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# GPM, is this going to be a problem?

Member Posts: 123
My boilers BTU/h specs. are 15,000 min and 120,000 max. If I did my math right that's 1.5 gpm min and 12 gpm max. My manifolds max gpm is 1.3, is this going to be a problem?
Thanks,
«1

• Member Posts: 12,387
Well, the math looks OK... assuming 20 degree delta T... but if you are trying to stuff 12 gpm through a manifold rated at 1.3 gpm, it's not going to work very well...
Br. Jamie, osb

Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
• Member Posts: 671
Put the brand of manifold, unless its a copper one you built, in that case tell us the sizes
Tom
Montpelier Vt
• Member Posts: 1,032
Jack your boiler piping is designed to keep the boiler flow different from your loop flows. You have a pump with 2 close tees coming to and from the boiler. That separates the flow rates that is going to the system loops.
D
• Member Posts: 902
The boiler will have a minimum flow rate through the HX listed somewhere in the manual, Usually upwards of 4 for a 120k unit but yours may be an exception- what model boiler do you have? The majority of mod con boilers are supposed to be piped primary secondary to maintain proper flow across the HX while allowing whatever flow is necessary through the loads with the hydraulic separation created by primary secondary piping. I'm guessing the 1.3 GPM mentioned is "per loop" of your radiant manifold, how many loops are in your smallest zone and how long are they, in what size tubing?
• Member Posts: 12,963
1.3 gpm per manifold port may be what you are looking at

The trunk size of the manifold dictates how many branches

A 1” manifold should handle 12 or so branches
Bob "hot rod" Rohr
trainer for Caleffi NA
The magic is in hydronics, and hydronics is in me
• Member Posts: 123
My system is a two zone layout. Zone 1 is 30'x30' with 4 circuits of 1/2" pex, 229'-230'-230' and 229'. Zone 2 is 15x30 with 2 circuits of 1/2" pex, 212' and 214'.

The Boiler is a Hydro Smart 120 Condensing Gas Micro Boiler.
BTU/h is 15,000 min. - 120,000 max.

The manifolds are Rifeng 3 and 4 loop manifolds. The supply side is 3/4".

https://s3.amazonaws.com/s3.supplyhouse.com/product_files/Rifeng-RHM04-User-Guide.pdf
• Member Posts: 5,631
With primary/secondary piping, the manifold flow rate is not an issue.
"If you can't explain it simply, you don't understand it well enough"
Albert Einstein
• Member Posts: 123
DZoro what does that mean? Is that a good thing or a bad thing?
Thanks.
• Member Posts: 1,032
Your earlier piping drawings that you are going by, already take care of the 2 individual flows. So you have the proper hydraulic separation between the Boiler and System.
You are on track! Good luck!
D
• Member Posts: 12,963
Your design load is maybe around 30,000 but/hr. So 3 gpm of flow total. You have 6 loops so 1/2 gpm each works out about right..
Bob "hot rod" Rohr
trainer for Caleffi NA
The magic is in hydronics, and hydronics is in me
• Member Posts: 123
Thanks Dzoro I'm glad to hear that. I hope post a picture of what I've done so far for critique. Appreciate your help.
• Member Posts: 123
Thanks hot_rod I appreciate your input. Good to know.
• Member Posts: 123
Well I finally finished the re-build of my radiant heat system. I'm only running one zone at a time to begin with, everything seems to be working fine so far.
I do have one question though, where do I set the thumb screw at on top of the air eliminator. The instructions don't say.
Thanks.

• Member Posts: 411
edited December 2019
The thumb screws at the top of automatic air eliminators are to be open at least 1/2 turn. If closed ... no air will be released.
The reason for the cap is when they fail... if the float fails to completely close the air vent... you can close the cap (thumb screw) to stop the leak until such time as you can repair or replace the leaking air vent valve.
Since you do not have a dedicated water feed line to constantly add water as air is vented over the course of the first few weeks of operation, you will want to closely monitor your water pressure. if there is any drop in pressure that results from venting air, you will need to replace that with something (like water).
This system looks professional! Nice job! I don't see a Low Water Cut Off... Since this boiler requires the activation of a water Flow Sensor to initiate the burner ignition cycle, is there a need for a LWCO? Thoughts anyone?
• Member Posts: 12,963
Is the expansion tank supported somehow? It should have a bracket or band around it
Bob "hot rod" Rohr
trainer for Caleffi NA
The magic is in hydronics, and hydronics is in me
• Member Posts: 123
edited December 2019
Thanks @EdTheHeaterMan, I'll keep an eye on the water pressure. I'll also keep an eye on the thread concerning a LWCO. I thought that is what the flow sensor would do.
Thanks for the compliment.

@hot_rod I threaded and bent a 3/8" HR rod that's just to the right of the tank, you can see it coming out from the wall. If I need to support it from underneath I will, let me know. Thanks.
• Member Posts: 209
@JackW Looks good. I've seen a lot of "professional" jobs that would not measure up to your quality.

Do you have a condensate neutralizer?

I think this system will work very well for you. I bet you can run your boiler pump on low speed and still feed both zones.
• Member Posts: 123
@Jolly Bodger Thank you I appreciate the compliment.

I am running the circulators at low speed, my manifolds are set at .8 gpm and the boiler is running at 2.33 gpm, don't know if that is a problem or not.

I don't have a neutralizer, is neutralizing the acidic condensate important?
• Member Posts: 209
@JackW , .8 gpm per manifold or .8 gpm per loop? Not that it makes much difference. The primary secondary piping you have provides you hydronic separation. This way your zones and your boiler can run different GMPs without a problem.

Neutralizing the acid is important depending on where the drain is going. If you have any cast iron pipes or it is going into a sepic system I would recommend it. Does not have to be fancy.
• Member Posts: 123
@Jolly Bodger it's .8 gpm per loop. I can run it up to 1.3 gpm if needed. I just got it running today and at this point everything seems to be working well. Is there a way to tell what it should be?

I don't have any plumbing in my building so right now I just have it going into a small bucket. I might look at plumbing it outside later but for now I'm going to leave it as is. I went ahead and ordered a neutralizer anyhow, want to make sure everything is done right. Thanks for your help.
• Member Posts: 209
@JackW GPM per loop is dependent on loop length, spacing, supply water temp, BTU output needed of the slab. You can do a simple test to dial it in. Get the system running and stable. measure the temp going out to a loop and the temp coming back. Adjust the GPM to about 10 degrees Delta-T. .5gpm is common for 1/2" PEX.
• Member Posts: 1,032
Nice work @JackW !
D
• Member Posts: 123
Thank you @DZoro, I appreciate all your help.
• Member Posts: 123
@Jolly Bodger thanks for the info will look into that. I will have to figure out what "Delta-T" is first. Haha.
• Member Posts: 12,963
You have flow setters on the manifold, dual in the gpm you want .5-.6 is typical for 1/2 looos
Higher flow rates and tighter delta will require more pumping power
Bob "hot rod" Rohr
trainer for Caleffi NA
The magic is in hydronics, and hydronics is in me
• Member Posts: 123
[email protected]_Rod. I have it set at .8 now I'll dial it down a touch and see what happens. @Jolly Bodger suggested that I measure the Delta_T of a loop and dial it in that way.
• Member Posts: 12,963
> @JackW said:
> [email protected]_Rod. I have it set at .8 now I'll dial it down a touch and see what happens. @Jolly Bodger suggested that I measure the Delta_T of a loop and dial it in that way.
The delta t in a system changes based on the load, the flow rate is a constant number you see and set. Expect to see a wide delta on start and narrowing as the room approaches set point, regardless of what delta you designed for, it will and should move around a bit to best match the changing load conditions.

Trying covering the load at the lowest possible settings, flow rate and SWT if you are chasing best efficiency
Bob "hot rod" Rohr
trainer for Caleffi NA
The magic is in hydronics, and hydronics is in me
• Member Posts: 123
@hot_rod the white caps on the return lines are adjustable also, I have them all the way open, is this where I should have them set and use the supply side to adjust the flow?
• Member Posts: 12,963
Yes open the ports where the actuators attach. Then adjust flow by turning the flow meters. Some of the flowmeters have locking rings that need to pop off first. Good to adjust them sooner than later as those plastic windows tend to get dirty and hard to see the float inside
Bob "hot rod" Rohr
trainer for Caleffi NA
The magic is in hydronics, and hydronics is in me
• Member Posts: 123
Thanks @hot_rod will do. I've noticed there are some small bubbles in them also, suppose those will take some time to dissipate through the air eliminator.

Also one other question, what the devil does SWT mean?
• Member Posts: 209
SWT= supply water temperature
RWT= return water temperature
Delta-T= the difference between the two.

Now you know lingo too
• Member Posts: 123
@Jolly Bodger simple enough even I can understand it. Hahaha.
Thanks.
• Member Posts: 123
edited December 2019
@hot_rod I took these measurements at the manifold.. The SWT at the manifold 98 degrees, the RWT is 78, I have the manifold set at .8gpm. That makes the Delta-T a 20 degree difference, if I'm understanding this correctly. So is that a good or bad thing?

• Member Posts: 1,515
I love this thread. Such neat craftsmanship
1 pipe Utica 112 in Cedar Grove, NJ, 1913 coal > oil > NG
• Member Posts: 123
@ethicalpaul lots of great advice also.
• Member Posts: 2,657
I don't see a Low Water Cut Off... Since this boiler requires the activation of a water Flow Sensor to initiate the burner ignition cycle, is there a need for a LWCO? Thoughts anyone?
''

My W-M Ultra 3 boiler says its controls are such that no LWCO is necessary, but my contractor put one in anyway because the AHJ around here insists on it.
• Member Posts: 12,963
> @JackW said:
> @hot_rod I took these measurements at the manifold.. The SWT at the manifold 98 degrees, the RWT is 78, I have the manifold set at .8gpm. That makes the Delta-T a 20 degree difference, if I'm understanding this correctly. So is that a good or bad thing?
If you are warm and comfortable, that’s a good thing☺️
Bob "hot rod" Rohr
trainer for Caleffi NA
The magic is in hydronics, and hydronics is in me
• Member Posts: 209
It's all down to a complex selection method that takes into account tube spacing, btu/ft2 demand, SWT, circuit length, and final flooring selection. My systems are designed for 90 SWT, 10 Delta-T, and .42 GPM per loop. your system may be designed Different.
Low RWT makes your boiler more efficient but may make your floor uneven or fall behind in cold weather.
This is where you can play with it.
Hot_Rod is right. As long as your comfortable it is working
• Member Posts: 123
@hot_rod and @Jolly Bodger yes the rooms are very comfortable. The floor is warm, the room is warm and the circs shut off when the set temperatures are reached.

When is the difference between the SWT and the RWT too much? I would think if your boiler is putting out enough heat and once the slab heats up that there shouldn't be to big of a difference between the two.
• Member Posts: 12,963
Page 20 talks about delta T in a circuit, how and why it varies https://www.caleffi.com/sites/default/files/file/idronics_23_na.pdf
Bob "hot rod" Rohr
trainer for Caleffi NA
The magic is in hydronics, and hydronics is in me