Pressurized thermal storage uses sealed, insulated water tanks that store heat under pressure, allowing higher temperatures and more efficient energy use. These tanks act like heat batteries, absorbing energy during high-output burns and releasing it when needed.
Piping & System Integration
Many different piping options exist when using one or more thermal storage tanks. Some options include:
Parallel reverse return (Tichelmann System): Use this system with one to four tanks of the same size or in the same space. The equal pipe lengths for supply and return maintain balanced charging and energy use.
Series connection: If the tanks are of different sizes or in other locations, a series connection ensures the best operation. The first tank will charge completely, and then the next tank will be charged in the series. Reverse flow removes energy from the tank.
Froling Wood Boilers has many plumbing drawings available to address your thermal needs.
Pressurized thermal storage tanks play a vital role in optimizing the performance of wood and pellet boilers. By storing excess heat generated during burn cycles, these tanks help maintain efficient operation and reduce fuel consumption.
Below you will find everything you need to know about tank sizing:
Wood Boiler Tank Sizing
Boiler Model
Volume (gals)
Fröling S3 Turbo 30
600-900 gal
Fröling S3 Turbo 50
800-1200 gal
Burning boilers continuously at full output produces cleaner emissions and greater efficiency, but often generates more heat than needed. Heat storage tanks absorb this extra heat and store it for later use, acting as a buffer between the boiler and the heating load. Well-insulated tanks allow longer intervals between boiler cycles, giving wood boiler owners more flexibility.
Pellet Boiler Tank Sizing
Boiler Model
Volume (gals)
Fröling PE1 20
119-220 gal
Fröling PE1 35
220 gal
Fröling P4 100
600 gal
Automatic wood pellet boilers modulate heat output and start/stop automatically, but wood fuel’s slow ignition and variable heating demands make heat storage tanks essential. Heating needs fluctuate daily and seasonally, sometimes dropping below boiler minimum output, forcing shutdowns. Heat storage tanks allow boilers to run longer, storing excess heat and reducing frequent on/off cycles. This improves efficiency, lowers wear, saves fuel and electricity, and reduces emissions.
Fröling Energy Tank
The 119 gallon Fröling Energy Tank is an innovative indirect domestic hot water and thermal storage tank in one, designed to work seamlessly with small pellet boilers. This all-in-one solution reduces boiler cycling, extends equipment life, and lowers fuel usage while offering reliable hot water for bathing, handwashing, cooking, and cleaning.
Built for Best Performance
Our thermal storage tanks are pressure-rated, ASME certified and made to meet demands of high-efficiency biomass systems.
Pressure-rated up to 125 psi
Built to handle high-performance systems, our thermal storage tanks maintain safety and efficiency under elevated pressure conditions—ideal for modern biomass boiler setups
Certified with the ASME U-stamp
Each tank meets rigorous ASME Section VIII standards for pressure vessels, ensuring long-term durability, safety, and compliance with building codes across North America.
Sized to fit your system
You can choose from:
119 gal, 30” Dia, 73” Tall
220 gal, 30” Dia, 77” Tall
300 gal, 36” Dia, 73” Tall
400 gal, 36” Dia, 95” Tall
Froling Wood Boilers will work with you to appropriately size your thermal storage system
Minimal maintenance, maximum lifespan
Our tank’s closed, oxygen-free design help prevent corrosion
How many years does a pressurized water storage tank last?
A high-quality, ASME-certified pressurized tank can last 20 years or more with proper installation and water quality. Their oxygen-free design and robust carbon steel construction ensure a long lifespan with minimal upkeep.
How much does a new pressure tank cost?
Costs vary based on size, material, and certification, but a quality pressurized thermal storage tank typically ranges from a few thousand dollars up to $10,000 or more, including larger capacities and insulation. Always factor in installation and system integration.
What Our Clients Say About Us
Jacob from Vermont: S3 Turbo 30 w/ 600 gallons of Thermal Storage
“In 2023 I purchased a Fröling S3 Turbo 30 cordwood boiler with 2x300gal bulk storage tanks and installed the system to feed a multi-zone hydronic radiant heating system. Simply said, the Fröling is a wonderful wood boiler. With one load, I heat my home for 12-24 hours, depending on the outside temperature, and on average I'm closer to the 24-hour frequency. My home is 1500 square feet, and I keep my home around 62-64 degrees. The system is a wise choice for wood burners. By storing heat in bulk water tanks, S3 Turbo burns wood hot and fast, which is more efficient, and then uses the water tanks like batteries. It's a well thought out system and a pleasure to own; I love mine.”
Kris from Montana: S3 Turbo 50 w/ 800gallons of Thermal Storage
“I became interested in wood boilers due to the ability to provide all the heat and domestic hot water for my home without having to use propane or electricity. Mark and Brooks were very helpful in helping me create a system that fit my needs and helped me better understand how the system operates. They provided ample communication with me throughout the planning, ordering, and shipping process.”
Brian from Missouri: S3 Turbo 30 w/ 500gallons of Thermal Storage
“I love my Fröling boiler! I have an S3 turbo 30 with 500 gallons of thermal storage. I’m located in the middle of Missouri and I'm heating a 2500 square foot house and a 600 square foot apartment/garage with only 3-4 cords of wood annually.”
Jeremy from Maine: S3 Turbo 50 w/ 1000gallons of Thermal Storage
“I'm very excited to have made the investment in my new Fröling Wood Boiler. For many years I've heated my house with wood, most recently with a Tarm solo 60 gasification boiler. I can already tell that I'll get more heat out of each batch of wood. Every single part of the transaction with Froling Wood Boilers, went smoothly. I highly recommend this company for your wood heating needs.”
Breadtree Farms/Noah from New York - S3 Turbo 50 w/ 1200gallons of Thermal Storage
“We are operating one of the largest commercial agroforestry operations in the Northeast, and our cycles of annual stewardship often result in a lot of available firewood, as we manage hedgerows, improve forest stands, and (in the future) make thinning cuts in our chestnut and hickory orchards. We have been very happy to switch from fuel oil to the Fröling S3 Turbo, which is saving us thousands of dollars a year, substantially reducing our carbon footprint, and increasing the resiliency and energy independence of our operation.”
Klarissa and Byrke from Montana: S3 Turbo 50 w/ 800gallons of Thermal Storage
“Our Fröling S3 Turbo 50 is an excellent system! Easy to use, easy to clean and very efficient.”
Gordon from Wisconsin: S3 Turbo 30 w/ 800gallons of Thermal Storage
“I have used my Fröling boiler for the past 4 seasons and I could not be more pleased. We have all in floor heat, 3400 sq ft, and we have never been more comfortable. I have burned wood for 45 years and what I like best is: with the water heat storage we burn wood cleaner, safer, and more efficiently. No more of too much heat or not enough heat, it’s like heat on demand! This system enables us to heat the shoulder months of November and April efficiently, with one burn every 2-3 days. Then from December through March we do 1-2 burns a day allowing us to match our heat demand accordingly. In my opinion, the Fröling S3 Turbo is the best wood heating system out there!”
Doug from Connecticut: S3 Turbo 50 w/ 1000gallons of Thermal Storage
"I was a previous wood boiler owner for the past 16 years. I decided to upgrade my boiler and after researching and speaking with Brooks and Mark, I decided to purchase a Fröling S3 Turbo boiler. They both agreed that this unit would adapt flawlessly to my preexisting system. I would like to thank Froling Wood Boilers, especially Brooks, Mark and Kristin for their excellent and courteous customer service."
Todd from Colorado: S3 Turbo 50 w/ 800gallons of Thermal Storage
“I wanted to take this opportunity to thank everyone at Froling Wood Boilers, especially Brooks for all the over the phone support. They were always there to answer my questions and offer solutions. Once I texted Brooks after hours with a question expecting to hear back the next day. I was surprised when he called me back right away while he was at a baseball game! Now that is the definition of Customer Support! I can't wait to throw in the first log this winter and fire the boiler up to heat my house.”
Carl from Vermont: S3 Turbo 50 w/ 800 gallons of Thermal Storage
“I love my Froling S3 Turbo. I am burning half the wood versus my last wood boiler – 10 cords vs about 5 cords.”
Michael from New York: S3 Turbo 30 w/ 400 gallons of Thermal Storage
I’d like to thank Brooks for his assistance with purchasing the boiler. He made the whole process smooth and seamless. Pickup was easy and he was always available to answer any of my questions.
