| Tankless Hot Water Heaters – Not What They Seem? |
Plan to purchase a tankless hot water heater? If so, and if you aren’t familiar with how a tankless water heater operates, then there are some things you should know about before you make that purchase.
There are some big differences between the way tank type water heaters and tankless hot water heaters interact with you the user as you operate your hot water system. With a tank type hot water heater, when you turn on the faucet and the hot water begins flowing through the hot water piping on its way to your faucet. Since the piping is cold, it absorbs a portion of the heat in the water, gradually warming up to the temperature of the water.
This is why your hot water gradually goes from cold to hot if you leave your hand under the running water. If your pipe run is short, the warm-up will be faster. The longer the pipes and the heavier the piping material, the more gradual will be the warm-up because the pipes will absorb more heat from the flowing water.
Another significant variable in the warm-up time is the velocity at which the water is traveling. The more quickly the water flows, the quicker the warm-up. The higher the water velocity, the less time it is exposed to the cold piping material. The ambient temperature is also a big factor. If your pipes are in the attic, and you are in Bakersfield California, in mid summer, your pipes will be so warm that they won’t absorb any heat from the water.
However, if you are in Truckee California in January, your pipes will take far longer to warm up, and with very long pipe runs with un-insulated pipes, the high temperature might never be reached since the heat loss from the pipes to the surrounding air might be quite high.
Within a short time the hot water the temperature stabilizes. Since you have a tank filled with plenty of hot water that is at one temperature, the temperature at your faucet vary very little, even when you change the flow rate with the faucet. A tiny stream of water is basically the same temperature as with the faucet flowing at full stream.
Now let’s see how things change with a tankless hot water heater. The previous warming-up factors apply and there are a few more things that come into play. When you turn on the hot water faucet there is no big tank of hot water to start flowing to the fixture. There is, however, a tankless heater full of cold water that begins passing through the hot water piping on its way to your sink.
Heating the water to full temperature requires that the cold water entering the heater travel all the way through the heater. This will causes a longer delay in getting the hot water to the fixture, and results in running more water down the drain while waiting than with a tank type heater.
An easy way to visualize the workings of a tankless hot water heater is to picture a coil of copper pipe with a fire in the middle of it. As the water travels through the tubing it absorbs heat from the flames and gets hotter and hotter. An electric heater is similar but instead of fire the water flows over heating elements.
The temperature of the water coming out of the water heater depends on flow rate and what the incoming cold water temperature is. If your cold water is 45 degrees, and the heater is heats the water 90 degrees with a flow rate of 1 gallon per minute, then you will obtain 135 degree water at the outlet.
If for any reason the water temperature of the incoming cold water rises to 55 degrees, then outlet temperature will rise to 145 degrees. In most areas this will result in a different hot water temperature in the summer than in the winter months.
The flow rate has a large impact on the temperature rise the heater produces. If you increase the flow rate from 1 to 2 gallons per minute the temperature rise will be cut in half, and the outlet temperature will be 100 degrees. A change in flow will causes a change in temperature.
To make things even more interesting, a tankless hot water heater does not turn on until a sufficient flow of water occurs in the hot water pipe. Tankless hot water heaters typically require between ½ gpm and ¾ gpm to turn on.
If you like to run the hot water tap full-on to get the hot water to the sink quickly, and then throttling it back to a small stream while you brush your teeth or wash your hands, then the tankless water heater will change your behavior. With a tankless water heater, if you reduce the flow to a small stream, the water heater shuts off, and cold water is on its way. No more using a tiny trickle of hot water.
Tankless water heaters don’t work with most traditional water circulating systems. If the circulating pump produces enough flow to turn on the water heater, it will cause the water heater to run continuously until a safety mechanism shuts it off. Most pumps don’t produce enough flow to turn on the heater and will just circulate cold water.
There is a type of hot water pump that will work with the tankless heaters. The pump will get the hot water to the fixture more quickly and without running any water down the drain. You activate the pump with a push button and it automatically turns off when the hot water reaches it. Two such pumps are the Metlund D’mand pump and the Chilipepper CP6000. Unfortunately they don’t solve the other problems.
Tankless water heaters do have their place. They do eliminate standby and they do provide unlimited amounts of hot water.
Two FAST hot water demand systems compared: Demand Hot Water Systems
For more information about all kinds of water heaters: Water Heaters Instant hot water systems. http://www.htwtr.com
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