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Photograph of an indirect fired water heaterHeating System Expansion Tank Location
How to find & identify the expansion tank on hot water (hydronic) heating boiler systems

  • FIND the EXPANSION TANK - CONTENTS: how to identify the different types of expansion tanks used on heating systems & how to find the expansion tank. While most modern hot water heating systems use an expansion tank located close to the heating boiler, some older systems may use a remote, hidden, or less than obvious expansion tank, even one located elsewhere in the building!
  • POST a QUESTION or READ FAQs about heating system expansion tanks: their function, size, location, maintenance, and need for draining (on some models)
  • REFERENCES
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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.



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Honey I Can't Find the Expansion Tank!

Photograph of a heating boiler expansion tank

Article Series Contents

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.

Atmospheric expansion tank on hydronic boiler (C) Daniel Friedman Two Harbors MN

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.

LARGER VIEW of a heating boiler expansion tank

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.

Amtrol Extrol expansion tank installation schematic, adapted from Extrol (R) installation instructions (C) InspectAPedia

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.

Amtrol Extrol SX 30 to 170 hydronic heat expansion tank sits on the floor (C) InspectApedia Amtrol Corp. Adaptation

[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 REFERENCES)

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

Photograph of an attic expansion tank for a heating boiler

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 see HOT WATER TANKS, RANGE BOILERS.

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

Photograph of an attic expansion tank for a heating boiler

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 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.

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

Photograph of a heating boiler expansion tank

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.

Article Series Contents

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