volume vs pressure? swapping boiler lines out


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Old 06-12-14, 12:51 PM
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volume vs pressure? swapping boiler lines out

I had a topic up a while ago about swapping my boiler lines. I needed to move some out of the way to renovate in one of my apartments.
It is black iron now but Im swapping to pex.
I beleive this used to be part of the old steam system for the oldfashion big cast radiators in my second floor.
Im assuming when the house was converted from a single victorian to a multi family they used these lines and radiators to make it the heat for the floor which is now hot water.

anyway the feed out AND return coming from the boiler are 1" copper that ties into the 1-1/4 OR 1-1/2" black which then is downed to 1" for each radiator (each has one feed and one return).

I was going to just change everything to 1" Pex figuring water will fill and circulate normally once the system is fully charged, especially since right out of the boiler its 1" copper anyway but now Im curious if this will cause some kind of volume issue.


anyone have any input.
thanks
 
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Old 06-13-14, 04:48 AM
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I walked the entire system yesterday with my neighbor who is/was a boiler tech.
He said the system was a bit novel and it didnt even seem like there were any monoflow tees on the run. He had no idea how the radiators even circulated water and got hot without them.

He honestly couldnt say if he thought there would be a volume issue though. I was wrong as well, it seems the black run is actually minimum 1-1/2. He couldnt tell if it might be 2". I dont think its that big though.
 
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Old 06-13-14, 08:06 AM
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He honestly couldnt say if he thought there would be a volume issue though. I was wrong as well, it seems the black run is actually minimum 1-1/2. He couldnt tell if it might be 2". I dont think its that big though.
Steel pipe is sized by i.d. Google "Nominal Pipe Size Dimensions" and get the o.d. of sched 40 pipe.
 
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Old 06-13-14, 12:24 PM
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I know its sized by ID. I just dont have any cut yet I can measure and telling size by sight was never my strong point. Or his I guess.

Im just wondering if volume is an issue over pressure. I thinking water will circulate regardless once the system is charged. Like I said everything starts and end with 1"coppper and I could even install monoflow Tees to be safe. But I need to be sure before I start cutting more out.
thanks
 
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Old 06-13-14, 02:52 PM
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I'm not sure what you mean by "volume vs. pressure" - they are interrelated. The flow-rate through the piping will certainly be smaller with a higher pressure drop caused by smaller pipes, but the head-flow characteristics of the pump come into play, too.

If the system performed satisfactorily with the existing piping, replacement with the same size piping is the safest approach - without doing some complicated calculations. The flow-rate and pressure drop though a system is determined by the total flow resistance, not the flow resistance of the smallest segment in the main. You mentioned that the boiler connection starts out with 1" and ends with 1", but that doesn't mean that other parts don't need to be larger than 1" - fluid flow isn't like solids passing through strainers in series.

Tell us the approximate number of square feet in the apartment and the number of radiators in it - and how the radiators are piped, e.g., in separate 1" loops or multiple rads in parallel or series in one 1" loop off the main. There are rules of thumb that might help us do a sanity check. An individual radiator can often be supplied by a 3/4" risers off the main, but if several radiators are supplied by the same loop off the main, then the loop will likely need to be larger. And the mains, larger yet.

What is the net heat rating of the boiler? That will provide some indication of the required main sizes. Posting rough sketch of the piping system, with pipe sizes, would be a big help. You don't need to until you cut into the steel piping to determine pipe sizes - go by o.d. and tables of pipe dimensions that are available on the web.
 
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Old 06-16-14, 04:37 AM
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there are 5 radiators in the apt.
They are not series. Each one has its own looped feed and return. 3 do come off this 1.5" black pipe but with their own risers a piece.
Id have to get the info off the boiler and sq feet
 
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Old 06-18-14, 05:30 AM
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so me and my buddy were brainstorming yesterday and possibly came up with a safety situation for this. I will leave the 1.5" black up to the point it needs to be lifted. Then split it into 2 separate 1" pex lines. One line feeding the first radiator which is one bedroom. Then the second line feeding the second two which are a bathroom and then one I actually think is cut and capped somewhere which I may eliminate if I can prove this.

I will use some monoflow tees where needed to be sure the water gets in the lines and then my masssive circulator pump on the furnace should do the rest.

does this seem plausible. I have the info from the boiler and its capacity is 116000btu/hr
the rooms are about 12 by 12 except the livingroom/dining room which are like 15x13, actually one big room each with their own big radiator. Those are on a separate branch though from what I can see that wont be touched
 
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Old 06-18-14, 06:34 PM
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T,
You size your main line by how many btu's your heat emitters need.
First you must size your rads and get the BTU output of each and how many btu's your main will have to supply.
A 1" line will carry 75,000 btu's, an 1/1/4 will carry 160,000 btu's
Check out this sight for pipe sizing.
Hydronic Heat Pipe Sizing.
This might help you.

Each rad, depending how it's made either has volume or sections and height has a rated BTU output. You must first get their rating. Your buddy might have some info.

You said your boiler is 116,000 btu's. I can't see why you would need 11/2" main line pipe.
Once you figure your 5 rads I wouldn't be surprised if you could use your 1" you wanted.

You said you have 1" feeding & returning. Your only going to get as many btu's as your smallest pipe.
1" will give you 75,000. Connecting 11/2 to it will not get you any more.

Hope this helps a little.
Good Luck,
 
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Old 06-20-14, 09:40 AM
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awesome thanks.
I used to do boiler installs but never did more than that. I was only an apprentice and the boss did the main stuff.

For the radiators in question its really only 3 so I think you are prob right on the 1" then

as for my buddy, he is just handy like me. A plumber by no means. Like I said even the boiler tech next door was confused by it all when he saw it.

the sizing of the 1" and the 1.5 was all retrofit.
Like I said I think it was an old steam setup and they converted but just used the existing pipes.
They just plopped a bioler in and connected it to the old 1.5 black with 1" copper and crossed their fingers.
 
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Old 06-21-14, 11:18 AM
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T,
This sight will help you figure out the heat value of each rad and the total for the main line sizing.
You will probably find that you will have a 1" main and can feed the rads with 1/2" pipe as long as you're feeding them individually.
By the way you might want to think about making it a 2 pipe system rather than a monoflo. Much easier to bleed and easier to set up for the homeowner.

http://www.columbiaheatingsupply.com...ron%20Radiator...

You take your sq. ft of radiation per sec. X the number of sec x 170 and that will give you the BTU rating of the rad.

Good Luck, hope this helps.
 
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Old 06-23-14, 05:35 AM
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yes Im going to make it a 2 pipe system using 3/4 branched off the 1.5 main(thats still in the neighboring garage).
I think 3/4 going to each radiator should be plenty enough.
Also I was confused, there is actually only TWO radiators Im feeding and both are smaller ones. The main HUGE ones in the 2 living spaces are off another feed going the opposite way.

now that the cielings are all torn down I can actually see everythign and I think I was working myself up over nothing.

Wish me luck
thanks
 
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Old 06-23-14, 07:47 PM
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T,
You sound like you've got it under control.
1/2" pipe is good for up to 15,000 btu's and if your rads are small I doubt you're anywhere near that. Just for information. 1/2 or 3/4 will be good.
One more thought comes to mind. With the larger pipe and the cast iron rads you might want to go with a #60 extol tank because of the water content in the system. Any time cast iron emitters are used they want a minimum of the #60 expansion tank.
If you go with the #30 and you build pressure and relief valve starts to let go that will most likely be the reason. Change the tank and you should be OK.
Good Luck,
 
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Old 06-24-14, 04:44 AM
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not a bad idea.
Its a 30 now and the releif has popped once or twice. I keep 5 gallon buckets under each furnace relief which has saved me a couple time.

I have a small boiler for the apartment Im reno'ing now and it only has a 2gallon (20?) on it.

That tank has gone on me like 3 times in 8 years and I have decided Im swapping to a bigger one. So maybe Ill upgrade the big furnace and use its E-tank on the smaller boiler.

Im gonna go 3/4, a 2 pipe system (each rad with its out feed/return) and start ripping it out this sunday. Cant wait to scrap all this cast, black, and galv Ive been pulling out and get a dumpster with the cash $$$$ c'mon BIG MONEY!
 
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Old 06-24-14, 10:01 AM
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T,
If these rads were used for steam before and now for hot water make sure you have bleeders on the top of the rads. Steam has them about half way up which is no good for hot water.

Some rads can be used for both and some only steam. Just a thought that is sometimes overlooked.
 
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Old 06-25-14, 04:28 AM
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there are bleeders on the upper sides.
They are used for water now. I bleed them in the beginning of the season every year and show the tenants how to do it if one radiator every doesnt heat well.
My thought is they were used for steam originally when the house was an old single family vistorian. After the conversion they used the existing pipe to get to the second floor since it would be the easiest way without having to run new piping through the first floor.
 
 

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