Newly Commissioned Radiant System Not Keeping Up

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harrisd19

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Hello there. Have been lurking around these forums for a couple of years now and probably should have asked questions sooner when designing and planning my radiant system for my old house (1920s). After some years of renovation, I finally have almost all my loops up and ready to go. I hastily commissioned the system when temps were dropping a couple weeks ago, so I am now trying to figure out where my deficiencies are and why I am not seeing the comfort level I am hoping for. The basic info I can provide about the system is as follows, please feel free to ask any questions if I leave anything out:

The House:​

- ~2600sqft. of floor space covered (~1300 each floor) first floor- original 3/4" subfloor + 3/4" red oak strip, second floor 3/4" original pine single layer
- about 2000sqft. is structural clay block construction with stucco, the remaining is 2/4 framed, with stucco exterior and insulated with rockwool batts
- lots of original large single pane windows (most) having storms. However not much solar gain because of positioning with nearby homes (city)
- 9ft ceilings throughout

The System​

- Staple up 1/2" pex-al-pex, 8in o.c. w/ aluminum plates, foil bubble insulation 2" under 2nd floor, basement still in progress (See below)
- 11 loops total, all around 240-300 feet none exceeding 300ft. (1 inactive in a unused space still under reno. - we need to track down a puncture still)
- Cross 12 loop manifold (so only 10 active loops connected at the moment of this post)
- Crown Phantom Combi II 150k 10:1 modulating ng boiler (installed previously to run home radiators)
- HTP SSU-30N as a buffer tank zone for radiant take-off (Digital high limit aquastat on well, 115 high, 10 offset to maintain supply temp)
- 1" coil feed from boiler (taco 007)
- 3/4" feed to radiant manifold (grundfos UPS26-99fc)
- 3 zone taco switching relay to allow expansion of zones for future
- Single thermostat on first floor currently

Some Background Context​

So I have been running this system for a couple weeks now and it has been a slow to respond, but mostly working in moderate (50ish degree days). I had a 007 feeding the manifold and realized that was not going to be able to overcome the head pressure and replaced with the beefy Grundfos. I also purged the system with an external transfer pump to ensure air was out. I observed some response improvement and dispersion of heat. However, now as temperatures have been dropping (overnight mostly) I have the thermostat at 74 (high I know, but I am stress testing the system before it gets frigid) and it's struggling to stay 68 overnight. Not really uncomfortable, but we are only getting into the 30s now and the problem I fear will be exasperated as we get to some days in the 20s come deep winter.

I have not fully completed the install from the basement (for the first floor), I have about 50 more 4' plates to install this weekend and then following that with a plain foil-faced radiant barrier (2" down from plates) and then I want to put r-19 or better batts in below the barrier. This is probably about 1/4 of the floorspace without the aluminum transfer plates and none of it is currently barrier-ed or insulated. The basement is also missing bulkhead doors at the present moment (I will be installing plywood temporarily for the winter to seal it up), but there is an entry door at the stairs, but I tend to believe there is a parasitic draft hindering the performance of my system. I intend to expand the system to tie in some of the larger radiators on the first floor only, teeing off the primary loop of the boiler as a "stage 2" heat source on the real cold days (based off the outdoor reset). I intend to also add some additional thermostats to the second floor to "break up" the load and make use of the valve system on the cross manifold.

I observe a pretty low DeltaT between my supply and return temps, less than 10 deg. through the middle of the day. This increases a little overnight, but still seems to be under 10 deg. My boiler runs duty cycles over 10 minutes on off. I am supplying a bit higher than I intended at 110 deg. return is around 105-100 like I said, depending on ambient temp it moves a bit. I do not have a reading on the actual floor temp, but it is nowhere near that and I can feel warm points around the house, more-so upstairs (where there is only 1 layer of decking under-foot). I considered bumping up the temp, but I am worried about the wood expanding and buckling ruining the floor. It is 2-1/4 strip so I luckily have the ideal circumstance for wood over radiant.

I would like to have some of the experts thoughts on my install and have a slurry of questions below, if anybody can weigh in I would appreciate it!

My Questions:​

Does bumping up the supply temperature sound reasonable? I am worried mostly about the affect on the wood floors themselves.

Is the 3/4" piping between my "buffer tank" and 1" manifold a potential bottleneck, not allowing the full output of the system? I am not understanding this logic though because my delta T is in very good range from my research. So it seems like maybe more of a heat transfer issue?

Do we think that the completion of plate installs, radiant barrier addition and insulation in the basement will make a significant difference? I have read the claims about the radiant barrier on both sides of the debate, and am very unsure what to think. I would think that stopping air movement (from drafts) would help, but I could certainly be wrong.

Does it sounds reasonable to put the radiators on a "stage 2" zone setup? Do we think this might alleviate the problems I am seeing?

Would it be a concern that one of the loops in the second floor is currently inactive? Would that be likely to "sop-up" some of the heat output from the other loops on that floor or below?

Is there anything with my install that raises eyebrows?

I will follow up with some pictures of the install.

Thank you in advance!
 

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Fitter30

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The temp difference between supply and return are to low should be up to 20°. Take a few pics of the system including piping, expansion tank and boiler. 10 loops at 3000' with 20° temp diff 96k btu
 

Fitter30

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Taco pump going to HPT tank needs to repositioned pump motor needs to be in the horizontal plane. There is so much going on with your piping need more pic can't follow it. Should be piped like page 76 in this manual. Wood floors shouldn't get over 80° lower the better.
 

John Gayewski

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The lower the delta t the higher the output into your space. Delta t is just a diagnostic and sizing number there is no correct number.

When I have done heat loss calculations on old houses a radiant floor hasn't been capable of giving the output needed to heat the structure alone. Unless you replace all of your windows and doors and fully insulate you likley won't reach the target. FYI I only scanned your post as I don't have time to fully digest it.

You WILL notice that the more you insulate below the tubing the better your floor will heat. Your likley losing more heat than your gaining unless you use the reflective bubble insulation WITH full bats of fiberglass or rock wool insulation below. I know you said you started some of this but without fully directing the heat toward the floor it'll mostly be lost.


I do think you should add some radiators, but they should be high temp vs your floor which is low temp so the zones need to be seperate.
 

harrisd19

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Taco pump going to HPT tank needs to repositioned pump motor needs to be in the horizontal plane. There is so much going on with your piping need more pic can't follow it. Should be piped like page 76 in this manual. Wood floors shouldn't get over 80° lower the better.
I did not know that orientation of the pump mattered. Rotating it on the pipe axis should be an easy-enough fix thanks for that heads up!

I will take some more detailed pictures of the piping and add them as a reply. It is piped as primary/secondary, I used that same manual and I believe I followed it as written, but manufacturer did not show anything that pertained to my situation. The HTP tank is on the secondary and then I left another secondary to add on radiators later and not have to cut apart anything.

Question to your first comment:
I presume you are referring to the supply/return on the boiler screen supply 155 / return 143? This is the primary loop, heating the HTP tank via the internal coil. I will also be adding the radiators that should drive this delta higher.

The gauges were the supply return temps on the actual manifold that feeds the radiant tubes ~100 supply / ~90 return. Are you saying this should be a greater delta? Just asking for my own clarification.
 
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harrisd19

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The lower the delta t the higher the output into your space. Delta t is just a diagnostic and sizing number there is no correct number.

When I have done heat loss calculations on old houses a radiant floor hasn't been capable of giving the output needed to heat the structure alone. Unless you replace all of your windows and doors and fully insulate you likley won't reach the target. FYI I only scanned your post as I don't have time to fully digest it.

You WILL notice that the more you insulate below the tubing the better your floor will heat. Your likley losing more heat than your gaining unless you use the reflective bubble insulation WITH full bats of fiberglass or rock wool insulation below. I know you said you started some of this but without fully directing the heat toward the floor it'll mostly be lost.


I do think you should add some radiators, but they should be high temp vs your floor which is low temp so the zones need to be seperate.
I know it was a long post, so I appreciate any input you are able to provide! Much gratitude!

I am finding now, that some delusion a couple years back (probably a bad calculation) led me to believe that the numbers worked out. Recalculating now between what I have learned and am witnessing are leading me to your observation, radiant won't do the job on its own. But it is not all for nothing at least!

I am definitely going to move forward with foil insulation and full batt insulation in the basement. We have not done any in the basement yet, which is our biggest contender at the moment. Second floor is mostly comfortable, first floor is hurting. Every window in the house is pretty much original wood single pane however with storms, solid brick construction (no instulation, just 12inches of block and stucco). But there are some larger windows on the first floor without storms and those are drafty! Working on either getting indows or some other interior insulating window to cut that down to minimal.

I already ordered the things I need to add in the 3 largest radiators on the first floor back into the unused secondary loop hopefully that will help, I will see come Sunday!
 

harrisd19

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Here are some closer images of the piping of the system.
 

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Fitter30

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harrisd19

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Looking at a manual for - Crown Phantom Combi II it has its own pump for heating side why is there a taco pump on the inlet of boiler? Model of boiler? If your going to add radiators your also have to run two different water temps unless using low temperature fin tube.
Boiler model number: PHNTM150CB

The boiler has an internal circulator to run the primary loop so the loops are hydraulically separated. Then the taco pump pulls off the primary loop to the secondary loop (zone 1) to direct flow into the tank coil when the aquastat calls for heat. This allows for me to have the tank to run at the setpoint on the aquastat (lower than the boiler setpoint). I'll then run the yet another circulator (zone 2) for radiator loops, this loop is intended to run rads at the setpoint of the boiler (higher temp).
 

Fitter30

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What is the taco control or pump below the boiler? Never have I've seen a primary loop piped liked yours where the return to the boiler is straight thru the tee and with all fitting and very little straight pipe to straighten out the water.
 

harrisd19

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What is the taco control or pump below the boiler? Never have I've seen a primary loop piped liked yours where the return to the boiler is straight thru the tee and with all fitting and very little straight pipe to straighten out the water.
The taco device beneath the boiler is a low water cutoff. The dimension "B" on page 76 of the manual you linked above states "no further than 12" or 4 pipe diameters, whichever is less". This is less, so should be well within the parameters. I did not see a requirement for straight pipe, besides 18" for a conventional air scoop. I have a spiro air eliminator and magnetic dirt separator on the return as pictured., but still 18+ inches of straight pipe there too. What do you mean to "straighten out the water? To eliminate turbulent flow, how does that affect the delivery of heat?

Thanks!
 

Fitter30

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The pressure drop isn't the same on both tees. Scroll down to ironman
Your low water taco control being below the boiler isn't protecting the boiler. Page 2 install manual
 
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