Multiple Water Heaters: Reverse Return Piping Method

In the evolving world of water heating technology, the reverse return, or ‘first in, last out’, configuration has emerged as a superior method for dual water heater setups. This approach not only improves efficiency but also offers notable flexibility and reliability. This is not the only way to pipe water heaters but it is recommended by Bradford White.

Why Choose Reverse Return Configuration?:

There are several compelling reasons to opt for a reverse return configuration:

  1. Efficiency & Longevity: This setup ensures balanced water flow and usage between both heaters, enhancing system efficiency and extending the lifespan of your heaters.
  2. Adaptability: Reverse return can be modified to incorporate additional features like a recirculating line or a mixing valve, providing flexibility for diverse scenarios.
  3. Reliability & Flexibility: One key advantage is the ability to bypass either tank if a malfunction occurs. Unlike series setups, you won’t be left without hot water if an issue arises with one of the tanks.

Challenges with Series Setups and Single Tank Replacement:

Replacing a single tank in a dual water heater setup, especially when piped in series, can pose significant challenges. Reconfiguring a series setup into a reverse return arrangement can be difficult and time-consuming. That’s why we always recommend installing two new water heaters instead of replacing just one if the tanks are both similar age. This approach not only ensures optimal performance but also makes future maintenance and potential replacements much easier.

Series Setups: A Thing of the Past:

Series setups, once commonplace, have been disallowed by code since 2018. They can lead to issues like potential bacterial growth if the first tank doesn’t run and the temperature falls below 120 degrees.


With a reverse return configuration, you benefit from an efficient, adaptable, and reliable water heating system. Ready for an upgrade? Contact us today to discuss how a reverse return configuration could benefit your home or business.

Piping Diagram for two gas water heaters. Includes recirculating line.

Venting for Multiple Water Heaters

When it comes to installing multiple water heaters, one of the most critical yet often overlooked aspects is proper venting. Ensuring that your venting is correctly sized is crucial not just for the performance of your water heaters but also for safety. Incorrect venting can lead to poor combustion and even hazardous conditions such as backdrafting.

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Vent Connector Size Matters

The vent connector’s size depends on a few key factors: the BTU rating of your water heaters and whether the water heaters are common-vented with another appliance. For instance, a 40,000 BTU water heater that isn’t common-vented typically requires a 3-inch vent connector. However, if it’s common-vented and the connector rise is less than 3 feet, you’ll likely need a 4-inch vent. The connector rise refers to the distance from the top of the tank to the bottom of the wye connecting the two appliances.

What is Common Venting?

Common venting refers to the practice of using a single vent to exhaust multiple appliances. When common venting, it’s important to determine the size of the vent connector where the water heaters combine. Usually, you’d be looking at a 5-inch vent connector in such cases. They would combine into a 5-4-4 wye, then run 4-inch connectors to each water heater.

Factors to Consider

Determining flue capacity is an intricate calculation involving multiple variables. For example, if you have a 5-inch B vent venting a 110,000 BTU furnace and two 40,000 BTU water heaters (totaling 190,000 BTU), you need to consider the flue’s height to determine its capacity. A 20-foot tall flue typically has a max BTU of 183,000 for natural draft and fan-assisted appliances, making it incorrect to add a second water heater in this scenario.