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Why am I getting no heat on one end?!

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I have been in the field doing hydronic design for over a decade and in the field for 5 years. I finally got the opportunity to install a hydronic system in my home with a Rinnai i090 boiler.

I have it zoned with 2 Grundfos Alpha pumps upper and lower floor. Piped it based on the Rinnai schematic drawing. Pretty much a parallel system, all the supplies connected, and the very last rad has a return back to the boiler, also picking up all the other rads on the way back. The 2nd to last room gets a trickle of heat, the last room gets none. We've installed a purge point and air bleeders up high to clear any lingering air, but no change.

We had a local contractor come out and he said the problem is it wasn't piped in series, where each rad flows into the other and the final rad is a home run back to the boiler. He also says the pri/sec piping is wrong.

The only room that gets super warm is Bed 1 on the picture, everything else is questionable.

Any ideas before I have to start ripping open walls?






Any ideas before I have to start ripping open walls?

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 23,544
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    At first glance, one might be inclined to say that it should work. But... it's worth remembering that water is incredibly lazy. While it isn't quite true that iIt will always take the route which has the least resistance -- it is true that the flows will divide so as every possible path has the same resistance to flow, and thus the shorter or least resistance routes will get the most flow.

    So... Looking again at the drawing, it is obvious that bedroom 1 will get the most flow, with the others getting less -- or much less.

    How to fix. The easiest, although not the most elegant, solution would be to place flow control valves on each section of the radiation (you could get fancy, and make those thermostatic valves). By adjusting those valves, you could balance the flow to each section. If you rerouted the return so that instead of going from bedroom 1 directly to the boiler, you closed that line and took a long return line from the far end between bedrooms 3 and 4 that would help -- but not eliminate the imbalance, as the lengths of the various laterals differ (and rather perversely -- bedrooms 2 and 3 having much more radiation than other spaces, but longer laterals.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    ethicalpaulmattmia2
  • RayWohlfarth
    RayWohlfarth Member Posts: 1,529
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    I agree with Jamie I am thinking you are having excess flow through the bedroom 1 zone Is there a manual valve on that loop to reduce the flow in that zone. A couple things I would try
    Turn first floor zone down and 2nd floor zone up. What sort of delta t do you get? Will it heat the second floor? You have an outdoor air reset. If the first floor is overheating it may shut off the boiler on reset control.

    Where are the pumps for each zone? It looks like there is one supply and one return pipe


    Ray Wohlfarth
    Boiler Lessons
  • hot_rod
    hot_rod Member Posts: 22,353
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    Are you running one of the fixed speeds on the circs? The Auto Adapts function do not always learn the system well.

    Any shutoff valves on the radiators? If so shut one off, that will tell if they a series piped.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • hydronicfeline
    hydronicfeline Member Posts: 4
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    Running in Autoadapt. But have also tried fixed gpm and head.

    The system is definitely parallel, but it's simpler to repipe to series than deal with adding balance valves to each rad.

    One pump serves the top floor, one pump for lower.

    Even at 160F water it doesn't seem to radiate much heat, and I sized the Slant Fins for 140F temps.

    The Bed 1 is the closest to the boiler, so makes sense the system is taking the path of least resistance.
  • Jamie Hall
    Jamie Hall Member Posts: 23,544
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    If you repipe in series, I can guarantee you that the balance between rooms will be no better than what you have now, and very likely worse, with no way to adjust it.

    Don't do it.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    mattmia2SuperTech
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,153
    edited May 2023
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    From strictly a design point of view, I am assuming that all the radiators are some type of baseboard. Are you sure there is no air in the last radiator? The direct return design shown in the diagram you provided is not exactly the same as the reverse return design shown in the Factory diagram. Here are 2 slides from my Hydronics course that illustrate the difference.


    when animated, this slide shows that the first (closest) radiator in the supply will heat up and return to the boiler before the last (furthest) radiator on the supply even starts to get a little warm. I used a rooming house as an example and illustrate the if the thermostat is located in the coldest room, the room that is first on the supply will overheat.

    In order to resolve this problem a reverse return design would make the pressure drop across every radiator be about the same. If the first radiator on the system was the last radiator on the return, and the last radiator on the supply becomes the first radiator on the return, the total distance the water must travel from start to finish is closer to equal.


    Since you probably removed air from the problem radiator several times and found that there is no air in the problem radiator, I can offer you a simple solution. hopefully one that requires the least amount of ripping walls and ceilings open.


    Hope this saves some major remodeling. This all depends on the pipe size of the main supply and/or return at the end of the main. The shared piping (the main pipes) must be able to move ALL the water (GPM) for every radiator on the system

    If you have questions about my last statement, please feel free to ask for clarification. I will need you to fill in the pipe sizes of each section of existing pipe on your diagram and the total heat capacity of each section of radiator @ 140°F.

    Mr. ED

    Edward Young Retired

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

  • mattmia2
    mattmia2 Member Posts: 9,840
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    How are you balancing it?
  • hydronicfeline
    hydronicfeline Member Posts: 4
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    There is no balancing on the system. I had a 35 year heating veteran come in and he suggested we repipe in series as it will guarantee flow through every rad and stop future airlocks. He put in a hose bib on the farthest rad and it let a big air block out but never managed to get continuous flow to that end. That end gets a trickle of heat.

    Side note, for a system that can put out lots of BTUs the recovery from setback is dismal. Heatloss was a slight bit too much for the smaller boiler, so we've got 90mbh feeding a 55mbh load.

    If we go the balancing route, what is the most common route? Ball valves to choke it, or something like an Oventrop style valve, or ?
  • Big Ed_4
    Big Ed_4 Member Posts: 2,818
    edited May 2023
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    You want to pipe radiators home run or diverters . Best in that order...

    A gravity system was the only one that I know of that had a direct return .

    Pipe size matters :)...

    There was an error rendering this rich post.

    mattmia2
  • hydronicfeline
    hydronicfeline Member Posts: 4
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    This is all ¾ Raupex except ¾ copper at the baseboards and 1" copper for the pri/sec piping.
  • Big Ed_4
    Big Ed_4 Member Posts: 2,818
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    Baseboard job ? Since it looks like you are going to rip the system out (sorry to say). I noticed your lack of wall space . I would recommend to take a look at panel radiators . You already have the circulator. Set the manifold up in the space, Closet or make space . Tip; 3/8" HeatPex is great for retrofitting .

    There was an error rendering this rich post.

  • mattmia2
    mattmia2 Member Posts: 9,840
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    Assuming the mains are large enough you just need to balance the emitters.(did we determine that they are?)

    If i did my math right for 50,000 btu at 20 degrees delta t you need 5 gpm so you need 3/4" copper minimum for the mains. If they were 1" it would balance better. Your circulator needs to be able to push at least 5gpm through the length of 3/4" copper you have. This also means you won't get more than your design conditions, you won't be able to use the larger capacity of the boiler.

    Is the 55,000 btu/hr load both the hydroair and the fin tube or is it just the fin tube? If it is both you have plenty of capacity in 3/4" pipe, if it is just the fin tube your mans are kind of at the limit.

    Globe valves are good for balancing because they can be adjusted more precisely. Ball valves will work in a pinch. There are special balancing valves with a vernier drive but those aren't really necessary. A radiator valve will work if you installed the emitters with valves. It would have been better to size the mains and runouts so it was close to balanced to begin with but you can do it with just valves since you didn't.

    You will either need to close the valve on each emitter and purge each separately or install bleeders on each emitter.

    You can get better balance with your setup now than with series emitters,
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,153
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    By reading the part about "placing a hose bib on the furthest radiator" indicates to me that the baseboard radiators do not have individual air vents. This is a poor design. You will never get all the air out of all the radiators. If you are going to have only one purge valve in the boiler room, you MUST have only one path for the water. Every time you require water to move thru a Tee fitting, it will take the path of least resistance. The closets radiator will be filled with water. all the other radiators will have some air left in them.


    After adding only one vent to the last radiator, you may get some additional heat however all the other radiators that do not have a vent will be air locked



    Looks like you are learning the hard way that a series loop might be the best way to go here. You need to keep the amount of element under 65 lineal feet. that is because 3/4" baseboard and piping should not exceed 4 GPM flow rate. and you can only get about 40,000 BTU of heat with that flow rate based on a 20°∆T. If you have a series loop with more than 65 feet you should split it up between 2 different loops.

    Edward Young Retired

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

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,153
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    This is a worrisome Quote
    I have been in the field doing hydronic design for over a decade and in the field for 5 years. I finally got the opportunity to install a hydronic system in my home with a Rinnai i090 boiler.
    How many of those designs of yours actually work? Have you been paid for this kind of work? You might want to read up on this Hydronics thing you are getting paid to do. I and others will be happy to help you understand this error, so that you do not get paid to make it again.

    From the looks of you diagram, you may or may not have more that 40,000 BTU of radiator in your design. Can you provide the total lineal feet of actual element in the green sections of your diagram? I see by your photos that you are feeding all the radiators with 3/4" PEX. If you are designing at a lower ∆T then you may only be able to support 50ft or 40ft or less total lineal feet per loop. You mentioned 140° average water temperature, or is that the high temperature at the first radiator and the temperature drops from there.

    Edward Young Retired

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

    mattmia2
  • retiredguy
    retiredguy Member Posts: 919
    edited May 2023
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    I haven't done one of these residential systems for many years but I can tell you that your design will not work. You should have piped the system in a reverse return with bedroom #1 being the first in the supply line and the last in the return line. I can't tell you if the piping is large enough to supply all the BTU's you will need since I did not design the system. The guys on this site can answer the pipe size question. The easiest fix that I see would be to disconnect the return from bed #1 to the boiler and reverse the return starting with bed #1 and ending with the last radiator which looks like bed#3 and running a new line from there, directly to the boiler. This would insure that all the radiation would receive water flow. Direct return systems will work if they are piped and pumped correctly, yours is not. Your design work is obviously doing large buildings not a small residence like yours. my 2 cents.
  • mattmia2
    mattmia2 Member Posts: 9,840
    edited May 2023
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    I haven't done one of these residential systems for many years but I can tell you that your design will not work. You should have piped the system in a reverse return with bedroom #1 being the first in the supply line and the last in the return line. I can't tell you if the piping is large enough to supply all the BTU's you will need since I did not design the system. The guys on this site can answer the pipe size question. The easiest fix that I see would be to disconnect the return from bed #1 to the boiler and reverse the return starting with bed #1 and ending with the last radiator which looks like bed#3 and running a new line from there, directly to the boiler. This would insure that all the radiation would receive water flow. Direct return systems will work if they are piped and pumped correctly, yours is not. Your design work is obviously doing large buildings not a small residence like yours. my 2 cents.

    Why won't it work if the missing balancing valves that any system with parallel flow paths needs? Ideally the piping should be doing most of the work and the balancing valves should only need to tweak the balance, but as long as the mains are sized for the load, why won't doing it all with balancing valves and a way to get the air out work?

    I think the lack of a way to get flow started in some sections is actually the bigger problem. A pump cart might be able to get enough flow in everything all at once to purge it but having emitters and mains that are close to the same size will make that tough.
  • Jamie Hall
    Jamie Hall Member Posts: 23,544
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    It will work -- but only with balancing valves for each emitter section. What they will do is make the flow resistance for each path equal. Just like riding the brakes...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,153
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    I still want to know if there are air vents on each radiator!

    Edward Young Retired

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

  • Big Ed_4
    Big Ed_4 Member Posts: 2,818
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    Bleeders on baseboard that sucks ... Hope all the pipes are properly pitched . Every high point would need a bleeder or each loop needs a set of purge valves .


    A better way to even the BTU's across the baseboard is run a single pipe diverter system . With tees and risers . Each riser needs to have a constant rise and one bleeder on the high end of each baseboard run ....

    There was an error rendering this rich post.

    EdTheHeaterMan
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,153
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    Big Ed_4 said:

    Bleeders on baseboard that sucks ... Hope all the pipes are properly pitched . Every high point would need a bleeder or each loop needs a set of purge valves .


    A better way to even the BTU's across the baseboard is run a single pipe diverter system . With tees and risers . Each riser needs to have a constant rise and one bleeder on the high end of each baseboard run ....

    Agree with this. I'm not sure that @hydronicfeline does. Why would anyone run Baseboard in any style other than a series loop? Or a couple of series loops if needed. (to go over 40,000 BTUh. Per loop)

    Edward Young Retired

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

  • mattmia2
    mattmia2 Member Posts: 9,840
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    Big Ed_4 said:

    Bleeders on baseboard that sucks ... Hope all the pipes are properly pitched . Every high point would need a bleeder or each loop needs a set of purge valves .


    A better way to even the BTU's across the baseboard is run a single pipe diverter system . With tees and risers . Each riser needs to have a constant rise and one bleeder on the high end of each baseboard run ....

    Agree with this. I'm not sure that @hydronicfeline does. Why would anyone run Baseboard in any style other than a series loop? Or a couple of series loops if needed. (to go over 40,000 BTUh. Per loop)
    I mean if you split it up by room you can still use cheap emitters and it will be balancable. With a series loop you have to have your math pretty close if you want it to be balanced.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,153
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    mattmia2 said:

    Big Ed_4 said:

    Bleeders on baseboard that sucks ... Hope all the pipes are properly pitched . Every high point would need a bleeder or each loop needs a set of purge valves .


    A better way to even the BTU's across the baseboard is run a single pipe diverter system . With tees and risers . Each riser needs to have a constant rise and one bleeder on the high end of each baseboard run ....

    Agree with this. I'm not sure that @hydronicfeline does. Why would anyone run Baseboard in any style other than a series loop? Or a couple of series loops if needed. (to go over 40,000 BTUh. Per loop)
    I mean if you split it up by room you can still use cheap emitters and it will be balancable. With a series loop you have to have your math pretty close if you want it to be balanced.
    Most Baseboard manufacturers have dampers on the enclosure. You can use them for balancing the system. It works like this, Place the thermostat in the coldest room, any room that gets too hot >>> close the damper slightly until you get the balance you desire.

    Kids these days... have no common sense!

    (I wonder if out parents said that about us?)

    Edward Young Retired

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

  • Big Ed_4
    Big Ed_4 Member Posts: 2,818
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    You would have to force the system into balance using resistance . Then the air traps . Too much work for me ...

    There was an error rendering this rich post.

    EdTheHeaterMan
  • Jason_13
    Jason_13 Member Posts: 304
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    Looking at the picture I believe the problem is flow is backwards on the loop between circulators. I have never had success putting the supplies side by sides and returns side by side on a loop. It may be circulating fine but nis blended down pulling return and blending with supply water
  • mattmia2
    mattmia2 Member Posts: 9,840
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    Big Ed_4 said:

    You would have to force the system into balance using resistance .

    You have to do that with any hydronic system whether it is through selection of pipe size and length or the cv of valves or through balancing valves.

  • Jamie Hall
    Jamie Hall Member Posts: 23,544
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    It's really fundamental hydraulics, folks. Remember that the flow drops with increasing friction loss. In the arrangement presented, the pressure difference at the take off for that nice warm radiator must be the same as the pressure difference from that point to all the other radiators -- but the pipe lengths are much greater, and thus the friction loss to them is much greater and the flow to them is much less. Fix that -- balancing valves at the radiators or rearranging the pi[ping to be reverse return -- and the problem goes away.

    I'd be very inclined to add thermostatic radiator valves in addition to the balancing valves, while I was playing with the piping, for temperature flexibility, but that is an unnecessary tweak.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    EdTheHeaterMan
  • mattmia2
    mattmia2 Member Posts: 9,840
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    I'd be very inclined to add thermostatic radiator valves in addition to the balancing valves, while I was playing with the piping, for temperature flexibility, but that is an unnecessary tweak.

    Another option would be to install the valves with manual controls to control them as just balancing valves and add control heads later if needed. select the cv to balance the system.
    EdTheHeaterMan