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Did a condo today. Two units in one building. Each had a forced hot water by gas heating system. The odd thing was that they shared the same expansion tank. Never seen it done that way before. Any potential issues? It apparently has been like this for around 15 years.

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Dennis,

What type of tank? How big is it? Was it flooded? I am just curious. I Have never seen this before either.

I am picturing the old steel tank. Could it be that one rusted out so the just doubled up, or was it an original set up? I can't see how this could work unless the boilers were piped and wired in tandum. Were they?

Did you take any photos? I sure would like to see this set up.

George

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Originally posted by a46geo

Dennis,

What type of tank? How big is it? Was it flooded? I am just curious. I Have never seen this before either.

I am picturing the old steel tank. Could it be that one rusted out so the just doubled up, or was it an original set up? I can't see how this could work unless the boilers were piped and wired in tandum. Were they?

Did you take any photos? I sure would like to see this set up.

George

George,

The pipes from both boilers connected into the pipe that ran to the tank. It was the older metal non-diaphram type tank. It sounded around half full. Didn't take a photo of the tank, but I took one of the boiler. Care to take a guess at the approx. age?

Dennis

Download Attachment: icon_photo.gif boiler.jpg

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Dennis,

I am with Jim, I would have said circa 1980. How close are we?

Is that a 1 inch gas line feeding this thing?

It looks to be about 125,000 BTU at the most.

How about the gas cock, is the handle broken or is this one that needs a wrench? If so is that legal in your area? We can't do that here.

George

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George,

Share your wisdom with me... I don't see any issue with the two boilers sharing the same expansion tank if it has enough capacity for two running systems. If the tank were located outside the circulation loop the water in the line to the tank would be essentially static.

As a benefit of a shared system, an additional valved loop could be created in case one boiler failed; both units could still be heated while the failed items were repaired. It may be a planned redundancy.

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Hello Dennis:

Were there two separate condos in one building, each condo with it's own boiler sharing a common expansion tank?

Also, looking at the picture the circ pump is on the return line to the boiler. The pump should be located on the supply line. If the pump is pushing into the boiler it is wrong (on bigger systems with larger horse pumps they can lift the RV when the boiler is running at the higher limits).

If it is pulling out then the flow on the boiler is bassackwards.

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Chad,

There isn't much to share, you are right. Large commercial and industrial applications will do just what you describe for the reasons you site. It is also much cheaper than one very large boiler. The boilers are "staged" and will use one tank.

I have never seen this done in a small residential application. I admit I have jumped to conclusions here, I am assuming that the two boilers supply heat to two different systems controled by two different thermostats and they are not connected any other way. It evidentally works.

If it the "house" paying for the heat, I guess it is not a big deal. If not, 2 units are sharring the same hot water. Depending on the conditions, water heated by one boiler will be drawn back to the other.

Terry,

I have never seen a pump on the supply line. What do you mean?

George

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Originally posted by Jim Morrison

Dennis,

That Repco boiler looks identical to the one my father had installed in his house in 1978. I think they made a steel boiler at that time as well.

I found the remnants of an old oil line near the boiler. So I was figuring that this boiler was installed at the last "energy crisis", which was 1978. That's when a lot of people were "scared" into dumping their oil systems for clean, cheap, abundant natural gas systems.

I have an oil system myself and pay $1.19 per gallon, which is cheaper that the equivalent amount of natural gas. I think someone figured out that oil would have to be $1.70 per gallon to be the same current energy cost as natural gas.

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Originally posted by Terence McCann

Hello Dennis:

Were there two separate condos in one building, each condo with it's own boiler sharing a common expansion tank?

Also, looking at the picture the circ pump is on the return line to the boiler. The pump should be located on the supply line. If the pump is pushing into the boiler it is wrong (on bigger systems with larger horse pumps they can lift the RV when the boiler is running at the higher limits).

If it is pulling out then the flow on the boiler is bassackwards.

The condos were in the same building. Around here all the systems have the circulator pump on the return side.

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Dennis wrote;

The condos were in the same building. Around here all the systems have the circulator pump on the return side.

Hot air (and water) naturally rise. Cooler air (and water) naturally fall. That's why we see old gravity systems both air and water. The pump is just there to assist nature. To try to reverse this would not help the situation at all.

The idea of the pump is to evacuate the line faster to make room for more supply. As with most anything else, it is easier to pull than push.

George

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Hello George:

Circ pumps should pull out of a boiler vs. pushing into a boiler. Attached is a link from Weil-McLain. I'll look around for some more information on this. On quite a few larger commercial job I have seen the circ pumps pushing into the boiler and the maintenance man was always complaining about the relief valve weeping and too high of a pressure on the boiler. I have also seen 50# relief valves on applications where there should only be a 30# in a attempt to rectify a pressure problem with the boiler due to improper pump placement.

http://www.weil-mclain.com/contractor/T ... SB0206.pdf

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Terry,

Technically, you are correct, but it is a rarity for Dennis or me to see a circulator installed on the supply side of a forced hot water boiler. It is almost never done this way and in residential applications, it really doesn't matter.

Boiler manufacturers (including Weil McLain) ship their residential boilers with circulators installed on the return side (if they were located on the supply, it would be impossible to stack one atop another in a warehouse), so that's how they are installed. In the real world of residential home inspections, it is a non-issue.

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Well, it has been a long long time since I have been on a service truck. Many things have indeed changed. However, as I read it, we are talking about pumping away from the tank, not the boiler. With the pump on the return, you are indeed pumping away from the tank.

If I am missing something, and if supply pumping is now the norm, I have still never seen it. Even on brand new installations.

George

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FYI

I just got off the phone with a local boiler expert.

I can't repeat verbatim what he said, Mike would have a heart attack. But in a nut shell, he said the Ivory Tower Engineers haven't seen the real world since high school.

Although he has never installed a pump on the supply piping, he has had to relocate 3 from the supply to the return because of the poor performance.

Since I admit that I really don't know, you will have to ask your own guru. I can say however, I don't recall in 20 years ever having any problems because a pump was on the return.

George

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Chicago here. Looked at somewhere in the vicinity of 4500 boiler installations. Every last one has the pump on the return. Every boiler installer in Chicago, including my boiler/steam guru Chuck, installs on the return. The pumps are almost always B&G. Seen these same pumps approved by the B&G rep. As Jimmy said, it is a non-issue in small residential systems.

Does the pump "push" the water to the boiler, or does it create a pressure differential that "pulls" water out of the boiler? This is similar to the endless discussion in sailing circles regarding "does the wind push on the sail, or does pressure differential pull on the sail?" I've had it explained to me my a Phd in aerodynamics that it does both, or neither, & it doesn't matter anyway. What is more important are efficiencies, or co-efficients, or something like that; I've forgotten. The important part is it doesn't matter.

If one reads both articles, they do not mention "pumping away from the boiler". They both reference pumping "away" from the expansion tank, no? That can matter, but if one places the expansion tank off the main line, as most steel tanks are, then it stops being relevant (again).

This is somewhere in the realm of piping tandem hot water in parallel or series; both sides believe themselves to be right. I've plumbed my tandems both ways, & never found a difference.

Depending on the setup, I don't know why sharing the expansion tank would be bad, wrong, or otherwise unacceptable. Then again, I know someone who is religious about seperate expansion tanks; he's a rep for Xtrol.

Boilers around 23-28 years old. It's just got that look.....

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On the push/pull discussion: In the end I'll defer politely to experience in the field, but in my mechanically oriented mind there is simply no difference in a closed loop where a pump is stationed. EXCEPT for the temperature of the water it handles. A pump in a closed loop isn't subjected to any of the forces that we normally associate with water moving systems; it doesn't have to lift to overcome gravity, there is no rise, and there's virtually no pressure differential. All there is is "head" in the form of plumbing resistance. Pumps on the return side are just bound to have a longer life given the fact that they're operating at least 40 degrees (and probably more) cooler than a pump on the boiler outlet.

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Originally posted by Chad Fabry

On the push/pull discussion: In the end I'll defer politely to experience in the field, but in my mechanically oriented mind there is simply no difference in a closed loop where a pump is stationed. EXCEPT for the temperature of the water it handles. A pump in a closed loop isn't subjected to any of the forces that we normally associate with water moving systems; it doesn't have to lift to overcome gravity, there is no rise, and there's virtually no pressure differential. All there is is "head" in the form of plumbing resistance. Pumps on the return side are just bound to have a longer life given the fact that they're operating at least 40 degrees (and probably more) cooler than a pump on the boiler outlet.

Clearly, some of us don't have inspections this morning......

Your mechanically oriented mind is in exactly the right spot. The temperature is the main reason that everyone in these parts puts it on the return. Other than that, it don't matter. And, as the article stated, its about the tank location, not pumping to or from the boiler.

For my challenged right side brain, doesn't "head" involve pressure differences? (or, as we like to say when we want to appear technically proficient, pressure differential).

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Head off the pump is the delta P (if the suction and discharge side of the pump were at the same pressure the pump would be off or broken, take your pick). When a pump pulls out of the boiler it is not increasing the operating pressure of the boiler - when a pump discharges into the boiler it raises the operating pressure of the boiler hence the verbiage from Bell & Gossett about it tricking the pressure relief valve.

In a small residential application this doesn't account for much with a fractional HP motor but on 15+ HP circ pump it can account for quite a bit of added pressure.

In the end I'm comfortable with the manufacturer's recommendations.

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Hi Chad:

When you size a pump for a system you need to know all the particulars of the system, boiler, how many feet of piping, how many fittings, etc. This all equates to pressure drop...

Ya know I had a thought. They have numerous communication programs like team speak and roger wilco for internet real time communications. We could even use ICQ or Messenger for a white board or something as easy as Mike's chat room for typing or a combination of the above. Mike's chat room would be the base for the discussion. Is that ok Mike?

I would be glad to talk with Armstrong - Bell & Gossett - Weil-McLain, Burnham, whoever you guys would like to see. We could put on a real time mini-seminar on the topic? Explain we are home inspectors interested in continuing education.

Anyone up for it? I'll do all the leg work.

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