Heating System Expansion Tank Location
How to find & identify the expansion tank on hot water (hydronic) heating boiler systems

How to find the heating boiler expansion tank & how to identify the tyype of exansion tank installed on a building heating boiler.

This article series describes how to identify, inspect, install, repair, or service heating boiler expansion tanks: here we explain the function of expansion tanks on hot water (hydronic) heating systems.

We provide a heating system expansion tank Troubleshooting & Repair Guide.

Honey I Can't Find the Expansion Tank!

Article Series Contents

• ATTIC & ANTIQUE EXPANSION TANKS, HEATING
• FIND the EXPANSION TANK
  • EXPANSION TANKS in the Attic
  • EXPANSION TANKS in the Basement
  • REMOTE or OPEN EXPANSION TANKS on very old heating systems

What if I can't find the boiler expansion tank?

Don't feel bad. Heck sometimes we have trouble even finding the heating boiler!

Actually the heating boiler in our photo above sporting a six point buck has an expansion tank, it's hiding behind that small deer in the right center of the photos. A basement full of deer may be unusual, but basement clutter is not. Look with care.

But indeed, some older heating systems may not have an expansion tank in the basement at the heating boiler. What then?

Well you've got one, if it's a hot water heating system, but the expansion tank may not be right at the boiler where young heating guys put them. On older homes there may be remote expansion tank, perhaps in the attic.

If you see a heating boiler with no expansion tank and maybe no relief valve, it may have one of these systems that simply allow heating water to over-expand up into an attic tank that in turn drains outdoors.

Watch out: no heating boiler is safe without a pressure temperature relief valve right at the boiler, even if its expansion tank is remote.

Check All Three of These Possible Locations for and Types of Expansion Tanks at Your Heating System

Before we move on to talk about remote expansion tanks found in attics, and open cistern expansion tanks, take a look up at the ceiling in your boiler room.

If you see a tank that looks like the atmospheric or traditional boiler expansion tank shown below, you've found it.

Next follow the heating boiler piping from the point at which it exits near the top of the boiler.

This is the supply side or hot water side of the boiler. Usually the expansion tank is mounted on the hot or supply side of the boiler and usually it's located before any circulator pumps.

If you see a tank that looks like the unit below, your boiler has an internal-bladder type hydronic heating boiler expansion tank. Unless that tank is damaged or leaky it does not normally need a pressure adjustment, draining, nor air charging after its initial installation.

OK well it might if you built a third or fourth floor onto your home since the tank was first installed.

OK so you've followed all the pipes around the boiler and there is no expansion tank in the ceiling, no exansion tank mounted hanging down under the hot water supply side line over the boiler, as we illustrate just below.

So just when you figure there is no expansion or compression tank on this boiler ... WAIT WAIT!

If your heating boiler is a really big one, heating say a large building, your boiler may have required a larger-capacity hydronic boiler expansion tank - too big to hang from the system heating water piping. In that case the tank may be floaded on the hot water heating line but sitting on the floor.

Our sketch bdlow, adapted from Amtrol's Extrol expansion tank manual uses blue to show you where that tank might be located and how to find it by following the (red) hot water heating piping.

[Click to enlarge any image] For stand-type expansion tanks Amtrol warns:

Do not install the EXTROL on a dead-end pipe or wherever air can collect. This can cause corrosion and possible leakage.(Amtrol atReferences or Citations )

Ok so there is also no stand-alone expansion tank on the floor near the boiler either. It's time to look elsewhere. There may be no expansion tank; your boiler may be vented to the atmosphere at the highest point in the building, and there may be an expansion tank (sort-of) in the attic.

attic Expansion Tanks for Heating Boilers

Antique non-pressurized attic expansion tanks as pressure relief systems for boilers

Don't confuse an old heating system attic-mounted expansion tank like the one shown here for a water tank storage tank.

The heating system expansion tank will be connected to the heating system radiators or basement boiler and may have a simple overflow pipe to permit excessive water (or system pressure) to spill outside.

This attic expansion tank may have been connected to a drain that spilled outside of the building in case the tank became over-full. You can also see a sight glass on the front of this tank, allowing the service person to see its conation.

Don't confuse this little heating system expansion tank with a water storage tank, nor with the larger range boiler tanks discussed here.

Heating systems with this equipment installed may not have a modern pressure and temperature relief valve.

Certainly in the original design the tank was put in the attic so that heating water could rise to the upper floors of the building by pressure within the heating system, but if pressure got dangerously high, heating boiler water would just spill up into the attic and thence to outside

In identifying old steel tanks found in building basements and attics, also s

ee HOT WATER TANKS, RANGE BOILERS.

Really Old "Expansion Tanks" are Header Tanks: Attic Cisterns Open to the & Air that Don't Need Draining

But at left, this little "box" found in an attic was more likely a header tank, an expansion tank supporting a boiler no longer even in the building.

Details about attic expansion tanks and header tanks are

at ATTIC & ANTIQUE EXPANSION TANKS, HEATING

Cisterns - true water storage tanks, or open overflow tanks in basements or attics are an open-type water storage reservoir found indoors, and are discussed further at CISTERNS, WATER STORAGE.

This article series answers most questions about Heating System Boiler Controls on central heating systems to aid in troubleshooting, inspection, diagnosis, and repairs.

Basement Expansion Tanks for Heating Boilers

Our client is pointing to a do-it-yourself insulating job on a water heater. But look over his head.

The reddish-brown horizontal tank over his head is a ceiling-mounted atmospheric (bladderless) hydronic heating system expansion tank for the heating boiler in this building.

This is not a water storage tank, it's not a range boiler, it's an expansion tank. A big one.

This large basement expansion tank is expected to be on a heating boiler that also has a pressure and temperature relief valve.

From the size of the tank either the building is a large one with extensive (high volume of) hydronic heating baseboards or radiators, or the prior owner got tired of recharging the air in the tank.

...

Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

Question: is it safe to remove and replace an old steel expansion tank with the newer type? Which is better?

is it safe to remove the horizontal type tank and replace it ? Is the old type better? is it ok to let the valve relieve the pressure and not have a tank at all? - Anon 9/11/11

Reply:

Anon, you can usually replace an old bladderless expansion tank with a much smaller internal diaphragm tank, as we describe above. The new tank will be smaller yet can handle the same job. Newer internal-bladder heating system expansion tanks such as the Fill-Trol® Diaphragm-Type Expansion Tank have the advantage that you don't need to periodically drain the tank to re-charge its air.

In choosing the size of a heating system expansion tank, the service technician will consider the size of the building being heated, or more accurately, the volume of water in the boiler and heat distribution piping & radiators.

Question: New steam heater installed for first floor; old boiler had two expansion tanks - was it ok to remove one?

I am a home owner, i had a plumber switched and installed a steam heater in the first floor. when he saw my oil boiler that had two Expansion Tanks, he said it would work more efficient if he removed one on the two. He removed a green horizontal one at no charge, but took the Expansion Tank with him. Now that same steam heater he installed does not warm up at all. Is this because he removed one Expansion Tank.
please help - Laura 10/30/11

Reply:

Laura: steam boilers won't use an expansion tank, not normally, as the boiler is making steam and open to the atmosphere up through the radiators and steam vents.

Usually on a modern hot water (not steam) heating system you wouldn't need two expansion tanks, certainly not if one of them is a new internal bladder type. So, recognizing that I can only guess from afar, it sounds like two different problems.

There are some steam heat systems that use steam to distribute heat to upper building areas and use hot water from the same boiler to circulate through hot water radiators or baseboards in a lower building area. Maybe that's what you've got ?

Question: I have to empty our boiler's expansion tank every month - the relief valve spills; how far away can I put the new replacement tank I'm planning?

I have oil burner and I have to empty the expansion tank about once a month. I know it's full when the relief starts passing water. It's an old tank that lay's on top of the heater. My question is if I install the new type what is the max distance can it be from the heater? Is 8' to far? - Tony 6/5/2012

Reply:

Tony,

Amtrol makes both thermal expansion tanks and hydronic expansion tanks used on heating and plumbing systems. Amtrol's expansion tank installation instructions specify "Install the EXTROL on the supply side of the boiler, on the suction-side of the heating circulator(s) (see Figure 1)." That is, the location is more critical than the distance.

Question: what do I need to do after my contractor removed an attic expansion tank?

Would you be able to help me determine what to do when my contractor removed my tank. I'd like to send you a before and after photos if possible? - Contractor removed attic tank 7/8/12

Reply:

We will try. Use the CONTACT US link at page top or bottom to send photos for comment, best accompanied by a specific question or concern. Keep in mind that if your building is quite old there may have been an old, unused, atmospheric pressure expansion tank in the attic.

Question: why would my heating system's expansion tank lose its air after just 3 or 4 days - the sight glass fitting shows no air

what makes expansion tank lose air in 3-4 days. I checked for air leaks with soap bubbles around tank and sight glass fittings, found none. Serviceman says domestic hot water coil may be leaking. How does that make tank lose air? Replacing coil will be expensive because of position of furnace. - J Warden 10/1/2012

Reply:

J Warden, I have to agree that I'm confused by this question. I've not found a hot water heating system whose expansion tank included a sight glass (a feature I find on steam boilers) - can you give me some details: boiler brand, type, model, and some photos to allow further comment?

In any case, if your expansion tank (if that's what we've got here) is losing its proper air charge every few days, there is either a leak out of the tank piping and fittings.

Question: confusion about how to drain an expansion tank and what boiler pressures should be found

I drained exp.tank and shut valve and bleeder valve. I noticed the entire system was low. I brought system up to proper pressure and bled all radiators. Then I opened the valve to the expansion tank. When water entered tank the pressure for the heating system dropped. Do I now add more water to system or will pressure come back when water is heated .? Thank you - Lee Davidson - Filling entire system 10/8/12

Sirs, drained the exp. tank with tank supply valve closed. Closed drain valve and bleeder valve. Entire system pressure was low so brought it up and bled whole house system. Bleeding drops pressure so brought up then i opened tank supply valve this makes pressure drop but i think it will come back when water is heated. Right or wrong? - Lee Davidson 10/8/12

Reply:

Lee, I agree with your procedure except the last step. On opening the expansion tank connection between the tank and the boiler, I would expect the boiler pressure drop briefly as water feeds into the expansion tank to bring it (and its air) up to the standard heating system cold pressure, eg. 12 psi presuming that the boiler is cold.

But unless your system lacks an automatic water feed valve, the automatic water feeder would be expected to add the necessary makeup water. Or doesn't your system gave one?

Or finally, if at a low pressure heat makes it to the highest radiator or baseboard you are provably OK.

Lee, about your second question:

Wrong.

It is a mistake to set the water pressure in a hot water heating system to an abnormally high level, and further, you shouldn't need to. Presuming that your equipment has a water feed/pressure reducing valve in place, that valve will automatically feed water to the system up to the usual COLD water starting pressure. Typically that's around 12 psi, though it may be higher for some taller buildings.

Expecting the problem to be fixed when the water is hot is also an error. It's the cold starting pressure that we attend.

Watch out: some readers have been confused about the bladderless expansion tank drain procedure: one has to close the water feed valve into the tank (from the boiler) before opening the tank drain. Otherwise we are not draining the water out of the tank to let air in, we're just running water through the heating system: from the building water supply, through the water feed valve, through the boiler, and up and out through the expansion tank drain - accomplishing nothing.

Question: once or twice a year the expansion tank needs to be emptied - else heating system pressure goes above 30 psi. How do I stop this problem?

Hi. I seem to be having an issue once or twice a year that the expansion tank needs emptied, i.e. pressure goes above 30. Is there something I can do to stop this? Thanks. Sandy. sweisber@pitt.edu - Sandy 11/12/12

Reply:

Sandy,

Sure. You can eliminate the need for periodic draining the heating boiler expansion tank by replacing it with an internal bladder type tank like the Extrol shown at the top of thus article.

Question: Comment - thanks for discussing old bladderless expansion tank systems

Thank you for this informative information. Many articles just mention the expansion tank with bladders but I have an old bladderless system and I was not sure if I should let the water out The over pressure valve was periodically going off. Thanks again, I believe you solved my problem. - John OHare 11/16/2011

Reply:

Thanks for the nice comment, John. We work hard to make InspectAPedia information accurate, complete, and unbiased and are thrilled when a reader reports that our data has been helpful. Indeed, there are still lots of buildings around whose heating systems use an older type of steel bladderless expansion tank - a component that needs periodic attention to keep the heating system working safely.

An bladderless expansion tank that loses its air charge not only causes the relief valve to spill, it is a more subtle safety hazard - as a spilling relief valve may eventually clog up from mineral deposits and crud, then stop opening, risking a BLEVE or boiler explosion. Sp if you see water on the floor under a relief valve it is something that should never be ignored.

Just how often we need to drain the water out of a bladderless heating boiler expansion tank varies from one installation to another; some need attention twice a year while I've worked on other systems that ran OK for three years or more before the expansion tank became waterlogged. If your bladderless tank doesn't need attention too often, say not more than once a year, there is no reason it can't continue in service.

Question: banging pipes vs new Amtrol Extrol® expansion tank

(Jan 11, 2013) Rick said:

I have a fairly new Amtrol expansion tank (~2 years old). Lately we are getting banging in the pipes when the heat is circulated. I know I probably have to bleed the system, but the valves that are on the unit are the handle-less type that have to be turned with a wrench to open, and they take a while to seal again once closed.

Will loosening the valve at the top of the expansion tank a little more allow the trapped air to escape eventually - or will I have to bleed the lines manually with a hose and bucket? I have loosened it a bit and I can hear air escaping occasionally and I am hoping this will eventually bleed the heating system.

Also, I cannot find any other leaks in the system to allow air in. All help is appreciated.

Reply: Rick, it should not be necessary ever to bleed a captive-air type expansion tank such as the Extrol® unit and I'm not sure how a waterlogged expansion tank would cause banging pipes in a hot water heating system. Instead please take a look at our banging pipes diagnostic article:

BANGING HEATING PIPES RADIATORS(more often a concern on steam heating systems) or if your heating system is only a hydronic unit (hot water heat only)

seeHEATING SYSTEM NOISE DIAGNOSIS where we comment:

Bubbling or rumbling heating system noises in hot water heating piping can be caused by air in the heating lines. If the amount of air becomes excessive the heating system may be unable to circulate hot water and extra steps to bleed unwanted air will be required.

See AIRBOUND HEAT SYSTEM REPAIR by WATER FEED VALVE

Reader Question: Water-logged Amtrol Extrol Expansion Tank No. 30 - vs tank mounting position?

(Jan 29, 2013) claude st-pierre said:

Hi I find your site very helpful.

I have an Amtrol Extrol Expansion Tank No. 30 (with disphram inside). The pressure inside the system was under 12 psi before I pumped it back up to over 15 PSI (18 PSI). The tank has a tendency to loose its air over time, especially after many days of cold weather (minus 15 Fareiheit).

The tank was installed in 2007 and is mounted with the water inflow into the tank at the bottom and the air valve on the top. The maintenance guy mentioned that this type of tank could be mounted upside down and that does not matter but on the Amtrol web site, they always show the Extrol tank with the water intake at the top and the air valve at the bottom.

Could mounting an Extrol tank upside down reduce the life of the tank or reduce the capability of the tank to keep the pressure under 30 psi when the heating system works at its maximum temperature?

Reply: Claude, Amtrol does not specify tank mounting position in the installation instructions (found at the References section of this article) for the Amtrol Extrol Expansion Tank No. 30 but the company does provide these notes:

1. Although the EXTROL does not have to be installed at the base of an air purger, this installation is recommended to reduce air in the system and provide a compact installation. Some method of air elimination is required to ensure an oxygen-free system.

2. The EXTROL must not be placed overhead in the floor joist space. When replacing a plain-steel tank, the EXTROL should be relocated per Figure 1. [see our schematic drawings in the article above]

3. Do not place the EXTROL on a dead-end pipe. Air can collect in the EXTROL, causing internal corrosion and possible leakage.

4. Radiant systems with non-barrier tubing or high oxygen content should use a Radiant EXTROL ® expansion tank with a plastic liner. See the EXTROL brochure, or call (401) 535-1216 for sizing assistance.

* Models #15 through #90 come with a 5 year warranty. All other EXTROL models come with a 1 year warranty. See reverse side for warranty information.

* Do not hang models SX-30V through SX-160V. They are floor standing models only

- Extrol® (2014)

You state "The tank was installed in 2007 and is mounted with the water inflow into the tank at the bottom and the air valve on the top." which leaves me a little uncertain. There is only one water connection on the Extrol expansion tank and one air valve fitting. The air valve is used to adjust the initial tank pressure to match the boiler cold or fill pressure at the time of installation.

As water entering the tank enters an internal bladder, I'm doubtful that the tank orientation affects its position. I think that the reason you see the tank mounted with it water entry port at the top is that it is being connected to the bottom of a typical air purging device whose tapping for that purpose is on the under-side of the air purger.

See AIR SCOOPS PURGERS SEPARATORS

If your expansion tank is water logged and it's an Extrol unit it needs to be replaced as most likely the bladder has burst.

Reader Question: water-logged expansion tank prevents boiler operation?

2/27/2014 Trish said:

Can a waterlogged expansion tank cause an oil boiler to not kick on?

Reply:

In short, no, normally a waterlogged expansion tank doesn't keep a boiler from turning on, but there could be these exceptions:

The principal effect of a waterlogged expansion tank would be spilling at the temperature-pressure relief valve.

Residential hydronic heating boilers (hot water heat) usually are rated for a maximum of 30 psi - the TP valve will open at that pressure and spill water.

I suppose if a boiler lost water and didn't include an automatic water feeder, a low-water cutoff safety switch on such a boiler in that circumstance would shut down the boiler.

Some heating systems might include a pressure control sensor switch that would shut down the boiler if its pressure became abnormally high - a condition that follows a waterlogged expansion tank, but that's not a control I've seen on a residential heating boiler.

Question: separate tank for electric water heater?

(May 31, 2014) Matt said:

I have a HWB heating system with an expansion tank. I am now installing an electric water heater. Does this need a separate expansion tank? Thank you.

Reply:

You might, Matt, depending on local regulations and the operating properties of your system, including water pressure.

Take a look at our article on the topic over at

HOT WATER EXPANSION TANKS

and let me know if questions remain.

Question: have to add air to expansion tank

(Oct 16, 2014) Tom B. said:

My Amtrol-Fitrol Model 110 needs to be topped-up w/air to every now and then to bring it up to 12 PSI. I figure it needs replacing. There is a shut-off valve in line immediately before the tank. Can I just shut off that (I guess water inlet valve) and swap out the old tank for a new one of the same model and manufacturer? Thanks.

Reply:

Look for a leaky air valve or a burst internal bladder in the tank - replace it.

Question: troubleshooting expansion tank

(Oct 18, 2014) Swen said:

Hi there and thanks for running this site. Great resource since hydronic heating is not commonplace in the US yet (at least not in CA).

I am trouble shooting a broken brass fitting on my hydronic system and here is what I found:

- The valve to the Extrol expansion tank was shut-off
- The expansion tank (and the air trap) are on the return side and not the supply side

Here are my questions:

- Is the return side installation of the Extrol tank a serious issue?

- What is the right pressure to preload the entire system (My heating system is in a basement in a two story above ground house)?

- Is there ever a need to check pre-load charge of the Extrol tank in accordance of the set system pressure (see above)?

BTW, the brass fitting burst during the summer month without any system load (it is a weak fitting - or rather connector type element - most likely not suited to the application).

Thanks for your answers in advance,

Swen

Reply:

Swen:

The Extrol tank comes pre-charged at the factory recommended pressure and will work on either side of the boiler water circulating loop but I would indeed prefer to follow the manufacturer's instructions - as described in the article above.

Probably 12 psi cold is the start pressure you need, but first read the details of how to decide on and set heating boiler pressure found in our article at

inspectapedia.com/heat/Heating-Temp-Pressure-Settings.php

Question: leaks at expansion tank pressure gauge

10/26/2014 Jason Little said:

Came home to a flooded basement. The Amtrol Extrol Model 30 is leaking from the pressure gauge. Is this a easy repair?

Reply:

Jason,

I'm not sure what's going on with the pressure gauge: water intrusion vs. a damaged gauge vs. some other trouble. If the gauge was immersed by flooding or is damaged/leaking, I'd start by replacing the pressure gauge.

...

Continue reading at ATTIC & ANTIQUE EXPANSION TANKS, HEATING or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• EXPANSION TANKS, BOILERS - home
  • AMTROL's EXTROL®, the FILL-TROL®
  • ATTIC & ANTIQUE EXPANSION TANKS, HEATING
  • BOILER DRAIN DAMAGES EXPANSION TANK
  • EXPANSION TANK AIR VALVE LEAKS
  • EXPANSION TANK DIAGNOSIS
  • EXPANSION TANK DRAIN & AIR RE-CHARGE
  • EXPANSION TANK IO MANUALS & SIZING GUIDES
  • EXPANSION TANK LEAK REPAIRS
  • EXPANSION TANK PRESSURE ADJUSTMENT
  • EXPANSION TANK SIZING GUIDE
  • EXPANSION TANK WATERLOGGING CAUSES
  • EXPANSION TANK WON'T DRAIN
  • FIND the EXPANSION TANK
  • HEADER TANKS
  • RELIEF VALVE LEAK DUE TO EXPANSION TANK
  • TANKLESS COIL INTERNAL LEAKS INTO the BOILER
  • THERMAL EXPANSION of HOT WATER
  • THERMAL EXPANSION TPR VALVE LEAKS
  • WATER PRESSURE TOO HIGH: DANGERS

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FIND the EXPANSION TANK at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this

INDEX to RELATED ARTICLES: ARTICLE INDEX to HEATING BOILERS

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