A hot water recirculation system works by keeping hot water flowing through your pipes so that it’s always ready when you need it. Here’s a simple breakdown of how it operates:

For the preceding example, if the expansion tank has a factory precharge of 40 psig and it is not increased to the line pressure of 80 psig, then the required total capacity of the expansion tank increases from 5.4 gallons to 9.4 gallons.

Hot water recirculation systems offer a range of benefits that enhance your convenience, conserve water, save you money, and reduce your environmental footprint. They are an excellent investment for any homeowner looking to improve their home’s efficiency and sustainability.

How to size an expansion tankfor a chilled water system

Overall, while the pump does use some electricity, the savings in water and improved efficiency can offset this, making hot water recirculation systems a smart and eco-friendly choice for your home.

To further reduce costs associated with energy-saving retrofits, homeowners can take advantage of various rebate programs. The Home Energy Rebate Programs, introduced as part of the Inflation Reduction Act, offer significant financial incentives for energy efficiency and electrification projects.

Some manufacturer's now also have sizing calculators based on these engineering equations on their websites.  Click here for an example.

AMTROLExpansion TankSizing Chart

This is the amount of water that the thermal expansion tank would have to accept to prevent pressure spikes in the system. I know that this is a simplified approach. I have ignored the expansion of the heater tank and the hot water piping. It is my experience that the impact of these factors are small and have little effect on the ultimate tank selection. Keep in mind that when we complete the calculations, we select expansion tanks that come in rather large size increments. That’s why including factors that do not significantly impact the total amount of thermal expansion needed, can safely be omitted from the calculations. The equations provided in the ASPE Design Handbook include expansion of pipe material if you want to be more precise. By the way, I also don’t bother correcting for altitude. We typically don’t need that much accuracy. Also, since we are assuming a 100-degree water temperature differential in the calculations, we have some built-in conservatism.

The positive environmental impacts of hot water recirculation systems are substantial. By reducing water waste and energy consumption, these systems help conserve valuable resources.

Whether you’re washing dishes, taking a shower, or doing laundry, you get hot water instantly. This can significantly improve your daily routines, making your home life more comfortable and efficient.

Expansion tanksizing calculator

By saving water, you also save money on your water bills. Additionally, because hot water recirculation systems reduce the time it takes to get hot water, they can lower your energy bills as well.

If the expansion tank has a 150 psi allowable working pressure, I use 149.7 psia (135 + 14.7 = 149.7) for P, which is 10% below the set point of the relief valve. Using our example above, let’s assume that the actual line pressure and precharge pressure is 80 psi.

A hot water recirculation system is a system designed to provide you with instant hot water throughout your home. It works by continuously circulating hot water through your pipes so that when you turn on a tap, hot water is immediately available, eliminating the wait time and reducing water wastage.

Second, the manufacturer’s tables are based on a tank precharge pressure of 40 psi. Precharge is the air pressure on the air side of the tank bladder. This setting, by the way, is not founded upon an engineering principle but is the Department of Transportation’s  limitation for transporting tanks. To reduce the size of the thermal expansion tank, the precharge air pressure should be set equal to the line pressure of the system, not the 40 psi tank precharge pressure that is set from the factory. (Note: if expansion tanks are sized by an engineer based on a precharge air pressure equal to line pressure, the plumbing drawings and specifications should instruct the contractor to charge the expansion tank with air pressure equal to the line pressure.) Since the manufacturer’s sizing table is based on a tank precharge pressure of 40 psi, they do not accurately size an expansion tank when the precharge pressure is equal to the line pressure,.

To select a thermal expansion tank, the total tank capacity and the acceptance volume must be determined. The total tank capacity is the volume of the tank. The acceptance volume is the amount of water that the tank will accept with air pressure on the air-side of the diaphragm. First determine the expansion volume of the water in your system. This is volume of water the expansion tank will have to accommodate, which is also called the “acceptance volume.” The volume of expanded water is depends upon the specific volume of water at the entering and heated temperatures and the volume of stored water.

How tocalculateexpansion tank sizefor chilled water system

This blog post will educate you on how hot water recirculation systems work, their benefits, and why they might be the perfect solution for your home. By the end, you’ll understand how these systems can save you time, water, and money while enhancing your daily comfort.

There are three main types of hot water recirculation systems: demand-controlled, timer-based, and continuous. Each type has its own advantages and is suitable for different needs and preferences.

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Expansion tanksizing rule of thumb

To design a thermal expansion tank for a maximum allowable pressure less than 150 psi, a precharge air pressure different from 40 psi, and a temperature differential greater than 40-F, we can’t consult the manufacturer’s tables. Also, on large systems the storage tank sizes are often larger than the values given in the tables. So what do we do? We must calculate the proper expansion tank size using engineering equations. Here is a simplified method for sizing expansion tanks. A more detailed method is presented in the ASPE Design Handbook, Volume 4.

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One of the primary benefits of hot water recirculation systems is the convenience they offer. Imagine never having to wait for hot water again.

Hot water recirculation systems are designed to solve this common problem by providing instant hot water throughout your home. These systems continuously circulate hot water in your pipes, ensuring that you don’t have to wait for the water to heat up each time you turn on the tap.

Lower water usage means less strain on local water supplies, and reduced energy consumption means fewer greenhouse gas emissions from power plants. By installing a hot water recirculation system, you’re not only making a smart choice for your home but also contributing to a healthier planet.

First, for most manufacturers, the tables are based on a maximum allowable line pressure of 150 psi. This is the maximum allowable working pressure of most water heaters and thermal expansion tanks. It is also the setting of the water heater relief valve. In other words, the thermal expansion tank, if selected by the tables, could accommodate the thermal expansion up to a system pressure of 150 psi, which is the relieving point for the water heater relief valve. Remember that the purpose of the thermal expansion tank is to avoid the relief valve from relieving. Sizing the thermal expansion tank for a maximum allowable pressure of 135 psi, which is 10% below the relief valve set point, is a better alternative.

The less hot water you waste, the less energy your water heater has to use to reheat water. Demand-controlled and timer-based systems, in particular, are designed to be energy-efficient, running the pump only when necessary to minimize energy consumption. This can lead to significant savings over time.

How to size expansion tankfor boiler

Investing in a hot water recirculation system not only improves convenience and efficiency in your home but also aligns with sustainable practices, making it a smart and eco-friendly choice for homeowners looking to enhance their quality of life while reducing their environmental footprint.

The sizing method described above is for thermal expansion tanks installed in a hot water system. If you are sizing tanks for a booster pump system, the procedure is different.

Given a calculated total tank capacity of 5.44 gallons and an acceptance capacity of 2 gallons, consult the manufacturer’s data  and select a tank that meets your specific application.

(Note that the pressures are absolute pressures (psia). Add 14.7 to gauge pressure to convert to absolute pressure. Also, note that this equation assumes that the air precharge pressure is equal to the line pressure. This equation should not be used if the precharge pressure does not equal the line pressure.)

The final step is to determine the total tank capacity. The equation for total tank capacity is derived from Boyle’s law. When the precharge pressure will equal the line pressure, use equation (2) below.

Hot water recirculation systems offer a seamless solution to the common frustration of waiting for hot water. Whether opting for demand-controlled, timer-based, or continuous systems, the benefits of instant hot water, reduced water wastage, lower energy bills, and eco-friendliness are compelling reasons to consider this technology for your home.

Hydronicexpansion tanksizing calculator

If the precharge pressure does not equal the line pressure, equation (2) cannot be used. The appropriate equation for a precharge pressure that does not equal the line pressure is equation 3 below.

Hot water recirculation systems are excellent for water conservation. In a typical household, a significant amount of water is wasted while waiting for hot water to arrive at the faucet.

TacoExpansion tanksizing

The specific volume of saturated water at various temperatures can be found in tables of thermodynamic properties, or there is a handy table in the ASPE Data Book Volume 2, Table 6-5 Thermal Properties of Water. Here is a good number to remember. Water heated from 40-F to 140-F will expand 1.7%.  For example, let’s assume we have a 120-gallon water heater and the water is heated from 40-F to 140-F.

Understanding these components and types can help you decide which hot water recirculation system best fits your needs and lifestyle, providing you with the convenience of instant hot water while saving time, water, and energy.

By circulating hot water through your pipes continuously, these systems ensure that hot water is immediately available, drastically reducing the amount of water that goes down the drain while you wait. This can save thousands of gallons of water annually, making a big difference in your overall water usage.

By constantly circulating hot water through your pipes, the system ensures that when you turn on a tap, you get hot water instantly without waiting for it to travel from the water heater to the faucet.

Referring to sizing tables in an expansion tank manufacturer’s catalog is the easiest method, although not the best method, for sizing thermal expansion tanks. Sizing tables provided by the manufacturers, give the tank model number and size based on the water heater’s volume and the system supply pressure. These tables, however, are based on three important assumptions that designers need to be aware of.

Third, most manufacturers’ sizing tables are based on a 40-F temperature rise of the stored water. Think about this for a moment. The water heater is typically sized based on a 100-F temperature differential. For instance, often we assume cold water enters the water heater at 40-F and is heated and stored at 140-F. If we design the water heater to raise the water temperature 100-F, a conservative approach is to size the thermal expansion tank to accommodate the amount of water expansion resulting from the same 100-F temperature increase. This is, of course, a worst case scenario (complete emptying of the tank and filling with 40-F cold water). Designing the expansion tank based on only a 40-F temperature rise is less than conservative.

Additionally, combining hot water recirculation systems with energy-efficient technologies like heat pumps can further enhance overall efficiency and reduce energy costs. Heat pumps are known for their ability to transfer heat efficiently, and when paired with a hot water recirculation system, they can provide an optimal solution for maintaining hot water availability with minimal energy use.