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expansion tank sizing with pex

Jake Timmerman
Jake Timmerman Member Posts: 10
in THE MAIN WALL
When sizing an expansion tank for a staple up type radiant system using pex, should I use the standard method of sizing of that tank? Or does the natural expanding properties of the pex-a pipe have an effect on the size of the tank. For example, would a system that holds 150 gallons in an all copper pipe job use the same size tank as a system that holds 150 gallons in mostly pex thats free to expand [not in concrete]?

Comments

  • Mark Eatherton1
    Mark Eatherton1 Member Posts: 2,542
    Don't mess with mother nature...

    Jake, technically, you could reduce the size of your expansion tank based on the free expansion of PEX.

    I know of one contractor in Evergreen, who shall remain nameless, who WAS installing staple up PEX with NO expansion tanks AT ALL. 'Course, this same contractor also USE to do combination potable water/space heating systems. The county AHJ's put the kaibosh to that practice.

    His customers always complained about never being able to get a cold drink of water too...

    Stick with proven principles, and avoid conflict resolution...

    As soon as you state that you do PEX staple up with a smaller or no expansion tank at all, some guy who puts PEX in concrete is going to try the same thing, and it WON'T work.

    Besides, the price differential between a #30 tank and a # 60 tank is so negligable... And in reality, the possibility of getting every linear foot of tubing to the maximum temperature is NIL. The sizing charts are already conservative enough when it comes to room for error.

    There is no right way to do things wrong...

    ME
  • DaveGateway
    DaveGateway Member Posts: 568
    expansion tank

    Jake,
    I didn't have an expansion tank for 2 yrs. This is mentioned in Dans' book "Hydronic Radiant Heating" on pg.117 It almost worked for me, but got fed up with pressure fluxuations & 2 wks ago I put on a small tank. It may have worked if I didn't have 660' of 1/2" copper pipe under 1 room! The copper makes no noise, as it slides in plastic bushings.
    BP
  • hr
    hr Member Posts: 6,106
    Forgive me for I have sinned !

    I have a few of my small low temperature 6 gallon electric water heater radiants running without expansion tanks. The entire one loop systems contains less than 10 gallons of water total.

    I have filled them to 10-12psi at say 50° water. They run up to around 25-28 psi when they reach 130° setpoint. The T&P installed in the tanks protects the system to 150 psi at 210°. On one I added a 45 psi B&G secondary relief.

    I just had to see how it would work :)

    Keep in mind DHW recirc pumps run without expansion tanks, often. plenty of empty second homes work that way without anyone using DHW for months.

    Although I tend to agree with ME for the cost of a small expansion tank, is it worth it??

    hot rod

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