Tankless Water Heaters – Things You Should Know Before You Buy!

If you are thinking about switching from a tank type water heater to a tankless unit, be aware that your hot water system as a whole will work a little differently than what you are used to.

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Tankless water heaters vs. tank type water heaters

If you are thinking about switching from a tank type water heater to a tankless unit, be aware that your hot water system as a whole will work a little differently than what you are used to. Living with a tankless hot water heater might take some getting used to.

Tank type water heater operation

With a standard water heater, when you turn on a hot water faucet, the hot water is usually around 140 degrees, depending on what the thermostat setting is, and it immediately begins flowing through the pipe on its way to your faucet.  As the water travels through the cold pipe, it looses heat to the pipe until the piping material warms up.  Your hot water doesn’t instantly go from cold to hot, it gradually warms up, and the longer the piping run the more gradual the temperature rise.

Many large homes have hot water circulating pumps and piping to circulate the hot water through the pipes. This provides quick hot water at all of the sinks.  Circulating systems can save a lot of water, but are wasteful of energy, because the water heater  fires up more often to replace the heat being lost through the pipes.  The pipes act like a big radiator even when the pipes are insulated. 

There are some pumps that deliver the hot water to the fixture from the water heater only when you want to use hot water and no water gets run down the drain. You still save water, time, and money.

Tankless Systems

Tankless water heaters are advertised as providing unlimited hot water and as being more energy efficient  than tank type water heaters.  Both of these facts are true, but there are other things to consider.

If you are thinking of replacing your water heater with a tankless unit make sure you get one large enough to do the job.  Since you are heating water as you use it, you must heat it much more quickly than a tank type heater which can leisurely heat your water, so you need to add heat much more quickly. 

For a gas type heater this means you will be using a larger burner than with a tank type heater.  Your exhaust flue will have to be larger and the gas line might need to be bigger. For electric heaters you might have to have larger gauge wiring put in to handle the high loads needed by a whole-house electric tankless water heater.

With a tank type water heater you can set the flow rate to anything you want from full-on to just a trickle, and you get pretty much the same temperature, once the piping has warmed up.  With a tankless unit there is a minimum flow rate needed to turn the heater on.  Typically they require a flow of ½ gallons per minute to ¾ gallons per minute.  So you won't be able to get a trickle of hot water. In addition, as you vary the flow rate the temperature will vary unless you have the more expensive modulating type units, and even then the temperature will still vary somewhat with flow.

Most circulating systems don’t pump at a high enough flow rate to turn on the tankless water heaters.

Changes in your water temperature from winter to summer will have an impact the tankless heater.  Tankless water heaters are rated on their maximum temperature rise, not the outlet temperature.  So the lower the incoming water temperature, the lower the outlet temperature, which can vary substantially from winter to summer in some areas.

For example, if your incoming water temperature in the summer is 55 degrees, and your heater raises the temperature 80 degrees at a flow of 1 gallon per minute, you have a hot water temperature of 135 degrees.  If your incoming water drops to 50 degrees in the winter, your top temperature will drop to 130 degrees.  And don’t forget, as you increase the flow rate the temperature rise will drop.

To fully heat the hot water, the cold water entering the water heater must pass all the way through the water heater.  This means that it will take longer to get your hot water than with a tank type heater, and you will run more water down the drain.

The water conservation issue can be resolved with a “demand” type hot water system. Demand hot water pumps pump the hot water from the heater to the fixture without running water down the drain. The pump only runs for a short time, usually less than a minute, and thus only consumes about $2.00 per year in electricity costs for a typical family. A demand pump will get your hot water to your fixture about twice as fast as normal and you won’t waste any water. Demand pumps can be found for less than $200.00 and are very easy to install.

Tankless water heaters can save you a modest amount of energy, typically around $8.00 - $10.00 a month. Since tankless units are more expensive than tank type water heaters, and more expensive to install, that savings may not be so great. They can also provide you with endless supply of hot water. However, forget getting a trickle of hot water, be prepared to wait a little longer, and adjust to having the temperature vary with the flow rate.