Expansion tank location

[NCPABill]

Would it cause any problem to install an expansion tank on a riser from a hot water storage tank? I will be installing my tank and one end will reside under my stairs. I'd like to install an expansion tank up under the steps, but I won't have any lines in that area. I would install a riser off of the top of the tank, 90 to horizontal, and tee down into the top of the tank?

What do you all think?

Thanks for your time,

Bill

 

[NCPABill]

I'm not sure if I should be proud to have posted a question which has stumped the collected knowledge of hearth.com or if I should be embarrassed to have posted a question that is so simple that I shouldn't have asked it!

I think that it would be fine for this tank to be on a separate line, but I'd like to know that I'm right from you that, in my opinion, have much more knowledge than I.

Thanks,

Bill

 

[Clarkbug]

I dont know if Im the right guy to answer, since really Im just taking a guess as well....

I would think as long as you tee down into your expansion tank, with an air vent on that tee, you would be OK.

A sketch in this case I think would help out considerably, even if its just something simple. That may get you more responses than just mine! (plus its vacation time, or people are out cutting wood!)

 

[woodsmaster]

From what I understand the expanshion tank or at least the line to the tank should be located just before the circulator. That being said people often have them in different places without trouble.

 

[kevindauch]

Typically you install the expansion tank on the low pressure side, right before the first circulator pump. That way the pump is not rising the pressure to the tank. You can pipe it away from the low pressure side. I'm assuming that you are putting an air separator there. Then plumb it to the expansion tank. A pic/schematic would be nice.

 

[Frozen Canuck]

Have a look through the stickies "simplest pressurized storage system" & "primary secondary piping for boilers" there should be something that applies to your situation, or that you can use as a guide. Either way plenty of necessary reading in those stickies.

 

[NCPABill]

Thanks for the responses. I knew the answer was here!
I need 22+ gallons of expansion for the new stove and 500 gallon tank, and want to be able to close out the tank itself if ever need be, so I think I'd like to break the expansion into one for the boiler and one for the storage tank. This would be a simple vertical pipe up, plumbed into an expansion tank, with some way to bleed air out of the system (hose bib plus coin vent?).

I have attached some form of sketch. I'm sorry in advance if I hurt anyone's eyes!

Bill

 

[Morgan]

Typically you install the expansion tank on the low pressure side, right before the first circulator pump. That way the pump is not rising the pressure to the tank. You can pipe it away from the low pressure side. I'm assuming that you are putting an air separator there. Then plumb it to the expansion tank. A pic/schematic would be nice.

A pump cannot raise the pressure to the expansion tank, it`s just simply not possible. Good plumbing practices will have you `pump away`from your expansion tank connection. This is also the point you want your feed water to connect to the system. This is the one point in your entire plumbing system that the pump cannot cause a pressure change. If you pump towards the expansion take you subtract the pumps differential from the system fill pressure(which could cause problems). If you pump away from the expansion tank you add the pumps differential to the system fill pressure, which is ideal. You will want your air eliminator/scoop (I recommend a microbubbler air eliminator) installed at or before the expansion tank, as this is the point of lowest pressure in your entire system and will help to remove air.

 

[in hot water]

A couple tips, yes you can remote mount the expansion tank. If you use multiple tanks, tee them in at the same location. The best location is the suction side of the system pump. If you have multiple pumps selecting the best location is trickier.

Always mount the tank with the connection nipple pointing up to prevent any O2 from corroding the thin steel tank. Most tanks are bladder tanks and contain the fluid in the steel vessel. there are some bag type that contain the liquid inside the bladder membrane. With the fluid in the steel part of the tank it can cool better, this is more critical on solar piping where the tank can see a shot of temperatures in excess of 300F after a stagnation condition.

Remote mounting the tank can add the benefit of cooling the liquid the tank sees during heating, to prevent reducing the capacity due to the warmed fluid.

If you mount the tank below the connection point a fair distance remember the static pressure increases and the tanks expansion volume will be slightly decreased. Many installers build a unistrut rack system above the boiler to mount multiple small tanks. A base mounted tank is another option, it's connection point is usually at the bottom of the tank. Installers often use pex tube to pipe to remote tanks.

Check the air charge in the tank BEFORE you fill and pressurize the system. It should be pressurized to within a few pounds of what you intend to pressurize the system to, generally 12- 15 psi for a one or two story home. You want a few pounds static pressure at the highest point in the piping system.

If you do install an isolation valve on the tank(s) I'd remove the handle so it does not get turned off by mistake. There are some special expansion tank valves on the market. Some are dual checks, some have a lockable shut off handle.

Here is a drawing from Modern Hydronic Heating 3rd edition. A great book to own if you want to learn the fine points of hydronic design and piping www.hydronicpros.com The drawing clearly shows how pumping away from the expansion tank connection point behaves in the piping and pressure.

hr

 

[NCPABill]

Thanks all, especially"in hot water" for the graphic. I'll rethink things.

Bill