Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Looking for make up water options on closed loop radiant system

garya Member Posts: 7
I am looking for options for makeup water for a radiant floor heating system in a shop in Seattle WA, with no water.
System has 3 zones with 3 - 230' loops of 1/2"pex, 2 zones in concrete on 1st floor, 1 zone between joists on second floor, using a 75gallon domestic hot water heater.
System will run fairly constantly to establish a core room temperature around 55 degrees with forced air heat to bring room up to working temperature when shop is in use.
Make up reservoirs I have found are cost prohibitive. My initial plan is to use a #30 4.4gallon expansion tank which should be oversized enough to buffer, then monitor manually. I am not sure how to monitor the water level other than monitoring pressure and occasionally topping off to the design pressure (15psi) with a hose.
Any help or direction appreciated.


  • Zman
    Zman Member Posts: 7,569
    If you are just running water, most folks just install one of these.

    If you are running glycol or don't have water available, Axiom makes a nice little unit. https://www.supplyhouse.com/Axiom-MF200-MF200-PRESSURE-PAL-Hydronic-Mini-System-Feeder-6-Gallon
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • GroundUp
    GroundUp Member Posts: 1,907
    The Axiom units are very nice. My question is why do you need makeup water? Fix the leak and be done with it
  • garya
    garya Member Posts: 7
    The Axiom system would be the proper thing especially if installed on someone else's site but this is my place so can I can monitor. I don't forsee a leak so was hopping once the air worked its way out the expansion tank would be enough buffer. System has 75 gallon water heater with 35 gallons in the lines (110g) working range of 50-180 degrees at 12-27psi. The Taco calculator calls for expansion of around 3gallons but other calculators call for 9gallons? But using six #30 Extrol expansion tanks at 2.5g acceptance volume each must be overkill just judging from the installed systems I have worked on. Using the 3g expansion it seems like two #30 tanks gives a couple gallon buffer for make up water.
  • GroundUp
    GroundUp Member Posts: 1,907
    edited December 2018
    Why would the system ever be at 50 or 180 degrees and why would pressure vary from 12 to 27? I think you're overthinking this but underthinking the idea of makeup water. Let's say temp drops and the water mass contracts, where you would consider adding water. Then it heats up and expands, now you've got too much water. If it's not leaking, there is no need for makeup water. Running radiant floor temps of usually 80-120 depending on system, a single 30# XT will be sufficient for 110 gallons set at 12 PSI cold static and will stay at 12 PSI forever. Fill it once and set the pressure, it's all done. No makeup, one simple 30# XT, nothing further. Radiant is not complicated, no need to make it that way
  • garya
    garya Member Posts: 7
    The reason I was using the 50-180degrees and 12-27psi is because that is what the tank sizing charts called for.
    The temperature of the 85 gallons of water out of the slab gets down to 45 degrees when the shop is not heated then up to about 150 degrees when the water heater is on. The 25gallons in pex slab should range from 50-120.
    Different charts call for different tanks sizes; Zilmet calls for 6 gallons, Taco calls for 2gallons, Amtrol 15#. So was confused in sizing, thanks for the help sounds like a 30# is plenty, yes i do have an over thinking problem. Thanks for the help.
  • hot_rod
    hot_rod Member Posts: 22,120
    Once the system is air free, and leak free it should not need additional fill? Amtrol and Wessel have expansion tank sizers based on system fluid capacity.

    Here is a simple fill system. A Webstone valve works also, with a single hose connection.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • garya
    garya Member Posts: 7
    Thanks for the input GroundUP and Zman also appreciat all your webinars hot rod_7.