. It's not a temperature problem, it's a volume-of-hot-water problem. Instead of the water heater producing ample hot water for everyone to shower in the mornings in winter like it does in the summer, we're lucky if we get 12 minutes of hot water in the shower in winter mornings... regardless of whether we use our two-handled shower faucet or our one-handled shower faucet. The initial temperature of the water is same as in summer, measured from any faucet... it's just that it doesn't last nearly as long as in the summer.
 
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Old 11-26-10, 12:34 PM
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Have to ask...how exactly have you determined it's not getting to temp or providing enough? If it's just from showering...see my response below.

Ahh...disregard.
 
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Old 11-26-10, 01:22 PM
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A 3rd answer which would be the same as mitch and Gunguy.

You state you added a new gas boiler shortly after buying the home but donít specifically state when the hot water issue first surfaced. A reader would make the presumption these two events are connected. If the timing difference didnít coincide the first winter after installing the new boiler, that info might make us think in a different direction.

Another thing probably occurred that would help validate what mitch and Gunguy are saying. Before adding new boiler, I would think your gas usage (i.e., gas bill) would skyrocket during the winter months as compared to summer months.

Another factor to consider is where this water heater is situated. If in an unheated room, that also strains it to keep up. It seems you might be on the edge of where that extra 10 minutes is important. Perhaps insulation of a water pipe and/or water heater could make the difference to get you back close to where you were before adding the boiler.
 
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Old 11-26-10, 01:59 PM
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Ahhh...I forgot to mention one thing...or just thought it was assumed. Don't forget, as you draw off hot water, you have to replace it with cold, thus lowering the total amount of hot water available.

In my case..that 30 degree difference makes my total amount probably 75% of what it is in the summer. Not a big issue most times as it's just the 2 of us, but if we have family here in the winter there's about a 30 min wait between long showers/baths. Summer is a non-issue unless 3 or more need to bathe.
 
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Old 11-26-10, 03:05 PM
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My guess is that the too small line is starving the water heater when the boiler is running, they both should be able to run at the same time, without charting your line I know it's too small. (Any time the boiler is running the water doesn't get enough gas and it has to play catch-up)
 
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Old 11-26-10, 06:12 PM
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Hi, How about turning the boiler off about an hour or half hour before taking a shower then take a shower with out turning the boiler on and see how the tempeture holds up without the compation for gas. This may tell you if you have a gas problem or a tempeture problem.
Good luck Woodbutcher
 
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Old 11-26-10, 08:13 PM
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Rob -- Good observation. Truth is, the installation of the new boiler happened so soon after moving into the home, neither my wife nor I can recall whether we noticed the problem before or after the boiler was added. But you raise a good point. I need to think on that. I'm pretty sure (not positive) we noticed the problem the very first winter, and I don't think we added the boiler until the second winter.

Woodbutcher -- Yeah, I've been meaning to wake up at 5am and try that test you mentioned. Will do.

Shacko -- I agree that the line is too small, but shouldn't the heater simply keep heating until the thermostat is satisfied? Pilot light is not going out, so obviously the WH is getting "some" gas, so it seems like it should just keep heating until the tank is heated, right?

Gunguy -- I hear ya', I realize the colder incoming water means the WH will strain a bit in the winter. Understood. But I don't live very far north (Maryland), and this problem occurs long before it gets truly "cold" outside by any reasonable standard. And this problem never happened in my prior home, which is located just a block away, nor does it happen with any of my neighbors.

Thanks again, everyone, for all the input. I'm not trying to be cheap and avoid replacing my 3/4" gas line... in fact I'd gladlly pay the money.... I just want to be confident that the too-small-gas-line theory is correct and will solve the problem before I incur the cost/hassle.
 
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Old 11-26-10, 08:19 PM
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It's not a gas line problem at all.


If it was, that burner would be making an odd noise when it operated, along with burning up orifices over prolonged use.

Worst case scenario would be the true interruption of gas flow when the boiler kicks on. You're well within limits of the gas line feed.


Sounds like a failing dip tube in the water heater or malfunctioning thermostat, long before a gas line issue.


I've seen gas water heaters fed with 3/8" soft copper, 20+ feet and run without issue, even though it is completely wrong.


Here's the test:


Run all the hot water out of the tank.

Sit nearby and wait 30-45 minutes while it runs its cycle, replenishing the hot water into the tank.

Grab a one or 2 gallon bucket, start counting the number of buckets being filled, dumping out the hot water coming from the faucet.

If you have a 50 gallon water heater, you'll have 38 gallons of ready to use hot water.

40 gallon, 28 gallons
30 gallon, 18 gallons

You'll never pull full capacity out of the tank...it takes cold water moving into the tank to make the hot water leave.
 
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Old 11-28-10, 07:32 PM
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You may have already done this, but check the temperature of the hot water at your faucet. It should be around 110 - 120 degrees. Anything lower you'll end up going through more hot water than needed (resulting in shorter shower times).
 
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Old 11-30-10, 09:50 PM
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Zorfdt: I measured the temp at the faucet with an infrared thermometer. 132 degrees (I turned-up the thermostat in order to help compensate for the lower volume of hot water it's producing during this season.) Temp doesn't seem to be the problem.

Dunbar: Wow, thanks for the thorough response! I doubt it's the dip tube, because the water heater is only two years old (2008 model), and it seems like if it was the dip tube I wouldn't have plenty of hot water in the summer. I've been thinking it was a malfunctioning thermostat from the beginning, but again this wouldn't explain the dramatic seasonal difference. I'll try the test you mentioned, seeing how many gallons of hot water I can get from my 50 gallon tank. I'd be shocked if I'm getting anywhere near 38 gallons, but I'll see. Thanks again.
 
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Old 12-01-10, 12:52 PM
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If it is a GE/Rheem/Ruud water heater, yes; it can be a dip tube. I've had those dip tubes fall out of the built-in cup on the cold side where the threaded die pattern was out of range, the threaded dielectric nipple would travel further than it should and then the dielectric nipple would push the dip tube out, laying in the bottom of the tank


All they use on that design is a rubber foam ring to hold it in, which is a crazy design.


Robertshaw is having issues with some of their thermostats, they used to be bullet proof with reliability but White Rodgers is now the common gas valve on PowerVent models.

I've done quite a few thermostat replacements on malfunctioning water heaters between home depot and lowe's house brand water heaters.
 
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Old 12-01-10, 09:56 PM
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Dunbar -- Yep, it's a Rheem ("GE" brand, from Home Depot, but made by Rheem). If it weren't for its stellar performance during the 8 non-cold months of the year, I would agree with you on the dip tube theory. I do think it's possible it could be a malfunctioning thermostat/valve that works fine in warm weather with warmer intake temps but doesn't perform well with the 20 degree colder intake water in the winter months. I dunno. Still seems unlikely to me, but it doesn't seem to be the gas pressure and if it's not the dip tube then there aren't a whole lot of possible causes remaining.
 
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Old 12-01-10, 10:16 PM
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It took 4 months for the customer to call me back stating "luke warm water" as the culprit.


When I spun the nipple out, dip tube was down in the tank. Another plumbing company put one in, fell immediately into the tank. They heavy wrapped the dielectric nipple and got it to hold, but the tank malfunctioned a year later due to leaking.


That couple did not listen to me: She worked at Home Depot and I told her to buy a different brand.

Twice I replaced her water heater, same brand due to problems. It got replaced 3 times in total in 2.5 years, they paid for the replacement each time because GE absolutely would not refund her money and kept giving her new water heaters.

I would not own one of those GE water heaters due to the chronic problems they have.
 
 

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