No heat on new panel rads, monoflow system

BobJoe

New poster, long-time lurker. Finishing a major remodel on a 1955 Cape Cod style home with a single-loop monoflow hot water system. This includes adding two new panel radiators in a new mudroom and laundry room, replacing a convector with a panel radiator in a new location in the kitchen, and replacing a kick-space heater with a panel radiator in a small bathroom. Unfortunately, the plumbing sub does not understand monoflow systems, and I am not getting ANY heat in the new mudroom and laundry radiators. Please see the attached diagrams (before, after, and my recommended changes).

My question is: Do you think my recommended changes will work? Anything more I can do? I need heat for Christmas!

Background::
- All original convectors are recessed finned tube fed by 3/8” soft copper tubing (no fittings, all soft bends), single monoflow tees on return
- Single 1-1/4” copper main loop (accessible in basement).
- Some of the convector loops are “stacked” within other loops, presumably to help increase pressure to 2nd floor convectors
- All the new panel radiators are connected into the loop with diverter tees on the return, but < 8” apart from the supply tee, fed by ½” PEX.
- The laundry room loop is particularly convoluted, with about 20’ of PEX with at least 6 elbow fittings on supply and return. This is all now buried in spray foam insulation.
- The new kitchen panel radiator is a Runtal; all others are Ecostyle/Purmo.
- For reasons I can’t explain, the plumber did not reuse the original kitchen convector loop, and just connected the feed back to the return.
- At one point, the Grundfos UPS 15-58 FC circulator was left running for several hours while the system was drained; only discovered when it started squealing like a siren. Has been working for several weeks since.
- The plumber has bled everything to death. Despite forwarding Dan’s videos and posts, he still does not seem to get it.
- Before the reno, the system worked fine; well balanced, quiet, comfortable, with the exception of the -12F day last December (I'm in Boston area) where things did not seem to keep up.

Problem:
- Kitchen and bathroom panel radiators are heating fine
- Mudroom and Laundry radiators are stone cold. And yes, all the valves are open.

After researching here, my recommended solution is:
- Move the mudroom radiator to the original kitchen supply/monoflow tee loop (which is 'stacked' with a 2nd floor convector)
- Add diverter tee to both supply and return on the new laundry panel radiator, and separate them at least 1-2’ from each other. Remove the remaining new loop.
- Replace the circulator with a like model

THANK YOU!!!!

mattmia2

How is the pex pitched? It really needs to slope to the emitter so the air can get out, monoflow doesn't really produce enough flow to carry air out so it has to be able to get out by gravity. You could add purge stations to the new loops and purge them with a hose to get enough air out to start flow. What sort of air elimination is at the boiler?

Are the monoflow tees in facing the right direction? If they are the wrong direction they won't force any flow to the emitter and will restrict the main loop.

EBEBRATT-Ed

THIS "All the new panel radiators are connected into the loop with diverter tees on the return, but < 8” apart from the supply tee, fed by ½” PEX."

All the Monoflo tees are way to close together.

Any supply tee or monoflow must be at least 18" away from any tee connected to a different radiator and 18" from any elbow or valve etc.


Butt the real problem is the distance from the supply tee to the return tee for you new rads cannot be less than 8" apart you will not get any flow that way.


Rule of thumb with base board was the tees should be as far apart as the length of the baseboards.


You have two problems the tees are too close together and the branches for the mud room & Bath/laundry are too long although the 1/2" pex is probably fine. 20' is a fair distance for a monoflow to work


You need to install a Monoflo tee on the supply AND the return for the mud room and the same for the bath/laundry.

Get the supply and return tees far apart like 6-8'....the farther apart the better. And the tees have to be installed in the correct orientation.

It's possible you might get away with 1 Monoflo on the mud room & 1 on the bath/laundry if you space the tees far enough apart.

But you probably don't want to drain the system again

BobJoe

Thank you for the replies. To answer some of the question asked:
1) How is the pex pitched? In a word - poorly, though most is generally up toward the rads. They have been bled A LOT with strong streams of water (from what I saw), so I doubt air is the problem.

2) Mono's the right direction? I didn't supervise every step of the install (I shouldn't have to - I hired a professional!), so I don't know. These are Veira-brand 1-1/4 by 1-1/4 by 1/2 copper tees with no external marking, so presumably with diverter inserts. It's even possible they are not diverter tees at all (which makes the rest of the discussion moot), though I did specifically ask (English is not his primary language, so communications is tough).

3) Re: spacing on the diverter tees - I know the current 8" spacing is way wrong, which is why I mentioned it. Getting them separated by anything close to 6' will be challenging - the diagram is loosely representative of the physical loop, and that portion of pipe with all the tees is ~15' end-to-end. I hope monoflows on both supply and return will do the trick.

BTW - I am getting a different plumber from my GC. The guy who did this is a nice kid trying to make his way, but he needs to learn when he's in over his head.

SuperTech

It sounds like you hired the wrong guy for the job. You should have hired an experienced professional who knows these systems.  As you found out the average plumber or hvac tech is probably not going to be familiar with your setup. Find someone who can follow the advice given by @EBEBRATT-Ed. Witn the amount of work performed I'm surprised you didn't ditch the monoflo setup and just recipe everything to manifolds at the boiler in reverse return. 

Ironman

If using two Monoflo tees and separating the spacing doesn’t fix it, you could add a small circulator on to the radiator loop, then you’d have a primary/secondary setup and wouldn’t need the monoflo tees.
You'd just need to make sure that secondary isn’t pumping more than the primary.

Ironman

Another consideration is that panel rads have flow setter valves which add more resistance to flow and they should be set to fully open.

Big Ed_4

On a long horizontal riser run you need to add a purge valve set up on one of the risers . It is very hard to get a 1/4" pitch .

The wider the spacing of the tee the better the flow through the riser . Long run with the extra resistance ... Move them tees apart ... Tip ... You can increase the main distance with a loop of Pex between the tees .

mattmia2

BobJoe said:

1) How is the pex pitched? In a word - poorly, though most is generally up toward the rads. They have been bled A LOT with strong streams of water (from what I saw), so I doubt air is the problem.

If it goes down hill anywhere a pocket of air will sit in there and it will not circulate. you won't be able to get that air out with a regular coin key vent. there is no guarantee of which end the flow to the bleeder is from if there are no isolation valves. With a purge station or some valves and some boiler drains you can force enough flow with a hose to carry the air out.

I couldn't find a "viera" diverter tee. Viega makes a lot of premium fittings. Are you sure they are diverter tees at all?

Now understanding that diverter tees actually partition the pipe in to 2 separate smaller branches I really don't think the separation is as important as it is made out to be unless someone can show me otherwise. If the inlet is say 3/4 in^2 and one outlet is 1/4 in^2 and the other outlet is 1/2 in^2 the flow is going to divide, the different areas will have a lot more effect on the flow than the slight differences in resistance in the 2 sections of pipe.

BobJoe

Thanks again for the comments. I am assuming he used a "venturi insert" with a Propress Tee (though I never saw it). Plumber was a supposed "heating specialist" sub under the plumber (a different story) chosen by my General Contractor for the reno. I didn't choose him, but I am choosing to force a change. Live and learn.

Re: getting air out, I am hoping the euro-type shut-off valves at the in/out of each rad would help effectively bleed each line individually. we'll see.

For what it's worth, the Runtal panel rad in the kitchen has similar new tees space ~8" apart and it seems to be heating fine. But it is a much closer run.

If monoflows on both supply and return don't do it, I may resort to putting the new stuff on a separate zone and circulator.

Anyone think near-burn out of my circulator could be a factor? Would running-dry likely to cause a performance loss vs. 'just' reduced life?

mattmia2

Still think its air.
you'd need to put a valve something like this on one side at the main so you could purge through the emitter with a hose if they didn't pitch it all up toward the emitter. You could probably purge it out to a drain at the boiler somewhere:
https://supplyhouse.com/Webstone-40612-1-2-Threaded-Pro-Pal-Full-Port-Ball-Valve-w-Hose-Drain

you will never get enough flow through a coin key vent to pull a pocket of air down hill.


Must be something like this:
https://supplyhouse.com/Viega-78810-1-1-4-x-1-1-4-ProPress-Venturi-Bronze-Insert-Zero-Lead

Ironman

I’ve not seen an insert made for a press tee. The ones for sweat tees sit against the bottom of the socket and are held there by the pipe.

Interesting.

EBEBRATT-Ed

Who knows what he did just guessing at this point. It would be nice to see the tees he used.

You can also install regular tees with a ball valve or balancing valve between the tees to adjust the flow to the rads


Monoflo tees are particular if they are not spaced right, you will not get flow. Read the "Taco Guide for Hydronic Engineers " or and old B & G handbook to learn how to design a Monoflo system. It's pretty complicated to do it right and since Monoflow was done in the 50s and early 60s most don't know and just guess.

I have a copy of the Taco Guide which I don't think is available any longer i will see if I can get it on this site.

Even though Monoflo is rarely installed anymore it is a perfectly good system. I had a house with it for 34 years. The only issue is troublesome bleeding. But there are a lot of them around and they don't need to be ripped out they work.

We get may monoflow questions on the wall

BobJoe

Thanks Ed and everyone. My GC has another guy with 30+ years experience coming to assess and hopefully fix. Already his questions before seeing anything show much more knowledge. Thanks for the references - I’ve been trying to find a good “design how to” not just for this issue but to determine if my system will be out of balance when all done. I’m adding <200 well insulated sq ft to the house, so hoping all will be good. 

FWIW - attached is photo of the tees before install was complete.

Will let you know how it goes. Don’t want to DIY this but will if I have to.

109A_5

Hello @BobJoe,
My guess is that they are just regular Tees, since with the age of crimping tools soldering is becoming a Lost Art. I can't find any crimp type Monoflo Tees on the web either. All the Monoflo Tees I've seen are labeled somehow.

mattmia2

109A_5 said:

Hello @BobJoe,
My guess is that they are just regular Tees, since with the age of crimping tools soldering is becoming a Lost Art. I can't find any crimp type Monoflo Tees on the web either. All the Monoflo Tees I've seen are labeled somehow.

there is an insert that makes a regular tee in to a diverter tee. hopefully they used those.

mattmia2

Actually, look at the cut sheet, they are designed to be installed the way they are installed:
https://s3.amazonaws.com/s3.supplyhouse.com/product_files/78810-product.pdf

I'm not saying that is the optimal way to use them but that is what veiga shows.

pecmsg

mattmia2 said:

Actually, look at the cut sheet, they are designed to be installed the way they are installed: https://s3.amazonaws.com/s3.supplyhouse.com/product_files/78810-product.pdf I'm not saying that is the optimal way to use them but that is what veiga shows.

I don’t see a new clean piece of brass in the picture between those 2 T’s. 

mattmia2

oh i see, it is the pipe. it looked like it inserted inside the pipe

pecmsg

The brass has stops on it. 

bburd

It looks like those venturi inserts were not used. I don't see them in the photo. They are supposed to be installed in the main line between the tees.

Big Ed_4

Use two 1.25" X1"x riser size tees and a 1" ball valve between the tees....

EBEBRATT-Ed

Those venturis are designed for plumbing. Don't know if they will work on heating. Different water velocity and flow rates

EBEBRATT-Ed

I don't see any crimp marks on the tees in the pictures the op posted

mattmia2

EBEBRATT-Ed said:

Those venturis are designed for plumbing. Don't know if they will work on heating. Different water velocity and flow rates

It is not a venturi. it actually partitions the pipe. It is going to divide the flow. A venturi would restrict the flow without an alternate path to increase the velocity to decrease the pressure in that region, usually to use that lower pressure to pull a fluid in through a branch in that region.

A diverter tee simply partitions the pipe in to 2 smaller passage with a reducer built in to keep the run at full size. You could accomplish the same thing with reducing tees with the smaller runs connected together and the larger runs connected to the inlet and outlet of the loop.

mattmia2

I didn't understand that until i saw this:


The flow is forced to be divided.

That also makes it clear that it won't work at all with a single tee if that tee is backward.

EBEBRATT-Ed

It doesn't matter what you call it diverter, restrictor, valve between to regular tees etc they all work the same way. Restrict the flow in the main to make the water flow through a branch. Without the tees the branch would have higher PD than the main and no water will flow through the branch unless you put a pump in the branch pipe.

It is still a venturi that is how it works but the terminology doesn't matter its a "restrictor tee" Some of them have a conical inner reduction and some have an angled scoop. Restrict the main so that some water goes through the branch. Below the main radiation and above the main with long runs may require two restrictor
tees to make it work.

The reason the tees are supposed to be spaced is that the distance along the main adds addition restriction to the main to help they system work. This is critical.

I one of Dans books "Primary secondary pumping made easy" on the first page he describes such a job.he describes an install of two tees for a second-floor bathroom that never heated. The tees were installed next to each other and the rad did not heat at all 1 Monoflo tee and 1 regular tee. The pressure drop along the main has to be more than the pressure drop through the branch to get water to flow through the branch . However you accomplish this that is what it needs to make it work

mattmia2

EBEBRATT-Ed said:

The reason the tees are supposed to be spaced is that the distance along the main adds addition restriction to the main to help they system work. This is critical.

I'd like to see the math on this but i'm not quite sure how to calculate resistance for an orifice. I'm pretty sure you will find that the resistance from a few feet of pipe is negligible compared to the resistance of the orifice in the diverter tee.

109A_5

Hello @mattmia2,

mattmia2 said:

I'd like to see the math on this but i'm not quite sure how to calculate resistance for an orifice. I'm pretty sure you will find that the resistance from a few feet of pipe is negligible compared to the resistance of the orifice in the diverter tee.

Maybe think of it as balancing a Wheatstone bridge. In this case the resistance of the main between the Tees does not have to equal the resistance in the branch. So the Wheatstone bridge has a constant but usable imbalance. Maybe nowhere close to a balanced bridge, it just needs to be enough to get the needed BTUs diverted through the branch to that radiator.

Usually more than two radiators so I would think a 50:50 would not be needed.

Big Ed_4

The ball valve is adjustable resister for fine tuning . You never want to over restrict the main . It would take flow away from the other radiators...

mattmia2

Big Ed_4 said:

The ball valve is adjustable resister for fine tuning . You never want to over restrict the main . It would take flow away from the other radiators...

It splits the flow. if the diverter tees are in the right way it doesn't change the flow in the main. If you add a balancing valve in the bypass in the main or you have very restrictive emitters then you will start increasing the resistance notably.

EBEBRATT-Ed

The "restrictor tee" changes the flow in the main but only between the two tees for that one particular radiator. The flow in the main at the inlet to the regular tee and the flow in the main on the outlet of the restrictor tee is the same. You're just diverting some of the main flow through the radiator. The amount of water the diverter tee sends through the radiator is very small. .5gpm will do 5000 btu. Thats enough for 10' of baseboard. That's why many monoflow systems use branches as small a 3/8 od copper tubing.

In my Taco book it says " minimum distance of 18" between the standard tee and the venturi tee must be maintained, if this distance is increased branch flow will be slightly higher."

The length and size of the branch piping has a major effect on whether you get enough flow.

Also, the main pipe has to have the correct flow. If the flow in the main is too small for that main the branch flow will suffer.

This is why with baseboard they recommend putting the two tees apart the same length as the baseboard.

If you saw the math involved in designing a venturi system correctly you would quickly see why they are no longer popular. No one will take the time to do this now.

But they work if done correctly and at the time after WW!! pipe and material were in short supply and a venturi system save 1/2 of the main piping that needed to be installed for a direct return system and a lot less pipe than a reverse return.

That is why they also went with the series loop system. Problem with a series loop is the rads at the end get cooler water so you compensated by putting more radiation at the end of the loop. Monoflow temp drops as well but not as much as a series loop

mattmia2

It is not a venturi. This is a venturi:
https://en.wikipedia.org/wiki/Venturi_effect#:~:text=The%20Venturi%20effect%20is%20the,or%20choke)%20of%20a%20pipe.

This is just splitting the flow with an orifice. If the flow is low enough that the resistance on the main branch produces almost no pressure drop then there will be little flow in the emitter branch.

The math involved in doing a series loop right is harder. in a monoflo you can to some extent increase the flow in the main loop to keep the delta t low. with a series loop if you want it to be balanced you need to get the heat loss of each room right, figure the delta t for the emitter of each room one at a time and use the water temp from the pervious emitter to size the next emitter.

EBEBRATT-Ed

@mattmia2

I agree with the series loop but a Monoflo system is much more difficult to design. I have about 8 pages of tee selections in my Taco book. We spent hours on this in school. The tee selection are all based on branch diameter, branch flow, main diameter and main flow above the main, below the main, standard venturi tees and super venturi tees each of those calculations x the # of radiators

And it is a venturi Taco calls them venturi tees. B & G calls theirs Monoflo

mattmia2

They call it a venturi but it is not, it is just an orifice. (and me thinking it was a venturi, that it induced flow like in a carb or an atomizer or a lawn sprayer is what confused me).

I don't know how they would teach designing them in a trade school. the easy way would be to write a system of equations(though solving that is tedious without a computer). I suppose for the most part you can solve for each emitter independently. I suppose you could take a guess at the flow in the main and see if it all works out at that flow then try again if it doesn't.

It is essentially a combination of series and parallel resistors, it is the same thing as solving an electrical circuit.

109A_5

I think the Return would qualify as a Venturi and the Supply (if used) as a diverter. Just calling them an orifice, I think that is over simplifying the actual situation. If it was just added resistance needed in the main pipe a valve or a smaller main pipe would be appropriate. With the Return as a Venturi the velocity changes.

"The Venturi effect states that in a situation with constant mechanical energy, the velocity of a fluid passing through a constricted area will increase and its static pressure will decrease. The effect utilizes both the principle of continuity as well as the principle of conservation of mechanical energy."
https://www.comsol.com/blogs/exploring-the-venturi-effect/

bgohn

OK - it's been a year since I originally started this discussion, but to close out the story for future posterity:

1) @109A_5 wins the prize for why the two new panel radiators where not heating. Turns out the original nice-young-but-incompetent plumber who installed the new rads did not install diverter tees of any kind, despite all the links, pictures and commentary I provided. No wonder there was no heat.

2) The "more experienced" plumber brought in by my GC installed scoop-type diverter tees on the supply side of the mudroom and laundry rads. We had quite the ‘discussion’ on supply vs. return and distances between tees, but he got them working. He did leave behind a mess of capped off tees though.

3) Since then, I've had trouble with the second floor convectors - upstairs is typically 6-8 degrees F colder than the 1st floor. Thinking that perhaps some of the capped-off tees might still be diverters impacting flow, I cut out ALL the new work this Fall and DIY'd proper B&G monoflow tees according to the diagram I proposed at the start of this thread. This is how I discovered (1) above (doh!)

4) Interestingly, the Runtal panel radiator in the kitchen that was heating fine ALSO had no diverter tees. Whatever flow it had was apparently only due to hot water rising! (I also corrected this). However, none of this addressed the 2nd floor balance issue. Today it’s 10 deg F out, and even with the circulator running continuously all day, I still can’t get upstairs rooms above 64 degrees. Going to start a new discussion on this but wanted to close this out one first, and offer a *very* belated thank you to everyone who responded!

bgohn

Also, just noticed somehow I've managed to create two accounts - bgohn and bobjoe are both me (sigh). Sorry for any confusion.