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Hydronic Slab on Grade Delta T pump problems.

We were able to get our Hydronic floor heat going just in time for winter in Northeast Indiana this year!! Things are working good and i would like to Thank everyone on this forum that has given great advice.

The problem i am having is when the taco vt2218-hy1-fc1a0 Delta T pump turns on, it does its start up cycle at max speed (60 watts) and then the sensors read the input and output of the water going in and out of the floor. The pump then goes into its auto cycling to keep the Delta T at the programmed Temperature.... All good at this point.

Then the problem happens.... The pump reaches Delta T and slows down all the way to minimum speed (6-7 watts) at this point the water is flowing so slow that it is not transferring through the pipe enough for the external sensor that the pump came with to accurately read the temperature. At this point, pump stays at the slowest speed and stays there.... since the pump sees the delta T less than programmed, nothing tells it to speed up again.

Since this is Concrete Slab heat, Everything i can find says that it is like starting a stopping a train so decreasing the Delta T may solve my pump problem, but then it seems like i would be trying to heat too fast.

28'x96' slab on grade garage
140 degree F. Supply temp. from boiler
105 degree F. out of Thermostatic valve into floor

any advice?

Thank you in advance and Merry CHRISTmas!!


  • Brewbeer
    Brewbeer Member Posts: 616
    You could try decreasing the delta T setting on the pump, or setting the pump to a fixed speed.
    Hydronics inspired homeowner with self-designed high efficiency low temperature baseboard system and professionally installed mod-con boiler with indirect DHW. My system design thread: http://forum.heatinghelp.com/discussion/154385
    System Photo: https://us.v-cdn.net/5021738/uploads/FileUpload/79/451e1f19a1e5b345e0951fbe1ff6ca.jpg
  • Gordy
    Gordy Member Posts: 9,546
    edited December 2017
    Make sure your sensor is firmly placed against pipe wall and some heat transfer paste. Then make sure it is well insulated.

    Beyond all that as mentioned fix speed could be the best solution.

    People get to crazy about deltas. On a floor radiant you shoot for 10. However a lot depends on the load the slab sees, and I see it’s a garage slab so that delta could be 20 unless you are barefoot. Is the slab kept to temp all the time, or for intermittent use?
  • mikeg2015
    mikeg2015 Member Posts: 1,194
    Is there a way to set a minimum speed on it?
  • Gordy
    Gordy Member Posts: 9,546
    Also you did not say what delta you are using, and if the garage is meeting, and holding setpoint.
  • Rich_49
    Rich_49 Member Posts: 2,766
    edited December 2017
    How many loops ? What temp ? Loop lengths ? Programmed Delta ?
    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
  • JDmachinist
    JDmachinist Member Posts: 7
    I have researched a lot about how Europe does hydronic heat since they have been doing it longer and still do it more than we do in the USA. So some of this goes against what you normally read. I like to try what is in respected trade magazines and much of the design is based on a collective of what i have found using those two starting points.... with that being said, please don't yell and scream too loud when you read what i am running things at :)

    * 140 degrees F Heated water going into thermostatic valve
    * 105 degrees F leaving Thermostatic valve going into floor
    * 42 degree F Delta T
    * 9 loops at 300 feet each
    * 55 degree thermostat setting (this is a garage and i don't mind a sweatshirt, but most days i work in a t-shirt)
    * i have tried the pump on all 4 speeds and the automatic Delta T works the best except for it locking in at minimum speed.
    * On two consecutive 15 degree mornings with 10-30 mph winds, the pump, thermostat, and heat source were all turned off, so Yes it is keeping up (daytime highs were in the upper 20s low 30s)
    * I am using an adjustable flow manifold and when the pump is flowing maximum, the temperature coming out of the floor is within .8 of a degree using an infrared thermometer on the outside of the PEX.
    * 28x96 building with 10' walls R22+ walls, R30+ blown in ceiling. 3 (3'x4') windows, 2 (10'x8') garage doors, 1 (7'x8') garage door, 1 (36") entry door with glass). drywall walls, steel ceiling (all seams and light fixtures silicone sealed), 3 ceiling fans

    This may seem like a crazy set-up, but it is working pretty darn good!

    Thank you in advance for any suggestions or comments you may have!!

    Make it a GREAT Day!!
  • Gordy
    Gordy Member Posts: 9,546
    edited December 2017
    What are you using for a boiler?

    What is the return water temp to the boiler?

    Shooting pex with an IR thermometer will not give accurate measurements. The surface should be dull, and black to give best readings.

    What is actual slab temps?

    Is the temp across the slab reasonably the same?

    Not sure what the fuss is if it’s working to your satisfaction other than the delta t circ not responding as you think it should.

    You have to think about the whole systems dynamics not just the circ.