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New Garage Radiant Floor Heat system only getting air temp up to 55F



  • Gordy
    Gordy Member Posts: 9,531
    hot rod said:

    If most of the tube is at the bottom of the slab, you may need to crank the supply temperature also. Hopefully some of it was lifted into the middle or upper part of the slab.

    This model is for a 4" slab, notice the output hit as the tube is deeper in the slab. To achieve a 30 btu/ sq ft on this example would require around 134° SWT.
    About 102° for a 15 btu/ ft output.

    With that large of dia. Pex it may have floated up...with a little coaxing.
  • Gordy
    Gordy Member Posts: 9,531

    Well, when we bring the Pex out of the concrete, it normally has a pvc 90 deg electrical sweep over the tube to protect it from abrasion with the concrete which could lead to the Pex being cut. Pex expands at 1" per 10' per 10 degrees change in temperature. I think I got that right? Anyway it is constantly expanding and contracting as the temperature changes. Where it is locked into the concrete, the tube walls get thicker or thinner. The movement where it exit the concrete can cut the pex.

    I didn't see any sweeps in your photo of the manifold. I'm blind in one eye and can't see out of the other, so I might have missed it.

    The reason that I would have done the tube layout in a serpentine pattern is the I can then cut control joints in the slab easier. Where I plan to cut the control joints I cover the Pex with pvc pipe for the same reason as I stated above, abrasion. Also, it is a more balanced layout temperature wise.

    As the slab expands and contracts, the control cut allow the slab to crack at those cuts instead of randomly on the slab. Look at the slab the next time you go to Costco. About every 10' X10' square.

    1" per 100 feet.

    The coefficient of linear expansion formula usually works as per 100' per 10 degrees rise, or fall from a given starting temp.
  • HomerJSmith
    HomerJSmith Member Posts: 1,289
    Ok. I was looking at an earlier pic to the OBS covered manifold. The later pic show copper connecting to the Pex in the slab. The answer is yes. Cover any copper buried in the concrete with electrical tape or any such thing and any exposed copper with pipe insulation. Your manifold header & supply pipe should be 1 copper pipe, or 1 1/4", not 3/4". Assuming the flow is 1 gal/min X 5 zones = 5 gal/min. 3/4" pipe has a velocity of about 3.67 ft/sec and a pressure loss of over 9 ft/hd per100' of pipe. Adding up all your pressure losses thru the boiler, supply and return headers, and 300' of Pex (one zone) and looking at the pump curve for the UPS 15-58 circulator at one gal flow rate should tell you the head energy that the pump is capable of producing at that flow rate. With anti-freeze reduce the pump head energy by 12-15%. At 1 gal/min, speed Hi (3) should give you about 16' of head energy.

    Is that a lot? I don't know, but it has to overcome the pressure losses in your system. If a company did the design, I would think that they did computer modeling and that it is correct. I always want the lowest pressure losses vs cost as possible because you can use a smaller pump which equates to less electrical cost to run that pump which over the system lifespan can be considerable. It was nice that you used 3/4" pex instead of 1/2" pex. The heat delivery isn't much different, but the pressure loss is very different.

    I think that pulling the wire mesh up with a rake while standing on it left it at the lower depths of the slab and it will take a lot more time to bring the slab up to temperature and may require a higher supply temperature.
  • HomerJSmith
    HomerJSmith Member Posts: 1,289
    That seems to me to be a messy installation, I like symmetry and balance, a work of art.

    Also, I don't like high loops without there being some method to bleed entrapped air out of these high loops like either a coin air vent or auto vent.

    Better add up your pressure losses because I see a lot of them in your boiler installation.
  • HomerJSmith
    HomerJSmith Member Posts: 1,289
    I like a tridicator on the output of the boiler as it provides important information. What with this coil in the supply piping, looks like a washing machine hose bibb supply line with an ID of 1/2". Good grief.
  • HomerJSmith
    HomerJSmith Member Posts: 1,289
    If you called me over there, I would tell you that I would have to re-pipe your whole boiler system. The boiler doesn't have to be that high up on the wall and none of it is conventional piping.
  • HomerJSmith
    HomerJSmith Member Posts: 1,289
    I did that wrong, You have 5 zones at 1 gal each? the UPS 15-58 would be, based on speed hi (3), have 15'/hd energy less 15% for glycol losses leaving you with 12.75'/hd energy to cover all your pressure losses.
  • HomerJSmith
    HomerJSmith Member Posts: 1,289
    It takes more head energy to pump 5 gal/min thru a 3/4" copper pipe than thru a 1" pipe. It's 6.09' hd vs 1.74' hd per 100' of type M copper pipe.
  • Zman
    Zman Member Posts: 6,539
    I am assuming the OP does not want to repipe it all. With that in mind, I would get rid of the washer hose and check the delta t's. If they are 20 degrees or lower under steady state conditions, you are good to go. If not, I would swap to the 26-99 circ.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Rich_49
    Rich_49 Member Posts: 2,564
    1" per 100' @ 10* climb
    You didn't get what you didn't pay for and it will never be what you thought it would .
    Langans Plumbing & Heating LLC
    Serving most of New Jersey, Eastern Pa .
    Consultation, Design & Installation anywhere
    Rich McGrath 732-581-3833
  • delta T
    delta T Member Posts: 843
    Get rid of the washing machine hose on the supply and it may work. Agree that there are a lot of sources of flow restriction. A higher head pump may work wonders.....
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