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domestic hot water thermometers

ChrisJ Member Posts: 15,921
Does anyone make a good clip on thermometer?

I want to monitor domestic HW temperature and would rather just clip these on the pipes in a few spots.

If not, what is typically used in this application?
Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment


  • Daveinscranton
    Daveinscranton Member Posts: 148
    I use cheap eBay digital thermometers. They are about 7 dollars. About 36” of lead to a probe that is 3/16 x 5/8 or so. F or C selection by removing a jumper (easy). Can run on battery or wall wart power supply. Tape them on with “sports tape” which was friction tape when I was growing up. When I set out 8 to check for consistency, they were within 0.8 degrees F at the most extreme spread. A bit of glass wool insulation on top of the sports tape seems to zero them if you are anal about it. I used them to read delta T for primary and secondary loops, exhaust pvc temp, intact pvc air temp, ambient temp inside the (Munchkin) plastic sealed boiler case. Helps me see what is going on for very little money. But then I also have valved manometers on gas pressure and differential pressure for air intake and exhaust. Works. Mostly to satisfy curiosity.
  • old_washer
    old_washer Member Posts: 4
    I’ve used 30 or so of these for a variety of projects involving solenoid valves, pump contactors, fan control, etc.

    I currently have 4 monitoring my boiler supply and return temps as well as DHW tank and supply temps. I’ve even used one in place of the indirect’s aquastat. (Good for old eyes...I can see them from across the basement.)

    They are quite accurate and amazingly inexpensive. Downside…they do require 120VAC to operate.

  • hot_rod
    hot_rod Member Posts: 22,482
    I like the Azel duel thermometers, shows temperature and ∆. Battery or 24VAC

    Got a VOM, or stick meter? Most have temperature heads available.

    3/4" copper? These Caleffi just stretch enough for 3/4", up to 120F however.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • mattmia2
    mattmia2 Member Posts: 9,962
    I bet a little thermal paste and picking a location with good flow goes a lot more toward accuracy than which specific thermometer you pick.
  • ratio
    ratio Member Posts: 3,701
    I like to instrument with K-type thermocouple wire. The wire's cheap, the terminations are cheap, the accuracy is adequate, and like @hot_rod said, many (trades oriented, I suppose) DMMs have a K-type input, either direct plug-in or via an adapter.

    The best part is that I take all the ends to one location, so I don't have to go running around to see everything. And if I ever do go all PLC on the thing, the Chinesium transducers are cheap too.