Home>Discussions>INSULATION & HVAC>Replace compression tank w/ expansion tank?
5 posts / 0 new
Last post
Replace compression tank w/ expansion tank?

We have a 1954 ranch house with hot water baseboard heating. The system is comprised of three zones with the heating pipes running under the slab of the house to each zone. The water is heated with an older Weil-McLain CGM boiler which is configured with the recirculating pump pumping through the boiler. A smaller pipe comes out the top of the boiler to the make-up connection and up to a steel compression tank. I've attached pictures to help illustrate.

I've had numerous problems with removing air from the system. I'm thinking about replacing the compression tank with an expansion tank and installing a B&G EASB-JR air separator. My question is how this should be configured? My thought is to cut the pipe running to the compression tank, north of the make-up connection, and install the auto air vent at this point (which is currently located at the suction side of the pump). I would then install an expansion tank vertically where the auto air vent was and install the air separator (with built-in auto air vent) in the horizontal run of 1" pipe before it turns down to the pump.

Are there any potential problems with this new configuration? Thanks in advance for any input or advice.

Re: Replace compression tank w/ expansion tank?

you can install the tank on the bottom of the air separator, usually with a nipple and a threaded ball valve. Have never used b&g always used spirovent, regardless they work much better than air scoops. Also depends if you the have room

Re: Replace compression tank w/ expansion tank?


I agree with Shaun---recommend you hang the
Extrol # 30 bladder-type expansion tank from a horiz. section of the 1" hot water supply pipe (the supply pipe usually comes out of the top of the boiler)---having the ET isolated from the main by a ball shut-off valve so the ET can be replaced (they fail occasionally---the ball valve allows an easy change of ET without draining the whole system).

A Spirovent or air scoop is installed next to it---sometimes the ET is hung w/shutoff from the bottom of the Air Scoop/Spirovent with a hydronic air vent at the top.

Ideally, the circ. pump should "pump away" from the ET so positive pressure is maintained throughout the piping circuit.

You will also have to install tiny bleeder valves on the baseboards, if not there now, especially the ones at the highest points in the house---the older system with the steel tank usually doesn't have these.

Will try to find photos of the components mentioned.

Re: Replace compression tank w/ expansion tank?

Thanks for the feedback.

I'll see if I can locate the tank off the bottom of the air separator, but the gas line to the boiler may make it problematic. Either way, I'll keep it on the suction side of the pump. I like the ball valve idea to help with repair in the future. Thanks.

Re: Replace compression tank w/ expansion tank?


The site below has a "typical" diagram of the piping arrangement for the Extrol #30---note it's not necessary to place each component EXACTLY as pictured---you could easily offset the ET and its piping with two short 1/2" sweated copper elbows if the gas pipe is in the way---I assume you can sweat (solder) copper tubing???

For example, many boilers have their circulator on the large RETURN pipe of the boiler, yet they work fine in practice---if this is how it is on your system, leave it where it is.

The setup I prefer is to put an AIR SCOOP ($20) as in the diagram on the horizontal part of the supply pipe coming out of the top of the boiler, with an Amtrol #700-C air vent, or a #67 MaidoMist air vent ($5 each) on top, then hang the Extrol ET #30 ($40) to the bottom of the air scoop with a 1/2" threaded fitting, then go to 1/2" copper tubing & a 1/2" sweat ball shutoff just above the ET, then a 1/2" threaded female fitting to accept the male 1/2" thread of the ET.

You'll do much better to go to a heating supply parts house (Yellow Pages:Heating Parts) rather than the big box stores---not only on price, but the counterman will know all these fittings by heart & get them for you quickly, without mistake---tell them you need a setup to install an Extrol 30 with a ball valve on a boiler---bring in a list with the items you need on paper with a little diagram.

A sturdy metal strap going up to the ceiling floor joist is recommended to support the ET at its screw-on connection or at the large horizontal supply pipe at the air scoop (if the ET internal bladder fails it fills with water & gets 30 lbs heavier & could put a strain on the piping).

The water supply on the diagram coming in near the base of the air scoop may be in a different position on your system---leave it where it is.

There may not be a flo-chek valve, system purge or backflow preventer on your system, as portrayed in the diagram.

There is also a Watts ET-30 (exactly the same ET) that has another diagram on the Watts website--to access the Watts site Google "Installation of a Watts Expansion Tank"--scroll down to "Non-Potable Systems" and click onto the boiler diagram at the right of the page.

For more piping diagrams of HW heating systems, Google "near boiler piping diagrams hot water heating systems" (without the quotes) or "near boiler piping diagrams for hydronic heating systems" (without the quotes).

This is a lot of work to complete in one day try to get just a certain amount done each day---start in the A.M. by shutting off & draining the system, soldering components, then filling the system, checking for leaks, & getting the heat back up before nite falls---don't try to do it all at once.


TV Listings

Find TV listings for This Old House and Ask This Old House in your area.