Should Water Heaters Be In Series Or Parallel? & Why?

If you like the following content, please share it, so we can grow and improve the site for you


It is pretty difficult to imagine life without a water heater. Heaters are part of the essential appliances needed in your home. If you have just acquired water heaters for your bathroom, you definitely want to get them to deliver at their best. A common question when you are about installing water heaters is which configuration you should go for and you might be found asking

Should water heaters be in series or parallel?

Water Heaters can be in either series or parallel. Generally speaking, parallel connections are ideal when you need large volumes of hot water delivered frequently while series connections come in handy when your hot water demand only peaks occasionally.

Though parallel connections are the best for efficient performance and maximization of the water heater life span, our tip for you is to ascertain what your needs are first. Being able to understand your needs will serve as a guide to deciding whether you should opt for a series or parallel connection.

The circuit used depends on the water heater type, storage capacity, existing circuit system (in the case of replacement), and its use. We advise you to use a parallel circuit for its longevity and better performance.

However, the fact that a parallel circuit is better doesn’t mean that a series circuit doesn’t work. The use of parallel circuits occurs mainly in situations where there is a great demand for hot water simultaneously over a short time. Such situations are chain shower time or filling a hot tub or swimming pool. Series circuits can only handle more concise immediate use of hot water. It is better for personal use.

Why Do Water heaters Use Series Circuits?

Water heaters use series circuits because they have only one pathway between two electrical current points. This configuration makes each water heater to be dependent on the other. The result is that if one water heater turns off, the other goes off too.

Even though this might seem obnoxious, it favours the users’ ability to conserve energy. Water heaters also use series circuits if both heaters are of different types and sizes. The disadvantage of using series circuits is that the other will stop heating water when one heater turns off. 

In such cases, there will be no other source of hot water available till the heater comes back on. Also, one heater will do more work than the other, causing faster wear down of that water heater.

Why Are Water Heaters Connected In Parallel?

Water Heaters are connected in parallel when there is a need for hot water in large quantities in a short time. The parallel water heater Connection delivers more hot water than the series connection, and the hot water output is taken equally from each unit.

For every amount of water discharged from one unit, the same amount is replaced instantly into the 2nd water heater. The Water heater unit in the parallel circuit uses the same amount of heat to work, and this equal voltage is due to the length of the supply and delivery piping. The supply and delivery piping are the same sizes to prevent the cold inlet piping from overworking due to constant water pressure.

Piping in parallel allows equal heater use. The water heater system acts as one heater instead of two independent ones.

How Can I Tell If My Water Heaters Are In Series?

You can tell if your water heaters are in series by turning off one of the water heater’s switches. If none of your water taps still run hot, your water heaters are in series. But if they continue to work even with one heater off, then the water heaters are connected in a parallel circuit. 

This testing method works because series circuits have one pathway for both electric current points of the water heaters.

Can I Run Two Water Heaters In Series?

You can run two water heaters in series. However, it is not the best connection and will cost you over time. Running two heaters in a series entitles water to flow from one heater into the other. This directional flow has some disadvantages, such as: 

  • High Utility Bill: More energy is consumed to heat the water flowing into the first heater from the 2nd. The high energy use results in an increase in utility bills.
  • Stratification: Water will come out in different degrees of hotness. Water flowing out of the first water heater will be very hot but the 2nd water heater will get warm and eventually cold at the bottom level of the water heater.
  • Bacteria: Since the bottom of the 2nd water heater rarely gets hot, bacteria will start eating up and eroding the heater lining.

Though you can run two water heaters in series, we do not advise you to do that if you want a consistent hot water supply and a long-lasting water heater.

Are Water Heaters Necessary?

Essentially, your house has a gas water heater for easy and immediate access to hot water. Whether for personal use, chores, or commercial purposes, it is essential that your house has water heaters. To have a water heater is to have a ready supply of hot water.

Though water heaters are necessary for a home, it is still an appliance most people easily ignore when it acts up.

How Do You Install Two Water Heaters?

To install two water heaters In series, observe and follow these procedures:

  • Note that the two water heaters can be of different types and sizes.
  • There are no rules to which water heater comes first, but installing the larger heater closest to the faucets is better. The reason is for proper maximization of the smaller heater, so less cold water enters the first water heater.
  • Each water heater can have different temperature settings, unlike the parallel connection where the temperature has to be the same.
  • You can adjust the temperature of both heaters the same to store more heat energy and get more hot water from each heater.
  • You can set the first heater at a higher temperature and the second heater lower to get very hot water immediately.
  • Set temperature at 125° to 130° to avoid scalding.

After these placements and settings, open the drain valve and check if hot water flows. If there is any dripping from the drain, install a brass hose cap to the valve.

 The equipment needed for installation includes: 

  • Temperature gauges
  • Brass drain valve
  • Brass hose caps
  • Kitchen thermometer


Generally, you can use either a series or parallel circuit while installing your water heater. However, it is better to use parallel for efficient heating and preservation of your water heater. Different water heater types can be used in series, and the same current controls both heaters.

While in parallel, it uses the same water heater type and size, and each heater has the same voltage but a different current. With this information, you can determine which connection method works better for you and make great use of your water heaters.

Don`t copy text!
Scroll to Top