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.

Replaced my expansion tank with a DHW version- do I need to swap out?

Bucky
Bucky Member Posts: 47
Hi all, well, it was a Saturday afternoon, and here I was with a shot expansion tank. All the supply houses closed at noon. The only thing I could find at a Big Box store was a potable water version made for DHW. So, one 1/2-to-3/4 adapter later, that's what is hooked up to my boiler now to effect The Point of No Pressure Change.
Many many folks say that this is no good for hydronic heat- so I'm looking for confirmation here. Of course, I was able to bleed it down to 15PSI for my system. It's rated for 200° F. My boiler limit is set to 180°F. So should I make it a priority to swap this out for the right thing, or is it something that I should wait for it to fail- possibly many years down the line? Thanks!

p.s. Here's what I installed: https://www.homedepot.com/p/Everbilt-4-5-gal-Thermal-Expansion-Tank-EF-TET-4T/304122098

Comments

  • Dave Carpentier
    Dave Carpentier Member Posts: 109
    Thats pretty close to the stated "max" on a bigbox low-bid supply item , playing a fairly critical role.

    20 years into my boiler system, the gate valves from HD are leaking from the stem. The supply-house valves are all fine.

    Imho, swap it out before next winter.
    30+ yrs in telecom outside plant.
    Currently in building maintenance.
  • hot_rod
    hot_rod Member Posts: 16,118
    Amtrol claims they use the same butyl blend for the diaphragm and the  DHW tanks can be used on Hydronics. It is a coated tank with a stainless nipple, in theory it should outlast the plain steel version?

    I don’t think they build special tanks for the consumer stores? Perhaps different label or packaging

    Correct sizing, correct pre charge, the best air removal, and good fluid quality are what help them last.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    EdTheHeaterManGGrossmattmia2Rich_49
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 2,983
    Keep the one you have until it fails. Just remember that you can not properly adjust the tank air pressure if it is connected to another pressurized system. If you have 3 PSI charge in the tank and it is connected to a system that is pressurized to 15 PSI, the tank pressure reading will read 15 PSI. That is because the water (or gas) pressure will enter the tank and compress the 3 psi charge to equal the pressure of the higher pressure system (illustration to follow)
    Edward Young
    Retired HVAC Contractor from So. Jersey.
    Services first oil burner at age 16
    P/T trainer for EH-CC.org
    Zman
  • Dave Carpentier
    Dave Carpentier Member Posts: 109
    hot_rod said:

    I don’t think they build special tanks for the consumer stores? Perhaps different label or packaging

    I dunno about pressure tanks specifically, but for other things apparently - it's all over the map.
    An off-brand could be the same tank as on-brand but diff labels or package, or maybe failed some quality check like rough seams. It could be the same maker but different components or accessories, cheaper adhesives etc etc. Or, it could be a different maker (good or bad).

    I guess the prudent use of a tank like that would be to check the air-side pressure at least annually (ie, not "set and forget" like many do).
    30+ yrs in telecom outside plant.
    Currently in building maintenance.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 2,983
    edited May 13
    Here is the illustration:



    Edward Young
    Retired HVAC Contractor from So. Jersey.
    Services first oil burner at age 16
    P/T trainer for EH-CC.org
  • hot_rod
    hot_rod Member Posts: 16,118

    Here is the illustration:



    I'm not sure that orientation is necessarily wrong, or bad? If the tank is supported with a bracket, stress on the nipple is a non issue.

    Seems all the Euro brands show any install position, up, down, or sideways as acceptable.

    Amtrol shows how to properly support a horizontal Extrol tank in their engineering guide.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    EdTheHeaterManRich_49
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 2,983
    edited May 13
    I think you pointed out the diagram had this issue in 2020
    hot_rod said:

    Great graphic @EdTheHeaterMan , mind if I use it? Interesting too that it shows the tank installed nipple down!
    I've always heard that traps moist air above the diaphragm and shortens the life expectancy?

    ... so I updated it. And yes, You can still use it.

    BTW... who uses European tanks anyway?
    Edward Young
    Retired HVAC Contractor from So. Jersey.
    Services first oil burner at age 16
    P/T trainer for EH-CC.org
  • Dave Carpentier
    Dave Carpentier Member Posts: 109
    Ed, your pic got me wondering something.
    I'll acknowledge that this might be a stupid question, and just go for it anyhow lol.

    The OPs tank was meant for a nominal 50psi pressure, and then would have a nominal 50psi of water on the other side, resulting in a water to air volume ratio in the tank.
    If he uses it at 15psi, with 15psi of boiler water on the other side, is the water to air volume ratio the same ?

    Would it matter anyhow ?
    30+ yrs in telecom outside plant.
    Currently in building maintenance.
  • hot_rod
    hot_rod Member Posts: 16,118
    If the air is at 50 psi, and the fill pressure is 50 psi, both seeing the same diaphragm size, no fluid is in the tank. Heating and expansion will add fluid into the tank.

    An excellent read on expansion tanks.

    Even a formula to calculate how much a large plain steel rank will expand and allow addition acceptance volume as it heats!

    It may still be available online at Amtrol.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 2,983
    edited May 13

    Ed, your pic got me wondering something.
    I'll acknowledge that this might be a stupid question, and just go for it anyhow lol.

    "There no stupid questions... there are just stupid people asking questions"

    I'm not sure if I Quoted that correctly. but close enough. LOL

    @Dave Carpentier The design parameters of the tank will not change the actual physics of air and water pressure. If a tank rated for a boiler system is rated for max pressure or max temperature that is different from the previous tank, the actual operation of the devise will not change. As long as the maxumum ratings are not exceeded, the device will function properly. I have done this in a pinch, BUT... I MARKED THE LABLE, from Factory charge 50 PSI to "adjusted to 12PSI"

    What was there:


    What was used to replace it:


    Can use this one also but set limit to 180° on aquastat.

    The max pressure is higher in the rating of the optional tanks, but as long as you still have a 30PSI relief valve, you are nowhere near the max setting. The operating temperature is higher on the original tank. as long as you don't get anywhere close to that temperature, you will be fine.

    BUT....

    There are some poorly (cheaply) designed systems with insufficient radiation, that a service tech may have adjusted the high limit to say 220°. this fixes the insufficient heat service call for those few days where the temperature drops below design temp (every 5 years or so). When this control starts to go out of calibration in 10 years and the boiler overheats from time to time (regularly), then that tank may fail as a result of operation too close to the Max Temp.

    Edward Young
    Retired HVAC Contractor from So. Jersey.
    Services first oil burner at age 16
    P/T trainer for EH-CC.org
  • Dave Carpentier
    Dave Carpentier Member Posts: 109
    No fluid is in the tank (when tank psi and water psi are equal) ?

    This is way different than the water pressure tank on my well, it contains water that is used to prevent the well pump from cycling too much. Im not entirely sure if it's a membrane or a bladder bag.
    On a properly working (non leaking) boiler expansion tank, if you close off the ball valve to the system and then disconnect the tank.. no water comes out ?
    30+ yrs in telecom outside plant.
    Currently in building maintenance.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 2,983
    edited May 14
    If you have 15 PSI pressure in the system and you close the valve off, then you unscrew the tank off the valve you may get water or you may not.  It all depends on the pre-charged pressure (empty pressure) of the tank.  For example if you empty charge is about 6 PSI and you unscrew that tank you will get wet.  The amount of water in the tank needed to compress 6 PSI to 15 PSI is significant. 

    If however you have the tank charger to say 20 PSI and you remove it from a system with only 15 PSI then there will be no water in the tank

    Does that answer your question?
    Edward Young
    Retired HVAC Contractor from So. Jersey.
    Services first oil burner at age 16
    P/T trainer for EH-CC.org
  • Bucky
    Bucky Member Posts: 47

    No fluid is in the tank (when tank psi and water psi are equal) ?

    This is way different than the water pressure tank on my well, it contains water that is used to prevent the well pump from cycling too much. Im not entirely sure if it's a membrane or a bladder bag.
    On a properly working (non leaking) boiler expansion tank, if you close off the ball valve to the system and then disconnect the tank.. no water comes out ?

    You're talking about a "Pressure" tank in an open-loop system there. Although they have some similar characteristics, the plumbing and method of operation is totally different. A well tank is made to store fresh water pumped up from the well so you have plenty of water on the ready. When the tank reaches the desired pressure, it turns the well pump off, and then when outlets are opened water flows from the pressurized tank to the faucet, toilet, shower, etc.
    In a closed-loop hydronic system, the expansion tank is there to absorb excess water when the water gets hot (water expands when heated, as you know) to prevent the pressure on the system from getting too high. An expansion tank on an open-loop system (DHW) works the same way as the latter and is not the same as a "pressure tank" like in your well application.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 2,983
    edited May 14
    The DHW expansion tank, the well water tank and the heating boiler closed system expansion tank are all the same design. Air pressure on one side of a membrane and water under pressure on the other side of the membrane.  There is minor differences in the end product like interior coating and membrane temperature tolerance, but for the most part you can use any of them for a lower temperature closed heating system.   But I recommend using the proper item for the job whenever possible.  

    I would not use the closed system expansion tank on potable water systems.  The interior is not properly coated for that and will fail rather quickly 
    Edward Young
    Retired HVAC Contractor from So. Jersey.
    Services first oil burner at age 16
    P/T trainer for EH-CC.org
  • hot_rod
    hot_rod Member Posts: 16,118
    Jody was a trainer at Caleffi for a bit, he worked for Amtrol for years also. He did a Caleffi webinar for us on expansion tanks. Here are a few slides. Find similar slides at Zilmet showing no fluid in the tank when air charge and fill pressure match.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Dave Carpentier
    Dave Carpentier Member Posts: 109
    Ah.. that was my stumble here then. I didnt know the internal diff between a pressure tank and an expansion tank. I always assumed an expansion tank contained water when the set air and set water pressures were equal.
    Thanks for allowing me to sidetrack guys, it's always good to learn.
    30+ yrs in telecom outside plant.
    Currently in building maintenance.