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## Runtal MonoFlo return question (18 Posts)

• ### Runtal MonoFlo return question

Hello All,

Quick overview at my house I have 3 buildings. A house where my gas boiler is, my office which is roughly 1400 sqft of radiant heating at the bottom of 10" of sand. I have underground pipes 40' long connecting the boiler to my radiant manifolds. This has been great for 8 years. I have added a second building with underground pipes that I will be heated with 82' of runtal uf-2 basedboard around the perimeter of an approximately 600 sqft building.

My initial plan was to run each half the perimeter as a separate run. The return for both runs would run separate tubes running behind a kickboard.

I'm told by local professionals to give up and install a boiler out there(not an option). I assume it is due to Head Pressure but no one is very articulate so that is only a guess.

I discovered monoflo tees which will reduce my head pressure but I think I give up the separate zones. Monoflo Tees eliminate the cumulative effect for radiators in series.
Requiring less pumpling.

I have a spreadsheet with all my calculations and I feel good about everything except this area. If I'm understanding it correctly on the coldest days I won't be able to push enough btus through system because of head pressure.

I guess my question is does anyone have guidance?

Thanks,

Ben
• ### Some Questions

Hi Ben:

I've got some questions regarding heating your new building:

Have you done heat loss calculations?  A 600 square foot building should have a design load of between 10,000 and 13,200 BTU's and 82' of Runtal UF-2 will give you three times the output and that's at 150F.

To figure out your pressure drop, you will need to know the total feet of supply and return piping between the radiators and the boiler, the size of the pipe and the material (copper, PEX?).  You will also need to know the pressure drop through the boiler (available from the manufacturer) and the pressure drop through the radiators (available from Runtal).  The total pressure drop plus the required flow (gpm) will let you size the pump.

True, a Monoflo system makes piping easier, but can make air purging a nightmare.  I don't see the advantage in your system.
This post was edited by an admin on December 4, 2011 3:01 PM.
• ### details

Hello Alan,

My heat loss calculations are 3x yours, maybe due to climate I'm in Massachusetts and looking at the reality of -7 f.

In any case my worse case scenario is about 20,000-32,000 depending on wether it is 20 degrees F or -7 degrees.

I want to run at low water temperature to make use of solar panels and my radiant heatslab. I want to run the boiler to heat my slab and then mix water for the other building during normal operation then during cold snaps a mix directly with hot boiler water.

I was originally planning on 130 degree f water until Runtal removed that temp from their documentation.

I have

15' of copper supply and return leading from the to the insulated underground tubes 40' 1" pex tubing This currently feeds 2 6x manifolds I'm using 10 of the 12 loops. The longest loop is about 200'. This system will work with the pump in the boiler as is. I also have a second circulator installed but not currently in use.

At this point I want to install a "primary circuit" that will circulate hot water from the boiler with my radiant set-up and the new runtal install as secondary circuits.
The runtal building is 90 feet away with 3/4 pex-al-pex.

I have calculated pressure drop across the radiators. If I split the runtal install into 2 zones. I have zone 1 at 5.16 and zone 2 6.88. If I'm reading the table correctly.

The reason I was told that I should use the monoflo tee is to keep the head pressure from building up.

Can I use a 3/4 - 1/2 monoflo tee like this to collect both returns from the runtal and run them out through a single pipe?

I have 2 zones each running around the 2 walls of the perimeter of a square room. Can I use a monoflo tee for my return run. Take Zone 1's return water and install into the supply side of the monoflo tee with the 1/2 section as the input to zone 2's return. With both returns exiting into a single tube.

Thanks,
Ben
• ### MonoFlo:

Is it 90' away? 180' round trip before you get to the radiation? Are you using "listed" 3/4" PEX? That isn't 3/4" ID. You need at least 1" PEX. Your pipes sound like they are too small.
When we did MonoFlo One Pipe Systems back when, we never ran less than 1" mains and they were split with 1 1/4" copper or steel pipe being the mains.
Are you planning on installing the highest head-high volume circulator you can buy to make this work? MonoFlows require a decent flow through them. I think that you might have misunderstood what you read.
• ### more into

Yes 90' away 180' round trip ID is 3/4". My plan is to install the appropriate sized circulator.

I thought the Monoflo was to help relieve the head pressure by arranging the baseboard in parallel rather then series.
• ### MonoFlows:

It sounds to me like there may not be a circulator made that will help you. MonoFlows don't depend on high pressure and high volume pumps. In fact, I was told and am under the impression that if the flow through the venturi is too high, they do not work as well.
Over pumped systems SUCK. In more ways than one.
• ### More detail please

I understand you have concern unfortunately it is not being expressed in way that helps me frame the issues. I want a low flow rate and sounds like I need a high head pressure.

I need to balance the 2. I that what you are saying?

Ben
• ### Don't take this the wrong way, but...

"I thought that Monoflo was to help relieve the head pressure by arranging the baseboard in parallel rather then series" does not equal a design. Monoflo circuits can be finnicky to lay out, and especially to figure the overall pressure drop for the circuit. You should move beyond marketing slogans and get thee some design documentation. Or get a remote manifold with balancing valves, which will allow you to create a true parallel layout (as opposed to series-parallel of Monoflo) and to balance the flow through the emitters.
This post was edited by an admin on December 5, 2011 8:39 AM.
• ### I know I'm a novice all advice considered

That wasn't a monoflo slogan that is my understanding after studying the monoflo docs on this website including the that free chapter from Dan:)

Although I have no experience in heating other then my home I relay on this board to give the practical real world view of wacky heating.

In the mono flow scenario:
I have such a simple layout I was going to place the mono flow on the return of each baseboard in my single level loop around the perimeter.

Place a thermostatic mixing valve where the baseboard supply is mixed with the boiler supply and the rest is returned.

to main circuit 90' feet away....

In the manifold scenario (my original plan):
I was going to install a 2 loop manifold. The return pipes would be run along the perimeter beneath zone 1 behind a kick plate.

I have to do something so I'm looking for guidance. I'll start researching balancing valves but I'm open to any advice as to what I'm looking for.

Thanks,

Ben
• ### update to my flow rate numbers

I decided to update my calculations for the lowest daily average for january in my area it seems 14 degrees is a better temperature to work with.

With this change my btu loss dropped by 10,000 btus. Which dropped my flow rates to zone 1 .95 and zone 2 1.2.

I'm leaning towards skipping the monoflo and just going with my original plan. The thing that is strange about my system is that I have a large (40,000 tons of sand) that is my radiant heat source and hot water storage supply. I can run my boiler at a very high temperature and pump it into my sand while mixing what I need for radiant baseboard. Then both the baseboard and the radiant can coast for a while.
• ### Pump Sizing

Icesailor: I don't think he needs that big of a pump.  At 3 gpm, 200' of 3/4" PEX will have a head loss of 8.4' of head, no?  Add another 3 or 4 feet for the radiator, boiler and fittings..................a Taco 008 should nail it.  If you want some insurance, put in a 009 or 0014.
This post was edited by an admin on December 5, 2011 6:40 PM.
• ### Well this is very satisfying

Hello All,

Thank you for all your comments. I'm definitely skipping the mono flow tees. The main reason is that I want to route individual temperatures in opposite directions around the perimeter of the building.

With that decided I think I want a grundfos alpha with auto adapt as the circulator for the runtal zone. Then I will use the boilers circulator for my main circuit. My existing radiant system will use it's currently installed taco 11-f4 for it's circuit.

The boiler Supply would 1" pex go straight into the main circuit 1" copper then to the first 3 way mixing valve this valve would control the supply to the radiant circuit which is 3/4" copper.

The second 3 way mixing valve will be the remote building 3/4" id pex-al-pex to the runtal baseboard zone.

Next is the radiant circuit return
Finally the Runtal baseboard return.

The radiant circuit supply has a 3-way mixing valve to remix the supply and return to design temperature then the taco 11-f4 then the supply manifold. The return goes to the mixing valve then the main circuit.
The radiant slab has tens of tons of sand and 10 radiant loops 1/2" pex-al-pex all under 220'. The sand is used as heat storage for a passive solar collector and radiant floor heating. Once the floor is charged with 5 hour boiler burn I can keep it warm by running the boiler on a timer.

The runtal baseboard circuit will probably have a similar mixing valve set-up as the radiant only using a circulator with auto adapt to supply a manifold with thermostatic mixing valves 3/4" pex-al-pex 90' feet away. The manifolds will split into 2 zones.

Current questions:

Would it be worth changing the radiant's system circulator grundfos?
Does this seem like the correct approach?
Should I start a new thread?
This post was edited by an admin on December 5, 2011 9:27 PM.
• ### MonoFlo, Old Flow:

Alan,
My point is this:
I work on a lot of old systems. I NEVER see the problems with old systems that I see with the new ones. Old gravity systems were piped big and slow. The first pumps pumped lots and slow. 1725 RPM pumps. All the old MonoFlo systems were pumped with 1725 RPM, 3 piece circulators like B&G 100's and Taco 110's. Along comes the 007 wet rotors that were direct replacements for 100's and 007's. Spinning at over 3000 RPM. Then the fun seems to have started. If you don't pipe it so you can use a 007, maybe you designed too much restriction in it. Get a bigger pump. Get more cavitation. Get more air in the system. Get the head pressure way up in the system. Get the differential pressure way up. Put more air eliminators and absorbers that the high flow through may cause internal cavitation and bubbles. Ad Nauseum.
Where I work, my Wholesaler mover all the fin tube baseboard upstairs. Almost everything is scorched air and/or hydro-air. What I see done is against everything I ever learned from the old dead guys and their stuff works just fine. No air, no noise, no cavitation.
That discussion here on the guy that needed a compound gauge on his system pump. I tried to explain that using the biggest pump available to pump to an air handler in the second floor attic didn't need a bigger pump to get the water up there, it needed more system pressure. The same discussion I had with a guy in the supply house. And that the can vents needed to be closed once the system was vented. I learned that here, DUH!!! How stupid of me for not realizing that.
I don't know what changed but in the Yellow IBR #240 piping guide, there was confirmation to what my old dead boss always told me/us. 15,000 BTU's on 1/2", 35,000 BTU's on 3/4" and 65,000 BTU's on 1". The #240 just explained how there were limits to the overall length of the circuit.
180' round trip (without radiation) didn't fit in the equation. That's all I'm saying.
• ### Monoflo design details

As Gordan says, monoflo design is not as simple as one might initially think. Here is a link to the chapter in the B&G handbook on system design, including all the details:

http://www.heatinghelp.com/article/123/Bell-Gossett-Handbook-Second-Edition-1949/955/Section-II

I agree also that you are probably better off running the mains to manifolds and then distributing to each section of baseboard in a parallel fashion.
• ### Thanks Mike!!

That is a REAL treasure chest...

Its like TLAOSH,every time you read it, you find something new...

It pays to wander off the Wall. What a fantastic resource this place is :-)

THanks to Grandpa and Grandma Holohan for making it happen.

ME
It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
• ### Everything worked out

Well here it is summer and I never posted the results. The good news is that I skipped the monoflo and everything worked out fine.

So here is the final set-up. I have 3 buildings. First building holds the heat source a weil-mclain gv gold 70,000 btu boiler. This boiler's built in circulator is used to deliver hot water through buried 40' insulated 1" pex tubing to building 2. The boiler supplies my main loop with hot water and I run it at 180 degrees f.

The main loop has 2 secondary loops one is a radiant heat system for a open floor plan 1,000 sqft. The other secondary loop is a Runtal uf-2 baseboard radiant which is another 90' feet away from the second building also underground and insulated using 3/4" pex-al-pex(which as pointed out by icesailor was a smidge less then 3/4" ID)

Both Secondary loops are fed with a mixing valve to temper the supply water with the return. They each have their own grundfos alpha which I have set to constant speed.
The main loop and both secondary loops are in building number 2.

The radiant slab is in builidng 2 and made up of over 40,000 tons of sand with pex-al-pex installed at the bottom. The sand is covered with 2 interlocking sheets of 3/8 inch birch plywood as a floating floor. I have 10 radiant loops installed I used Dan's radiant heat book as a guide.

The radiant baseboard is in building 3 which is about 90' away from building 2. I want to run the baseboard at the lowest water temperature possible so I covered the perimeter of the 20'x30' building with Runtal UF-2 baseboard my thinking was that by going extreme with the baseboard coverage I could dump more btus at a lower water temperature. I have thermostatic control valves in building 3 controlling the water flow.
The Grundfos alpha has been tried in AutoAdapt and constant speed at both settings I don't recall it going over 2gpm. It is quiet and uses between 6 and 13 watts.

The result is that when my radiant slab is charged(full of heat). I can run my boiler a couple of hours a day and have good heat in both buildings. If it is a sunny day I may not run the boiler at all due to solar gain in building 2(the sand slab has good sun exposure). If it is a cold day I run the boiler more.

Although this wasn't a cold winter I could dump enough btus into building 3 to make it way to hot when it was 20 degrees outside never exceeding 2gpm.

I wanted to thank Dan for the book and the website and everyone on the website for being will to discuss heating ideas.

It is in that spirit that I returned to note the results of my experiment.

Next steps
This year I will be adding a custom control computer with outdoor reset and weather forecast planning.

I have room for 210 sqft for hot water solar panels. Transition to using the boiler as auxiliary heat source. With solar panels will come a large hot water storage tank which I will need to integrate.

Earth tubes anyone?

Thanks for the help.

Ben
• ### GV boiler circulators:

Did you pipe that GV boiler as the manufacturer shows?
You say you used the boilers internal circulator to feed the floor loop and the other circulator to feed the system. If that is so, the intent of the boiler pump was to stop installers from dumping cold water back into the boiler and causing condensation. The Cast Iron GV do not like condensation. Unless the floor loop is run through a thermostatic mixer, it will condense.
FWIW
• ### GV boiler circulators

The boiler is piped directly to the main loop which has the floor and baseboard as secondary loops each with their own circulator.

The boiler pump is need only to run the main loop. The return to the boiler is connected to the main loop. Other then the initial start up the return water should be warm. I could add a mixing valve to the main loops return to control the temperature of the water to the boiler. What temperature would be good.

Ben
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