Tankless water heaters have some advantages over tank water heaters that make them superior in a number of different ways. One major advantage is in terms of efficiency since tankless water heaters typically use anywhere from 10-35% less energy. Tankless units also have a major advantage in terms of life expectancy and will often last nearly twice as long as tank units. Nonetheless, tankless water heaters do have two distinct downsides or areas where they can’t compete with tank units, and those are in terms of lag time and flow rate. In this article, we’ll explain all you need to know about these downsides and how opting for point-of-use tankless water heaters can help to overcome them.
How Tankless Water Heaters Differ From Tank Units
The main difference between tank and tankless water heaters is that tankless units heat on demand. Instead of storing hot water, tankless water heaters only heat water when needed. That means the unit won’t need to occasionally turn on as tank units do to keep the stored water fully hot. This is the main reason that tankless water heaters are more efficient since tank units still occasionally use energy even if no hot water has been used recently.
Why Tankless Water Heaters Have Longer Lag Times
Lag time is how long it takes from when you turn the hot water on at any plumbing fixture until the water begins flowing as hot as it should. Tank water heaters have a fairly short lag time since the water is already fully heated when it flows out of the tank into the building’s pipes. In most cases, you won’t have to wait more than a few seconds before the water flowing out of the shower or faucet is fully hot.
With a tankless water heater, you’ll normally have to wait for at least 30 seconds before the water is fully hot. That’s because it takes some time from when the water heater turns on until the gas burner or electric heating elements raise the temperature of the heat exchanger to where it needs to be. That means that the water flowing out of the unit will still be fairly cold at first until the heat exchanger gets hot enough to fully heat the water to whatever temperature you have the unit set at.
In winter, you may need to wait for at least a minute or two before the water is fully hot. This is partly because the water flowing into your house is slightly colder in winter. Another reason is that some of the pipes in your home will also be colder in winter. That means the water temperature will decrease as it moves through the pipes until the hot water finally warms the pipes up. This also happens during the warmer parts of the year, but the effect is lessened since your pipes generally aren’t as cold.
Another thing to understand is that the lag time is directly affected by the distance between the water heater and the plumbing fixture you’re using. This is also true for tank water heaters, but not nearly as much as it is for tankless units. The main reason is again that the water is already fully hot when it flows out of a tank water heater, which means it takes less time for the pipes to heat up.
Why Tankless Water Heaters Have More Limited Flow Rates
Another minor drawback to having a tankless water heater is that most units can’t compete with tank water heaters in terms of flow rate. The flow rate of a water heater is how many gallons of hot water it can supply per minute. With a tank water heater, you’ll usually have no issues using hot water in multiple fixtures at the same time. That means you should be able to shower while also having the dishwasher or washing machine running. There will be a noticeable change in water temperature sometimes if someone else turns on another fixture, such as turning on the hot water at a sink to wash their hands. Nonetheless, this typically lasts for only a few seconds before the water is hot again.
The flow rate for a gas tankless water heater is typically between 3 and 5 gallons per minute, while electric units often can only supply around 2 gallons of hot water per minute. That means with an electric unit, you generally will only have enough hot water to run one shower at a time. If you had hot water running at a sink and shower at the same time, you’d end up with the temperature fluctuating or the water being too cold. If you have a gas unit, you’d normally have enough hot water for two or possibly three fixtures to be on at the same time. However, it depends on the flow rate for each of the fixtures. Dishwashers and washing machines can use 3 to 5 gallons per minute, which means you likely won’t be able to shower with one of these units running if you have a tankless water heater.
Advantages of Choosing Point-of-Use Tankless Water Heaters
If you’re concerned about the longer lag times and limited flow rates, the best option is to install several point-of-use tankless water heaters instead of a whole-house unit. Point-of-use units are installed near each plumbing fixture that requires hot water and only supply hot water to those fixtures instead of the whole house. That means you’d have one unit in the kitchen, usually underneath the sink, that supplies the sink and possibly the dishwasher. You’d also have one unit in the bathroom that supplies the shower and bathroom sink. Depending on where your washing machine is located, you may also need a separate unit for it.
One reason that point-of-use units can be such a great choice is that they have much shorter lag times since they are typically within a few feet of the sink or shower. That means you should have hot water within a few seconds of turning the fixture on. An added benefit of the shorter lag time is that it means point-of-use units use a bit less energy and waste less water.
Another advantage of having multiple point-of-use units instead of a whole-house unit is that you don’t need to worry about using multiple fixtures at the same time. You may still have issues if you try to use the bathroom sink and shower at the same time. However, someone using the kitchen sink or running the dishwasher wouldn’t affect the hot water in your shower since they are supplied by different units.
Our Water Heater Experts
As the Knoxville area’s most trusted plumbing service, Tennessee Standard Plumbing is the company to turn to for all of your water heater needs. We offer tankless and tank water heater installation services. If you’re unsure of which type of water heater is the better choice for your home, you can count on us to provide expert advice and assistance. Our team also specializes in maintenance and repairs and can help ensure your water heater works exactly as it should.
Contact us today for more information on the benefits of installing a tankless water heater in your home or if you need to schedule any type of plumbing service.
