Homeowners replace traditional water heaters with tankless ones for two reasons. Tankless water heaters save energy and provide a never-ending stream of hot water. Unlike traditional water heaters, however, tankless ones only provide hot water when the water running through them is equal to or greater than a pre-set flow rate. If you're considering replacing your home's current hot water heater with a more energy-efficient tankless system, you'll want to make sure that your home's faucets draw enough water to activate the tankless water heater.
Flow Rates of Tankless Water Heaters
Unlike traditional water heaters, tankless water heaters will only turn on when the hot water being used exceeds their minimum flow rate. Flow rate is a measure of the volume of water flowing through a pipe at any given moment; gallons per minute (gpm) are the units usually used for residential tankless water heaters. If the amount of water being used at the time is not greater than the tankless heater's activation flow rate, you will not have hot water.
As an example, assume you had a tankless water heater with a minimum threshold of 0.6 gpm installed in your home. If you only used a trickle of hot water when washing dishes, you might only need 0.4 gpm. Unless you increased how much water you used to wash dishes, so that the flow rate went above 0.6 gpm, you would only have cold water for washing your plates and bowls.
To avoid this issue, M. Scott Gregg recommends looking for a tankless water heater with a minimum threshold of 0.5 gpm for most homes. Most shower, sink and bathtub faucets use at least this much water, so there should not be an issue activating the system.
Retrofitting a Tankless Water Heater
When installing a tankless water heater in a new home, the flow rate is usually not an issue. Although an issue could arise in theory, contractors know to only use faucets that will draw enough water to activate the tankless system. There is actually rarely ever an issue with a new home's system, barring any equipment failure.
When retrofitting a tankless water heater to an existing home, however, it is important to make sure that the flow rate of each faucet in the house exceeds the minimum activation rate of the tankless system. If any of the existing faucets have a rate lower than the flow rate of the water heater, then you will have trouble getting hot water through those faucets.
This is an issue sometimes when homes have low-flow faucets, which are designed to save water, far away from the tankless heater's location. For, as M. Scott Gregg notes, the flow rate decreases the further away a faucet is. A low-flow shower head that has a flow rate of 1 gpm may not actually activate a tankless water system with a 0.75 gpm flow rate, because the rate drops at every fitting and with every foot of piping it travels through.
Flow Rate Problems
If a tankless system has already been installed in your home and specific faucets are not activating the system, there are a few solutions to consider. You might:
- run multiple faucets at once, thereby increasing your home's entire flow rate
- see if a plumber can adjust the activation flow rate of the tankless system
- install new faucets with higher flow rates
It is preferable to avoid these issues, though, by looking up the flow rates of your faucets before having a tankless water heater installed. The company installing the tankless system should be able to check the flow rate at each faucet for you. Ask them to do so, and confirm that all the flow rates exceed the system's minimum rate. This simple step could save you from having problems activating your new tankless heater.
For more information, contact a local water heater installation company.