Tank type water heaters are quite different than tankless water heaters!
Most of us have grown up with a standard tank type water heater. As such we are used to the way our hot water system works. Switching to a tankless water heater will have an affect on the way your hot water system works.
Tank type water heater operation vs. tankless operation
With a tank type heater, when you turn on a hot water faucet, the hot water, typically 140 degrees, immediately begins flowing through the pipe to get to your faucet. As the water travels through the cold pipe, it cools off until the piping material warms up. That is why your hot water doesn’t instantly go from cold to hot; it has to warm up the pipes first.
Many homes have hot water circulating systems that circulate the hot water through the pipes to obtain instant hot water at every sink. Circulating systems can save a lot of water. They are wasteful of energy though, since the water heater will fire up more often to replace the heat being lost through the piping which acts like a big radiator even if the pipes are well insulated.
There are also pumping systems that pump the hot water to the fixture from the heater only when you want to use hot water and you don’t run any water down the drain. You still save the water and time, but you don’t waste water.
Tankless water heaters are being promoted as providing endless hot water and as being energy saving over traditional water heaters. While both of these facts are true, there are other things to consider.
If you are considering replacing your tank type water heater with a tankless unit, and you have a typical house, 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 so you need to add heat much more quickly.
For a gas type heater this means you will be using a lot more gas volume/ minute than with a tank type heater. Your exhaust flue will need to be much larger and the gas line might need to be larger. For electric units you might have to have special wiring put in to handle the high amperage loads created by a large 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. With a tankless water heater there is a minimum flow rate required to turn the heater on. Typically it ranges from about 1/2″ gallons per minute to 3/4 gallons per minute. So you can’t get just a trickle of hot water.
Most circulating systems don’t pump at a high enough flow rate to turn on the tankless water heaters. If they do, they will void or restrict most warranties, because they will cause frequent on-off cycles for the heater.
Changes in your water temperature from winter to summer will impact the tankless heater. The tank type heater always heats your water to the same temperature. The tankless units increase the temperature a certain number of degrees with a given flow rate.
For example, if your incoming water temperature in the summer is 60 degrees, and your heater raises the temperature 80 degrees at a flow of 1 gallon per minute, you have a hot water temperature of 140 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.
On Demand hot water systems
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.