Estimating Total Water in System.


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Old 09-14-06, 04:37 PM
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Estimating Total Water in System.

I need to estimate the total water in my hot water heating system.

My system has a mixture of 1-2" water supply/return pipes along with about 15 cast iron radiators of various sizes. I am currently measuring the lengths and diameters of the piping and plan to contact the boiler manufactuer for its total water capacity. Then I will calculate the water volume in the pipes and add in the boiler holding capacity.

Question: Is there a site that gives the amount of water for various size/shape cast iron radiators ? Or maybe you have a rough way to estimate them. In any case, I plan to add a 10-20% safety factor after I complete my estimate.

I have experienced pressures in excess of 35 PSI at about 170-180 deg F.

I currently have a "size 12" bladder expansion tank. I tried adding a "size 60 Amtrol" bladder expansion tank to the system without much success. I checked both expansion tanks for proper pressure. Clearly, the size 12 expansion tank in the original system was way under-sized.

I strongly suspect the water is expanding beyond the capacity of the both expansion tanks. The current system was tied into an existing gravity feed system. There is a bunch of existing 2" gravity feed piping. Also, I have added an "Amtrol Air Purger" and am pretty good about bleeding the radiators to provide maximum heat.

I have heard I should allow a column of air to remain in the radiators to allow some expansion there. I feel that may hurt the efficiency of the heating system significantly and cause excessive rust inside the radiators. (Or maybe the water will compress the air so much it will not be a big deal).

Or maybe the excess pressure is something else.

Steve
 
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Old 09-14-06, 05:14 PM
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System capacity

I really don't know how to estimate the water capacity of radiators. You might want to visit the library & look for some books by Dan Holohan. Your over pressure problem could be caused by a reducing valve leaking thru or if you have a domestic coil, it could be leaking. Regarding the air in the radiators, there should NOT be air in the radiators.
 
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Old 09-14-06, 07:36 PM
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One of the simplest ways to guesstimate the volume in a hydronic system is by using the water meter serving the house. If you don't have a meter (on a well) you are out of luck with this method.

First completely drain the system. Then you send everyone away and note the reading on your water meter, including all dials right down to the last cubic foot. Refill the system and bleed all of the air. Read the water meter and convert the difference between the first and second reading to gallons by multiplying by 7.48. The result is the volume of the heating system in gallons.

You need to send the family away so that no one flushes a toilet or washes their hands.

This method is time-consuming but it will give a very close guess as to the heating system volume with minimal measuring and calculation.
 
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Old 09-14-06, 08:42 PM
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Im with Grady. Hot water coil leak or auto fill leak. Never had to find out How much water is in a system. "If you dont mind just why do you"

ED
 
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Old 09-15-06, 01:07 AM
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Ed, knowing the total volume of a hydronic system is required to properly size the expansion tank. It is also good to know if one desires to use chemical treatment of the water. There are a few more reasons why the volume of the system is important but they usually are not that important in residential systems unless one has a huge house.
 
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Old 09-15-06, 05:47 AM
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If you are draining the system anyway, why not just drain it in gallon increments (in a bucket) and measure it that way - you could use the meter on the re-fill to double check.

Since it takes a while to get all the air out of a system, measuring what's already in it may be quicker.
 
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Old 09-15-06, 09:19 PM
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Pressure too high in hydronic system

Thanks guys.

I'll avoid the "column of air in radiators" suggestion.

Grady, when you say "domestic water" I assume you mean a system that uses the boiler to heat potable water. I don't have that. Just a hot water heater tank.

Side note: When the hot water heater tank fails, I plan to install an instant heat unit. I heard you have to have relatively new piping to handle the pressure when you install instant hot water heaters. Not sure why... ?

Last fall, I checked the auto fill valve by shutting off the water supply and observing the pressure build up as the water temperature rose. The pressure rose just as high (35 psi+) whether the water supply valve was on or off. When the water cooled, it returned to about 13-15 psi.

Its too late. I already drained the water from the system for repairs. In any case, I'll make some estimates for the radiators or call a local radiator supplier. I may try the furds water meter method and compare it to my estimate.

furd is right, I need the water volume to estimate the expansion tank and (possibly) estimate the amount of rust inhibitor.

I installed a ball valve at both expansion tank locations for ease of installation.

Grady is also right. Air is the main rust culprit.

Steve
 
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Old 09-16-06, 07:01 AM
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System pressure

With no domestic coil & having checked the reducing valve that eliminates those two possibilities. Good work.

Re: Side note: I don't know why you would need new piping to handle the pressure of an instantaneous water heater. Just a heads up on these devices. Many will not handle the load of a shower & another hot water user at the same time. When/if you get one look at the specs closely.

Amtrol may have some expansion tank sizing charts on their web site, not sure but it is worth a look.
 
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Old 09-16-06, 07:48 PM
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System pressure/Rust Inhibitor

Thanks Grady.

I am working on a 3-flat so I'll check the instant hot water specs - pretty important when you have 3 morning showers that can demand hot water at the same time.

Other than the air topics we talked about any opinions on hydronic rust inhibitors ?

The reason: There were a few small leaks in not important areas last winter so I am trying to head off future issues. I suspect the high pressure was a significant factor. Also, the leaks occurred near (not to) some black pipes I was working on. Maybe bumped them or used them for a bit of leverage during the installation of the new pipes.

The leaks seemed to fix themselves. Still...

Are there additives for sealing potential leaks ?

Steve
 
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Old 09-16-06, 09:47 PM
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Are there additives for sealing potential leaks ?

Sure is check at any supply house.

ED
 
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Old 09-17-06, 06:22 AM
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Leak Sealants

There are liquids & powders which are primarily made for sealing leaks in the boiler but would probably work in the piping as well.
The only rust inhibitors with which I am at all familiar with are called "Hydronic Formula #5" & "8-Way". I don't think you would want to use either one in conjunction with a leak sealant because they are made not only as a rust inhibitor but also for sludge removal. The leak sealants I've used are kind of a band aid to get a customer thru a cold spell until the boiler could be replaced. They really "goop up" a system.
 
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Old 09-17-06, 09:22 PM
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Thank guys.

Okay, Thanks everyone.

I will contact my supply house tommorow for rust inhibitor and avoid the leak sealer. If they do not carry it, I will not pursue it any further. Air and high pressure are (I think) the main issues.

Also, I plan to refill the system tommorow and use furd's water meter method to estimate the total water in the system.

I am about 80 % done measuring pipes, radiators etc. and will compare the results. Then I'll add a safety factor to the total water estimate and install an expansion tank. Then I'll just faithfully purge the air (along with the Amtrol air purger) this winter and watch the system.

This pressure problem has been puzzling to me so I am crossing my fingers.

Steve
 
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Old 09-18-06, 06:13 AM
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Time out!

Before you go introducing a lot of weird chemistry into your system, how about some more info? Can you post some pics? Got specs on the boiler?

It is entirely possible the air and pressure problems are related to your near-boiler piping. I've been there. If you went to such a large expansion tank and still had pressure and air problems, then this may not be related to tank size, but the physics of the system. Very solvable, but need to see the piping layout first.
 
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Old 09-18-06, 02:10 PM
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Hi xip and thanks for the concern.

I agree there could be a pipe or clog issue. See below. It looks like I need to first increase the expansion capacity. Then cross my fingers again.

I just completed the total water content estimate based on pipe sizes, boiler, radiators etc.

Here are the details:

Pipes: 65 gallons
15 Radiators: 52 gallons
Boiler: 8 gallons

Estimated Total System Water: 125 gallons (wow !)

I have not filled the system (yet) using furd's water meter method - tenant issues. I'll report back later when I have the results.

The Amtrol manual says I need a size 90 (based on water content and max operating temperature) or a model SX-30V (based on boiler output and type of radiation - cast iron). I am not sure how the model SX-30V is different from a model 90. In any case, I think the using a water content estimate is superior to the more general boiler/radiation type method.

I last tried a combo size 12 previously installed by the original contractor with the size 60 from Amtrol I installed. The pressure with that configuration was still too high (35+ psi). The Amtrol charts confirm a 12 and 60 combo would be inadequate in my system.

By the way: The Amtrol chart have a safety factor built in. I do not recall exact number. Conclusion: The Amtrol chart is conservative, thanks to the Amtrol engineers.

FYI for xip:

I have a Dunkirk 225K btu boiler.

The air purger/expansion tank access pipe is located on the supply side of the boiler - some say that may not be best - not sure why. The water is all "connected" and expands at roughly the same rate.

I normally leave the water supply on unless I am performing a test. I have no auto low water shut off.

There is only "one zone".

I replaced the original Grunfos circulator with a locally built Bell and Gossett. The B&G is not as swift as the Grunfos but it was much cheaper. It works just fine, is comfortable in the winter and much quieter - much less motor "hum" - than the Grunfos.

I adjusted the boiler flame so that I get just over 400 deg F out of the boiler flue. I measured about 1 foot above the boiler with a digital thermometer through a small hole - later plugged with a threaded screw.

I installed a programmable thermostat when I first bought the 3-flat.

The local supply house sells a "Protect" brand rust inhibitor in 1 gallon and 5 gallon containers. How much is "normally" used ? Something new: One of the salesman gave me a hard time about purchasing from them directly. Something about "protecting the contractors". The way I see it, its a lost sale. If my 20 year old boiler goes out, I'll shop elsewhere. Likely, we'll work it out.

Apologies to the contractors out there. I have paid professionals for many jobs in the past with good to mixed results. If I called a plumber/carpenter/repairman/etc. every time I encountered a problem on my 3-flat, I would be broke.

A little grumpy today - but made good progress.

Steve
 
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Old 09-18-06, 06:18 PM
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the more I think about this...

The expansion tank location on supply or return is not critical. What is critical is that the expansion tank connection is on the inlet (suction) side of the circulating pump.

Air elimination is best done on the supply side close to the boiler. Hotter water has more free air, so you maximize air scavenging right as it comes out of the boiler.

Check out these articles

This is on 'pumping away' generally.
http://www.contractormag.com/articles/1200/chydrotemp.asp

This is a very good primer series on expansion tanks. There's one there about "bigger than residential systems" as well. Sounds like it's speaking right to your situation.

http://www.contractormag.com/articles/column.cfm?columnid=45

http://www.contractormag.com/articles/column.cfm?columnid=60

http://www.contractormag.com/articles/column.cfm?columnid=75

I would also add that I have talked with Eatherton about pumping away and other issues. The guy is awesome. He told me a story once about apartment buildings and air and pressure problems that upon reflection, is almost EXACTLY what you are describing. Although it does sound like you need proper tank sizing, you should also look carefully at where the tank connects to the system relative to the pump(s).

I assume you sized your B&G pump properly, or at least got a pump with a similar pump curve (head and flow capacity) to the Grundfos. You might, maybe, possibly, also be having a problem like this with not enough pump. More likely it's a pumping away and tank sizing thing.
 

Last edited by xiphias; 09-18-06 at 06:41 PM.
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Old 09-18-06, 06:28 PM
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Exp. Tank

I remember well Xiphias' problems last winter/spring. They were largely remedied by changing the piping/tank/circulator to a "pumping away" configuration.

To answer your question about the different tanks: The #90 would screw on just like your #60 where the SX series is made to sit on the floor using the built in stand.
 
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Old 09-19-06, 08:05 AM
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Thanks to Grady and xip

Thats just great. Thanks guys. Terrific information. I read all 4 articles. Although I cannot apply ALL the info, I will in the future.

FYI my system:

1.) Draws colder water from the return side into the circulator pump.

2.) The pump pushes directly into the boiler.

3.) Hot water is pushed out of the boiler into the air purger/expansion tank combo.

4.) It then circulates to the rest of the system.

Looks like it not ideal per the articles. Still...

I have had minimal problems - other than the high pressure.

Very little noise or gurgling.

One radiator would not work after some plumbing was done (by a local plumbing co.) They installed a 90 up and 90 over that (I think) created an air bubble pocket. It worked its way out. May add an air valve later.

Other than those above - the system works pretty well.

xip: I compared the B&G curve to the Grunfos. The Grunfos was a bit better than the B&G - but not by a lot. The B&G has worked well for the last 3+ years. I hear that the comfort level is the most important factor in a circulator.

Grady: I am pretty sure I will install a #90. I need to do more research and measurements around the boiler. Also, I have decided to hold off on the rust inhibiter for now and actively remove air for the system this Fall/Winter.

Off to fill the system - and measure the water content with the water meter.

Steve
 
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Old 09-19-06, 08:52 AM
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Originally Posted by stevemason5
Looks like it not ideal per the articles. Still...

I have had minimal problems - other than the high pressure.
That's what I used to think: "Sure it's not ideal, but...." I absolutely went through the wringer last winter/spring due to not pumping away from the expansion tank. Your setup is exactly what mine used to be. The ONLY thing I changed on my system was the point where the expansion tank connects to the piping so it's right before the circ inlet. It is now silent, pressure stable, wonderful.

Call me a zealot, but it works.

Look at any boiler manufacturer's installation diagram, and they show the expansion tank on the inlet side of the circ. Most pump on the supply, but pumping on the return is also acceptable in most cases, as long as the expansion tank connection is on the inlet side of the circ.

If you can cut in a tee before the inlet of the circ, hang your expansion tank off that. Support it properly or better yet stand it on the floor.

FWIW, pump sizing has everything to do with meeting the frictional loss through the piping and radiators at a flow rate that allows heat to be distributed properly through the system, and keep the water moving at a velocity that will move entrained air through the system to the elimination point. The only time "comfort" enters into it is if your pump is adjacent to a living space. My boiler room is right under the living room. For a brief few days, we had a Taco 0010 in there to see if that cured the air/pressure problem. It didn't and was noisy as all get out. Back in went the 007. Whew!
 
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Old 09-20-06, 12:12 PM
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Water Content Results

I drained the system yesterday.

Draining Procedure: I drained the system using the boiler drain valve. I opened all the radiator air bleeders and the air vent on the air purger. I also ran the boiler a bit to loosen any air pockets before the last air bleeds and the final water meter reading.

Results using furd's method: 105 gallons
Calculated results: 125 gallons

Thats pretty good considering there was likely some left over water in the system. Add a 20% safety factor and its very close.

Thanks furd.

xip: I am well aware that my system set up is close to Eatherton's "problem configuration" (Figure 1). My concern is first to size the expansion tank then look at the configuration.

If I do not have a large enough expansion tank, the water expansion alone would overwhelm any configuration.

I am already piped for an expansion tank. Why not give the set up a test before taking the risk of cutting into existing pipes with my limited skill set ?

Also, when I looked at the diagrams for the circulator pumps, I was most concerned about the pumps ability to overcome head resistance. Most of that head comes from overcoming gravity going from the basement to the second floor, third floor, etc. I think head pressure and pipe friction are similar. I just think head pressure is more important in a multi-story dwelling. If you are heating a large 1 story Ranch, then pipe frictional loss is likely more important.

FWIW Tip: Per an Amtrol engineer, if you start a boiler with the water supply on, it can create a complex condition that allows a few extra psi of pressure into the system.

I could be wrong so fire away if you like !

Steve
 
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Old 09-20-06, 01:13 PM
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Cool on the water volume calcs. Sounds like a winner.

I hear you on the plumbing skill set. If my heating system was made out of wood and fiberglass, I would be all over it. It'd be gorgeous and run like a fine watch. But I'm not tooled up and don't have the time to mess around with plumbing much beyond sweating the occasional domestic sink piping, installing fixtures, etc.

Sure, pipe the new tank where you've got it. Maybe there won't be a problem any more. Thousands of systems are piped with the pump pumping into the expansion tank and they don't have issues. They luck out. If there is still a problem, then the next step is to move the expansion tank connection point to the inlet side of the circ. If you're not up for it, hire someone. Only take an hour, probably.

An aside on circulators. Head is basically all the resistance in a system: gravity, frictional losses, etc. There is also a difference between pumping a column of water that is exposed to the atmosphere (e.g. a fountain at the top of a long vertical pipe), and circulating water in a closed system that is already full of water. We often call them pumps, but they are really circulators. Proper pump selection involves calculating the resistance of the system to flow and the desired flow rate. There's an excellent set of literature at Taco on this. Check out:

http://www.taco-hvac.com/uploads/FileLibrary/PumpCurves.pdf

http://www.taco-hvac.com/uploads/FileLibrary/SelectingCirculators.pdf
 
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Old 09-26-06, 12:54 PM
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The latest info...

I have not installed the expansion tank yet. I am still looking at various brands/types. Amtrol looks like the best bet.

furd: A correction - I meant "I FILLED the system yesterday" (not "I DRAINED the system yesterday"). I think you caught it and graciously said nothing. Thanks again.

xip: I have a hunch the configuration one of the culprits causing over pressure. What I would like to know is roughly how much over pressure are we talking about with an expansion tank installed on the (wrong) delivery side ? Does it basically eliminate the effectiveness of the tank or reduce it ? I would not mind a bit of over pressure as along as it is well within the specs of the boiler, piping, etc.

I will re-read the article to see if there are any clues.

Thanks for the 2 taco articles. I read them both. I had seen one of the articles and strongly considered getting a taco 007 but it was not available in my area without some lead time. I liked the taco 007 curve (very very close to my installed B&G) and had heard good things about it. In the end the B&G was readily available, well recommended, well guaranteed and its curve was good. It works well in my 3-flat. Now that I have laboriously measured all my linear pipework, I can throw in some 90's and 45's and estimate the total PIPE friction. Oh well, maybe next time.

A new problem: After filling the system with water, the cold pressure on the boiler read about 20 psi. Thats a change from last Fall (about 13 psi). I shut off the water supply then used the boiler's sill **** and drained the system of water (about 8 gallons) to reduce the cold pressure to about 10 psi. I then turned on the water again. The pressure went back up to 20 psi.

Looks like my pressure reducer valve is not working. Any tips beyond replacing the whole unit ?

FYI: Its a B&G FB-8 rated at 12 psi. It has a "flip over" that defeats the valve. I checked to make sure the flip over is in the correct position.

Steve
 
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Old 09-26-06, 01:17 PM
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It's entirely possible to negate the expansion tank by pumping toward it.

The truly awesome book Pumping Away by Dan Holohan describes it well. Google it and consider buying. In the interim, let's see if we can do the math

I can do some pressure calcs. Need to know:

1) What is the model of B&G pump?
2) What is the approximate vertical height of the system from boiler to highest radiation?
3) What kind of system piping through the building? Series loop, monoflow/diverter tee, or what?
4) What is the rating on the boiler pressure relief valve?

On the 20# fill pressure, it sounds like the PRV just needs some adjusting down to whatever you need. Which the above exercise should tell us.

OK, got a fishing appointment.
 
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Old 09-26-06, 01:57 PM
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Follow up for xip

xip: I re-read the Eatherton's "pumping away" article. The two main points I drew from the article are:

1.) If you pump away from the PONPC, the system will likely be much quieter/smoother.

2.) If you place the make up water in the wrong location relative to the PONPC, fresh water can be introduced which can cause problems.

I noted a few example references to pressure circulator differentials but nothing extreme.

Last Fall I was getting 35+ psi at about 170 F. I have a pretty standard household level pump. The existing expansion tank is undersized.

I must have missed something in the article...

Steve
 
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Old 09-26-06, 07:32 PM
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Post the data for the questions above and let's run the numbers.

Holohan's book lays out in detail what Eatherton had to cram into a few paragraphs.

The important point is that a circulator moves the water by creating a pressure differential. It has to. Only way to move the water in a closed system. (My job is to understand fluid and sediment movement in the coastal ocean; I've got a decent grasp of the physics behind all this.... Because the expansion tank acts as a point of no pressure change, placing the tank on the inlet side of the circ means that the pressure differential is achieved by creating positive pressure on the outlet side. When pumping into the tank, you generate the pressure differential by negative pressure on the inlet side. In my system's case, pumping into the tank was causing about a 4.3 psi pressure drop, or about a third of the total system pressure. Air problems big time, and oddball pressure behavior throughout the system. Moved the point of no pressure change to the inlet side of the circ, and voila! Stable pressure throughout the system, no more air.

Not sure I understand how you're getting 35psi in a quasi-residential system. It is my understanding the residential pressure relief valves blow wide open at 30psi.

The bottom line is that the system needs to be piped right. Many systems get away with otherwise, but it really sounds to me that, like mine, your system isn't tolerating not having the right piping/plumbing layout and equipment (in your case, exp tank).
 
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Old 09-27-06, 01:33 PM
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xip: Info you requested

xip:

Here is the info with some comments:

1) B&G Model NRF-22 circulator

2) Approx vertical height: 16 feet measured from the center of the boiler where the circulator is located to the top of the highest radiator. Note: the highest radiator gets piping hot.

3) System piping: Not sure what you mean so here goes - There are continous parallel pipes with tees on the supply side and return side. There is no "special" piping that I know of, just straight pipes with 45's, 90's and radiator valves and cast iron radiators. The only pipe valves are located around the boiler which I use to isolate it for repairs. There is a mix of 3/4 to 2" copper and black pipe. Hope thats enough.

4) PRV: 40 psi

Comments:

I have had very little noise issues. Usually after I have drained and refilled I hear a bit of gurgle/air "rush" as the introduced air works it way through the system. The gurgle/"rush" gradually disappears as I bleed the radiators and add additional of water during the cold months.

I now shut off the water fill valve during normal operation to avoid the extra shot of psi during boiler start up. Also, shutting the fill valve reduces the risk of feeding a leak.

All the radiators get hot during the winter. One radiator is a bit stubborn due (I think) to a 90 up and 90 over piping configuration installed a few years ago. I think a bubble gets stuck in the upper 90. It works its way out as the winter progresses. I may add an air valve down the road.

I read another post that claimed the a new expansion tank can get "stuck" to the top of the tank interior. Amtrol recommended letting air out of the tank until you hear a "pop" then refilling to 12 psi. Something to consider.

Off to work on another project.

Steve
 
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Old 09-27-06, 04:45 PM
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40# Relief Valve?

All boilers are tested to at least 50# but very few are listed to operate over 30#. If this boiler is not listed for operating pressures in excess of 30# and something should happen I doubt your insurance would be worth the paper on which it is written.
Twenty PSIG should be enough pressure for this system. Like Xiphias, I believe if you went to the pumping away configuration your problem would go away. I've become a believer in pumping away.
 
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Old 09-27-06, 05:18 PM
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I'm guessing this "3-flat" apartment is how big? 3000 sq ft or so?

The NRF-22 should be ok. Your experience and hot rads suggest so, some air problems notwithstanding. We'd have to do the full estimation of piping lengths, etc. to really check this out. But let's call it functional.

Agree with Grady. You really shouldn't need any more than 20 psig to run this system, and maybe a bit less.

I would relocated the expansion tank connection when you install the appropriate tank.

Give a shout with results.
 
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Old 09-29-06, 12:59 PM
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Thanks Grady and xip

Okay, I'll inform you of the results of my tests.

xip: RE: Your reading of Holohan's "Pumping Away" Book.

The 4.3 psi differential (pumping in) on your system makes sense but I was getting 35+ psi from (last years) cold start of 13 psi.

I'm beating a dead horse so...next up is a #90 expansion tank.

A few years ago, I talked to the engineers at Dunkirk. They say my boiler is rated at 50 psi but has a built in safety factor of 1.5. Its tested in the plant at 75 psi or more (I cannot recall the exact number). Of course, "tested in the plant" is for a new, rust free boiler.

I'm still getting a 20 psi reading on my cold boiler. Last year it was 12-13 psi. I talked to the B&G folks yesterday about my B&G FB-8 pressure reducer. They said there are 2 primary areas to look at. 1) The filter/screen which can be cleaned and 2) The gasket that seals the city water from the reduced pressure water. Both are replaceable, if the parts are still available. If I remove the gasket, the calibration is lost and I would have to re-adjust to 12 psi.

Or I may just replace the whole thing. Too bad they do not sell the exact item anymore - more plumbing.

Steve
 
 

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