Make Sure Your Tankless Water Heater Will Work With Your Shower Head

Many homeowners either have or are considering replacing their traditional hot water heater with a tankless water heater in order to save energy and enjoy a never-ending supply of hot water. In order to enjoy an endless supply of hot water, though, homeowners need shower heads that will use enough water to activate their new tankless water heater. Some low-flow shower heads won't draw enough water to turn on a tankless water heater. If you're thinking about installing a tankless water heater in your home, here's how to make sure the model you choose will work with your shower heads.

Tankless Water Heaters Have Minimum Flow Rates

All tankless water heaters have a minimum flow rate, and they won't turn on if the rate isn't met. Flow rate is simply a measure of how much water moves through a pipe in a set amount of time. It's usually expressed in gallons per minute. A tankless water heater's minimum flow rate is the lowest flow rate that will cause it to kick in. If there's not enough water moving through a tankless water heater, it won't begin heating.

For example, assume a model you're looking at has a minimum flow rate of 0.7 gpm. If you turn on a trickle of hot water to wash your hands, you might only draw 0.4 gpm. Until you turn the faucet up to 0.7 gpm, the tankless water heater won't turn on. As soon as the minimum threshold is hit, the water heater will provide all the hot water you need. Until it is, however, you'll only have cold water.

Problems Can Arise When Replacing a Traditional Water Heater

In new home construction, minimum flow rates usually aren't an issue. Homebuilders know that tankless water heaters have minimum flow rates, and they make sure that the shower heads and tankless water heaters they use are compatible.

When replacing a traditional water heater, however, issues can arise. Because traditional water heaters don't have minimum flow rates, homes that have traditional water heaters sometimes have shower heads that draw only a little water. If a tankless water heater's minimum flow rate is greater than a shower head's flow rate, the new water heater won't be activated when people shower.

While this problem can arise with any faucet, it's particularly common with shower heads for two reasons. First, homeowners that are keen on tankless water heaters' energy efficiency may have low-flow shower heads that only use a minimal amount of water.

Second, showers are often on the second, or even third, floor of homes. As M. Scott Gregg explains, flow rate decreases as water moves away from a water heater. A low-flow shower head that draws 1 gpm might actually only draw 0.75 gpm if it's far from the water heater.

Problems Are Easy to Address, Though

If the tankless water heater you're looking at has a minimum flow rate that's too high for your shower heads, there are a few solutions. You can try the following:

  • run the bathroom sink when you shower to increase the total flow rate of hot water
  • install new shower heads with higher flow rates yourself
  • ask a plumber to manually lower the minimum flow rate of your tankless water heater after it's installed

If you're looking for a tankless water heater and have one or more low-flow shower heads, look for a model that has a minimum flow rate that is less than your shower heads' flow rates. (You can check your shower head's flow rates by looking up the model number with the manufacturer.) Should you have trouble finding a model, there are other solutions you can try. Once you settle on and implement a solution, you'll be enjoying long, long hot showers without any issues. For more information, see the website