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 a heating boiler expansion tankHeating Boiler Expansion Tank Size Guide

How to choose the right expansion tank size

Hot water heating system expansion tank / compression tank size guide:

This article provides basic sizing charts for hydronic (hot water) heating boiler expansion tanks or compression tanks.

We include links to additional expansion tank sizing guides from equipment manufacturers such as Amtrol / Extrol and PEX as well as links to online calculators that can give an expansion tank sizes based on known water volume of the heating system.

This article series explains 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.

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Expansion Tank Sizing Procedures

Expansion tank isolating valve (C) Daniel FriedmanThe photo at page top shows a modern Extrol(R) bladder-type heating system expansion tank.

[Click to enlarge any image]

Shown here is a gray cylindrical ceiling-mounted traditional bladderless expansion tank for a hot water heating boiler using cast iron baseboard heat in most of the building with a radiant floor slab in one small room.

Question: expansion tank sizing for large older home, cast iron radiators

2016/11/20 Steve said:

Expansion tank sizing: In a very large old home, there is a huge boiler(size of a small car) and an old style expansion tank in the rafters. The tank recently started leaking, so I'd like to replace it with the newer bladder type.

Understand that for hot water heating boiler expansion tank sizing calculations, you need to take the system volume, temperature differential, etc. into account.

But with a house so large with dozens of radiators & seemingly miles of piping, I can't begin to imagine how you could calculate the total volume. Isn't there a way to make this determination using the size of the old expansion tank? Its 12" x 60", so about 30 gallons. Thanks for the help.

This question was posted originally

at EXPANSION TANK LEAK REPAIR FAQs

[Click to enlarge any image] Shown here, an Amtrol Extrol expansion tank on a hydronic heating boiler.

Reply:

Amtrol's adapted Extrol Fill-Trol Expansion Tank © D Friedman at InspectApedia.com Steve

I agree this is an onerous task - expansion tank sizing. Typically the big manufacturers offer a calculator that begins by requiring you to enter exactly what you don't know: the total water volume of the system.

The technical factors in boiler expansion tank size include total volume, operating temperature, and starting operating pressure.

I think that most heating service techs eyeball the system and pick what they guess is a safe (big) expansion tank from the range of standard sizes they've seen in residential properties.

There are actually just a few typical expansion tank model sizes (and thus model numbers) and some heating companies map those against boiler net BTUH output and the type of heating system: finned copper baseboard, convectors/unit heaters, or radiators, or cast iron baseboard

You'll also choose between (using Amtrol / Extrol as an example) an expansion tank that includes a fill valve (Amtrol Fill-Trol) and one that does not (Amtrol-Extrol) the latter means you're using an external or separate boiler fill valve.

Typical Expansion Tank Sizes for a Cast Iron Radiator type typical residential heating system

In other words, unless you're an HVAC design engineer you would probably eschew measuring the number of linear feet of pipe, and its diameter and counting the number of radiators and adding the volume of these to that of the boiler. Instead you'd choose a reasonable model from the rather short list of what's actually sold.

Below are tables sizing expansion tanks for typical hot water (hydronic) heating boiler systems.

To use these boiler expansion tank sizing charts you need to know just the type of heating system radiation used: finned copper baseboard, convectors/unit heaters, cast iron radiators, or cast iron heating baseboards and the heat output of the heating boiler in 1000s of BTUs / Hour or Output BTUh.

Photo: an Amtrol Fill-Trol expansion tank that incorporates a brass fill-valve - just visible under the air-scoop/air purger and found on the top of this expansion tank.

More about Fill-Trol tanks from Amtrol is at AMTROL's EXTROL®, the FILL-TROL®

Expansion Tanks for Finned Copper Baseboard Heating Systems

Table of Hydronic Heating Boiler Expansion Tank Size vs. Finned Copper Baseboard Heat Radiation Method & Boiler Output in 1000's of BTUS/Hour

Baseboard, Finned Copper Tubing Heat Typical Hydronic Heating Boiler Output in 1000s of BTUS / Hour (data tag)
BTUH Output 25-50 K BTUh 75-150 K BTUh 175-250 K BTUh 300 K BTUH 350-400 K BTUH
Expansion Tank Model Amtrol Extrol a #15
or

Amtrol Fill-Trol b #109
Amtrol Extrol #30
or

Amtrol Fill-Trol #110
Amtrol Extrol #60
or

Amtrol Fill-Trol #111
Amtrol Extrol #90
Amtrol Fill-Trol #SX-30V
Expansion Tank Volume 2.0 gallons 4.4 gallons 7.6 gallons 14 gallons 14 Gallons

Notes to the table above

This data is for hydronic heating boilers - that is, building heating systems. It is not intended to size thermal expansion tanks for domestic hot water heaters. See the references below.

Adapted from PexUniverse and Amtrol data sources cited below at EXPANSION TANK SIZING CALCULATORS

Watch out: these are "ballpark" data points. Check with the installation and maintenance manual for your heating system, with its manufacturer, and with your local heating equipment service company or supplier for their opinon on accurate boiler xpansion tank sizing.

Expansion Tanks for Cast Iron Baseboard Heating Systems

Table of Hydronic Heating Boiler Expansion Tank Size vs. Cast Iron Baseboard Heat Radiation Method & Boiler Output in 1000's of BTUS/Hour

Cast Iron Baseboard Heat Typical Hydronic Heating Boiler Output in 1000s of BTUS / Hour (data tag)
BTUH Output 15 K BTUh 30 K BTUh 75-100 K BTUh 125-150 K BTUH 175-200 K BTUH 250-300 K BTUH 350-400 K BTUH
Expansion Tank Model Amtrol Extrol a #15
or

Amtrol Fill-Trol b #109
Amtrol Extrol #30
or

Amtrol Fill-Trol #110
Amtrol Extrol #60
or

Amtrol Fill-Trol #111
Amtrol Extrol #90
Amtrol Fill-Trol #SX-30V Amtrol Fill-Trol #SX-40V Amtrol Fill-Trol #SX-60V
Expansion Tank Volume 2.0 gallons 4.4 gallons 7.6 gallons 14 gallons 14 Gallons 20 Gallons 32 Gallons

Notes to the table above

This data is for hydronic heating boilers - that is, building heating systems. It is not intended to size thermal expansion tanks for domestic hot water heaters. See the references below.

Adapted from PexUniverse and Amtrol data sources cited below at EXPANSION TANK SIZING CALCULATORS

Watch out: these are "ballpark" data points. Check with the installation and maintenance manual for your heating system, with its manufacturer, and with your local heating equipment service company or supplier for their opinon on accurate boiler xpansion tank sizing.

Expansion Tanks for Cast Iron Radiator Heating Systems

Table of Hydronic Heating Boiler Expansion Tank Size vs. Cast Iron Radiator Heat Radiation Method & Boiler Output in 1000's of BTUS/Hour

Cast Iron Radiator Heat Typical Hydronic Heating Boiler Output in 1000s of BTUS / Hour (data tag)
BTUH Output 25 K BTUh 50-75 K BTUh 100-125 K BTUh 150 K BTUH 175-300 K BTUH 350-400 K BTUH
Expansion Tank Model Amtrol Extrol a #15
or

Amtrol Fill-Trol b #109
Amtrol Extrol #30
or

Amtrol Fill-Trol #110
Amtrol Extrol #60
or

Amtrol Fill-Trol #111
Amtrol Extrol #90
Amtrol Fill-Trol #SX-30V Amtrol Fill-Trol #SX-40V
Expansion Tank Volume 2.0 gallons 4.4 gallons 7.6 gallons 14 gallons 14 Gallons 20 Gallons

Notes to the table above

This data is for hydronic heating boilers - that is, building heating systems. It is not intended to size thermal expansion tanks for domestic hot water heaters. See the references below.

Adapted from PexUniverse and Amtrol data sources cited below

at EXPANSION TANK SIZING CALCULATORS

Watch out: these are "ballpark" data points. Check with the installation and maintenance manual for your heating system, with its manufacturer, and with your local heating equipment service company or supplier for their opinon on accurate boiler xpansion tank sizing.

Expansion Tanks for Convector-Type (Unit Heater) Heating Systems

Table of Hydronic Heating Boiler Expansion Tank Size vs. Convectors / Unit Heaters Heat Radiation Method & Boiler Output in 1000's of BTUS/Hour

Convectors / Unit Heaters Typical Hydronic Heating Boiler Output in 1000s of BTUS / Hour (data tag)
BTUH Output 25-50 K BTUh 75-100 K BTUh 125-200 K BTUh 250 K BTUH 300-350 K BTUH 400 K BTUH
Expansion Tank Model Amtrol Extrol a #15
or

Amtrol Fill-Trol b #109
Amtrol Extrol #30
or

Amtrol Fill-Trol #110
Amtrol Extrol #60
or

Amtrol Fill-Trol #111
Amtrol Extrol #90
Amtrol Fill-Trol #SX-30V Amtrol Fill-Trol #SX-40V
Expansion Tank Volume 2.0 gallons 4.4 gallons 7.6 gallons 14 gallons 14 Gallons 20 Gallons

Notes to the table above

This data is for hydronic heating boilers - that is, building heating systems. It is not intended to size thermal expansion tanks for domestic hot water heaters. See the references below.

Adapted from PexUniverse and Amtrol data sources cited below at EXPANSION TANK SIZING CALCULATORS

Watch out: these are "ballpark" data points. Check with the installation and maintenance manual for your heating system, with its manufacturer, and with your local heating equipment service company or supplier for their opinon on accurate boiler xpansion tank sizing.

Hydronic Heating Boiler (Hot water heating boiler) Expansion Tank Sizing References

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Reader Comments, Questions & Answers About The Article Above

Below you will find questions and answers previously posted on this page at its page bottom reader comment box.

Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2021-02-12 - by (mod) -

Gary

Please take a look at the expansion tank sizing tables given above on this page - as that gives the most-accurate answer to your question.

Please don't hesitate to ask further if any of that is unclear.

On 2021-02-12 by GARY PARIKH

i had old c.i. boiler w/375000 btu output for my bldg. fintube radiation. what size expansion tank to install

On 2020-11-01 - by (mod) -

OK.

Sounds as if the Extrol is doing its job.

On 2020-11-01 by William conklin

I ha 8 small radiator. Thete is a new peerless boiler. Installed 100.000 btu 1/2 pipe goung to extro l. 30 there us no expansion trouble. On running or off

On 2019-01-16 by Tom

I'm in trade school for HVAC and we were sizing expansion tanks and we have some expansion tanks that are undersized and some that are oversized. The question was posed: how much can you undersize and oversize the expansion tanks on a hot water boiler?

On 2018-11-05 - by (mod) -

Thank you for the nice comment, Rod. We're glad that you found it useful.

We also welcome questions and critique. Working together is good for both of us.

On 2018-11-04 by Rod

Great information I thank you for it


...

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