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# Heating Boiler Expansion Tank Size Guide How to choose the right expansion tank size

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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.

## Expansion Tank Sizing Procedures

The photo at page top shows a modern Extrol(R) bladder-type heating system expansion tank. At left over our client's head is a reddish tan steel heating boiler expansion tank (or compression tank in some texts).

[Click to enlarge any image]

### 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. I understand for 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 DIAGNOSTIC FAQs

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

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

• For a 100 MBTUH boiler you'd use either an Amtrol Extrol #60 or an Amtrol Fill-Trol #111
• For 125-150 MBTUH you'd use an Amtrol Extrol #90
• For a 175-200 MBTUH boiler you'd use an Amtrol Extrol #SX30V
• For a 250-300 MBTUH boiler you'd use an Amtrol Extrol #SX40V
• For a 350-400 MBTUH boiler you'd use an Amtrol Extrol #SX60V

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 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®

### 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:

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

• Note a: The Amtrol Ex-Trol models provide am expansion tank that does not include an automatic fill valve. An external control valve will be needed to fill and maintain water in the heating boiler.
• Note b: The Amtrol Fill-Trol expansion tank models provide an expansion tank that includes an automatic fill valve incorporated with the tank
See details at AMTROL's EXTROL®, the FILL-TROL®
• "K" BTUh = Thousands of BTUS per Hour of Output Heat from the Boiler
• The BTU output per hour or BTUH used is the net hydronic boiler output BTUs, typically found on the boiler's data tag.
• For mixed systems combining radiators and baseboard, use the larger expansion tank size.

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.

### 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:

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

• Note a: The Amtrol Ex-Trol models provide am expansion tank that does not include an automatic fill valve. An external control valve will be needed to fill and maintain water in the heating boiler.
• Note b: The Amtrol Fill-Trol expansion tank models provide an expansion tank that includes an automatic fill valve incorporated with the tank
See details at AMTROL's EXTROL®, the FILL-TROL®
• "K" BTUh = Thousands of BTUS per Hour of Output Heat from the Boiler
• The BTU output per hour or BTUH used is the net hydronic boiler output BTUs, typically found on the boiler's data tag.
• For mixed systems combining radiators and baseboard, use the larger expansion tank size.

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.

### 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:

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

• Note a: The Amtrol Ex-Trol models provide am expansion tank that does not include an automatic fill valve. An external control valve will be needed to fill and maintain water in the heating boiler.
• Note b: The Amtrol Fill-Trol expansion tank models provide an expansion tank that includes an automatic fill valve incorporated with the tank
See details at AMTROL's EXTROL®, the FILL-TROL®
• "K" BTUh = Thousands of BTUS per Hour of Output Heat from the Boiler
• The BTU output per hour or BTUH used is the net hydronic boiler output BTUs, typically found on the boiler's data tag.
• For mixed systems combining radiators and baseboard, use the larger expansion tank size.

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.

### 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:

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

• Note a: The Amtrol Ex-Trol models provide am expansion tank that does not include an automatic fill valve. An external control valve will be needed to fill and maintain water in the heating boiler.
• Note b: The Amtrol Fill-Trol expansion tank models provide an expansion tank that includes an automatic fill valve incorporated with the tank
See details at AMTROL's EXTROL®, the FILL-TROL®
• "K" BTUh = Thousands of BTUS per Hour of Output Heat from the Boiler
• The BTU output per hour or BTUH used is the net hydronic boiler output BTUs, typically found on the boiler's data tag.
• For mixed systems combining radiators and baseboard, use the larger expansion tank size.

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

• Amtrol Corporation, Hydronic Expansion Tank Sizing [Online Calculator], AMTROL Inc. Corporate Office 1400 Division Road West Warwick, R.I. 02893 Phone: (401) 884-6300 Fax: (401) 884-4773 For general inquiries: info@amtrol.com For warranty inquiries: warranty@amtrol.com - retrieved 2016/11/20, original source: http://www.amtrol.com/support/extrol_com_sizing.html
Requirements: you'll need to know total heating system volume, minimum and maximum operating temperature, and minimum/maximum operating pressure.
• Amtrol Corporation, Thermnal Expansion Tank Sizing [Online Calculator], Op. Cit., Original source: http://www.amtrol.com/support/therm_res_sizing.html
• Amtrol Corporation, Well Tank [Pressure tank] Tank Sizing [Online Calculator], Op. Cit., Original source: http://www.amtrol.com/support/well_sizing.html
• HOT WATER EXPANSION TANKS at InspectApedia.com - requirements for thermal expansion absorbing tanks or relief valve systems on hot water heating systems
• HOT WATER PRESSURE EXPANSION RATE - what is the expansion rate and volume of water when it's heated?
• PexUniverse, "How to size and select a proper Expansion Tank", PexUniverse, PexUniverse.com 5407 Foster Ave Brooklyn, NY 11234, USA, vendor of PEX supplies, heating and plumbing supplies, pumps, valves, fittings & components for HVAC and IAQ equipment, Email: sales@pexuniverse.com, Tel: 800-818-3201 Website: PexUniverse.com - retrieved 2016/11/20, original source: http://www.pexuniverse.com/how-size-and-select-proper-expansion-tank

#### Article Series Contents

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Continue reading at FIND the EXPANSION TANK or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see EXPANSION TANK DIAGNOSIS - troubleshooting

Or see HOT WATER EXPANSION TANKS - requirements for thermal expansion absorbing tanks or relief valve systems on domestic hot water heating systems

Or see WATER TANK SIZE & VOLUME - water pressure tank or water storage tank size requirements

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