How to plumb a compression tank

pblackwood

I wanted to raise my old black steel heating pipes in my basement to creat more headroom. As a result I decided to strip out ALL my heating pipes and everything hocked up to my oil furnace and start from scratch. I’m going to install a Pex manifold and run pex to my cast iron radiators. The only item I figure I might try to salvage is the large compression tank installed in the joust space above my furnace. My question is how should I plumb the compression tank to my furnace, and do I need to install a separate air separator or will the compression tank do double duty?

My boiler mechanic said to install a tee on the 3/4” nipple located at the top of the furnace. Install the pressure relief valve to one part of the tee and run pipe directly to the compression tank from the other part of the tee. He also said to install a shut off valve in the pipe leading to the compression tank and to install a drain valve in the second hole of the compression tank. He also said there was no need for an. air separatorNot sure if the boiler mechanic advice is sound or merely what he always does without knowing if it’s correct or not. Any advice?

Jamie Hall

Your boiler mechanic's advice is fundamentally sound. However, there are two fittings available, one of which will make life MUCH easier down the road, and the other of which is useful but not as much a requirement.

The first the called an "Airtrol Tank Fitting" and it is connected to the compression tank and the pipe to the rest of the system is connected to it, rather than running directly from the system into the tank. This fitting helps to maintain the correct air cushion in the compression tank. The other fitting is an "Airtrol Boiler Fitting" and is used at the other end of that pipe, at the boiler, and acts to more effectively collect air.

That said, piped correctly a compression tank will be OK without either fitting — but you do need to check the water level in the tank from time to time.

No other air separator of any kind can be on the system. If there is, the compression tank will water log, guaranteed, and the whole system won't work.

hot_rod

I would install a good microbubble air sep, like a Caleffi Discal or others, installed at the boiler supply out connection.

The Airtrol tank fitting, pipe it like they show in this Airtrol schematic.

leonz

https://forum.heatinghelp.com/discussion/197643/how-to-plumb-a-compression-tank

First things first, is your current boiler a steam and hot water boiler or a hot water boiler? Do you have a low water cut off installed in the boilers water vessel/steam chest?, If not you need one to bring it up to code.

Do you know if the radiators have orifice discs in them to control and slow the water flow?

You need black iron pipe to create a new pump module.

Do you know if your boiler has a cast in place air baffle????????

Is this steel compression tank a galvanized steel tank or a domed steel compression tank that has thicker steel and a sight glass level gauge that is plumbed into the end of the tank???

The fellow is wrong in telling you do not need an air separator. You can use an air scoop that will be connected to the Airtrol valve by using the tapping that is in the top the air scoop.

Mr. Holohan's book PUMPING AWAY shows you how to do this using one of his pump modules and how to do it simply with less work.

If the circulator is plumbed into the boiler sump it the piping is slightly different but it will still strip air out of the water flow.

Starting at the boiler riser tapping you use the same size pipe as the boiler riser tapping(THIS IS A MUST DO ITEM).

Now you install a long pipe nipple to come out of the riser tapping-the longer the better. After the pipe nipple

you use a Tee the same size as the riser pipe nipple. After that you place a reducer bushing in the top of the Tee and then a boiler drain in the top of the Tee; This lets you remove air quickly and also use the Furnox boiler treatment by attaching the can of Furnox to the male thread of the boiler drain then open the boiler drain valve and then the Furnox can and the air charge in the Furnox can pushes the boiler treatment into the boiler.

The right angle tapping of this Tee must be the same size as the sir scoop.

The pipe nipple needs to be at least 18 inches long to allow the most trapped air in the system to be captured by the air scoop and sent to the Airtrol valve that will rise into the steel compression tank.

The riser tapping out of the air scoop must be 3/4 N.P.T. to allow the riser pipe to connect with the airtrol valve at the far end of the steel compression tank.

The connection from the air scoop to the far end of the steel compression tank should have a gradual slope to the Airtrol valve to allow the air bubbles to rise gradually into the Airtrol valve.

The tapping on the other end of the air scoop goes to your header pipe

I cannot help you with the location of the relief valve but they are located in the top or side or end of the boiler in a separate tapping.

Please purchase a copy of the well written book "PUMPING AWAY" from the Heating Help Bookstore Page this book will help you install your new piping simply and create a system that is not affected by trapped air bubbles that will help eliminate slugs of air preventing water flow and microbubbles. By purchasing this excellent book on heating from the Heating Help Bookstore you will be supporting the author of the book Mr. Holohan and the Heating Help Forum.

pblackwood

The compression tank, 12x36” horizontal galvanized steel tank with no glass gauges, is original to the house and it has a manufacture date of 1948. The original oil fired boiler has been replaced a few times, the last being in 2005. It’s a relatively “modern” boiler, but not one of those high tech condensing ones. 1-1/4” supply and return nibbles come out of the boiler, plus two 3/4” nipples, one on the top of the boiler and one at the bottom. I can’t say whether or not there is a low-water cut-off device installed. Not even sure where to look for it.

I wasn’t originally going to install a boiler drain at the top of the boiler but will after hearing your idea for quick manual air venting and facilitating the input of furnace cleaning fluid, I just might do that.

I understand the air scope is connected into the 1-1/4” pipe coming out of the boiler, with a 18” horizontal nipple located between the boiler and the air scoop. If I wanted to substitute an air scoop with an air separator (I want to avoid the 18” horizontal run if I can) can I do away with the 18” long horizontal nipple and come out of the boiler directly into the air separator and then connect the circulator on the other side of the separator? Where do I hook up the compression tank pipe? Do I hook it up to the 3/4” nipple located at the top of my boiler, as described in my initial posting? Lastly, I understand you must not have perfectly level horizontal piping running between your boiler and your compression tank, but can the pipe actually be perfectly vertical….running straight up from the boiler into the Airtrol valve?

leonz

I do not think it will work unless unless the boiler has a cast in place air baffle.

You need to have a run of pipe from the Tee to the air scoop to assure the air bubbles will be captured and diverted to the air scoop slowly and then captured by the upper part of the casting to be diverted to the steel compression tank.

If you can find the name of the boiler and tell us what brand it is and the model number we can help you more effectively with your piping

hot_rod

With an air separator

Screenshot 2024-08-18 at 9.54.56 AM.png

Screenshot 2024-08-18 at 9.54.47 AM.png

Screenshot 2024-08-18 at 9.54.38 AM.png

you do not need 18" of straight pipe. Locate it close to the boiler. Either a vertical or horizontal version.

A 3/8 copper tube up to a connection on top of the tank, tank Airtrol fitting optional.

This shows a Caleffi air/ dirt/ mag separator with a fitting adapter NA12004 to give you 1/4 NPT thread. Should be a bottom connection on the tank for a drain?

Personally, I would get rid of the 76 year old compression tank, a diaphragm tank will speed up and clean up the upgrade. The tank attaches to the bottom of a sep or a tee near the pump

Jamie Hall

Two miscellaneous comments. Having a microbubble separator might — or might not — be a good idea. If there is to be one, though it absolutely must be plumbed in such a way that any air that it captures is directed to the compression tank Not vented to the atmosphere. Therefore, among other things, it must be connected after any circulation pump, with the compression tank connected before the pump. Otherwise it's just an expensive pipe coupling.

The second is that the pipe from the system or boiler or airtrol or whatever to the tank airtrol fitting can be perfectly vertical. Any near horizontal runs much pitch up towards the tank, and should be kept as short as possible.

None of this is rocket science. The idea is to capture any and all of the air in the system and direct it to the compression tank.

pblackwood

My boiler is a Kerr Control Saturn boiler. The boiler’s manual can be downloaded at https://kerrcontrols.ca/wp-content/uploads/2019/04/SATURN-STEEL-BOILER-OIL-MANUAL.pdf The manual makes no reference to an air baffle inside so I assume it doesn’t have that feature.

So…. what I gather then is that I essentially have three options. (1) find a way to install a 18” horizontal nipple and therefore install an air scoop, which in turn is connected to my compression tank. (2) install an air separator that has a take-off so I can pipe any released air directly into the top of my compression tank and not released into the atmosphere; or (3) abandon my compression tank altogether and instead install an air separator and connect it to a diaphragm type tank. If I end up going with option 3, then the question is what size tank do I get if my compression tank was a 12x36”?

pblackwood

As a added bit of information, with the nozzle currently installed on the burner, my furnace has a rated output of 120,000 BTUs

EBEBRATT-Ed

I would do as @hot_rod mentioned. Ditch the compression tank and put in a bladder tank. Keep in mind with a compression tank you can use no air vents.

Jamie Hall

If you abandon the compression tank and use a bladder tank, the air separator is vented to the atmosphere — not the tank.

Charts for sizing are on many manufacturer's web sites. The size would depend on the volume of your system and the maximum temperature rise.

And keep in mind that a properly plumbed compression tank will last for a century or more. A bladder tank? Might be looking at 10 to 15 years…

pblackwood

Thanks for all the good advice.

Jamie, if I was to keep the compression tank and use an air separator that vents via a pipe to the compression tank, then I’m a bit confused regarding your comment “it must be connected after any circulation pump, with the compression tank connected before the pump”. Could you elaborate a bit? Sorry for being slow…lol! For clarity my circulator is going to be installed on the supply side of my boiler.

hot_rod

https://forum.heatinghelp.com/discussion/comment/1808227#Comment_1808227

a number 30 expansion tank should be plenty. All the manufacturers have sizers on their website to confirm

Amtrol, Wessel, Zilmet, etc

Id get that 100 year life expectancy in writing, not that a typical owner plans in being around in a century😗

If it is not properly piped it can be a big heat loss and keeping air going in and out of the system

Price the components to do a compression tank properly to help determine how much you want to invest in that tank

leonz

https://forum.heatinghelp.com/discussion/comment/1808227#Comment_1808227

First things first, you need to call the manufacturer of your boiler on Monday to obtain the piping diagram for your Canadian boiler to know what tapping is where and for what and the proper location for the pressure relief valve.

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There are charts that allow you to size a bladder tank according to the number of stories your house is and the equivalent 2/3 water volume in your steel compression tank and the total amount of water in your heating system.

Before you do anything, purchase a copy of PUMPING AWAY and a copy of CLASSIC HYDRONICS from the Heating Help Bookstore PLEASE.

The weigh of the water in the steel compression tank and the weight of the water in your radiators allows your system to work more easily because it has water and mass above it is pushing the total weight of the air bubble free water into the boiler.

Automatic air vents go bad and will leak, been there done that never again, nor do I miss crawling around on bad knees trying to bleed the 3/4" fin tube baseboard in my home.

The bladder tank can become out of balance with a loss of pressure if the bladder fails and you will lose your point of pressure change because the system becomes waterlogged.

You do not have that issue with a compression tank as all the air in the system is trapped in the upper third of the compression tank and it stays there AND you do not have to have to leave the water feed valve open.

If you order these 2 books they explain how your system works in great detail.

EdTheHeaterMan

For reference, I have beed doing this for over 40 years, Early in my career, I was lucky enough to have some very good teachers. But I did some things wrong because I didn't know WHY I did them. I was just doing what I was told. Once I understood WHY… I never made those mistakes again. Locating the expansion tank is all about understanding how they work in conjunction with the rest of the system. To get it right, you don't need to understand everything, You just need to follow the instructions of someone who does. But if you misunderstand what the instructions are, then you can get it wrong. However, that does not mean it won't work. It may work just fine on your system. It just won't work on everyones system.

Know this "The compression tank or Bladder tank are there for only one reason. To accept the increase in water volume when the water expands when heated. as the water cools, the air pressure in the tank will push the water back into the system as the water volume shrinks when cooling down after the heating cycle is completed.

Weather you need to vent the air to the atmosphere or vent the air to the tank depends on the type of tank. with the diaphragm or bladder tank the air never leaves the tank so you want to vent the system air to the atmosphere. When using a compression tank (non bladder) the air in the system should be directed to the tank and you should never use air vents to the atmosphere.

As to the best location, it is on the supply pipe just between the boiler outlet and the circulator pump. The book "Pumping Away" has the reason WHY.

leonz

https://forum.heatinghelp.com/discussion/comment/1808222#Comment_1808222

Hot Rod and I are at polar opposites as far as air control and elimination of air bubbles are managed as a science.

1. you have a steel compression tank that has hung in the ceiling joists of the basement since the home was built doing its job of trapping and holding air bubbles to keep your hot water heating system in balance and to provide thermal mass for heating your home.

An Airtrol valve has one moving part which is the drain valve that you open with a small box end wrench to allow the proper amount of water to drain after the steel compression tank is filled and at the same time dumping the excess water out of the tank through the dip tube to assure it has the 1/3 air blanket volume and 2/3 water volume to assure the system is balanced. A Drain-o-Tank valve serves the same purpose.

Please purchase the 2 well written books on heating I have mentioned so you will be more informed and understand the means and methodology of air control in a hydronic heating system.

I hope you have called the manufacturer of your boiler to obtain a schematic diagram to employ a pump module to aid in making your boiler more efficient pumping away from the boiler and at the same time strip it of air bubbles.

hot_rod

https://forum.heatinghelp.com/discussion/comment/1808227#Comment_1808227

https://forum.heatinghelp.com/discussion/comment/1808328#Comment_1808328

The compression tank is an air management system.
The diaphragm tank is an air elimination system

jumper

If you vent to atmosphere, preferably at highest point in system, how often will tank get water logged? And even when I vent to tank doesn't it eventually fill with water?

leonz

The water in the open to air expansion tank is still open to atmosphere. If you leave the fill valve open it will fill up and eventually flow out of the vent pipe on to the roof, it does not become waterlogged as it is a gravity flow system.