Tankless water heaters work quite differently than tank type water heaters
Tankless water heaters sales have been booming lately. Unlimited hot water and energy savings are the features most often touted by the tankless water heater industry, and a smaller footprint is often mentioned. While they do provide an unlimited supply of hot water they are not without their own problems. There are important differences in the way they work compared to the tank type models.
Storage or tank type water heaters have been the standard in the United States, but recently tankless water heaters have begun to make an impact. Most people are familiar with storage (tank type) water heaters, where you have a big tank of hot water ready and waiting when you need it. The water can be heated with gas flames, electric heating elements, or any other method. Storage or tank type heaters have two potential problems, the first, is they use more standby energy than tankless water heaters, and the second, you can run out of hot water.
Tankless heaters require a minimum flow rate to turn on.
Tankless water heaters have some drawbacks to them as well. For one thing, tankless water heaters have a flow switch in the water line that turns them on when sufficient flow is detected. Usually a flow of about 1/2 gallon per minute or more is required to turn the unit on. This pretty much eliminates the idea of having access to a low-flow stream of hot water for anything.
Sometimes it can be difficult to fill a bathtub with a tankless unit. With tankless heaters, higher the flow rate of the water the lower the temperature rise since the water spends less time in the heater. With a bathtub you usually turn on the water full blast so it doesn’t take too long to fill the tub. Usually the faucet at the tub will have the highest flow rate of any fixture in your home, often 7 gallons per minute or more. With typical tankless heaters you end up with a tub full of tepid water. If you try to fill it more slowly to get it hotter, it takes so long to fill that it cools off before you get in anyway. So if you like to soak away in a hot tub, you better make sure you get a big enough heater to handle the job.
Tankless units are more expensive to buy and to service
Tankless heaters are substantially more expensive than storage heaters, and more complex, so they are more expensive to repair should anything go wrong. They also need larger flues and if they are electric, they often need special extra heavy wiring.
More wasted water
Another problem with tankless units is that they take longer to get hot water to the fixtures. That means you waste more water, which is not very environmentally friendly. The reason is that when you turn the hot water on, the flow switch turns on the heater, and it begins to heat the water. But to reach full temperature the water must travel through the entire heater. Now you have to not only dump out the cooled off water in the hot water piping, but also the cooled off water in the water heater as well, before you get hot water at the fixture.
Hot water circulating systems do not work with tankless heaters because either the flow of hot water won’t be enough to turn on the heater, or it keeps the heater turned on all of the time. Neither scenario works. However, there is a way to solve the long wait and wasted water problems.
On demand hot water systems stop the waste
An on demand hot water system will work with tankless and with storage type water heaters, providing the benefits of faster hot water delivery and eliminating the running of water down the drain.
The hot water pump installs at the furthest fixture from the heater, and connects to the hot and cold water lines. When you want hot water you press a button and the cooled off hot water in the hot water piping gets pumped back to the inlet of the heater, and when the actual hot water reaches the fixture the pump shuts off. That way you get your hot water faster than running the faucet, you don’t run any water down the drain while you wait, and you don’t fill the cold water line with hot water. You save time, water, and money. Typical savings can amount to over 15,000 gallons per year for a family of four. A hot water on-demand system used with a tankless water heater makes a great environmentally friendly package, saving both water and energy.
On demand systems work just as well with storage type water heaters, and if you are considering such a system, you might check with your water company as some offer rebates for such systems. Be sure to check the pump is powerful enough to turn on the flow switch, as not all pumps are strong enough. Metlund manufactures several models of demand pumps, at least one of which will run a tankless heater. Chilipepper Sales also manufactures the Chilipepper appliance which has a pump strong enough to run any tankless heater.
If your primary concern is having unlimited amounts of hot water and you can live with the few drawbacks, then the tankless water heater is for you, otherwise you might want to stick with a good old-fashioned storage tank type water heater.