Design proposal to convert monoflo Tee to series loop

iexpl

Hi, I have a forced hot water heating system using split loop and monoflo T, which was inefficient and heating up the basement more than the 2nd floor unit (~1000 sqft) and cost $$$ to run. I am thinking of replace it with 2 series loop (for 2 zones).

Heating professionals I consulted suggested the following 2 solution:
1 Use a reverse return 2 pipe system. This requires extensive re-piping and cost-prohibitive.
2. convert the whole system into a single series loop by cutting off the pipes in the basement, and replace monoflo tee with 90 degree elbow, and use bigger circulation pump to push the water faster through the system. However, there is a different imbalance due to a) long pipes runs up and down from basement to the second floor 5 times , b) a mixed 3/4" copper, and 1/2" Onix Radiant Hose (black one). My take is the 1/2" pipe will dictate the flow rate (which is lower than the 3/4" copper). The total baseboard for this run will be 61ft ; the total pipe run is ~231ft. My hunch is the room at the end of the loop will not be heated adequately even with high speed circulator pushing the water faster.

I am looking for feedback for this alternative design. Split the whole apartment loop into 2 separate series loop.

Loop 1: essentially going up to 2nd floor once and return down to basement once. It goes through 3 bedrooms. However, in order to minimize repiping, I need to do a u-turn at the end of heating run, and run ~26ft pipe to go down the existing piping to the basement. Q1: what is the drawback of this design?


2nd loop has more challenges: 1. it has a radiator as a first heating element, I plan to keep it on the monoflo tee since it is only heat the common area. 2. It also has to go up and down 3 times to minimize re-piping. 3. The kitchen return will be a 180 degree u-turn and return down the same path as it goes up.

My questions:
Q1: what is the drawbacks of loop 1's u-turn and 26 ft long return run? Maybe the long pipe runs will heat up the bedroom it is in too much?

Q2: for 2nd loop, is it ok to have the radiator as a first heating element via monflo tee? Or does it still need to be the last element in the series loop?

Q3: using 3/4" copper or 5/8" PAP (Pex-Aluminum-Pex) , can it heat up the kitchen area enough given that the kitchen is the furthest in the 2nd loop?

Q4: In 2nd loop: Kitchen's pipe with a 180 degree u-turn: any issues with this u-turn at the end of run?

Q5: are these two series loop better off in 2 separate zones or in 1 zone? The heating contractor said to control the loop 1 (all bedrooms), it is difficult and some bedroom will be too hot and other will be not warm enough. It is tough to place the thermostat optimally. My thinking is that bedroom with longest pipe run is also the biggest bedroom and has 2 exterior walls. It is better just put the thermostat at the 1st bedroom being heated (bedroom #3). Does it make sense?

Enclosed are the loop drawings and a floor plan (see the size of each room).

The boiler is 62K BTU boiler, should be more than enough to use two zones.


Many thanks for your help! You have helped to answer a lot of my questions in my other posts :-) Big thanks :-)

Jamie Hall

Monoflows are a curious sort of middle ground between parallel and series loop piping when considering heat output.

A full series loop, however, is almost impossible to balance. In your particular instance, going from monoflow to series and using the highest possible flow rates -- whatever you can get away with -- you might find it satisfactory, if quite inflexible.

Reverse return parallel is always preferable.

GW

I've been doing this for a while, this is a first: a one-pipe is overheating the basement. The copper doesn't throw off that much heat.

You can mix-match, what you describe should be fine. Most systems are over-pumped anyway.

iexpl

Thanks @Jamie Hall @GW for your kind reply.


Assuming using 2 90 degree elbows with like 3-4 inch of pipe to do the u-turn, will it create too much turbulence at the turn to cause problem?

Also, does this new series loop need to have pump installed near expansion tank to pump away? 2 heating professional did not think it matter. But I have heard pumping away is a good practice.

Jamie Hall

On the U-bend. Not to worry. That's why one allows a little extra footage of equivalent pipe in the arithmetic. Which, as someone pointed out, is none too precise anyway.

But yes. If it is at all possible the pump should be installed pumping away from the expansion tank. It really can make a big difference. Not that other arrangements can't be made to work -- they can. But it's much easier to get things working well all the time, for a long time, if the pump is pumping away.

mattmia2

If you're going to go through the trouble of changing it, especially if you have limited access to tweak it, use separate supply and return mains or home runs, don't try to make some combination of series loops work.

pedmec

like mattmia2 has said, the home run method would work best. you can use a pex manifold on supply and return manifold and balance out the flow at the manifold. pex from manifold to the risers.

hot_rod

If you want room by room control, a home run give your infinite adjustability and temperature control

EdTheHeaterMan

These two zones should work fine.
Look at the File diagram by zooming in to see the details. The shaded pipes and boiler are all below the second floor. The solid pipes are in the apartment.

The bedroom zone will work perfectly. If the front bedroom has the thermostat, because it is the last one on the run, you can balance the rooms with the radiator cover dampers. Hot rooms get the damper closed cold rooms get the damper open.

The Living Bath and Kitchen can be connected in the basement. You will not need a stronger pump, you may just need a balancing valve on the bedroom zone to restrict the flow to the shorter loop to balance it with the longer loop. Make a series loop with no monoflo tees at all. Connect the entry floor baseboard in series, without the TEE fittings, just 90° elbows.

The Cast Iron radiator in the front entry should have a home run to the boiler. You can make it so the radiator will operate with both thermostats or on only one of the thermostats based on where you connect it to the piping near the boiler. But it needs its own path that is not in series, unless it is the last radiator on the loop. Since you believe it can not be the last one on the loop, you need to connect it close to the boiler return and the boiler supply so it gets heated water without the restriction of the baseboard loop.

PEX tubing can be used to run the connections in the basement. ¾” for all the series loop connections. You can use ½” or ¾” PEX for the cast iron radiator. See second file for basement connection diagram

Just one question... What is heating the first floor below your apartment? Is there a second boiler?

iexpl

@EdTheHeaterMan , yes, the first floor below the apartment is another apartment. It has its own boiler and separate piping with 1 zone ( looks like the series loop). I see that you made the return pipe for the radiator the last return. Great idea! Now, for the supply pipe of the radiator, should it be a monoflo-tee as is? Looks like that way.


Thanks all for the suggestions. I am grateful for all these informative advice.

Now, 2 heating professionals told me that the series loop may have an issue with air bubble block the whole flow due to it is on the second floor and too many elbows??? They suggest some sort of knob aircans (or automatic bleeders)? Currently, each baseboard on the 2nd floor has 2 aircans (one for supply side, one for return side). Unfortunately, due to the small size of apartment, it is hard to access those aircans. Now, for the ease of maintenance, what is the best approach to bleed air out of the 2nd floor units?

The one hardest to access is the kitchen U-turn, which requires the haul out of the refrigerator.

The 2nd hardest to access is the supply entry for the bedroom loop, it requires moving the bed out of way (no room to move it too).

Is there some easy to use aircans to make turning on/off the bleeder an easy job?

EdTheHeaterMan

I would not recommend the use of any air vents on the second floor. If you repipe the boiler so the expansion tank and air eliminator is on the supply pipe, and the circulator is pumping away from the expansion tank, you will find that there is no need for an air vent any other place than the main vent by the expansion tank. Because of the physics of water, namely Boyle's Law and Henry's Law, air in the piping above the boiler will be absorbed in the water because of the pressure and temperature of that water. when that water gets to the air eliminator on the supply side of the boiler and near the suction side of the pump, the water temperature and pressure will cause that air to be released at the air vent where is will leave the system. So any air that might get caught in those high pipes will, by design, be eliminated.

If your plumber places the expansion tank on the discharge side of the pump and/or places the circulator on the return side of the boiler, then that air eliminator will be less effective and the Physics of water will work against you and cause air to accumulate in the high spots. That is how it works, you can't change the laws of physics, you plumber is not that good of a lawyer. The diagram for pumping away from the expansion tank is very specific. and you can not change the order of the components.

hot_rod

if any air vent, just a coin operated type at the end of the loop

A good air separator at the boiler will do most of the work

iexpl

@EdTheHeaterMan Thanks for the detailed explanation of pumping away. I just got the book. Now, what is those zone valves labeld M in your diagram? I am thinking of using 2 separate circulators to insolate the 2 circuit totally. Why should or shouldn't I do 2 zones with 2 separate circulators?

@hot_rod , for the air vent at the end of the loop, do you mean the furtherest pipe run to the last heating element?

EdTheHeaterMan

Either way will be just fine. Zone valves or Circulators. Remember with circulators the pump from zone one can cause reverse flow in zone number 2. So you always need to have a FlowCheck of some type to prevent reverse flow in the unused zone.

Internal flow check (IFC) pumps have the flow check built in. Or you can purchase separate flow control valves. and use your existing pump.

This will work however it is overkill in my opinion. A pair of zones valve will do the job just fine. and will be less expensive. When you add a circulator you need to account for both pumps operating at the same time in the shared pipes. You also need to add a flow control valve and you need a circulator relay for each zone to connect the thermostat to.

So you add:

A second circulator pump

A second thermostat

Two flow control valves

Two pump relays (or a 2 zone pump relay)

With zone valves you only add the 2 zone valves, a transformer and one thermostat That is about half the cost for the parts needed to make two circulator zones.

iexpl

got you, @EdTheHeaterMan . Thanks for the detailed explanation of zone valves vs 2 circulators.

Now, for the placement of the thermostat, I plan to put is in the first room (the north face corner room with 1 exterior wall, 1 wall shared with the hall way) where the heat enters.

The other choice is to put the thermostat in the last room (west/north facing coner room with 2 exterior wall). However, this room has the longest run of heating element and longest run of pipes.

I don't think it is a big deal where to put the thermostat. am I right?

EdTheHeaterMan

Thermostat location is on an interior wall, across from the radiator is best practice.  But you knew that.  The best room is the coldest room, but that is not always the easiest room to determine.  If you have a feeling that the room with more radiators is not the coldest room, then select the other room.   Why…. if the coldest room gets satisfied,  then the other rooms will be too hot.  If a room is too hot, you can throttle the air flow through the baseboard radiator, with the damper, in order to decrease the amount of heat in that room.   It is always easier to cut down a room that is too hot than it is to get more heat to a room that is too cold.   It shouldn't be, but it is a fact that adjusting something that is "too much" lower, is more logical for most people.  It is harder to understand that throttling down a “too much” room to get more in a “not enough” room.   I don't know why, it’s just human natureI, I guess.