What size water distribution line is needed for 115,000 btu boiler?

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Old 10-31-13, 01:39 PM
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What size water distribution line is needed for 115,000 btu boiler?

We are having a new gas boiler installed. Our house is ~1750 square feet. The distribution line is currently 3/4" copper. The vendor says this is fine, but the first contracted installer would not install unless the vendor allowed them to put in a 1" line for at least part of the system. The gas boiler vendor got another contractor to do the work.

What size line do I need? Can you provide me with a site where I can get reference the standards for size lines needed per btu (or whatever is appropriate)? This is a major investment, and a necessary one, but I don't know what to do. Thanks.
 

Last edited by NJT; 11-01-13 at 04:40 PM.
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Old 10-31-13, 03:18 PM
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Are you talking about water or the gas supply?
 
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Old 10-31-13, 04:27 PM
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Is that 115,000 Btu/hr input or net output? If it's output, it seems like quite a bit for a 1750 sq ft house that is reasonably well insulated. Was a heat-loss calc performed?

Personally, without knowing any more than you posted, I would use 1-1/4" for the supply and return mains, 1" for individual zones, 3/4" for any risers, and 1/2" for individual heat emitters. You can always get by with smaller pipe sizes by using a circulator with a higher head-flow curve, but that risks excessive flow noise - and nowadays, the circulator often is supplied with the boiler.
 
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Old 10-31-13, 04:45 PM
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Are you talking about water or the gas supply?
Ditto Tom's question.

seems like quite a bit for a 1750 sq ft house that is reasonably well insulated. Was a heat-loss calc performed?
Ditto Gil's comment and question.

I am willing to bet that you don't need more than a 60K BTU boiler. They are installing a boiler that is twice as big as necessary.

Gas line size is another issue entirely... so clarify your question.

For a proper flow rate in hot water heat distribution system:

1/2" - about 15K BTUH

3/4" - about 40K BTUH

1" - about 75K BTUH

1-1/4" - about 160K BTUH
 
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Old 10-31-13, 05:11 PM
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The O.P.'s sub-title said it was a water line. Plus, copper isn't commonly used for natural gas, at least around here. It may be prohibited in some jurisdictions. I would always use black steel for inside, but gas utilities use plastic for buried gas lines.

Some gas utilities have in the past used copper for buried service lines between the street and the meter, but much of it is now being replaced due to safety concerns. Mine is still copper, but I happened to observe the gas meter reader a week or so ago. After reading the meter, he walked along the buried copper line's route with a combination gas sniffer and line locator. Hmm.
 
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Old 10-31-13, 05:19 PM
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Yeah, I expect he's talking about the water lines too... I know it says 'water' in the title... but ya never know, and it don't hurt to ask.

They don't use copper around here for gas lines. Not too sure about the old underground services though. All the modern stuff these days is of course plastic.
 
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Old 10-31-13, 08:21 PM
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It's the water line.

For clarification, it is the water line I'm questioning. No, a heat loss calculation was not performed by either of the vendors that gave us a quote, nor was it mentioned. This is a one story ranch house with a 3-4 foot crawl space. The boiler sits in a utility closet in the house and the lines run under the house in the crawl space. The lines are insulated. Although we did not build the house, I would consider the house to be reasonably insulated. The house is 27 years old. The vendor originally quoted at 150K btu boiler then reduced it to 115K per the installer's recommendation (the same installer who said the lines weren't big enough).
 
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Old 10-31-13, 08:32 PM
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Re: Gilmorrie's Input/output? don't know!

Sorry. I honestly don't know the answer to that question. The original quote was for a XEB-5, 150K, gas boiler. The quote does not specify if that is the input or output. Too trusting. I know nothing about boilers. We were trusting that the "experts" would tell us what was needed to do the job right. Like I would do in such a situation. I would not have been happy with increased costs, but I prefer to do it right the first time. Very frustrating.
 
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Old 10-31-13, 08:32 PM
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The vendor originally quoted at 150K btu boiler
May I ask where you found this 'vendor'? Is the vendor ORANGE?

I think the installer who said the lines were too small sounds like he knows more than the 'vendor'.

Have you given anyone any money yet?

If not, call the 'dismissed' installer and ask him about a heat loss calculation... if he knows how to do one ask him to do so and size the boiler correctly and give him the job outside of the 'vendor'.

I seriously doubt that you need a boiler bigger than 60K ... ESPECIALLY in GA... I mean, how cold does it get there?

[edit...NJT... Sorry about that... why did I think Stumpy is in Georgia? where did I get such an idea? So, strike that. It gets cold in WVA! STILL 115K I'm SURE is too big!]

I'm stuck up here in Yankee land... gets a LOT colder... 2 story home, almost 2000 sq ft, older construction (but upgraded a lot) and my heat loss is only around 60K ... just for reference.
 

Last edited by NJT; 11-01-13 at 04:43 PM.
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Old 11-01-13, 07:34 AM
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The vendor is not ORANGE. I live in northern West Virginia. I have not paid yet but did sign a contract for the initial 150K boiler. Then the vendor reduced the size. I guess I'm not comfortable listing the name at the moment, but it is a very large and reputable company. Which is one of the reasons we went with them. I'm wondering if the commission was part of the factor here. Regarding a heat loss calculation--if one was done, the vendor(s) did it and didn't mention it to us. At least I don't remember it being mentioned. The vendor was here for a while and did work on his computer a fair amount of time so he may have been using some software to do that. We got multiple quotes for different heating sources (furnace, heat pump and boiler). We had another vendor quote a 100K btu boiler and no line replacement either. Hmmm. One vendor quoted only a multi-split heat pump because he told us outright he would not work in the crawl space.

One last thing for you all--replacing the lines was not part of the quote. So anything we do there will be on us or extra. What happens if the lines are not replaced or not replaced until next spring/summer? Our current boiler is not working at all at the moment and there are issues with it that we want it replaced.

Quoting the line sizes as listed in an earlier post--is there some website where I can find these documented? .

"For a proper flow rate in hot water heat distribution system:

1/2" - about 15K BTUH

3/4" - about 40K BTUH

1" - about 75K BTUH

1-1/4" - about 160K BTUH"
 
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Old 11-01-13, 08:52 AM
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is there some website where I can find these documented? .
What do you mean by 'documented' ? You want copies of someone's credentials? What would be different if you found the information on another website? Would another website be any more credible?

Everything on the internet is true. I'm a French Model, Bonjour.
 
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Old 11-01-13, 09:34 AM
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Siegenthaler's Modern Hydronic Heating, 2nd edition, Chapter 6, contains a 7-step procedure for selecting an appropriate pipe size. It involves several equations, multiple cost estimates, and alternative circulators. In my opinion, it would take a mechanical engineer at least a day to run through the procedure. I expect that if you hired a consulting engineering firm to do that, you'd expect to pay over $100 per hour, or about $1000 total - more if you wanted a written report.

Such a procedure is not followed for residential applications. Instead, competent installers size pipe based on their past experience with satisfactory installations. Naturally, some installers may shade the sizing one way or another. Sizing based on Btu/hr is merely a simplified short-cut and neglects various theoretical factors that are not worth the time to worry about for residential applications. So, typically there is a two-step process: hire an experienced installer and follow his advice.

It seems that you are purchasing the boiler from a "vendor," presumably with limited installation experience, and then using a separate installer? That is a bit unorthodox. I would select an experienced, well recommended installation contractor, and purchase the boiler through him.

Here it is Nov. 1 - not an ideal time to be replacing your boiler, particularly when there is some important homework to do first. If possible, it would be best to make repairs to your existing system to buy some time before possibly making a $10,000 mistake in haste.

I does appear that the replacement boiler being proposed is likely grossly oversized. A boiler salesman won't run a heat-loss calculation "on the come," even if he knows how. If you first select a contractor based his experience and references, he should agree to run a heat-loss calc to size the boiler that you're going to buy through him. Otherwise, do it yourself or pay somebody to do it.

Since you are out of time, I would select a contractor you trust, and put him on a time-and-material basis, at least for the installation. That's just me, though.
 
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Old 11-01-13, 10:37 AM
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Here is a graph for relating pipe size and Btu/hr. I would use 24"/sec flow velocity. Ignore friction head - that is for sizing the circulator.

For black steel pipe, but copper will be close.

Source: Bell & Gossett Handbook, 1940.



Uploaded with ImageShack.us
 
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Old 11-01-13, 01:02 PM
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And if you 'run the numbers' from that nomograph, it would be discovered that the numbers I posted are right on target.
 
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Old 11-01-13, 02:51 PM
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the numbers I posted are right on target.
Yes, I noticed that! I said that I would use a flow velocity of 24"/sec. Somebody else might be a little less cautious, and use 36"/sec, and that would probably be OK - but 48"/sec is regarded as the point where objectionable flow noise is encountered.

Whether the actual flow velocity is 24, 36, or some other velocity depends upon the characteristic curve of the circulator and the total friction loss of the system. That exercise beyond us mere mortals, so best to go with 24"/sec, I think - or trust an experienced installer (which is what people have done for many decades with satisfactory results).

The 1940 B&G Handbook (from which the pipe-size nomograph was copied) also has a lengthy design example for a residence with 120,000 Btu/hr heat loss. (I have computed my heat loss as 109,000 Btu/hr.) Anyway, the installer of my system, 60 years ago, followed the B&G design example, right down to the size of each segment of different sized pipe - it couldn't have been just coincidental. Some of those "dead men" didn't just go by the seat of their pants - they often followed "the book" meticulously. And, "the book" was whatever B&G published. By the way, my old system works very well.
 
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Old 11-01-13, 04:21 PM
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48"/sec is regarded as the point where objectionable flow noise is encountered.
We try to design for not less than 2 and not more than 4 feet per second... that gives adequate flow to move air bubbles through the system. Any slower and stubborn bubbles will not move. Any faster and you start to hear the flow. Larger pipe sizes can flow faster without objectionable noise.

This chart won't link as an image, so click here to see:

http://www.comfort-calc.net/pictures/Piping_chart.JPG
 
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Old 11-01-13, 04:33 PM
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Your Btu numbers may be based on a higher assumed flow velocity than my 24"/sec. Look at the Btu/hr ranges shown on the nomograph for a range of flow velocities.

The i.d. of black pipe and copper is quite close. Black pipe internals will have a little greater "relative roughness" than copper. That affects pressure drop a bit, but not how many Btu/hr a pipe carries for a particular flow velocity. That is unaffected by pressure drop, at least directly.

As far as shooting for 4 ft/sec flow velocity to help with air removal, velocity can be increased if necessary, in the case of a system with a single circulator, by valving out sections of the system, with zone valves or, in my case, shutting manual balancing plug valves. (My system has four "quasi" zones; they are fed from a single pump but each has a manual balancing valve.) I can solve any air problems, but am sensitive to flow noise in my bedroom.

That being said, I don't know what the flow velocity is in my system without additional instrumentation or some heavy-duty math. However, the B&G design example for which my system was evidently based is for 180 milinch pressure drop for all pipes.
 

Last edited by gilmorrie; 11-01-13 at 05:12 PM.
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Old 11-01-13, 04:36 PM
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I edited my post and retracted the part that you commented on... just saying so that ppl don't think you are talking to yourself! Because I looked again and my tired old eyes were crossed and blurry... and I had my head tilted to read the chart.

Yes, the numbers are 'close enough for government work'... I mean, what's 10-15% among friends?
 
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Old 11-01-13, 04:39 PM
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That exercise beyond us mere mortals
Naaahhhh... it's not that hard... I wish I could find the article again that simplified estimating the system curve to plot on the pump curve. Made it uber-easy... been looking though and can't find it again!
 
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Old 11-01-13, 05:17 PM
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I looked again and my tired old eyes were crossed and blurry...
If you click on the nomograph, you will go to my freebie hosting site. From there, click on the magnifying glass to blow up the graph.
 
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Old 11-01-13, 05:25 PM
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I did! That's how I discovered that my beer goggles weren't strong enough!
 
 

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