Head loss Calculation - Pump Sizing - 1 pipe monoflo system

Mono flow should be low head and high flow …. Volume is what you are looking for ..

Why was the pump replaced? It would be helpful to learn the model of the pump that was removed. If the system worked satisfactorily with that pump, that could be a starting point?

What is the Btu rating of the boiler?

Don't lower the factory pressure in the expansion tank. It should be factory charged at 12 PSI If it is lower than 12 PSI then you can add air pressure.

As far as a one story home over a basement, 12 PSI is more than enough, but i would not lower it.

And you want to be sure you have a one pipe monoflo® system to measure the pump head requirements. Look for these tee fittings

The one I circled looks like it could be a 3/4" thru with a 1/2" branch like you have described.

@paul3x16 Said: One Zone, Main loop 3/4 (60 linear ft), Branch out to cast iron radiators with 1/2 - total of 12 radiators assume 10ft off the main loop.

This tells me that you have only 40,000 BTU heat capacity on that one loop, and require only 4 gallons per minute for that loop (not the 10 GPM you indicate on your pump curve chart).

That means your boiler is oversized for the system, unless you have a second loop on the same single zone thermostat. It is possible that you had a B&G 100 pump at one time, and for the most part a Taco 007 will do most jobs.

If your system was a poorly designed monoflo® then the B&G 100 may have pushed a tad more flow rate, like maybe as much as 5 GPM. That may have been a little noisy but that noise may have been in 3/4" main pipe in the basement and was not transmitted to the first floor pipes.

if you do not have tee fittings like the picture above for each radiator (or another brand of similar design that would have an arrow embossed on the side) then you may have series loop design.

Here is the difference

Each red dot indicates a monoflo® tee and both the supply and return are connected to the same larger "one pipe"

Each section of baseboard radiator is connected to the next one on the line. Many times when the radiators are not physically next to each other, the pipe at one end drops below the floor then rises ul at the next radiator to continue the loop. Like this

There are other ways to pipe a radiator system also. Can you tell if you have the special Diverter tees or Monoflo® tee fittings anywhere or if you have a series loop? This can help determine the best way to fix your system

B4 you change the pump, you should remove the expansion tank from the system. You have to check and adjust the air pressure with the tank not having any water pressure on the tank. Then bleed the entire system and start the boiler.

Monoflo system if that is what you have are difficult to bleed you may have to go back and forth and bleed the rads 2-3 times. 10' of pipe on a Monoflo system is a little long so that could be the reason and you may need a larger pump for that reason.

You have the Diverter Tee system commonly known as Monoflo® (the same way the Royal brand gelatin, is called JELLO).

That said your pump head is determined by this rule of thumb.

In a post herein from 2002 someone suggested that you need to add 12 feet for each Diverter tee on the loop. I'm not sure that is correct but here is the comment

Still, the way I was taught (a former Bell and Gossett representative who used "milli-inches" as units of pressure drop in the classic B&G way) was to take the sum of the main circuit (pipe, elbows, normal and MonoFlow tees), PLUS the longest branch run and emitter pressure drop, plus the boiler. In your case what you figured was straight pipe, 50% for fittings (a guess let's admit it) and a pressure drop of 4 feet per 100 feet of pipe. You have to add the cumulative MonoFlow fitting losses to that plus the longest branch is how I was taught. (That was in 1977-78 by the way.)

So your 60 feet round trip for the one pipe loop plus the 20 feet for the longest radiator branch would be 80 feet.

• 80 feet longest run
• add 50% to this
• then add 12 feet for each tee on the loop
• multiply by .04
• That is your pump head.

[80 + 40 + (12ft x 12 tees)] x .04 =

(80 + 40 + 144) x .04 =

264 x .04 = 10.56 head

I think that is a little high, so I looked at the Cv rating of one tee fitting 3/4" x 1/2" which is 4.3 when the 1/2" branch is closed off. That means that you can get a little over 4 GPM to pass through that tee when there is a pressure drop of 1 PSI. Now 1 PSI is equal to 2.31 feet of head, and 3/4" pipe handles 4 GPM in a "quiet" hydronic system anyway. Now with that information in hand and the fact that all the diverter tee fittings are the same, then the 1 PSI drop is already handled by the first tee and all the other tee fittings will not have any smaller orifice for the water to pass thru, Is it logical to do the calculation this way?

• 80 feet longest run
• add 50% to this
• multiply by .04
• then add 2.31 ft head for all the tee fittings
• That is your pump head.

(80 + 40) x .04 + 2.31 =

(120) x .04 + 2.31=

4.8 + 2.31 = 7.11 head

And since none of the 1/2" branches off the tee fittings will be capped off, then is it fair to say that this Cv will not even be a factor? And the rule of thumb of adding only 50% to get the total equivalent length just means that I'm calculating just a bit high on the pump head? And I don't need no stinkin' milli-inches here.

Since the weakest link in the chain is the 3/4" pipe for the main one pipe loop around the building and a 3/4" pipe can only move about 40,000 BTUs at 4 GPM, then your heating system capacity is 40,000 BTUh with an oversized boiler with a NET output of 64,600 or 380 NET SqFt of radiation@ 170°   I hope you don't have more than 380 SqFt of radiation.

I have not run into this problem in the past, so I am just theorizing on the pump head calc. There are others that can give a more concise answer with the numbers you provided  Lets hope they chime in