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Delta T issue


I’m hoping that someone can help with my Hydronic Central Heat system. If you want to skip all the data and get right to the questions, just scroll down and look for this: ###

You can always refer back to the data if needed.

I just installed a new boiler after the old one went into nuclear meltdown. (don't ask ;-))

I installed this whole system when I built this home in 2003. I'm not a plumber or builder, just a DIY kind if guy. It's likely that I made mistakes on the original design and I'm just trying to get the system working the most efficiently that it can.

Here’s some info on the system, each item listed in order as it appears in the system.

1. Boiler: Trinity TFT 110,000 btu.

2. The primary loop is 1" copper.

3. Fill water tap. 12 psi

4. Air scrubber and expansion tank installed prior to main Circ pump.

5. Main Circ Pump is Taco 0011 (currently incorrectly installed, pump horizontal with motor vertical) This is a new pump that replaced the same kind.

6. Indirect 40 gallon hot water tank for DHW is tapped off main loop. Another Taco 0011 feeds tank. (seems like overkill, or am I missing something?)

7. In-floor hydronic Centra Heat system Tapped off Main Loop. About 5’ of 1” copper forms heat trap.

8. Central Heat return T’s in adjacent to CH feed. 1” Copper Heat trap installed on return.

9. Taco 0010 circulator installed vertically on outgoing heat trap.

10. Mixing valve installed, but currently closed.

11. ¾” pex delivers hot water to and from the zone manifolds on both levels of the house.

12. Zone valve installed just prior to Manifold.

13. Zone manifolds are Heat Link,

14. Loop tubing is ½” pex installed before concrete poured.

15. There are two zones on the main level, each with 5 loops per manifold.

16. I don’t know the exact length of the longest loop, but I estimate between 150-200’ based upon the area and the way it was done

17. Pex spacing in the floor is either 9 or 10”.

18. The floors are concrete poured on Insulated Concrete Forms, like this:

19. No floor coverings are installed on the concrete floors. They do have a few area rugs on them.

20. The exterior walls of the house are also ICF's.

21. House is approx. 2500 sq ft on each of two levels (5000 total). The lower level is a walk out basement with the same ICF floors and walls as the main level. Up to this time, the lower level has never had hot water run through the floor. I am currently only heating the upper level, the lower level never gets much below 50 degrees even in winter and without heat.

22. I ran a heat loss calc recently based on this method:

I used a design day of 0 Degrees and inside temp of 68 F.

I came up with a total heat loss of 77,318 BTUH for both levels of the house, 50,679 for the main level. However, since the home is made with ICF's we have much lower infiltration than a normal 2X constructed house. So I applied a reduction to the infiltration calcs of 20%. This yielded a total heat loss of 68,718 BTUH and 44,000 for the main level. I did not apply loss to the main floor, though it may have been prudent to apply some.


23. The method above showed that approximately 7-8 gpm was needed to service the radiant heat system.

24. 12 feet of head based upon a 200 foot circuit length

Here's the issue; on the main level of the home the water temp going to the manifolds is 140 deg**; there is a 37 degree drop on the return manifold, and this is after the floor is up to temp and the thermostat is ready to shut off the heat call. This is also with only one zone calling for heat and only two of the 5 loops open on the zone getting heat. When both zones are calling for heat with all 10 loops open, I still get the same 37 deg drop. There is a 3/4” pex run from the main boiler loop to the manifold, of about 25’. I calculated that based on the Delta T of 37, that I’m getting about 2 gallons per minute of flow through the ½” pex. I have read that this is about ideal for ½” pex, but I believe that it could pass more water if the circ pump was up to it.

It’s now obvious that larger tubing would have better served for the loops, but it’s too late to change that as they are totally embedded in concrete.

Taco shows a Head Range of 9 for the 0010 pump. If these calculations are correct, it would suggest that the 0010 is not the right circ pump for the job. So here are the questions:

1. Is 37 degrees too much Delta T for this system?

2. If so, what would be appropriate? 20?

3. Is my flow calc of 2 gpm correct?

4. Do you think that my head calc (12) is correct?

5. Will a pump with more head range provide more flow through the zones with ½” pex, even if it is not the ideal flow rate for ½” pex? It seems that even a little more flow would bring down the Delta T and allow the floor to heat up more quickly. THAT my friends, is the goal of this novella.

a. Despite the high Delta T, the system does indeed heat the home very well, I’m just trying to speed it up and have it run at highest efficiency.

** I realize that 140 might be too hot, It can be lowered either at the boiler or with the installed mixing valve. What temp would be ideal and should I lower it at the boiler rather than at the mixing valve?

I’m sorry for the long post here, but I wanted to provide as much data as possible, since it seems that most people don’t provide enough when asking for help.

Thank you for your assistance!


  • icesailoricesailor Member Posts: 7,265
    Way back when:

    Way back when, when the 007 was the go to circulator, if anyone would have suggested that you could get 7 to 8 gallons per minute through 150' to 200' of tubing that was smaller than 1/2" copper, they would have walked away shaking their heads wondering where that idea came from. Now that we have circulators that can wear holes in sharp turns due to turbulence, some are giving it a try.

    So, try this. Take your friendly garden hose, connected to your convenient hose connection outside, two five gallon buckets, and time how much water you can get out of that hose in a minute. Then, try doing it with 100. of hose. Now ask yourself, how you can possibly get 7 to 8 GPM through 1/2" PEX. 

    If it is working, stop over thinking about it.  Don't futz with success.

    Unless you have way too much time and money on your hands.

    OBTW. those circulators with the vertical aligned motors with the cans on the top, it says in the installation manual that it is acceptable to do that if you raise the system pressure to over 18" PSI. So that you squish the air bubble and the pressure makes it easier to absorb the air. 
  • barefootbarefoot Member Posts: 18

    Well, I did a test as you suggested. It turns out that we also have pex for domestic water supply. I have a hose bib at the end of a 75' run of 1/2" pex (approx). It delivered a whopping 3.5 gpm.

    I didn't need to get the full 7-8 gpm out of each manifold, 3 would likely give a nice flow increase and a reduction in Delta T.

    Oh well, my wife accuses me of over-engineering anyway... but, I may just swap out that 0011 that is on the DHW tank and see what happens.

    thanks for your input.

  • Charlie from wmassCharlie from wmass Member Posts: 3,922
    you seem to want to try your options

    you may get a better delta T or more even heat transfer by reversing the flow in each loop separately and together. Larger pump means more electricity being used. You can get a pump to get that up to 12 gpm but the floor may vibrate from the flow rate. If you really want to get efficient get a variable speed pump that goes above and below your range and use that.
    Cost is what you spend , value is what you get.

    cell # 413-841-6726
  • GordyGordy Member Posts: 7,106
    3/4" pex

    How long are the. 3/4" supply returns to the manifolds?
  • barefootbarefoot Member Posts: 18
    3/4 pex

    The manifold where I could only get 37 DT with only 2 loops open has about 25' of 3/4". The other manifold has about 50' leading to it.
  • barefootbarefoot Member Posts: 18
    edited March 2013

    Charlie, What would reversing the flow do? I agree about the variable speed pump. I'm looking into that. Do you have one to recommend?


  • GordyGordy Member Posts: 7,106
    edited March 2013
    Floor detail

    So is the two levels the basement, and main floor equaling the 5000 sf?

    Floor detail for the main floor? Is it flex core as shown in the detail ?

    There is 10 loops on main floor?

    IF you are getting 2 GPM through 1/2" pex at 200' is 10.6 ' of head. That would mean the manifold would need 10 GPM. I think your over pumping. Head goes up to the square of the flow rate. Bigger is not better. I don't think your getting 2 GPM through your 1/2 " loop.

    With 50' of 3/4 pex supply, and 200' 1/2" pex longest loop. Flow rate of 3.5 GPM to manifold, and .7 GPM for each loop puts you in the 7.5 ' of head range worst case.
  • TomTom Member Posts: 455
    as usual

    I want pictures of the boiler set up and any pics I can get of the manifolds. Your write up was precise but I can't start thinking like a marble without pics!
    Montpelier Vt
  • barefootbarefoot Member Posts: 18

    Thanks for the interest in my issue. I have to deal with other distractions until Monday or Tuesday of next week. I'll answer the questions and try to provide pictures at that time.

    thanks again,

  • ZmanZman Member Posts: 3,479

    When you checked your flow rate were you using the circ or house pressure?

    A delta t of 38 indicates the flow rate is too slow. It sounds like you either have longer tubing runs than you think or you circulator is under performing.

    Can you read the footage numbers on the tubing?

    My experience is that you normally see a delta of about 10 degrees at steady state in your type of system. That is with 200' loops pushing  just under 1 gpm each.

    You are measuring the delta at the secondary right? What type of gauge?

    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Charlie from wmassCharlie from wmass Member Posts: 3,922
    reversing flow

    introduces the heat to the floor in a different pattern that may or may not be more even. The hottest water I prefer to direct to the outside or colder area of a room. The real reason is to distribute the heat in the floor in a different pattern.
    Cost is what you spend , value is what you get.

    cell # 413-841-6726
  • GordyGordy Member Posts: 7,106
    edited March 2013
    Missing something

    OP says he has 44000 btu loss on main floor. He has two 5 loop manifolds supplied by 3/4" pex on main floor.

    So each manifold needs 22000 btus delivered to it. While each loop needs 4400 btus if each loop and manifold has an equal load, and each loop has an equal load all assumptions.

    His main floor btu per sf requirement is 17.6 . To get this he would need a average water temp of 86 degrees for each loop. Say 100 supply 80 return for a 20 delta t.

    His 3/4" supply would need to deliver 3 gpm to each manifold.

    A few things don't add up

    1. tube spacing verses loop length. If loop lengths are 150-200 feet 9-10" on center then there should be 5 -5 loop manifolds . 2500x1.2=3000. 3000/200= 15 loops at 10" spacing.

    If he has 2 -5 loop manifolds 10 loops then his tube lengths are 300' or his centers are wider than 9-10" or he has areas with out tubing otherwise its more like 15" oc if 200' loops and 10 loops.

    Clarification needed based on info provided other wise all calculations based on info provided is wrong.

    2. If im understanding description correctly. He is trying to deliver 2 GPM through 1/2" pex loop the head to do this is an astronomical 26.3' for a 200' 1/2" loop. Theoretically then each manifold needs 10 GPM , and 20 GPM from the secondary loop. For the heat loss provided this is over kill.
  • barefootbarefoot Member Posts: 18
    edited March 2013

    Good morning,

    I really appreciate the interest in helping with my flow issue. I don't have all of the answers to the questions asked, I'll answer several, but first here's what I did yesterday....

    I swapped pumps, I put the Taco 0011 on the CH loop and the 0010 on the DHW tank loop. The Delta T quickly dropped to 27 degrees and this was with a cold floor. This morning, as the floor is up to temp, it is still 27 degrees Delta T. I am measuring this at the manifold. The boiler is showing 135 deg at the outlet and 130 at the inlet.

    Temp at the inlet manifold is 131, this is at the closest manifold (25' run of 3/4" pex to manifold). Manifold temps are measured with an analog thermometer that came with the Heat Link manifolds. The thermometer fits into a probe hole in the manifold, so it is right in the flow of water. I simply move this thermometer from the inlet/supply manifold to the return manifold and see the difference. (yes, I let the temp stabilize for a while)

    (btw, I'm installing the outdoor sensor today)

    That 3.5 gpm flow rate I mentioned was a test with domestic water, not boiler water.

    Regarding loop length, Gordy, you are correct, there are many places where the pex was not installed, for example, under walls, cabinets, small closets, appliances, tubs, showers. This is why the square feet and loop size don't appear to add up.

    I was at the plumbing supply yesterday and mentioned the issue to my supplier (who appears very knowledgeable) He agreed that I'm just not getting enough flow, due to head required. He also mentioned that the Plastic Heat Link manifolds introduce a lot of head in addition to the 1/2" Pex. I can't see using a pump any bigger than the 0011, so it may be that 27 deg Delta T is the best I can do. Considering that even with a 37 deg Delta T the house gets heated, 27 may work out just fine. Oh, another thing... before swapping pumps I was getting Short Cycle alerts and the Boiler would not turn on again until the delay was met (5 minutes). After installing the 0011 on the CH loop, the short cycling has stopped. The boiler just chugs along at a steady temp.

    As for noise through the pipes with 0011... if you get within 3' of the manifold you can just barely hear water going through the manifold. I think this is the sound of the water making a turn and passing through the opening to the pex. Other than that, it is silent.

    Charlie, reversing the flow would require more re-engineering than I'm up for right now, but thanks for the suggestion. If ever I have to redo things in the mechanical room, I might experiment with that idea.

    There's one last data point that I did not mention earlier; when I installed the boiler, the bottom of the boiler ended up lower than the previous unit because the new one is taller. This meant that I had to add several elbows in the primary loop to get it reconnected to the boiler. However, it doesn't appear to slow down the flow in the primary loop as I get VERY low Delta T at the boiler, regardless of what is calling for heat, CH or DHW. It is in the 4-6 degree range.

    I think that the 0010 pump, now installed on the DHW loop, is overkill and moving the water too fast through the tank. What would you recommend for a DHW pump (40 gallon Slant Fin Tank)?

    Thank you very much for your assistance.

  • SWEISWEI Member Posts: 7,356
    135 deg at the outlet and 130 at the inlet

    tells me the boiler is overpumped.  P.49 and 50 of the TFT IOM show several suggested pump sizes and the HX curve for the 110.  What kind of pump is on the boiler loop, or is the system direct pumped?

    Manifolds with less head loss might be worth considering.  Is there any way to replace or supplement the supply and return piping to any of the manifolds?  Breaking a large manifold into two smaller ones with new supply/return pipes can help a lot.
  • barefootbarefoot Member Posts: 18


    The primary loop pump is also a Taco 0011, and I agree that is too much pump. Replacing manifolds would not be a simple matter nor would replacing the supply/return piping. Both would require removing and replacing dry wall in the home.
  • paulpaul Member Posts: 91

    gordy your calculations all ad up except you missed one step, and that is the head of the loops. calculated at close to 1.5 feet to 2 feet of head on the 1/2 in pex at 200-300 foot loops off of the manifolds. assuming the longest loop at 300 feet the head would be close to 2 foot of head. the mistake i think everyone has made in this process is that they have added all the head losses together. you don;t add all of them together just take the highest head loss and connected piping loss. now the the flow through each loop you do add all together which ends up being .3 gpm x 5 loops per manifold x 2 manifolds (main floor only) equals the 3 gpm you came up with. I don't know where the 20 foot of head total came from but it is wrong.
  • GordyGordy Member Posts: 7,106

    The 20 feet of head I was referring to was in reference to initial post the op said he was getting 2 gpm through the 1/2 inch pex. Maybe he meant to the manifold thus .4 gpm to each 1/2" loop, but it did not read that way to me. Sounded unrealistic to me.

    Yes my calcs were off I used the 25' 3/4" supply/return to the manifold instead of the 50' manifold. I did use the longest loop 200'.

    If the spacing is correct there is about 350 sf on the main floor with out tubing. That's quite a bit of area.
  • SWEISWEI Member Posts: 7,356
    edited March 2013
    change the primary pump

    I'd pick something that gave me 35F ∆T at maximum fire.  As usual, I'll ignore the manufacturer's pump suggestions and pick what actually delivers what I want.  99,000 BTU (DOE rating) at a ∆T of 35F will require 5.65 GPM.  If I look at their head loss curve, I see that will impose about 2.7 feet of head.  The way we pipe primary loops, there would be an additional half a foot or so of piping losses.  In Taco, that puts me somewhere between a 003 and a 006 in size.  I don't think Taco offers a VDT version of the 006, but that would be ideal.  If Laing is shipping the E10 brass that would be another good option (with ridiculously low electrical cost.)
  • paulpaul Member Posts: 91
    delta t

    gordy i see where you are coming from. the numbers don't add up. He has high supply water temp of 140 degrees and a 37 degree delta t . return water at 103. 140 degree on the 10 loops at 200 feet means he has btu's per square feet way above my calculating pad in the 50 btu an hour plus range. so even with the several hundred feet of missing pex loops he can still heat his main floor ok. to hot for my liking. but the thought is that he is also loosing heat to the basement because of lack of insulation below his slab. just a thought. it would explain the high delta t.. maybe he could see with his laser guided thermometer he could see what the basement ceiling is doing.
  • barefootbarefoot Member Posts: 18

    Interesting, why would you choose a Delta T of 35?
  • SWEISWEI Member Posts: 7,356
    edited March 2013
    Larger ∆T

    Will reduce the return water temp, which both increases boiler efficiency and reduces pumping costs.
  • GordyGordy Member Posts: 7,106
    Checking delta t on loops individually

    It may help to invest in an infrared thermometer for checking floor temps in areas, and individual loop delta t's.

    Obviously you have issues at the primary loop with circ sizing. Which SWEI has pointed out.

    I believe your initial concern was delta t at the supply return manifolds for the loops?

    Do you have flow meters on the manifolds? If so what are they set at?

    Wide delta t's can mean a variety of things when used to trouble shoot.
  • barefootbarefoot Member Posts: 18


    You are correct, my concern is the Delta T between the supply and return at the manifolds.

    I don't have a flow meter, and I don't have a way to check Delta T on individual loops. I doubt that I'll buy an infrared thermometer, I set the temp for the zone based on the main room connected to that manifold, then I set the flow of the other loops based on how the temperature "Feels" relative to the main room on that manifold. For example, on manifold one, the main room on that zone is the Family room, on manifold 2 the main room is the Master Bedroom. The thermostats for each zone are in the main rooms. When the Master BR is up to temp and feels comfortable, I go into the Bath and large closets and see how the temp in there feels. If too warm, I reduce the flow to that loop or vice versa.

    After putting the Taco 0011 pump on the Central Heat loop the Delta T dropped by about 10 degrees. At this point it seems that my only "practical" option left to improve the Delta T would be to replace the manifolds with something else that didn't have as much head loss. I may consider this option. I posted earlier that it would require removing drywall to do so, but I may be able to avoid that. Does anyone have suggestions on a low head loss, 5 loop manifold for 1/2" pex?

    Paul mentioned a lack of insulation below the slab, not so. The floor is poured on top of styrofoam forms (see the first link in my first post). I can't say exactly how thick, it is shaped to form structural "I" beams every 24". At some places it is 6" thick, in other places only 1" thick. If you pulled away the stryofoam, it would look like a "double T" roof in a warehouse, from below. I'm sure there is heat loss to the basement, but it's not excessive.


  • SWEISWEI Member Posts: 7,356
    improving ∆T

    means different things in different situations, as Gordy pointed out.  Condensing boilers run most efficiently with a large ∆T.  Most throw an alarm or shutdown when it hits 40F, so we like to run them at 35F when possible.

    Emitters are a bit more complex.  Radiators can handle 30F in many cases, but in-floor loops deliver uneven heat when ∆T gets above 15F.  Baseboard depends on the length and layout, with series loops probably being the most particular.  Remember that the quantity of heat delivered is based on the average water temperature, so if you increase the supply by 5F and decrease the return by 5F you will deliver the same amount of BTUs with a 10F greater ∆T.

    Commodity infrared thermometers are in the $20 range these days.  You can't rely on them for absolute temperature indication, but if you measure consistently (black electrical tape on pipes or fittings, hold the gun at the same close distance each time) they are entirely useable for relative measurements, which is what you need here.  A handful of clip-on dial thermometers could be useful, but you would have to calibrate them at least to the point that they match each other.
  • GordyGordy Member Posts: 7,106

    My thoughts are high mass, and heat loss to the basement also. He's giving btus up somewhere. That's why I think an infra red thermometer to check temps in more detailed areas.

    By checking only at the manifold thermometer the water can be mixed with hotter, and colder loops dumping into the return manifold. He may have one loop with a 10 degree delta, and a couple with 45 degree deltas mixing together at the manifold. By checking floor temps, and individual loop temps he could narrow down problem loops or areas.
  • barefootbarefoot Member Posts: 18

    I ordered an infrared thermometer as suggested.

    I was looking online at manifolds and it seems to me that this type would be the least restrictive (lowest head loss) :

    What do you think? Any other suggestions?


  • SWEISWEI Member Posts: 7,356

    may not be the best standard for determining complex flow mathematics.  Nothing personal, but you really need to step back and look at the whole system design.  Where are these manifolds located?  Is there any way to either increase or supplement a supply/return line or lines?   I think we mentioned splitting manifolds earlier.
  • barefootbarefoot Member Posts: 18

    Good point about the complexity of flow. When you suggest splitting manifolds, do you mean split the 5 port manifold into a 3 and a two, then provide separate feed lines for each from the boiler? If so, that would be highly impractical, involving ripping out walls. The same problem exists for trying to switch to a larger feed line for one manifold. Those options are off the table.

    I have taken a whole now look at the system, largely based on the great info provided here. I believe that my only practical option left is a manifold with lower head loss. Any ideas in this area?
  • SWEISWEI Member Posts: 7,356
    You really need

    a full system analysis.  This starts with a room-by-room heat loss calculation, a room-by-room radiation survey, and a table of all the distribution piping.  From this, you will determine what water temperatures and flows will be required at design conditions.  Then each segment of pipe is evaluated to see if it will carry what is required of it.  After all that is done, the appropriate system circulator is chosen (possibly more than one.)

    If this process led you to an undersized manifold feeder, the best answer would be to increase the size of the pipe.  Barring that, you might consider using a dedicated circulator for that manifold, since it differed from the other piping enough to warrant a different pump curve.  The point is that you need to deconstruct the original design and then reconstruct it properly before you start buying parts.
  • GordyGordy Member Posts: 7,106
    edited March 2013

    SWEI is dead on in his post as what you need to do. Throwing parts at your system is not the way to go.

    Again delta ts can mean a variety of things.


    Loops that run along exterior walls where higher loads are can have higher delta ts than interior loops in the same room. Varying loop flows can even this out. But you need to understand the flow rates required to heat the space. I think your water temps are higher than you need.

    Your heat load calc seems a little high for an ICF home of that square footage. But you only shared a total load. This will dictate boiler size, but room by room, or zone by zone heat loss btus needed to be delivered to that space. This Will dictate tube size, spacing which dictates max loop lengths, and water temps, and flow rates needed for each loops. Now you need to deliver those total needed btus from the secondary loop to the manifold distribution again the zones heat loss will dictate flow rate water temps, and tube size to get the btus there to be distributed.

    If your in doubt of your system head there is a metering way to check it.

    Install a 30 psi pressure gauge in a well on the supply side, and one on the return side of the circulator as close as possible to the inlet, and outlet of the circ. with the circ off observe the pressure gauges to make sure they both read the same psi. With the circ on observe how much the return side pressure gauge drops, and observe how much the pressure goes up on the supply side gauge. The difference multiplied by 2.31 is how many feet of head the system has. So if there is a difference of 5 psi then the system head is 11.55 feet of head. 5x2.31= 11.55 . Plot that on the circulator curve chart, and that's what GPM your getting takes a little pipe work, but is dead on to the accuracy of the gauges used.

    From there you can use other size pump curve charts to see if a circ matches what you need.
  • barefootbarefoot Member Posts: 18

    I understand the value of doing all the calculations. While I do have room by room heat loss, I don't have a radiation study, and I don't have the loop lengths. This data would certainly have been of great use. I'm not willing to spend more $$ to come up with any more data.

    What I do have is empirical data, ie, 37 degree Delta T using Taco 0010, 27 Delta T using Taco 0011. Installing pressure gauges would indeed tell me Head loss. While I may not have the exact head loss number, I know that it exists in sufficient amount to restrict the flow enough that it gives the Delta T's mentioned.

    I'm at a point where even a small additional gain in flow through the system would get it very close to the 20 deg Delta T target. Since I had the Taco 0011 on hand, it was a simple matter to experiment with it.

    As suggested by someone in an earlier post, I could change the feed lines from 3/4" pex to 1". Or I could find a less restrictive manifold. The latter seemed a more palatable choice to me, that's why I asked about low head loss manifolds.

    With the Delta T now at 27, I may just leave the thing alone and live with it. It doesn't have any problem heating the house. I'm just chasing the last bit of efficiency and performance.

    thanks for your assistance.


    ps, I would still like to hear about low head loss manifolds in case I decide to pursue that in the future.
  • GordyGordy Member Posts: 7,106
    Make your own manifolds

    Easy to do.

    I bet if you lower your supply temp to 115 to your loops your delta t will drop to less than 20.

    It may have more run time but the efficiency will be better.

    Getting to wrapped up in headless and gpm and forgetting needed supply temps.
  • barefootbarefoot Member Posts: 18

    Will do....
  • GordyGordy Member Posts: 7,106
    See what happens

    Because right now your boiler gets its efficiency partly from condensing the lower the return temp the more efficiency.

    It may take longer to reach set point but everything will be more efficient. Radiant is not about speed unless you have a low mass system.

    Never did ask are you using outdoor reset? Are you using set back?
  • barefootbarefoot Member Posts: 18
    outdoor sensor

    I've been in and out of the attic all morning. Nothing is ever as simple as it seems.The Outdoor sensor is now installed and working.

    The modulation line shows a max of 120 and a minimum temp of 95. The outdoor cutoff is at 65 F.

    Boiler setpoint for CH is at 120 so that the farthest zone will see at least 115 on design day.

    Right now, the modulation point on the Line is 103 (outdoor temp 45f). However, the boiler seems to be keeping the outlet temp between 95-100. I'm seeing 92 at the nearest manifold. Of course, NOW that I properly set the setpoint temp AND installed the Outdoor sensor, the Delta T is right in line.

    It will be interesting to see what happens to Delta T on design day, which we won't likely see until December. I may turn off the Outdoor sensor and let it run at 120 deg just to see.

    You were correct, I was so focused on Head loss and flow, I forgot to lower the setpoint, despite knowing that I needed to do so.

    I did notice that the boiler went into short cycle delay after installing the Outdoor sensor, I'll keep an eye on it.

    all the best,

  • GordyGordy Member Posts: 7,106
    I would drop it more

    And leave the outdoor sensor hooked up. Highly unlikely you will produce a design day test run if that's your intentions with out the sensor hooked up the loops need to have the load.

    Now you need to dial in the slope on your reset curve.

    Do not use setback with outdoor reset they do not work well together set it, and forget it otherwise your boiler will be playing catch up the whole time.

    Ideally when everything is in order. If your boiler is,properly sized for your total load which it's bigger. Your boiler should run 100% the whole time of the design day period, but yours won't because its larger than your heat loss if that is correct.

    Once you get your infra red thermometer, and if your still in heating season. Check floor temps are they even.

    Check individual loop delta ts.

    You will probably find that one loop may be 5* delta one maybe 20*, and yet another 10 or 15*. Don't get to wrapped up in that. The main thing is even surface temps max 85-87*'and satisfying the load of the zone. Those temps may only be at design day also. Remember there is the delta t between room temp, and floor temps. Interior temps, and exterior temps. Always throwing fistfuls of btus from hot to cold.

    Delta t is a number to design around, and not necessarily to be a set number exclusively unless total system is a cold startup, or at design conditions. It will usually be lower most of the time. Unless we are at the boilers primary loop.

    I honestly believe you could get by with a smaller circ on the secondary. Maybe even a bumble bee on each zone. Your burning a lot of watts with those 010, and 011s like 200 a piece.

    Another thing to consider is constant circulation.

    I think part of the issues you thought you had were from not having things properly set up at the mechanical room before seeing the whole picture. If everything is setup for the design, and then fine tuning things after so be it, but the math does not lie when properly calculated.

    Keep us posted.
  • barefootbarefoot Member Posts: 18


    Excellent post. I had already removed the setbacks, now set at a constant temp.

    I agree about the pumps.

    I also have that Grundfos 15-58 that I can try on the CH loop. That should help me nail down exactly what pump will be best on the CH. ( it has 3 speeds each with it's own output curve)

    When I get the Thermometer I'll be able to get a better handle on everything.

    I really feel like a dummy for not turning down the CH setpoint sooner. As I stood in front of the boiler to do it, I realized that it was the main source of my problem. Of course I had a big Delta T, with the source water temp at the manifold of 135+, I would have to set the thermostat to a very high temp before the floor could heat up enough and stop sucking heat out of the pex to allow a 20 deg Delta T. The floor was getting up to the temp that would satisfy the demand of my thermostat at 67 degrees then shut off. There's no way I could get a 20 deg DT with 1/2" pex at that high of an input temp. Dummy!

    Well, thanks to this forum I'm a lot closer to getting this system finely tuned.

    The Bumblebee is interesting.

    Here's a question about using two of them.... If I put one on the Primary Loop, then another on the CH Loop, (both in Delta T mode) could that cause flow problems? For example, lets say that the pump on the CH loop is running half speed or higher, but the one on the primary senses a low delta t and throttles back very slow. The supply and return Tees for the CH loop are adjacent to each other on the Primary loop. Could this cause the water to backflow from the return T into the supply T?

    I'm gonna ponder that one a bit...

    all the best,

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