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# what is the effect of mixing 1" pipe, 3/4" pipe and 1/2" pipe

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Member Posts: 48
I am trying to convert monoflo T to a series loop. The existing pipe has a main loop of 1" pipe, and some loops with 3/4: pipe, and some loops with 1/2" pipe. The heating professional said that it is ok to keep the existing mixed size piping and just cut enough pipes to make it a series loop. I am a bit hesitate on this.

What would be the right approach?
And the mix piping approach (even it is a heck), will it work ? What are some side effects?
«1

• Member Posts: 15,881
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You need to know the water flow you need on each separate loop after it is piped. To do this measure the total feet of baseboard on each loop. Just count the finned sections of baseboard.

Allow .056 gallons of water for each foot of finned baseboard.

So lets say you total the baseboard footage on one loop and get 50'. 50x .056=2.8 gpm which would mean all the piping has to be 3/4" (or larger)

1/2 Inch pipe can carry 1.5 gpm or 26 feet of baseboard
3/4" 4.0 gpm 70 feet
1" 8.0 gpm 142 feet
• Member Posts: 7,284
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A Sketch would help us and you understand this BEFORE you start cutting in to the pipe. Mad Dog
• Member Posts: 48
edited April 22
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@Mad Dog_2 here is the sketch for the proposed conversion (Thanks @EdTheHeaterMan for the proposal and drawing, which I copied here). There are 2 zones. 1 zone includes all the bedrooms, 1 zone include kitchen, bath, and living room.

When converted, the bedroom series loop has 35.5' bb. And bedrm1 will have a 1/2" return unless that do a u-turn and using existing 3/4" pipe about 26' away.

For the kitchen, it will be both 1/2" supply and return unless I repipe. It is the 3rd rise in the series loop.

@EBEBRATT-Ed For your example, 50' baseboard, need 2.8 GPM flow. What is the effect of a 1/2" pipe with a faster circulator pump to move water faster? This 1/2" pipe feed into a 3/4" pipe for the baseboard. Does the more powerful circulator help to get heat distributed without repiping? That was the theory one heating guy told me.

• Member Posts: 22,541
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Maybe add some balance valves on the two supplies to the radiator. So you can choke down the radiator loop if needed.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
• Member Posts: 48
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@hot_rod thanks for the tip on the radiator. The question here is if 1/2" supply /return. pipe mixed with 3/4" pipe for baseboard, does it affect the baseboard BTU output.
• Member Posts: 15,881
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You should stick to the flows for each pipe size I mentioned above, They are based on the industry standard that is probably80 years old.

If you install a larger circ pump to get more flow through smaller pipe you will get velocity noise and possible but not likely erosion of the pipe or tubing.

The proper steps to follow in the right order are:

1. Heat loss of the room
2. size of radiation to meet the above heat loss and calculate water flow
3. size pipe based on water flow
4. size circ pump based on water flow and pipe size.

If you want it to work without issue you have to follow the steps in that order above and one thing builds off the the other

If you jump into the middle or try to work backwards you will have issues. Guessing does not work.

• Member Posts: 22,541
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1" from the boiler to the zone valves, 2- 3/4 zone valves. Probably both baseboard loops could be 1/2". that would move 15- 18,000 BTU/hr per loop. 30- 36,000 BTU/hr

What is the total heat load of the home?

Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
• Member Posts: 48
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Thanks @hot_rod and @EBEBRATT-Ed . I agree with Ed's advise on proper steps. If it were me to do it (but I am just a stupid home owner and not handy enough to do this), I would change everything to 3/4" pipe. However, all the heating contractor say just leave the existing pipe as is. So, the flow will be like 1" pipe → 1/2" -> 3/4" (baseboard) → 1/2" → 1" pipe for the longest run . Also, that 1/2" pipe will have a 12-14 ft rise. I don't think this will work. He said a bigger circulator can push the load with higher flow rate. And higher flow rate somehow becomes higher BTUh output for 1/2" pipe. Can it be?

hot_rod, The house's baseboard seems enough based on my calculation. The same layout of baseboard works for the unit1 w/o problem. It is the unit 2 (upstairs) that is having trouble with getting heat due to monoflo Tees. This is the reason I want it to be a series loop. Just want to figure out if the mixed pipe will work statement true or not.

So, fundamental question is: should I insist on having everything change to 3/4" pipe to ensure we follow the proper order of system design as Ed outlined above?

• Member Posts: 15,881
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Like I said earlier measure the feet of finned element and determine the water flow as I posted above to find the water flow needed in GPM.

If the pipe you use is too small you will have noise issues. And it depends how much "over" you are. If 1/2" pipes is good for 1.5 gpm can you cheat a little and get 2 gpm through it. #/4 is good for 4 gpm can you get 5 gpm through it without issues? Probably but not recommended.

If you need to get 4 or 5 gpm through 1/2" or 8 or 9 through 3/4 forget it.

• Member Posts: 8,184
edited April 25
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Hgher flow rate thru te 1/2" pipe may get you from 1.5 GPM to 2 GPM which will give you about 5,000 BTU more in that loop with 1/2" pipe.

The better design will be 3/4" or larger for all the pipes. So I believe your bathroom radiator has 1/2" pipes going to the basement, the kitchen and living room has 3/4" going to the basement.

A more powerful pump may be enough but it will make the 1/2" pipe noisy. The reason to keep the flow thru 1/2" pipe at a maximum of 1.5 GPM is to reduce the noise.

Think of it like this. there is a 1/2" pipe feeding a 3/8" tube that fills the toilet tank. That has 45 to 70 PSI city water pressure behind that closed valve. when you flush, you hear the flush and when that noise goes away, you still here the water filling the tank until the tank is full and the float valve is closed. Now that noise in the pipe is normal and you do not think twice about it because you know that noisy pipe will stop in less than a minute.

Now think of that same noise in the 1/2" pipe every time your thermostat calls for heat. That noise continues for 20 minutes until the thermostat is satisfied. That will bother some folks late at night while in bed with no other ambient noise except the water running thru that radiator pipe. So you may not want that 1/2" pipe in the series loop system.

So, the flow will be like 1" pipe → 1/2" -> 3/4" (baseboard) → 1/2" → 1" pipe for the longest run .

I would leave that radiator out of the loop and make it a 1/2" or 3/4" PEX home run like the boiler room.

Edward Young Retired

After you make that expensive repair and you still have the same problem, What will you check next?

• Member Posts: 48
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@EdTheHeaterMan @EBEBRATT-Ed Thanks for the insightful advice. I think I am all set. 3/4" pipe all the way.

• Member Posts: 484
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This may have been designed by someone who really knew what they were doing. if the sketch is accurate, it looks like we have zones of series loop heating with returns back to the boiler. They may have relied upon laminar and turbulant flow rates to keep even heating throughout the home.

LANGAN'S PLUMBING & HEATING LLC
Considerate People, Considerate Service, Consider It Done!
732-751-1560
email: langansph@yahoo.com
www.langansplumbing.com
• Member Posts: 26
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Listen to hot rod

Your entire problem may be that too much flow is going to that stairway radiator. It may have a balance valve that you can turn down and fix your problem. Or just put the stairway on a separate zone.

• Member Posts: 8,184
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Your original issue is that some of the rooms are warmer than others and other rooms are cooler. You described that the home is not balanced. Each time you add a little more detail.

The best info so far is the floor plan. I took an educated guess at the location of the boiler in the basement and the radiators in the rooms. Based on this diagram, can you tell me if this is an accurate illustration of the design?

As you can see, I have incorporated as much info from your different comments. The Dark Red illustrates the Baseboard radiators, and the one cast iron radiator in the front entry on the first floor, The faded red illustrates the basement pipes and the 45° angle pipes illustrate the the risers from the basement to the second floor.

If this illustration is close to accurate, then it would also be helpful to know what rooms are cold in comparison to the rooms that are hot. If you can list the rooms from coldest to hottest that would be good in determining how to solve the problem.

I have made assumptions based on how the system is designed that have been proven incorrect. So I may have offered solutions that may be more involved that needed. This may not be as hard as I originally stated. Another helpful fact would be if the second floor system was ever balanced in years past. From one of you diagrams it appears that the smaller bedroom and the Den/Office radiators are connected together end to end without dropping the the basement. Your diagrams also indicate that there are 2 separate MonoFlo® loops that split off of a 1-1/4" main and rejoin at the other end of the basement to connect to a 1-1/4" return main. If this is also correct, there may be a balancing problem in that design. You may only need to do a littler basement pipe redesigning to solve your balance problem.

I will not recommend a solution until I have answers to

1. Is the basement 1" loop as I have described: actually 2 different loops?
2. What rooms are cold, what rooms are hot?
3. Has this been a problem since the building was built, or is this something that has happened in the past several years?
4. If question 3's answer is "Has not always been this way", then when did the problem start to happen?

Knowing the answers to these questions will help me make the next recommendation.

Edward Young Retired

After you make that expensive repair and you still have the same problem, What will you check next?

• Member Posts: 48
edited April 26
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@EdTheHeaterMan thanks for the drawing. This is almost correct.

First the drawing, couple of corrections:

1. there is another strip of baseboard of 8'4" at backhall that is on a monoflo tee. (the similar length as the one in the office/den)
2. Kitchen and bathroom are feed in the same loop using a 1/2" Onix Radiant Heat Hose , and 2 monoflo tee that is 6" apart (a big red flag for me). The baseboards in the kitchen and bathroom are 3/4" pipe. That is, there is a mixed piping in this loop.
3. Front bedroom also feed using 1/2" Onix in the side loop, and 3/4" baseboard pipe.
4. Front hall radiator is feed with 1/2" copper pipe.
5. All 1/2" Onix Raidant heat host are rated for max temp of 180F (black hose, with oxygen barrier)

Second: based on manual J calculation, this unit needs ~25k BTUh for winter heating without heating the front hall or backhall (each is about 50 sqft with 2 story high ceilings)

1. the basement is a split loop, NOT 2 separate loops.
2. It is uneven. Sometimes front bedroom gets hotter than the mid/back bedroom/office. Sometimes, the other way around. But in general, here is the order of coldest to hottest rooms: Kitchen (coldest) → bathroom → living room ; front bedroom (on par in terms of temperature) → mid bedroom & office → backhall → front hall .

kitchen/bath baseboard perpetually read ~ 69F. But front landing heat register can read 123F. Other rooms, reading can be in the range of 90 - 110F.
In addition, when thermostat turns down to say 60F for a day, then turns back on to 70F. It takes more than a day to get the temp back to normal.

3. I only owned this building for 3 years. So, not sure if this problem is original. Judging by the piping, it has been retrofitted in around 1980 to 1990s, and Onix Hose was put in later to avoid freezing pipes .

4. When I have the building, the piping has always this way. And the problem occurred in the first winter. 2nd winter, I asked tenants to keep heat always at 68 degrees, no complaints except slightly higher gas bill (30% higher than the same unit in first floor). 3rd winter (2024), the heating bill is doubled since the apartment was not heated up to 68F per thermostat. But basement, and front hall is heated up nicely due to high frequent call of heat.

Really appreciate everyone's help. I am learning a lot here as a home owner.

• Member Posts: 8,184
edited April 26
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Great information. This helps. The ONIX tubing is not original to the age of the building. Therein lies the problem. A repair was made at some point before you owned the building. When the 1/2" tubing was introduced to a well balanced system the balance was thrown out of wack. So using any of that 1/2" ONIX tubing is going to to cause you problems. All those 1/2" tubes will need to be replaces with 3/4" tubing. I think that you don't need to redesign the system, all you need to do is replace those ONIX tubes with 3/4" PEX with Oxy Barrier tubing.

Is this diagram a little closer to your existing system?

Now to address the thermostat setting when the first floor is unoccupied, (you need to keep the pipes from freezing so you should Leave the heat on at at least 50°F. As the first floor heat, when occupied, will make the floor of the second floor apartment warmer, there is less heat needed to heat the second floor when first floor is occupied than when it is unoccupied.

When both apartments are occupied the first floor does not have a cold ceiling, so it will always use less fuel that the second floor. The second floor will always use more fuel because it will loose heat thru the ceiling to an unconditioned attic, or if you have a flat room directly outdoors.

The Monoflo® one pipe design can be unbalanced at the point where the 1-1/4" splits into two 1" loops. If after you get all the 1/2" tubes replaced with 3/4" tubes you my find that the bedroom side gets more heat than the Living room side. You can fix this with balancing valves placed on each of the 1" branch pipes. as shown in this diagram.

And one note: did I get the bathroom to Kitchen radiator connection correct? From one of your pencil on graph paper diagrams I thought that the bathroom had 2 basement runs and the kitchen had 2 basement runs. I changed it to one 1/2" Onix run from the basement to the bathroom, then an original 3/4" copper run from the bathroom to the Kitchen, then a 3/4" copper basement riser from the kitchen to the basement.

This 1/2" to 3/4" monoflo® branch is a reason for improper balance. That is why I suggest that you find a way to replace all the 1/2" Onix with 3/4" PEX.

If there is no access to hide the 3/4" PEX in the first floor apartment wall, I might suggest that you run the PEX Exposed then box it in with pine boards and paint it the color of the wall

Also you may want to have the first floor heater share one of the hallway radiators in some fashion. It is not fair to have the second floor tenant foot the bill for all the common area heating. especially since that gas bill will always be higher on the second floor.

Edward Young Retired

After you make that expensive repair and you still have the same problem, What will you check next?

• Member Posts: 26
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Ah so the radiator is on monoflow Tee's as well.

Is there by any chance balancing valves in any if the baseboard. I had a home that had issues for years because there was an unexpected baoacing valve located on the first baseboard of a loop that served the front of the house.

My experience is that 1st floor apartments use more heat. Stack effect causes them to be where air mostly infiltrates the home so they have to heat up airflows where as upstairs is where the air generally exfiltrates. I have had tennant's upstairs not realizing they cause their downstairs neighbors to get chilled when opening windows in winter due to the airflow/pressure dynamics. I think what is happening for the OP is that due to the heat not properly going into the apartment there is excess heat loss to the basement and hallways. Once we help you fix that I would consider removing the hallway heat. There should be enough radiation surface to move the needed heat into the apartment itself. I have gone as far as insulating interiors walls to make hallways outside the thermal envelope with great results. I have witnessed closing of outside doors be an issue in apartments so isolating that space can be a problem reducer beyond just increasing overall fuel savings.

Going beyond on a little bit of a tangent but ensuring the ceiling and walls are insulated and the basement windows are kept closed/sealed can help balance room temperatures. 25kbtu is more than a decently insulated apartment of that size should need. Also an outdoor reset and motorized flue damper on the boiler can help with temperature balance in the apartment and potentially reduce the heat loss in basement piping as well. These things are just future ideas if you want to go beyond mostly fixing the current issue

• Member Posts: 8,184
edited April 26
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@JR3_Home_Performance

It is interesting that the first floor may have a larger load. But the heat loss calculations that everyone uses does not account for that. The Manual J and my Hydronics Institute forms account for infiltration equally from floor to floor. That makes the math add up to more outdoor unconditioned surface area on the second floor with a ceiling that is exposed to the outdoor temps while the first floor ceiling is exposed to a heated room above. But that is just the math not the fact that some of the second floor's infiltration is from the first floor's heated air. As I said… Interesting

The OP has been trying to find the answer to the unbalanced system for some time over 4 different discussions herein. I have followed the comments on all of them and I am learning a little bit more each time. The OP has asked plumbing professionals to solve the unbalanced system problem and has received different Quotes that are in some cases contrary to common sense.

I might suggest that whoever gets the job should include a performance guarantee. Perhaps 1/2 down and the other half when the system is performing satisfactorily next winter when the temperature drops below 30° for 3 days in a row.  That is the only way to get someone to get it right.

There was a saying “You Got To Sweat for your Money”.
That came from an old boiler installer requirement.  When installing a boiler and radiator system in the middle of the summer,  the contractor needed to jump the thermostat on the burner or fire the coal boiler to maximum on that hot summer day.  The inside temperature needed to get to 130° from an outdoor 80° evening temperature.  This ensured that the boiler could handle the load on a cold winter day.  Lots of candles melted from those tests but that is what was needed if the boiler installer wanted to get paid.

You can follow the OP's other discussions to get the whole picture. You can see where I was offering a completely different solution with the original information received in this discussion. Be sure to click on page 1 of the discussion to get to the beginning of the post.

Here are the other two

Edward Young Retired

After you make that expensive repair and you still have the same problem, What will you check next?

• Member Posts: 26
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• Member Posts: 26
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Okay I see it was 60kbtu so that size expansion tank should be okay but it wouldn't hurt to remove that one radiator to reduce water volume unless that stairway really needs heating

• Member Posts: 48
edited April 26
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@EdTheHeaterMan Yes, you are keeping track of my postings and you are right. I have got really mixed bag of suggestions and no solid way forward. I will be considering ask for a performance guarantee from now on.

Q: did I get the bathroom to Kitchen radiator connection correct?
Yes, bathroom is connected to the kitchen baseboard somehow. But either the heating professional nor I can find out how it is connected and we even used a FLIR heat scanner. I suspect it runs closer to the exterior wall like you draw since that is the area we can not get a good scan on.

For replacing 1/2" ONIX with 3/4" PEX, not sure if I can do it. My suspect the previous owner was not able to run 3/4" ONIX/PEX due to house construction. So, he resolved to use 1/2" ONIX instead. This is why I think doing a series loop with the kitchen baseboard's pipe does a u-turn and return back down the same route as the supply pipe (drill holes in the first floor and cover up with the pineboard and painted). Also, the 6" monoflo TEE spacing probably is an issue since it has both 2 ft bathroom baseboard, and 10.75ft kitchen baseboard on it.

Also, the 1/2" ONIX for the front bedroom is the similar issue. It is probably too cold to use copper pipe and judging by the way it is being routed, it is snaking through the first floor somehow. This is where I just want a straight pipe from mid bedroom to connect to the front bedroom and have the pipe to do a u-turn and going down using the existing hole in the mid bedroom.

Now, what probably can I get into with a series loop and u-turn pipes? Does I need to do the u-turn down for the return or u-turn up, or does not matter?

@JR3_Home_Performance besides aircans. I have not seen any balancing valves. All pipes are connected clean monoflo Tees. For balancing valves, do you mean something like this: . NO, I have not seen any in the property.

Basement is not well insulated (but 1/2 of it is under the ground), however, it is always heated by the loop due to unit 2 frequently call of heat.

The common areas (front and back hall) heater works well (maybe too well since monoflo delivered the heat to the first floor heating element much better than the 2nd floor baseboard). I am not sure stacking is an isssue since first floor unit never complains about the heat.

• Member Posts: 8,184
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OK now I believe I have all the needed information.  (I Hope)

This diagram will show what I might propose to solve your situation.

1. Cut and remove or abandon the green pipes in the illustration.  Place 90° elbows where the Tee fittings used to be.
2. Remove all of the Monoflo tee fittings
3. Connect the living room to the bathroom in some way, this will involve the new ¾” blue pipe (or PEX) in the illustration.  Try to snake the ¾” PEX thru the wall where I have drawn a brown square.  I believe that is the chase where the chimney goes from the basement to the roof.
4. If you can not see a way thru that area, then you need to find the chase where the drain and vent pipe for the toilet is located and try to snake the PEX thru there.  If that is unsuccessful, then run the PEX pipe exposed in the first floor bathroom.  Preferably near the corner.  Then you can cover that exposed pipe with a piece of molding and paint it the color of the wall.
5. This will complete the series loop for the living room side of the apartment.

On the bedroom side

1. Connect the front bedroom to the middle bedroom as you indicated.
2. Use the good ¾” copper riser as the return to the basement and connect that to the other end of the front bedroom radiator with a ¾” PEX that is inside the baseboard cover.  Use the U-Turn fitting or 2 slip 90° elbows to connect the PEX to the far end of the radiator.
3. This will complete the series loop for the bedroom side.

Your existing circulator will be able to handle that much piping friction loss for both zones.

You can use balancing valves on the 1” pipe or you can use zone valves with separate thermostats for the Bedroom side and the Living room side.

As far as the Cast Iron Radiator, I would see how easy it is to add it to the first floor boiler using Monoflo® tees on the series loop and try to place it on the return if possible.

I would offer you this if I were not retired and offer you the performance guarantee also.  I am confident that this plan will work.  The glitch is getting the pipe from the second floor to the basement.  Exposed piping is often the best and only option.  the file below is the Diagram above with the floor plan overlayed.

Edward Young Retired

After you make that expensive repair and you still have the same problem, What will you check next?

• Member Posts: 48
edited April 27
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@EdTheHeaterMan Thanks for this proposed design. I love you common and deeply appreciate your help. Couple questions.

The chimney you drew was there, but has been fully closed in both unit1 and unit 2. I think the major challenge is to snake the pipe through living room to the bathroom, and from bathroom to the kitchen without going down to the basement.

I am fairly certain that I can snake the pipe from basement to the 2nd floor bathroom w/o problem.

For the kitchen, I need have the bathroom pipe return down to the basement, and rise again (exposed ) to the kitchen baseboard, and doing a u-turn to go down to the basement again the same way since it looks like very difficult to snake the pipe through otherwise (more extensive work) and potentially too close to the exterior walls.

This is why I proposed the 2 series loop solution since two separate loops make each loop shorter . And each loop drives only half the load. I hope this makes sense.

another question: for the split loop system like the one you proposed, is it a possibility that one side of the loop is too little resistance, thus the water will favor that side more than the other side of the split loop?

Also, what is this new ¾” blue pipe (or PEX)? I would love a link on this blue pipe. For the 3/4" PEX for heating, any recommendations for proven choice of PEX? I am mostly afraid of freezing given the basement is not insulated (about 1/3 to 1/2 above ground)

• Member Posts: 8,184
edited April 27
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"This is why I proposed the 2 series loop solution since two separate loops make each loop shorter . And each loop drives only half the load. I hope this makes sense."

Good design. I would use zone valves in your situation.

"Also, what is this new ¾” blue pipe (or PEX)? I would love a link on this blue pipe. For the 3/4" PEX for heating, any recommendations for proven choice of PEX? I am mostly afraid of freezing given the basement is not insulated (about 1/3 to 1/2 above ground)"

There are several PEX tubing Manufacturers, Just select any oxygen barrier tubing for a closed system here is one that will work just fine. I have always used PEX-a The Wirsbo but I believe the PEX-b is just fine.

https://www.supplyhouse.com/Bluefin-T075-300-OXY-3-4-Oxygen-Barrier-PEX-b-Tubing-300-ft-Coil

https://www.supplyhouse.com/Bluefin-T075-300-OXY-3-4-Oxygen-Barrier-PEX-b-Tubing-300-ft-Coil

I believe that your Black Onix tubing was the replacement for frozen pipes. So placing the pipes inside the conditioned space is important.

"The chimney you drew was there, but has been fully closed in both unit1 and unit 2. I think the major challenge is to snake the pipe through living room to the bathroom, and from bathroom to the kitchen without going down to the basement."

It will be necessary to open the floor in the bathroom or the ceiling in the first floor apartment to access the bathroom radiator piping and get rid of the 1/2" risers. If you open the ceiling below, you may be able to make that series loop happen without going to the basement. If the bathroom has a tile floor that you may not want to disturb, then using the ceiling of the second floor bathroom may give all the access you need to snake PEX tubing everywhere you need to go. from the living room to the bathroom and from the bathroom to the kitchen. Are there soffits above the first floor kitchen cabinets?

Edward Young Retired

After you make that expensive repair and you still have the same problem, What will you check next?

• Member Posts: 176
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proven choice of PEX? I am mostly afraid of freezing given the basement is not insulated

PEX in a heating system won't freeze unless you go-away or lose power for a long time.

Also basements tend to split the difference between air-temp and 55F (popular ground temp). If you have extended days/weeks steady below 0F, it may freeze. Here in coastal Maine, we touch 0F a couple days a winter and that is not a problem.

TIL: PEX left over-winter CAN burst from frost expansion. I have a PEX jumper on the outdoor sink, last fall I didn't drain it (it looks like I left pressure on it all winter 😒), this week I got sprayed in the face and had to find fresh PEX and crimps.

• Member Posts: 48
edited April 28
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@EdTheHeaterMan Thanks for the all the suggestions. I am not sure what is going on in the kitchen yet. I will get back to that.

Now, for piping, I see the spec for 3/4" copper pipe is: 0.785" ID (internal diameter?) . What size of hePEX-a do I need? There is no exact size: 3/4" pex-a has 0.671" ID, 1" hePEX has 0.862" ID.

3/4" pex: https://www.supplyhouse.com/Wirsbo-Uponor-A1140750-3-4-hePEX-plus-100-ft-coil
1" pex: https://www.supplyhouse.com/Wirsbo-Uponor-A1141000-1-hePEX-plus-100-ft-coil

Do I have to size it up to 1" hePEX ?

@PRR Thanks for the experience sharing on PEX. It is good to know they do not freeze.

Another question: for the u-turn of those copper pipes, is it better to u-turn up for return or u-turn down for the return?

• Member Posts: 26
edited April 28
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Reposting as no one seemed to take note of this. Seems like a lot redesign discussion but unless I missed something there has not been verification that everything is working properly with the expansion tank, fill valve, and static pressures...because it seems like there's an issue there

• Member Posts: 8,184
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Based on the BTU output of the zone, the 3/4" PEX is just fine. See the problem you have with your 1/2" Tubing is the actual ID of the rubber Onix is smaller than the ID of 1/2" Copper, hence the additional restriction.

Edward Young Retired

After you make that expensive repair and you still have the same problem, What will you check next?

• Member Posts: 48
edited April 28
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@JR3_Home_Performance Good that you re-iterate of the basics is working properly. This winter, the problematic winter, the static pressure gauge reading is very low. This is the photo take 4/1/2024 (after a winter of super high gas bills, mostly heating up the basement). At the end of 2023 heating season, the pressure gauge was reading normal at 12 PSI. I am not sure what caused such a low pressure reading. But after filling system up with water, the PSI has returned back to 12 when cold and stayed there.

What are the reason that causes the pressure drop in the system? After open the fill valve to fill up, the system functions fine.

• Member Posts: 22,541
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temperature changes cause pressure fluctuations

Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
• Member Posts: 48
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Is this normal? The unit 1, which never had a tune up, does not have any drop of the pressure.

Something about uni2 is not quite right. I don't understand temperature changes can cause this much pressure fluctuations. Is it possible that the call of heat is so frequent, the water was heated up too hot and somehow evaporate? And when it is cooled, the whole closed system has less pressure?

• Member Posts: 8,184
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To give you an example of how pressure might change:

Say you have a 100 gallon tank of water at 60°F.

If you heat up that 100 gallons of water to 210°F the actual volume of that same water will expand to about 104 Gallons.

If your container is completely sealed and can only hold 105 gallons of water, then when that water expands there will only be 1 gallon of compressed air in the top of that pressurized tank. That one gallon area of air may increase in pressure from 0 PSI to 20 PSI when that happens.

If the tank only holds 103 gallons of water then there will be no room left in the tank for air, so the Hydrostatic pressure can build up to over 1500 PSI and eventually the tank will explode.  That is why boilers have relief valves.

If however, you have a 120 gallon tank for that 100 gallons of water, then when the water expands to 104 gallons there is still 16 gallons of air space in the tank, so the tank pressure will only go from 0  to about 5 PSI since there is lots of room left to compress the air.

These numbers are not mathematically accurate but are for illustration purposes

Now put that same logic in your boiler with all the connected pipes and radiators.  That is a sealed system.  And when it was installed there were two important parts that were included.  The relief valve, just incase the pressure from the expanding water gets above 30 PSI like the the 103 gallon tank example.  The other is the expansion tank.  That is the place where the expanding water goes.  If you have an overloaded or flooded expansion than (that is a tank with very little air space leaf because it is loaded with too much water) then there's no room left for expansion and the water pressure in the boiler will increase more than it would if the tank had the correct amount of air in it.

Some expansion tanks are just tanks. The air will compress as you fill the system with 12 PSI water.  Those tanks have both air and water in them with nothing separating the air from the water.  The other expansion tank has a membrane or bladder that is pre-charged at the factory with 12 PSI air pressure; the membrane will separate the water from the pre-charged air side of the tank.   If that Air pressure is released over time, then the 12 PSI water will fill the tank and leave less room for expanding water.  When that happens, you will get a greater pressure rise in the boiler, similar to the 104 Gallon tank example.

I hope this will answer your question about how the pressure changes differently on identical boiler systems connected to different expansion tanks.  You probably had an overloaded expansion tank on the problem system.

Mr. ED

Edward Young Retired

After you make that expensive repair and you still have the same problem, What will you check next?

• Member Posts: 26
edited April 30
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Well in a prior thread your photo showed about 10psi at a higher temp I think. I can't know for sure the issue remotely. But for general expectations I the system pressure to rise and fall with temperature. It should be around 12-15psi st room temperature. That is the automatic fill valve should let water in to that initial psi automatically. (On a regular operating basis no water should be getting lost anywhere and therefore no water added). As the operating temperature increases the pressure should increase. The expansion tank should prevent the pressure from reaching the relief point of (30psi typically). You shouldn't have to be adding water manually and no water should be getting lost anywhere. Make sure this is figured out before redesigning the system.

Say if in theory the fill valve and the expansion tank are both bad..you manually let in water to get pressure up and bleed thr system and it works for a time. Then due to the bad expansion tank it gets over 30psi when heated and leaks out the relief a little with each cycle and the room temperature static pressure falls a little with each cycle until low enough that water doesn't exclusively occupy the pipes, hence the air in the system that causes water to no longer flow through the baseboards.

• Member Posts: 48
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@EdTheHeaterMan @JR3_Home_Performance Thanks for the explanation. I will ask the plumber to look more into the pressure drop issue first, and double check the expansion tank, fill valve, and pressure relief valve again. And report back.

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Where about are you located? Maybe someone from this group would better serve you in person. Many plumbers aren't boiler experts.

• Member Posts: 48
edited May 2
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I am Boston area. Someone from this group can help to look at my system will be super helpful! @JR3_Home_Performance I see that you are in New England.

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Boston is too far from me but there's many professionals on this site

• Member, Moderator, Administrator Posts: 2,347
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@iexpl, here's a list:

President
HeatingHelp.com

• Member Posts: 48
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Thanks @Erin Holohan Haskell I will continue to reach out to the contractors on the list.

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Any luck?