100 Gallon Water Storage Tanks

100 gallon water storage tanks are passive vessels designed to hold and buffer potable hot water produced by a separate heat source, such as a boiler, indirect water heater, heat exchanger, or tankless coil system. Operating at up to 180°F and typically rated to 150 or 160 PSI working pressure, 100 gallon water storage tanks give commercial buildings and high-demand residential installations the reserve capacity to meet peak draw periods without stressing the primary heating equipment. Sizing at the 100-gallon mark hits a common threshold: large enough to support multi-fixture peak loads, compact enough to pass through a standard doorway. The right tank for a given job depends on insulation requirements, ASME code compliance, installation environment, and how the vessel integrates with the existing hot water plant.

AO Smith TJV Series: Factory Jacketed and Insulated Commercial Storage Tanks

The AO Smith TJV Series represents the go-to choice for commercial hydronic and domestic hot water buffering applications. TJV tanks arrive factory jacketed and insulated, with the insulation rated to meet or exceed the R-12.5 minimum thermal requirements of the U.S. Department of Energy and ASHRAE/IESNA 90.1. The interior is glasslined with an alkaline borosilicate composition fused to steel at 1,600°F, providing long-term corrosion resistance without relying on external power or controls. A magnesium anode rod provides additional cathodic protection. The TJV-120M carries a standard 160 PSI working pressure and fits through a 30-inch doorway, a spec that matters on retrofit jobs in mechanical rooms built decades before anyone thought to plan for equipment swaps. The ASME-stamped TJV-120A steps up to code-required installations, rated at 160 PSI with ASME certification and National Board registration available on request. Both models accept potable water at temperatures up to 180°F. T&P valve is field-supplied and must be sized to the total combined BTU input of all connected heating equipment. Warranty coverage is five years on the tank.

AO Smith T-120S: Uninsulated Bare Commercial Storage Tank

The AO Smith T-120S is a 119-gallon uninsulated bare commercial storage tank built for installations where the contractor supplies or field-fabricates external insulation, or where the tank will be housed in a conditioned mechanical room. The interior uses the same glass-lining process as the TJV series. Bare tanks like the T-120S tend to appear in large commercial mechanical rooms with custom insulation wraps, or in process applications where the tank exterior needs to be accessible for inspection or secondary containment purposes. Without factory insulation, the T-120S ships at a reduced footprint compared to the jacketed models, which can simplify logistics on tight jobsite deliveries. ASME certification sheets are available on request for code-required commercial jobs. Five-year limited tank warranty.

Bradford White AST-120-6: Residential Storage Tank

The Bradford White AST-120-6 is a 119-gallon residential storage tank built for high-demand single-family and light commercial applications where a separate boiler or water heater provides heat input. The AST-120-6 features Bradford White’s Vitraglas lining with Microban antimicrobial protection, fused to steel at over 1,600°F. The insulation system uses 2-inch non-CFC foam covering the sides and top of the tank. Working pressure is rated at 150 PSI, test-certified at 300 PSI. The 119-gallon model ships with 1-inch NPT outlet and boiler supply connections, stepping up from the 3/4-inch NPT used on smaller AST models. A brass drain valve, protective anode rod, and surface-mount thermostat with manual-reset high-limit cutoff come standard. T&P relief valve tapping is included on top; the valve itself is field-supplied. Bradford White backs the AST-120-6 with a six-year limited tank and parts warranty.

Amtrol StorageMate S-120: Thermal Storage and Booster Tank

The Amtrol StorageMate S-120 is a 120-gallon insulated hot water storage tank designed to expand existing hot water system capacity when paired with a tankless coil, conventional water heater, or boiler. The StorageMate line uses dense urethane foam insulation and is intended for both residential and light commercial applications where peak draw periods exceed what the primary appliance can recover in real time. Contractors reach for the StorageMate S-120 when adding storage to a tankless coil installation or when retrofitting an older boiler system with buffer capacity to reduce short-cycling. The tank’s design focuses on simple integration with existing piping, making it a practical choice when the mechanical room already has a working heat source and the job is purely about adding reserve volume.

ASME vs. Standard Working Pressure: When Certification Matters

The choice between an ASME-stamped tank and a standard working pressure model isn’t just a matter of budget. Many commercial building codes, insurance carriers, and local inspection authorities require ASME Section VIII certification for pressure vessels above a certain size or operating above a set pressure threshold. The AO Smith TJV-120A carries ASME U-stamp certification at 160 PSI working pressure. The TJV-120M and T-120S do not. Contractors specifying tanks for permitted commercial jobs should confirm local code requirements before ordering a standard-pressure model. For residential and light commercial retrofit work, the non-ASME models typically satisfy applicable codes, but always verify with the AHJ.

Choosing the right 100 gallon water storage tank starts with a single question: what’s providing the heat? Storage tanks have no heating element. They rely entirely on an external source, whether a boiler, indirect water heater, heat exchanger, or tankless coil, to bring stored water up to setpoint. Getting that interface right means matching connection sizes, working pressures, and flow paths before the order is placed.

Working pressure is the next variable. Most 100 gallon water storage tanks in this range carry either 150 PSI (Bradford White AST-120-6) or 160 PSI (AO Smith TJV series, T-120S) working pressure ratings. Neither is marginal for standard hydronic and domestic hot water systems, but code-required commercial jobs may mandate ASME certification. The ASME-stamped option, such as the AO Smith TJV-120A, costs more but removes ambiguity on permitted commercial installations.

Insulation matters if the tank isn’t in a conditioned space. Factory-jacketed models like the AO Smith TJV-120M and TJV-120A and the Bradford White AST-120-6 meet or exceed DOE R-12.5 minimums and are ready for installation out of the box. Bare tanks like the AO Smith T-120S require field-applied insulation. In heated mechanical rooms with minimal standby losses, bare tanks can be a practical fit. In unconditioned basements or utility spaces, factory insulation pays for itself quickly in reduced standby heat loss.

Connection sizing makes a difference at the 100-gallon tier. The Bradford White AST-120-6’s 119-gallon model ships with 1-inch NPT outlet and boiler supply connections, an upgrade from the 3/4-inch fittings on smaller AST models. The AO Smith TJV-120M and TJV-120A also use 1-inch NPT for the primary supply connection. Confirm the piping header sizing before finalizing the order to avoid adapter work in the field.

For retrofit applications where a contractor is adding storage to an existing system, the Amtrol StorageMate S-120 is worth evaluating as a straightforward booster tank that works with tankless coils and existing water heaters without requiring a full replumb. For new commercial construction requiring code compliance, start with ASME models and verify with the AHJ before specifying a standard-pressure tank.

FAQs

What’s the difference between an ASME and non-ASME 100 gallon water storage tank?

The difference between an ASME and non-ASME 100 gallon water storage tank is formal pressure vessel certification. ASME-stamped tanks, such as the AO Smith TJV-120A, are constructed and inspected to ASME Section VIII standards and carry a U-stamp, which many commercial building codes and insurance requirements mandate. Standard-pressure models like the TJV-120M operate at similar working pressures but don’t carry ASME certification. For permitted commercial jobs, contractors should confirm local code and AHJ requirements before specifying a non-ASME model.

Can a 100 gallon storage tank be used with a tankless water heater?

A 100 gallon storage tank can be used with a tankless water heater or tankless coil to buffer peak demand and reduce the frequency of firing cycles. The Amtrol StorageMate S-120 is specifically designed for this type of integration, working alongside existing water heaters and tankless coils to expand usable hot water volume. Correct piping configuration and aquastat placement are critical to ensure the tankless unit doesn’t short-cycle or overheat the stored volume.

Does a 100 gallon water storage tank include a T&P relief valve?

A 100 gallon water storage tank typically does not include a T&P relief valve as standard equipment. The AO Smith TJV series and Bradford White AST-120-6 both require the T&P valve to be field-supplied and installed. For AO Smith TJV tanks, the T&P valve must be sized according to the total combined BTU input of all heating equipment feeding the tank, not just the tank capacity. Always consult local code for T&P sizing and placement requirements.

How long does a 100 gallon commercial storage tank typically last?

The service life of a 100 gallon commercial storage tank can range from 15 to 20 years with proper maintenance, as documented for the AO Smith TJV-120M. Actual lifespan depends on water quality, anode rod maintenance, and operating temperatures. Magnesium anode rods on glass-lined tanks should be inspected every two to three years; replacing the anode when more than 50% of material is depleted is a reliable indicator. Periodic flushing to remove sediment also helps extend tank life.

What’s the working pressure rating for 100 gallon water storage tanks?

Working pressure for 100 gallon water storage tanks varies by model. AO Smith TJV-120M, TJV-120A, and T-120S tanks carry a 160 PSI working pressure rating. The Bradford White AST-120-6 is rated at 150 PSI working pressure and is test-certified at 300 PSI. Both are well within the operating range of standard residential and commercial hot water systems. For systems running at elevated pressures or requiring formal ASME certification, confirm the specific model’s stamping and documentation availability before specifying.