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New garage heat system not working. Any help?

gilbertsonp Member Posts: 1
edited December 2018 in Radiant Heating

What I thought would have been a simple system is giving me fits. A 17' x 25' 5" garage slab with 2" of insulation below and on sides has 2 135' loops of 1/2" pex on a single zone. It is a closed system with about six gallons of a 75% glycol solution heated by a small on-demand propane water heater (80k btu, 3gpm Eccotemp). The system uses one circulator, includes an expansion tank, an air scrubber, a Watts manifold, and a strainer. (See photo).
I quickly discovered that my first choice of circulator (Taco 006) was woefully under-powered, registering virtually no flow on either the manifold's or heater's gauges. I was able to make the system work by powering it with the 1/2 hp utility pump that I used to fill the system so I figured a larger circulator would do the trick. I swapped in a Taco 007 and still no cigar, although I did see a reading of .1 gpm flow. And now (problem numero dos) my utility pump trick would not work consistently. It would start fine, showing a flow rate of about 1 gpm but over the course of about three minutes the flow rate would drop below the .5 gpm necessary to keep the heater on. And ... I never saw an air free return of fluid to my transfer bucket, even though any slight leaks in any connections were minuscule weeps.
I temporarily bypassed the heater to check the integrity of the loops and system board and saw flow rates of .4 gpm with the Taco and 1.5 gpm with the utility pump, as well as a nice air free fluid flow.
So, while my initial thought is to add another circulator on the return side of the loop to provide more flow, I'm unsure as to what is causing that drop in flow rate and air intake when the heater is running.
I would be so appreciative of any advice!



  • STEVEusaPA
    STEVEusaPA Member Posts: 6,506
    First of all, why 75% glycol? North Pole or Antartica?
    None of your photos come thru. You can post them on here directly.
    I don't think that Ecotemp is going to work.
  • DZoro
    DZoro Member Posts: 1,048
    I couldn't download the pic.
    A few things,
    1-That's a water heater (very high head, wrong application)
    2-0011 pump (with P/S piping)
    3-Probably very little to no antifreeze (makes pump "slip")
    4-Must be primary secondary piped
    5-Really need a boiler for this

  • Jamie Hall
    Jamie Hall Member Posts: 23,276
    You have answered your own questions, but you may not realise it: with the water heater out of the loop, you get adequate flow. With it in the loop, practically no flow. As @DZoro said, an on demand water heater is the wrong appliance for this application. It does not seem to be commonly appreciated that to get the small size and rapid temperature rise needed in on demand water heaters that the head loss through them will be high -- typically on the order of 60 feet at 2 gallons per minute. This is acceptable in a hot water application, as the incoming domestic water pressure is almost always greater than that, and the outlet pressure is close to atmospheric.

    Therefore... if you insist on using an on demand water heater, you really do need to use primary/secondary, and the pump for the water heater must be capable of providing the flow required at that pressure drop -- which is not going to be a typical heating circulator. Further, it must be piped very carefully to avoid low pressures: it must pump into the water heater, and the expansion tank must be close to the inlet of the pump, and on that circuit.

    Or just use a boiler intended as a boiler...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Gordy
    Gordy Member Posts: 9,546
    edited December 2018
    Primary secondary use a grundfos 26-99 on the primary, or boiler loop, and the 007 on the secondary loop since you already have it.

    Primary secondary piping allows the boiler to have the high head, and flow rate it needs, and the smaller pump, and less flow rate the loops need with out interference with the two loops flowing.

    30% glycol mix max is all you need also. Glycol reduces pump efficiency, and decreases btu transfer.
  • Gordy
    Gordy Member Posts: 9,546
    Also that tankless says not to be used for radiant heating applications, but for the price may as well, but it won’t last long.